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					GENETICS
                  Genetics
• The study of heredity.

• Gregor Mendel (1860’s) discovered the
  fundamental principles of genetics by breeding
  garden peas.
          Gregor Mendel
• Austrian Monk in a Monastery in what is
  now the Czech Republic
• Trained as a mathematician and natural
  scientist
• 8 years of experiments with garden
  peas
Mendel’s 7 Traits
           Mendelian genetics
• Character
        (heritable feature, i.e., fur
  color)
• Trait
         (variant for a character, i.e.,
  brown)
• True-bred
  (all offspring of same variety)
• Hybridization
        (crossing of 2 different true-
  breds)
• P generation (parents)
• F1 generation (first filial generation)
                 Leading to the Law of
                     Segregation
•   Alternative versions of genes
    (alleles) account for variations in
    inherited characteristics
•   For each character, an organism
    inherits 2 alleles, one from each
    parent
•   If the two alleles differ, then one,
    the dominant allele, is fully
    expressed in the organism’s
    appearance; the other, the
    recessive allele, has no noticeable
    effect on the organism’s
    appearance
•   The alleles for each character
    segregate (separate) during
    gamete production (meiosis).
•   Mendel’s Law of Segregation
        The Law of Independent
              Assortment
• Law of Segregation
  involves 1 character.
  What about 2 (or more)
  characters?
• Monohybrid cross vs.
  dihybrid cross
• The two pairs of alleles
  segregate independently
  of each other.
• Mendel’s Law of
  Independent
  Assortment
                 Genetics
• Alleles
  1. Alternative forms of genes.
  2. Units that determine heritable traits.
  3. Dominant alleles (TT - tall pea plants)
         a. homozygous dominant
  4. Recessive alleles (tt - dwarf pea plants)
         a. homozygous recessive
  5. Heterozygous (Tt - tall pea plants)
              Phenotype
• Outward appearance
• Physical characteristics

• Examples:
         1.     tall pea plant
         2.     dwarf pea plant
                Genotype
• Arrangement of genes that produces the
  phenotype
• Example:
  1. tall pea plant
           TT = tall (homozygous dominant)
  2. dwarf pea plant
           tt = dwarf (homozygous recessive)
  3. tall pea plant
           Tt = tall (heterozygous)
          Punnett square
• A Punnett square is used to show the
  possible combinations of gametes.
    Breed the P generation
• tall (TT) vs. dwarf (tt) pea plants

             T     T


         t


         t
    tall (TT) vs. dwarf (tt) pea plants


       T     T


             Tt      produces the
t      Tt
                     F1 generation

t      Tt    Tt      All Tt = tall
                     (heterozygous tall)
   Breed the F1 generation
• tall (Tt) vs. tall (Tt) pea plants

               T     t


          T


          t
tall (Tt) vs. tall (Tt) pea plants

     T     t
                      produces the
     TT    Tt         F2 generation
 T
                     1/4 (25%) = TT
     Tt    tt        1/2 (50%) = Tt
 t
                     1/4 (25%) = tt
                      1:2:1 genotype
                      3:1 phenotype
          Monohybrid Cross
• A breeding experiment that tracks the inheritance
  of a single trait.

• Mendel’s “principle of segregation”
  a. pairs of genes separate during gamete
     formation (meiosis).

  b. the fusion of gametes at fertilization pairs
     genes once again.
•   Drop & Drag Genetics: Monohybrid Cross
        Punnett Square Practice
•   World Builders: Punnett Squares
•   Introducing Punnett Squares
•   Chicken Punnett Squares
•   Punnett Square Examples
•   Probability of Inheritance
•   Punnett Square Step-Thru
•   Punnett Squares for Dummies
•   Baby Steps thru Punnett Squares
•   Monohybrid Tutorial
     Homologous Chromosomes

eye color locus                       eye color locus
B = brown eyes                        b = blue eyes




                                      This person would
                                      have brown eyes (Bb)



                  Paternal Maternal
         Meiosis - eye color
                                     B


                    B                     sperm
                                     B

   Bb
                                         haploid (n)
                                     b
diploid (2n)        b

                                     b
        meiosis I       meiosis II
          Monohybrid Cross
• Example:        Cross between two heterozygotes
                  for brown eyes (Bb)
BB = brown eyes
                            B      b      male
Bb = brown eyes                           gametes
bb = blue eyes
                     B
      Bb x Bb
                     b


                         female gametes
          Monohybrid Cross

              B    b

                        1/4 = BB - brown eyed
          B   BB   Bb   1/2 = Bb - brown eyed
Bb x Bb                 1/4 = bb - blue eyed

          b   Bb   bb
                           1:2:1 genotype
                            3:1 phenotype
             Dihybrid Cross
• A breeding experiment that tracks the inheritance
  of two traits.
• Mendel’s “principle of independent assortment”
  a. each pair of alleles segregates independently
     during gamete formation (metaphase I)
  b. formula: 2n (n = # of heterozygotes)
   Independent Assortment
• Question: How many gametes will be produced
            for the following allele arrangements?


• Remember:       2n (n = # of heterozygotes)

  1.   RrYy
  2.   AaBbCCDd
  3.   MmNnOoPPQQRrssTtQq
                Answer:
1. RrYy: 2n = 22 = 4 gametes
      RY Ry rY ry

2. AaBbCCDd: 2n = 23 = 8 gametes
      ABCD ABCd AbCD AbCd
      aBCD aBCd abCD abCD

3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64
gametes
             Dihybrid Cross
• Example:        cross between round and yellow
                  heterozygous pea seeds.

 R   = round                RrYy x RrYy
 r   = wrinkled
 Y   = yellow
                     RY Ry rY ry x RY Ry rY ry
 y   = green          possible gametes produced
     Dihybrid Cross
     RY   Ry   rY   ry

RY


Ry


rY


ry
              Dihybrid Cross
      RY    Ry      rY    ry
                                 Round/Yellow:     9
RY RRYY     RRYy   RrYY   RrYy
                                 Round/green:      3
Ry RRYy     RRyy   RrYy   Rryy
                                 wrinkled/Yellow: 3

rY RrYY     RrYy   rrYY   rrYy   wrinkled/green:   1


ry   RrYy   Rryy   rrYy   rryy   9:3:3:1 phenotypic ratio
                Test Cross
• A mating between an individual of unknown genotype
  and a homozygous recessive individual.
• Example: bbC__ x bbcc
  BB = brown eyes
  Bb = brown eyes
                                 bC      b___
  bb = blue eyes
                           bc
  CC = curly hair
  Cc = curly hair
  cc = straight hair
                Test Cross

     • Possible results:

       bC      C
             b___               bC       c
                                       b___

bc    bbCc   bbCc   or     bc   bbCc   bbcc
      Incomplete Dominance
• F1 hybrids have an appearance somewhat in
  between the phenotypes of the two parental
  varieties.
• Example: snapdragons (flower)
• red (RR) x white (rr)
                                R     R

     RR = red flower       r
     rr = white flower
                           r
    Incomplete Dominance


      R   R


     Rr   Rr   produces the
r              F1 generation

r    Rr   Rr   All Rr = pink
               (heterozygous pink)
            Codominance
• Two alleles are expressed (multiple alleles)
  in heterozygous individuals.
• Example: blood
  1.   type A    =   IAIA or IAi
  2.   type B    =   IBIB or IBi
  3.   type AB   =   I A IB
  4.   type O    =   ii
             Codominance
• Example:           homozygous male B (IBIB)
                               x
                     heterozygous female A (IAi)

              IB         IB

       IA    IA IB      IA IB
                                  1/2 = IAIB
                                  1/2 = IBi
       i      IB i       IB i
             Codominance

• Example: male O (ii) x female AB (IAIB)


               IA     IB

         i    IA i   IB i   1/2 = IAi
                            1/2 = IBi

         i    IA i   IB i
              Codominance
• Question:      If a boy has a blood type O and
                 his sister has blood type AB,
                 what are the genotypes and
                 phenotypes of their parents.

• boy - type O (ii) X girl - type AB (IAIB)
                 Codominance
• Answer:

      IA     i

IB   IA IB          Parents:
                    genotypes = IAi and IBi
                    phenotypes = A and B
i            ii
          Sex-linked Traits
• Traits (genes) located on the sex
  chromosomes



• Example:      fruit flies
     (red-eyed male) X (white-eyed female)
           Sex-linked Traits
                 Sex Chromosomes

                         fruit fly
                         eye color




XX chromosome - female          Xy chromosome - male
          Sex-linked Traits
• Example:       fruit flies
     (red-eyed male) X (white-eyed female)
• Remember: the Y chromosome in males
  does not carry traits.

RR = red eyed                      XR        y
Rr = red eyed
rr = white eyed             Xr

Xy = male
                            Xr
XX = female
        Sex-linked Traits


      XR      y

Xr   XR Xr   Xr y
                    1/2 red eyed and female
                    1/2 white eyed and male
Xr   XR Xr   Xr y
          Population Genetics
• The study of genetic changes in populations.
• The science of microevolutionary changes in
  populations.
• Hardy-Weinberg equilibrium:
     the principle that shuffling of genes that occurs
     during sexual reproduction, by itself, cannot
     change the overall genetic makeup of a population.
• Hardy-Wienberg equation:         1 = p2 + 2pq + q2
             Question:
• How do we get this equation?

Answer:   “Square” 1 = p + q
                          
                    12 = (p + q)2
                          
                    1 = p2 + 2pq + q2
    Hardy-Wienberg equation
• Five conditions are required for Hardy-Wienberg
  equilibrium.
  1. large population
  2. isolated population
  3. no net mutations
  4. random mating
  5. no natural selection
            Important
• Need to remember the following:

    p2 = homozygous dominant
    2pq = heterozygous
    q2 = homozygous recessive
                Question:
• Iguanas with webbed feet (recessive trait) make
  up 4% of the population. What in the population
  is heterozygous and homozygous dominant.
                Answer:

1. q2 = 4% or .04   q2 = .04      q = .2

2. then use 1 = p + q
            1 = p + .2   1 - .2 = p    .8 = p
3. for heterozygous use 2pq
                   2(.8)(.2) = .32 or 32%
4. For homozygous dominant use p2
                         .82 = .64 or 64%
    Hardy-Wienberg equation

          1 = p2 + 2pq + q2
•   64% = p2    = homozygous dominant
•   32% = 2pq   = heterozygous
•   04% = q2    = homozygous recessive
•   100%
                  Karyotypes
      • New methods for identifying mutations




Hi Mrs. Hoover!
            A Karyotype
Definition
• A photographic
  arrangement of
                   1        2              3         4         5
  a complete set
  of chromosomes
  of a cell or
                   6    7        8         9    10       11    12
  organism

                   13       14        15        16        17    18


                   19            20        21        22        X Y
       Obtaining a Sample
• Fetal samples for karyotypes are
  commonly obtained in two ways
  1. Amniocentesis – sample taken from
     the fluid of the amniotic sac
  2. Chorionic Villus Sampling – sample
     taken fetal tissue that forms part of
     the placenta
  Variations in Chromosomal
            Number
• Euploidy – the normal number and sets
  of chromosomes

• Polyploidy – the presence of three or
  more complete sets of chromosomes

• Aneuploidy – the presence of additional
  or missing individual chromosomes
      Types of Aneuploidy
• Monosomy – one less chromosome
          (23 x 2) – 1 = 45

• Trisomy – one additional chromosome
            (23 x 2) + 1 = 47
     Aneuploidy in Humans
• When aneuploidy occurs in humans,
  syndromes can result. Examples
  include the following:
    1. Trisomy 13
    2. Trisomy 18
    3. Down Syndrome
    3. Turner Syndrome
    4. Klinefelter Syndrome
    5. XYY Syndrome
            Trisomy 13
• Chromosomal Variation – Trisomy 13
  (three copies of chromosome 13)

• Occurrence – 1 in 5000
       Features of Trisomy 13
•   Severe mental retardation
•   Head and facial abnormalities
•   Extra fingers and toes
•   Kidney malformations
•   Heart defects
•   Early death
            Trisomy 18
• Chromosomal Variation – Trisomy 18
  (three copies of chromosome 18)

• Occurrence – 1 in 5000
        Features of Trisomy 18

•   Severe mental retardation
•   Head and facial malformations
•   Malformations of the hands and feet
•   Skeletal malformations
•   Kidney malformations
•   Structural heart defects
•   Early death
         Down Syndrome
• Chromosomal Variation – Trisomy 21
  (three copies of chromosome 21)

• Occurrence – 1 in 800-1000
    Features of Down Syndrome
•   Low muscle tone
•   Head and facial malformations
•   Abnormalities of the extremities
•   Mental retardation
•   Heart malformations
•   Increased risk of infectious disease
•   Early death
        Turner Syndrome
• Monosomy of sex chromosome
  (only one X chromosome present)

• Occurrence – 1 in 2500 live female
  births
    Features of Turner Syndrome

•   Short stature
•   Lack of ovarian development
•   Neck abnormalities
•   Skeletal disorders
•   Increased risk of osteoporosis,
    cardiovascular constriction, diabetes,
    and kidney and thyroid problems
      Klinefelter Syndrome
• Trisomy of sex chromosome - XXY
  (An additional X chromosome in males)
• Occurrence – 1 in 500-1000 males
    Features of Klinefelter Syndrome

•   Tall
•   Sexually underdeveloped
•   Infertility
•   Sparse facial and body hair
•   Developmental delays
•   Increased risk of autoimmune disorders,
    breast cancer, osteoporosis, leg ulcers,
    depression, and dental problems
         XYY Syndrome
• Trisomy of sex chromosome – XYY
  (An additional Y chromosome in males)

• Occurrence – 1 in 1000-2000 men
  Features of XYY Syndrome
• Taller
• Comparatively low weight relative to
  stature
• Larger craniofacial dimensions
• Severe acne in adolescence
• Behavior problems
• Learning disabilities
• Slightly lower IQ than normal

				
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