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Development And Inheritance

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					Development And Inheritance

I. Embryonic Period
    A. First Week of Development
       1. fertilization
           a. genetic material of haploid sperm fuses with the genetic material of haploid
           secondary oocyte
           b. occurs in oviduct within 12-24 hrs after ovulation
                - pregnancy most likely to occur if intercourse takes place 2 days before to 1 day
               after ovulation
           c. sperm use flagella to get to cervix
               - once there contractions of uterus & uterine tubes propel them the rest of the way
                    prostaglandins from semen believed to stimulate uterine motility
           d. not capable of fertilizing an oocyte until about 7 hrs after entry into female
           reproductive tract
               - must undergo capacitation
                    functional changes that cause sperm’s tail to beat more vigorously & prepares
                    plasma membrane for fusion
           e. sperm must penetrate the corona radiate & zona pellucida
               - glycoprotein on zona pellucida that acts as a receptor for the sperm
               - when sperm binds to its receptor have acrosomal reaction
                    release of enzymes
               - enzymes digest a path through
           f. only 1 sperm allowed to fuse with the secondary oocyte
               - called syngamy
               - polyspermy prevented by
                    fast block
                        cell membrane of oocyte depolarizes which prohibits fusion with another
                        sperm
                    slow block
                           2+
                        Ca release due to depolarization which stimulates exocytosis of secretory
                        vesicles from oocyte
                        these molecules inactivate sperm’s receptor & hardens the zona pellucida
           g. oocyte must complete meiosis II
           h. nucleus of sperm develops into pronucleus & nucleus of ovum develops into
           pronucleus
               - they fuse producing a diploid zygote
           i. dizygotic (fraternal) twins
               - release 2 secondary oocytes & both fertilized
           j. monozygotic (identical) twins
               - single fertilized ovum
               - developing cells separate into 2 embryos usually before 8 days have passed
                    later and the risk of conjoined twins is very high
       2. cleavage of the zygote
           a. rapid mitotic divisions of the zygote without any increase in the size
                                                           st
           b. begins about 24 hrs after fertilization & 1 division takes about 6 hrs
           c. day 2, 4 cells
           d. day 3, 16 cells
           e. cells getting smaller, called blastomeres
           f. day 4, solid ball of cells, morula
               - surrounded by zona pellucida still
               - same size as zygote
       3. blastocyst formation
           a. morula enters uterine cavity on day 5
           b. endometrium secretes glycogen-rich fluid & it enters into morula
               - provides nourishment
           c. at 32 cell stage, fluid enters morula & collects between the blastomeres reorganizing
           them around a cavity, blastocyst cavity
               - now called a blastocyst
           d. rearranges some more developing
               - inner cell mass
                   becomes embryo
               - trophoblast
                   becomes fetal portion of placenta
                th
           e. 5 day, digests a hole in zona pellucida & squeezes out of it
Stem Cell Research And Therapeutic Cloning
   Stem cells
       unspecialized cells with the ability to divide indefinitely & give rise to specialized cells
       zygote is a stem cell
           totipotent
       embryo is pleuripotent
           give rise to many but not all different types of cells
           derived from embryos of infertility treatments not used & terminated fetuses
       pluripotent become multipotent
           stem cells with specific function
   Therapeutic cloning
       use genetic material of patient to create pluripotent stem cells for treating disease
   Adult stem cells
       4. implantation
           a. about 6 days after fertilization
               - loosely attached
           b. orients with inner cell mass facing endometrium
           c. endometrium now known as decidua
               - decidua basalis
                   between embryo & stratum basalis of uterus
                   becomes maternal portion of placenta
               - decidua capsularis
                   between embryo & uterine cavity
               - decidua parietalis
                   lines uninvolved areas of the uterus
Ectopic Pregnancy
   development of an embryo or fetus outside the uterine cavity
   movement of ovum through the uterine tube impaired by
       scarring
       decreased movement of smooth muscle
       abnormal tubal anatomy
   most common site is the uterine tube but also occurs in
       ovary
       abdominal cavity
       uterine cervix
   women who smoke are 2X as likely to have as nonsmokers
       nicotine paralyzes cilia
   signs/symptoms
       missed menstrual cycles followed by bleeding, acute abdominal pain & pelvic pain
   can rupture tube causing death of mom
   treat with surgery or methotrexate
   B. Second Week of Development
       1. development of the trophoblast
           a. at about 8 days, develops into 2 layers
               - syncytiotrophoblast
                   no distinct cell boundaries
                   secretes enzymes which enable blastocyst to penetrate into the uterine lining
        - cytotrophoblast
              between inner cell mass & syncytiotrophoblast
              composed of distinct cells
    b. become part of the chorion
    c. secrete hCG
        - maintains corpus luteum which is secreting estrogen & progesterone
              maintain uterine lining
        - indicator of pregnancy
2. development of the bilaminar embryonic disc
    a. at about 8 days
    b. inner cell mass differentiates into 2 layers
        - hypoblast
              primitive endoderm
        - epiblast
              primitive ectoderm
              small cavity appears & enlarges to form amniotic cavity
3. development of the amnion
    a. amniotic cavity enlarges & a thin protective membrane, amnion, develops from the
    epiblast
    b. eventually surrounds entire fetus
    c. filled with fluid, amniotic fluid
        - originally from mom’s blood
        - then fetus contributes by excreting urine
    d. acts as
        - shock absorber for fetus
        - regulator of fetal temperature
        - a preventer of dessication
        - a preventer of adhesions
    e. “bag of waters”
    f. amniocentesis
4. development of the yolk sac
    a. about 8 days after fertilization, cells along edge of hypoblast migrate & cover inner
    surface of blastocyst wall
    b. form exocoelomic membrane
        - with hypoblast form the wall of the yolk sac
    c. decreases in size as development progresses
    d. functions include
        - supplies nutrients to embryo during weeks 2 & 3
        - source of blood cells in weeks 3-6
                       st
        - contains 1 primordial germ cells which migrate into gonads, & differentiate into
        primitive germ cells
        - forms part of the gut
        - shock absorption
        - helps to prevent drying out of embryo
5. development of sinusoids
         th
    a. 9 day
        - blastocyst completely embedded in endometrium
        - syncytiotrophoblast expands developing small spaces, lacunae
           th
    b. 12 day
        - lacunae fuse to form lacunar networks
        - endometrial capillaries dilate & called sinusoids
        - syncytiotrophoblast erodes sinusoids & maternal blood flows into them
              good source of nutrients
              embryo waste disposal
6. development of the extraembryonic coelom
                   th
    a. about 12 day, extraembryonic mesoderm develops
       b. derived from yolk sac
       c. form mesenchyme layer around the yolk sac & amnion
       d. large number of cavities develop in the extraembryonic mesoderm & fuse to form the
       extraembryonic coelom
   7. development of the chorion
       a. extraembryonic mesoderm, cytotrophoblast, & syncytiotrophoblast form the chorion
       b. fetal portion of placenta
       c. protects embryo/fetus from mom’s immune responses
           - secretes proteins that block mom’s Ab production
           - promotes production of T suppressor cells to suppress normal uterine immune
           response
       d. produces hCG
       e. inner layer fuses with amnion
       f. extraembryonic coelom becomes chorionic cavity
                       nd
       g. by end of 2 week, embryonic disc becomes connected to the trophoblast by
       extraembryonic mesoderm, connecting (body) stalk
           - future umbilical cord
C. Third Week of Development
   1. gastrulation
       a. about 15 days after fertilization
       b. bilaminar embryonic disc (epiblast & hypoblast) becomes trilaminar embryonic disc
           - consists of 3 germ layers
               ectoderm
               mesoderm
               endoderm
            st
       c. 1 evidence of gastrulation is formation of the primitive streak
           - establishes head & tail ends of embryo
           - at head end, epiblastic cells form the primitive node
       d. epiblast cells then move inward below the primitive streak & detach from the epiblast
           - called invagination
           - some of these cells displace the hypoblast forming the endoderm
           - some cells remain in between epiblast & endoderm to become mesoderm
           - cells remaining in epiblast become ectoderm
       e. ectoderm & endoderm are epithelial cells
       f. mesoderm is CT (mesenchyme) & muscle
       g. endoderm forms
           - epithelial lining of the GI tract, respiratory tract
       h. mesoderm forms
           - muscles
           - bones
           - CT
           - peritoneum
       i. ectoderm forms
           - epidermis of skin
           - nervous tissue
       j. at about 16 days, mesodermal cells from the primitive node migrate toward the head
       end of the embryo
           - form a hollow tube of cells called the notochordal process
               this becomes solid cylinder, the notochord
       k. notochord is important in induction
           - inducing tissue stimulates the development of an adjacent unspecialized tissue into
           a specialized tissue
           - notochord induces mesodermal cells to become vertebral bodies
           - forms the nucleus pulposus
       l. oropharyngeal membrane develops
           - at head end
                                th
             - breaks down in 4 week to connect mouth cavity to pharynx
         m. cloacal membrane develops
             - at tail end
                                  th
             - degenerates in 7 week to form anal opening & openings of urinary & reproductive
             tracts
             - when this appears, yolk sac forms an outpouching called the allantois
                  extends into connecting stalk
                  in other mammals used for gas exchange & waste removal
                  in us, functions in early development of blood & blood vessels
                  also associated with development of the urinary bladder
     2. neurulation
         a. process by which neural plate, neural folds, & neural tube form
         b. notochord induces ectodermal cells over it to form the neural plate
                                     rd
             - by the end of the 3 week, lateral edges of the plate become elevated & form the
             neural folds
             - depressed region between the folds called the neural groove
             - neural folds approach each other & fuse forming the neural tube
         c. ectodermal cells from the tube migrate to form the neural crest
             - gives rise to spinal & cranial nerves & their ganglia, ANS ganglia, meninges,
             adrenal medulla, & skeletal & muscular components of the head
         d. at about 4 weeks, head end of neural tube develops into primary brain vesicles
             - prosencephalon
             - mesencephalon
             - rhombencephalon
         e. at 5 weeks, prosencephalon develops into telencephalon & diencephalons and the
         rhombencephalon develops into metencephalon & myelencephalon
Anencephaly
  neural tube defect
  cranial bones fail to develop & parts of brain remain in contact with amniotic fluid &
  degenerate
  usually stillborn or die within a few days after birth
     3. development of somites
               th
         a. 17 day
         b. mesoderm adjacent to notochord & neural tube forms paired longitudinal columns of
         paraxial mesoderm
         c. mesoderm lateral to that forms paired cylindrical masses called intermediate
         mesoderm
         d. lateral to that a pair of flattened sheets called lateral plate mesoderm
         e. paraxial mesoderm segments into somites
         f. each somite differentiates into
             - myotome
                  skeletal muscles of neck, trunk, & limbs
             - dermatome
                  CT including dermis of the skin
             - sclerotome
                  gives rise to vertebrae & ribs
     4. development of the intraembryonic coelom
         a. small spaces develop in the lateral plate mesoderm
             - merge to form intraembryonic coelom
         b. this cavity splits the lateral plate mesoderm into
             - splanchnic mesoderm
                  forms heart, visceral pericardium, blood vessels, smooth muscle & CT of
                  respiratory & digestive organs, visceral pleura & peritoneum
             - somatic mesoderm
                  gives rise to bones, ligaments, & dermis of limbs & parietal pleura, pericardium, &
                  peritoneum
      5. development of the cardiovascular system
               rd
          a. 3 , angiogenesis
              - formation of blood vessels
              - begins in the extraembryonic mesoderm, connecting stalk, & chorion
              - mesodermal cells become hemangioblasts
                  these develop into angioblasts & then aggregate to form blood islands
          b. heart forms from splanchnic mesoderm on days 18 &19
              - called cardiogenic area
                                           rd
              - begins to beat by end of 3 week
      6. development of the chorionic villi & placenta
          a. chorionic villi
                                     nd
              - develop at end of 2 week
                             rd
              - by end of 3 week have blood capillaries in them
              - intervillous spaces
          b. placenta
                                    th
              - by beginning of 12 week, have 2 distinct layers
                  chorionic villi
                  deciduas basalis
              - nutrient & waste exchange
          c. connected to embryo by umbilical cord
              - 1 vein
              - 2 arteries
Placenta Previa
   placenta implanted too low in uterus
   may lead to spontaneous abortion
   dangers to fetus
      premature birth
      intrauterine hypoxia
   dangers to mom
      mortality due to hemorrhage & infection
   main symptom is sudden, painless, bright-red vaginal bleeding
   C-section delivery
   D. Fourth Week of Development
      1. organogenesis
          a. development of organs & systems
              - minimal functioning
               th    th
          b. 4 – 8 weeks
      2. embryonic folding
          a. different rates of growth of parts responsible for this
          b. head fold & tail fold
          c. 2 lateral folds
              - incorporate a part of the yolk sac which will become primitive gut
          d. stomodeum
              - future oral cavity
          e. proctodeum
              - urogenital & anal openings
      3. pharyngeal arches
          a. develop on each side of future head and neck regions
          b. pharyngeal clefts are spaces in between
          c. pharyngeal pouches inside
      4. otic placode
          a. future internal ear
      5. lens placode
      6. upper & lower limb buds
      7. heart prominence
   E. Fifth Through Eighth Weeks of Development
          th
         1. 5 week
              a. rapid development of brain
              th
         2. 6 week
              a. limbs show substantial development
              b. neck and trunk begin to straighten
              c. heart is 4-chambered
              th
         3. 7 week
              a. regions of limbs distinct
              b. digits appear but webbed
              c. tail shorter
              d. eyes open
              e. auricles of ears visible
              th
         4. 8 week
              a. limbs apparent
              b. digits no longer webbed
              c. eyelids come together & may fuse
              d. tail disappears
              e. external genitals begin to differentiate
II. Fetal Period
     A. Tissue & Organs Grow & Differentiate
III. Teratogens
     A. Intro
         1. any agent or influence that causes developmental defects
     B. Chemicals & Drugs
         1. alcohol
              a. #1 fetal teratogen
              b. fetal alcohol syndrome
                   - one of most common causes of mental retardation
                   - slow growth before & after birth
                   - characteristic facial features
                   - defective heart & other organs
                   - malformed limbs
                   - genital abnormalities
                   - CNS damage
                   - hyperactivity
                   - ADHD type symptoms
         2. viruses
              a. Hep B, C, & papilloma
         3. pesticides
         4. defoliants
         5. industrial chemicals
         6. some hormones
         7. antibiotics
         8. anticoagulants, anticonvulsants, antitumor agents, thyroid drugs, thalidomide, DES, &
         others
         9. LSD
         10. cocaine
     C. Cigarette Smoking
         1. cause of low infant birth weight
         2. strong association between smoking & higher fetal & infant mortality rate
         3. higher risk of ectopic pregnancy
         4. may cause cardiac abnormalities as well as anencephaly
         5. factor in development of cleft lip & palate
         6. linked with SIDS
         7. respiratory problems
     D. Irradiation
       1. exposure to xrays or radioactive isotopes during development may cause
           a. microcephaly
           b. mental retardation
           c. skeletal malformations
IV. Prenatal Diagnostic Tests
    A. Fetal Ultrasonography
       1. uses include
           a. determining an accurate fetal age
           b. confirm pregnancy
           c. evaluate fetal viability & growth
           d. determine fetal position
           e. identify multiple pregnancies
           f. identify fetal-maternal abnormalities
           g. adjunct to procedures such as amniocentesis
    B. Amniocentesis
       1. withdraw amniotic fluid & analyze fetal cells & dissolved substances
       2. used to test for
           a. genetic abnormalities
                - Down syndrome
                - hemophilia
                - Tay-Sachs
                - sickle cell
                - muscular dystrophy
           b. survivability of the fetus
       3. done at 14-18 weeks of gestation
       4. use ultrasound to determine position of the fetus & placenta
       5. performed only when there is a risk of genetic defects because there is a 0.5% chance
       of spontaneous abortion
    C. Chorionic Villus Sampling
       1. CVS
       2. catheter guided through vagina & cervix to the chorionic villi by ultrasound or could use a
       needle like in amniocentesis
       3. gives same information as amniocentesis
       4. advantages
           a. performed as early as 8 weeks
       5. is riskier with a 1-2% chance of spontaneous abortion
    D. Noninvasive Prenatal Tests
       1. maternal alphafetoprotein (AFP) test
           a. protein synthesized in the fetus which passes to maternal circulation
           b. highest levels during weeks 12-15
           c. later, AFP not produced
           d. so high levels after week 16 usually indicate a neural tube defect
           e. 95% accuracy
       2. Quad AFP plus
           a. AFP plus 3 other molecules
                - Down syndrome
                - trisomy 18
                - neural tube defects
V. Maternal Changes During Pregnancy
    A. Hormones of Pregnancy
       1. progesterone & estrogens
                 st
           a. 1 3-4 months of pregnancy, secreted by corpus luteum
           b. helps to maintain endometrium & prepare mammary glands to secrete milk
           c. placenta takes over secretion when formed
           d. progesterone ensures myometrium is relaxed & cervix is closed
       2. hCG
             a. maintains corpus luteum
             b. test for pregnancy
         3. relaxin
                                                st
             a. produced by corpus luteum 1 then placenta
             b. increases flexibility of pubic symphysis & ligaments of SI & sacrococcygeal joints
             c. helps dilate cervix
         4. human chorionic somatomammotropin (hCS)
             a. from placenta
             b. helps prepare mammary glands
             c. increases protein synthesis
             d. decreases use of glucose by mom & promotes release of fatty acids to make glucose
             available to fetus
         5. corticotropin-releasing hormone (CRH)
             a. thought to be part of the “clock”
                 - establishes timing of birth
             b. women who have hi levels early in pregnancy more likely to deliver prematurely; low
             levels likely to deliver after due date
             c. increases secretion of cortisol which is needed for maturation of fetal lungs &
             production of surfactant
Early Pregnancy Tests
    detect levels of hCG
    8 days after fertilization
    B. Changes During Pregnancy
         1. weight gain
         2. increased storage of nutrients
         3. breast enlargement
         4. low back pain
         5. CV changes
             a. SV increases by 30%
             b. CO increases by 20-30%
             c. HR increases 10-15%
             d. BV increases 30-50%
         6. respiratory changes
             a. tidal volume increases 30-40%
             b. dyspnea may occur
         7. digestive
             a. heartburn
             b. constipation
         8. urinary
             a. increased frequency
         9. skin
             a. increased pigmentation
Pregnancy-Induced Hypertension
    major cause is preeclampsia
         sudden HTN
         large amounts of protein in urine
         edema
                               th
         usually after the 20 week
         might be an autoimmune or allergic reaction due to presence of fetus
    if there is also convulsions & coma, it is eclampsia
VI. Exercise And Pregnancy
    A. Moderate Physical Activity
         1. good
VII. Labor
    A. Parturition
         1. fetus is expelled from the uterus through the vagina
    B. Mechanism
       1. estrogens rise sharply in blood
           a. due to increase of CRH by placenta
           b. gives us ACTH
           c. ACTH stimulates fetal adrenal gland to secrete cortisol & DHEA
           d. DHEA is then converted to estrogen
       2. estrogens increase the receptors for oxytocin on uterine smooth muscle
       3. oxytocin stimulates uterine contractions
           a. positive feedback
    C. True Labor vs. False Labor
       1. true
           a. uterine contractions occur at regular intervals
           b. usually produces pain
           c. as interval between contractions shortens, contractions intensify
           d. may have localization of pain in the back
                - intensified by walking
           e. dilation of cervix
           f. “show”
                - discharge of blood-containing mucus
       2. false
           a. pain in abdomen in irregular intervals
           b. pain doesn’t intensify
           c. walking has no affect
           d. no “show”
           e. no cervical dilation
    D. Stages of True Labor
       1. stage of dilation
           a. onset of labor to complete dilation of cervix
           b. typically lasts 6-12 hours
           c. regular contractions
           d. rupturing of amniotic sac
           e. complete cervical dilation (10cm)
       2. stage of expulsion
           a. from complete cervical dilation to delivery of baby
           b. 10 min to several hours
       3. placental stage
           a. delivery of placenta
           b. “afterbirth”
           c. 5 – 30 min
    E. Puerperium
       1. 6 week period where maternal reproductive organs return to pre-pregnancy state
       2. uterus involutes
       3. for 2-4 weeks, women have discharge, lochia
           a. blood, then serous fluid
Dystocia & Cesarean Section
    Dystocia
       difficult labor
       due to abnormal fetal position or too small birth canal
    Cesarean section
       C-section
       Cut through abdominal wall & uterus
VIII. Adjustments Of The Infant At Birth
    A. Respiratory Adjustments
       1. after delivery, mom no longer supplying O2
       2. CO2 begins to build in the blood
           a. stimulates respiratory center in medulla
           b. respiratory muscles stimulated to contract
            st
       3. 1 breath is unusually deep as the lungs contain no air
           a. baby exhales vigorously & this produces cry
            st
       4. 1 2 weeks may breath 45/min
    B. Cardiovascular Adjustments
       1. closure of the foramen ovale
           a. at birth
           b. diverts deoxygenated blood to lungs for the first time
           c. becomes fossa ovalis
       2. ductus arteriosus shuts
           a. due to contractions of smooth muscle in its wall
               - probably due to bradykinin from lungs
           b. becomes ligamentum arteriosum
           c. doesn’t close completely until about 3 months
       3. umbilical arteries become medial umbilical ligaments
       4. umbilical vein becomes ligamentum teres
       5. ductus venosus collapses & becomes lagamentum venosum
       6. pulse may be 120-160/min
Premature Infants
    weighs less than 2500g (5.5 lbs)
    due to
       poor prenatal care
       drug abuse
       history of premature delivery
       mother below 16 or above 35
    major problem is RDS
       insufficient surfactant
IX. The Physiology Of Lactation
    A. Lactation
       1. secretion & ejection of milk from the mammary glands
       2. prolactin
           a. promotes milk synthesis & secretion
           b. from anterior pituitary
           c. progesterone inhibits effects of prolactin
           d. after delivery, inhibition is removed
           e. prolactin secretion is stimulated by sucking action of infant
               - decreases PIH
               - increases PRH
       3. oxytocin
           a. causes release of milk into mammary ducts via milk ejection reflex
           b. active suckling stimulates release of oxytocin from posterior pituitary
           c. milk ejection or milk let-down
           d. also stimulated by
               - hearing a baby’s cry
               - touching the mother’s genitals
       4. colostrums
           a. initial cloudy fluid
           b. not as nutritious as milk
               - less lactose & virtually no fat
                                               th
           c. true milk appears about the 4 day
           d. both provide antibodies
       5. each time baby nurses
           a. PRH increases
           b. PIH decreases
           c. without prolactin, milk secretion is lost
       6. lactation can block ovarian cycle
            a. however, this is inconsistent & should not be used as birth control
    B. Benefits of Breast-Feeding
        1. nutritional
            a. contains
                 - fatty acids
                 - lactose
                 - amino acids
                 - minerals
                 - vitamins
                 - H2O
            b. good for digestion, brain development, & growth
        2. beneficial cells
            a. WBCs
                 - neutrophils
                 - macrophages
        3. beneficial molecules
            a. Ig A
            b. B12–binding protein
                 - bacteria can’t get to the B12
            c. lactoferrin
                 - ties up iron
            d. fatty acids
                 - some can disrupt viral coverings
            e. lysozyme
                 - disrupts bacterial cell walls
            f. interferons
        4. decreased incidence of diseases later in life
            a. lymphoma
            b. heart disease
            c. allergies
            d. respiratory & GI infections
            e. ear infections
            f. diarrhea
            g. diabetes mellitus
            h. meningitis
            i. protects mom against osteoporosis & breast cancer
        5. miscellaneous benefits
            a. supports optimal growth
            b. enhances intellectual & neurological development
            c. fosters mother-infant relations
            d. more easily absorbed than cow’s milk
X. Inheritance
    A. Intro
        1. passage of inherited traits from one generation to the next
        2. genetics
    B. Genotype & Phenotype
        1. all human cells have 23 pairs of chromosomes
            a. one from mom
            b. one from dad
            c. called homologous chromosomes
                 - contain genes that control the same trait
            d. alternative forms of a gene that code for the same trait & are at the same location on
            homologous chromosomes are alleles
                 - one allele for coarse hair
                 - one allele for fine hair
2. mutation is a permanent heritable change in an allele that produces a different variant of
the same trait
3. relationship of genes to heredity
    a. PKU
        - unable to manufacture the enzyme phenylalanine hydroxylase
    b. allele that codes for enzyme is P
    c. mutated allele that fails to produce the enzyme is p
    d. use Punnett square to show possible combinations


                                 P                 p
                    P          PP                  Pp
                    p          Pp                  pp

    e. 3 different combination of genes, or genotypes
        - PP
        - Pp
        - pp
    f. PP or Pp will not have the disease, only pp will
    g. dominant allele
        - dominates or masks the presence of another allele & is fully expressed
        - trait is a dominant trait
        - P in this example
    h. recessive allele
        - allele whose presence is completely masked
        - trait is a recessive trait
        - p in this example
    i. homozygous
        - person with the same alleles on homologous chromosomes
        - PP is homozygous dominant
        - pp is homozygous recessive
    j. heterozygous
        - person with different alleles on homologous chromosomes
    k. phenotype refers to how the genetic makeup is expressed
        - physical or outward expression
        - PP & Pp both have phenotype of being able to produce the enzyme
    l. carriers are those that possess the recessive gene but do not pass it to their offspring
4. genome imprinting
    a. when phenotype is dramatically different depending on the parental origin
    b. Angelman syndrome which results when the gene for a particular abnormal trait is
    inherited from the mother & Prader-Willi syndrome when it is inherited from the father
5. dominant alleles for severe disorders are usually lethal & kill the embryo/fetus
    a. exception is Huntington disease which does not manifest until adulthood
6. nondisjunction
    a. error in cell division that results in an abnormal number of chromosomes
    b. homologous chromosomes or sister chromatids fail to separate
    c. cell has chromosomes added or deleted
        - aneuploid
            monosomic
                 (2n – 1)
                 missing a chromosome
            trisomic
                 (2n + 1)
                 has an extra chromosome
    d. usually occurs during meiosis but rarely in mitosis
7. translocation
       a. error in meiosis
       b. 2 chromosomes that are not homologous break & interchange portions of their
       chromosomes
C. Variations on Dominant-Recessive Inheritance
   1. incomplete dominance
       a. neither member of a pair of alleles is dominant over the other
       b. heterozygote has a phenotype intermediate between homozygous dominant &
       homozygous recessive
       c. sickle cell disease
                                             A   A
             - homozygous dominant, Hb Hb , has normal Hgb
                                             S   S
             - homozygous recessive, Hb Hb , has sickle cell disease & severe anemia
                                    A    S
             - heterozygous, Hb Hb , has minor problems with anemia & are carriers
                  have sickle cell trait
   2. multiple-allele inheritance
       a. genes may have more than 2 forms of an allele
       b. ABO blood group
             - A, B, AB, O result from inheritance of 6 combinations of 3 different alleles of the I
             gene
                   A
                  I produces the A antigen
                   B
                  I produces the B antigen
                  i produces neither A or B
             - type A
                   A A     A
                  I I or I i
             - type B
                   B B     B
                  I I or I i
             - type AB
                   A B
                  I I
             - type O
                  ii
                A      B
             - I & I are dominant
             - i is recessive
                A      B
             - I & I are both expressed & said to be codominant
   3. complex inheritance
       a. polygenic inheritance
             - inherited traits controlled by the combined effects of 2 or more genes
       b. complex inheritance
             - inherited traits controlled by the combined effects of many genes & environmental
             factors
             - skin color, hair color, height, etc
D. Autosomes, Sex Chromosomes, & Sex Determination
   1. 46 chromomsomes or 23 pairs
   2. 22 pairs look alike & have the same appearance in males & females
       a. called autosomes
          rd
   3. 23 pair are sex chromosomes
       a. look different in males & females
       b. X chromosome
       c. Y chromosome
       d. females can only produce X containing oocytes
       e. males can produce sperm containing either the X or the Y chromosome
       f. male & female embryos develop identically until about 7 weeks
             - if it is a male, the SRY gene on the Y chromosome becomes functional & initiates
             male development
                  if not functional, female development ensues
E. Sex-Linked Inheritance
   1. due to genes present on the X chromosome but absent on the Y
   2. red-green color blindness
           a. carried on X chromosome
           b. males affected more than females
           c. others include
               - hemophilia
               - fragile X syndrome
               - nonfunctional sweat glands
               - certain forms of diabetes
               - some types of deafness
               - uncontrollable rolling of the eyes
               - absence of central incisors
               - night blindness
               - one form of cataract
               - juvenile glaucoma
               - juvenile muscular dystrophy
       3. X-chromosome inactivation
           a. females have a double set of all genes due to 2 X chromosomes
           b. inactivation or lionization reduces the genes to a single set
           c. in the cell with the inactivated chromosome, have a Barr body
               - dark-staining body

Disorders
   Infertility
       female infertility
            inability to conceive
            occurs in about 10% of women
            may be caused by
                ovarian disease
                obstruction of the uterine tubes
                conditions in which the uterus is not adequately prepared to receive a fertilized ovum
                inadequate body fat
                     too little can delay menarche, inhibit ovulation or cause amenorrhea
                     also see this in very obese
       male infertility (sterility)
            inability to fertilize a secondary oocyte
            due to
                inadequate quantity of sperm
                obstructed transport through the ducts
                seminiferous tubules sensitive to xrays, infections, toxins, malnutrition, high scrotal
                temps
       fertility techniques
            in vitro fertilization (IVF)
                  st
                1 in July 1978, Manchester England
                fertilization in a petri dish
                female given FSH to superovulate, aspirate oocytes & transfer to a solution
                containing sperm
                when zygote is 8 cells to 16 cells, implanted into uterus
                intracytoplasmic sperm injection is same process but inject sperm into secondary
                oocyte
            embryo transfer
                man’s semen used to artificially inseminate an oocyte donor
                after fertilization in donor’s uterine tube, obtain morula or blastocyst & transfer to the
                infertile woman
            gamete intrafallopian transfer (GIFT)
                mix sperm & oocytes outside body & then introduce into oviduct
                bypasses too much acidity or mucus
   Congenital Defects
  abnormality present at birth & usually before
  occur during organogenesis as developing structures are very susceptible to genetic &
  environmental influences
  major structural defects occur in 2-3% of liveborn infants & are the leading cause of infant
  mortality (about 21%)
  many can be prevented by
      supplementation
          folic acid – neural tube defect
          iodine – Cretinism
      avoidance of teratogens
Down Syndrome
  due to trisomy 21
  1 in 900 infants born with it
  older women more at risk
      1 in 3000 for women under 30
      1 in 300 in 35-39
      1 in 9 at age 48
  characterized by
      mental retardation
      retarded physical development
          short
          stubby fingers
      distinctive facial features
          large tongue
          flat profile
          broad skull
          slanting eyes
          round head
      kidney defects
      suppressed immune system
      malformations of heart, ears, hands, & feet
      sexual maturity rarely attained
      shorter life expectancy