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					Genetics and Heredity
• Haploid
  – A cell with one of each chromosome. (n)
• Diploid
  – A cell with two of each chromosome (2n)
• Meiosis
  – Process that reduces the number of chromosomes to
    half the number in the original cell.
  – Produces haploid cells called gametes.
• Meiosis I
  – Similar to mitosis stages.
  – Difference: In metaphase-the chromosomes line up
    as a homologous pair. One entire “X”(the original
    and the duplicate) moves to each cell in anaphase.
• Meiosis II
  – Chromosomes do not duplicate at the beginning of
    meiosis II because they are already duplicated after
    Meiosis I.
  – At the end: Four haploid cells
• Forming Gametes
  – After meiosis in males four haploid cells are formed
    =spermatogenesis.
  – In females one haploid egg is formed=oogenesis.
• Why is it important that one egg form and four
  sperm?
               Karyotype
• A karyotype is a picture of an individual‟s
  chromosomes.
• A normal human karyotype should have 46
  chromosomes organized into 23 pairs.
• The first 22 pairs are the autosomal
  (regular) chromosomes.
• The last pair are the sex chromosomes.
  – XX=female and XY=male
        Chromosomal Mutations
• These are usually very harmful because they involve a
  large chunk of DNA.
• Deletion: piece of chromosome is completely lost.
  Inversion: piece of a chromosome breaks off and is
  reattached to the same chromosome upside-down.
• Translocation: piece of a chromosome breaks off and
  reattaches to another chromosome.

• Nondisjunction: chromosomes do not separate
  correctly during meiosis.
   – The organism that results after fertilization has too many or
     too few chromosomes.
        Detecting Nondisjunction
• Pre-natal
  – Amniocentesis: remove a sample of the amniotic
    fluid surrounding the fetus.
  – Chorionic Villi Sampling: Sample tissue near the
    placenta.
• These can be used to create a karyotype.
• Humans should have two of each chromosome.
  If there is only one the condition is called
  monosomy. If there is three the condition is
  called trisomy.
• Ex. Trisomy 21=Down Syndrome
                Gregor Mendel
• Conducted research on heredity-passing of
  characteristics from parents to offspring.
• Studied science and statistics.
• Based most of his studies on peas plants.
• Observed characteristics of pea plants:
  –   Plant height: long or short
  –   Pod color: green or yellow
  –   Seed structure: smooth or wrinkled
  –   Seed color: yellow or green
  –   Flower color: purple or white
    What did Mendel observe?
• When he planted seeds from purple
  flowering plants some offspring had purple
  flowering plants and others had white
  flowering plants.
• When he planted smooth seeds he had
  plants that produced smooth seeds and some
  plants that produced wrinkled seeds.
• Mendel discovered there were 2 forms of each trait/gene.
  Each form of a trait or gene is called an allele.
• Each parent gives ½ of the genetic material to a child,
  therefore each parent gave 1copy so people have 2 alleles
  for each gene.

• Mendel began to realize that one allele could “cover up” the
  other allele.
• Dominant and recessive alleles.
   One allele is dominant and is always expressed
   One allele is recessive and is “covered up” by the other allele
• How/When do we get these traits?
   – Law of segregation: a pair of factors is separated during gamete
     formation.
   – This means: Alleles for each gene pass to different gametes during
     meiosis.
• The traits you express are your phenotype.
• Alleles show your genotype. The actual genetic make-up.
• A gene is a trait and the alleles are the different forms of
  that trait.

Ex. Plant Height
  T=Tall, t=short
    Flower Color
  P=purple, p=white
• Use one letter to represent a gene/trait. Capital (BIG) letters
  for dominant, lower case (little) letters for recessive.

• If a plant is Tt for the height gene. This means you received
  a „T‟ allele from one parent and a „t‟ allele from another
  parent. They are on the same chromosome however.
• Homozygous (“homo” means same)- genotype where the
  organism has two of the same alleles for a gene.
   – a.k.a Pure-breeding or True-breeding
   – TT or tt
• Heterozygous (“hetero” means different)-genotype
  where the organism has two different alleles for a gene.
   – a.k.a Hybrid or Carrier
   – Tt
• When alleles are combined they may or may not be
  expressed (shown)
• Dominant traits are always expressed.
• Recessive traits are sometimes expressed. Only when
  the organism has two recessive alleles. Homozygous
  recessive.
              Breeding terms!
• Cross-
  – Monohybrid: cross that involves one trait. 4 box
    punnett square. Ex. Flower color
  – Dihybrid: cross that involves two traits. 16 box
    punnett square. Ex. Flower color AND pea color.
• P generation-first two individuals in a cross
  (parents)
• F1 generation-offspring of the P generation
• F2 generation-offspring of the F1 generation
• Self-fertilization (selfed)-organism is crossed
  with a genotype exactly like itself.
• Test Cross-A cross to determine an unknown
  genotype by crossing that individual with a
  homozygous recessive individual.
• Ex. Deafness in dogs is a recessive trait that is
  not favorable to dog breeders. A dog breeder has
  a dog that can hear and wants to mate him. How
  can he determine if the dog carries the allele for
  deafness? Show the cross(es).
• Rabbits
  – B: Big Feet, b: small feet
  – F: Floppy ears, f: straight ears
  – Bk: Black rabbits (dominant), Br: Brown rabbits


• Peas
  –   A: axial flowers, a: terminal flowers
  –   I: inflated pod structure, i: constricted pod structure
  –   S: smooth seeds, s: wrinkled seeds
  –    P: purple flowers, p: white flowers
                   Types of Dominance
• The type of dominance we have been studying is complete
  dominance.
   – Two phenotypes possible for each trait.


• Incomplete dominance: When the F1 generation has a
  phenotype completely different from the parents.
   – Three phenotypes are available for each trait. The third phenotype
     is a mix of the other two.
   – Ex. On overhead of flowers.


• Codominance: When both genes in a heterozygous
  organism are expressed.
   – Three phenotypes are available for each trait. The third phenotype
     shows BOTH of the other two.
• Polyallele Traits
  – Blood type
  – Several possible alleles for only one trait.
  – Fill in chart from bellwork.

• Polygenic Traits
  – Characteristics controlled by two or more genes.
  – Ex. Eye color is determined by the combination of
    approx. 3 genes.
  – Ex. TtBbGg all would contribute to eye color.
            Blood Type Practice
• If a woman has type A blood, and her child has type AB
  blood. She thinks the father is a man with type O
  blood. Could this man be the father? Explain your
  answer.
• Show the punnett square of a cross between a man with
  type AB blood and a woman with type O blood. What
  is the phenotypic ratio of their offspring?
• If a man that is heterozygous for type A blood marries a
  woman with type AB blood, what are the chances their
  children could have type O blood?
• Sex Linkage
  – The presence of a gene on a sex chromosome is called a
    sex-linked trait
  – Y-linked: genes located on the Y chromosome
  – X-linked: genes located on the X chromosome
    Men cannot carry an X-linked trait. They either have the
    trait or they do not.
• Ex. Eye color is an X-linked trait in fruit flies. Red
  eyes are dominant to white eyes. Show the punnett
  cross between a white-eyed female and a red-eyed
  male. What is the phenotypic ratio of the offspring?
             Colorblindness
• Colorblindness is an X-linked recessive
  trait. Show the punnett square between a
  normal male and a female that carries the
  trait. What are the chances their children
  will have colorblindness?
                 Pedigrees


• Family tree style graphic that shows how a
  trait is passed within the family.
• How are pedigrees written?
  – See shapes on the overhead
  – Generations are labeled from the top down.
           Patterns of Inheritance
• Y-linked: All males of a family have the trait.
• Autosomal Dominant:
  – Males and females are affected
  – See the trait when individuals have at least one copy of
    the dominant trait (AA or Aa)
  – Ex. Huntington‟s Disease
• Autosomal Recessive:
  – Males and females are affected
  – See the trait when individuals are homozygous
    recessive (aa). Individuals may be carriers.
  – Ex. Sickle Cell
• X-linked Dominant:
  – Males and females are affected
  – See the trait when individuals have at least one copy
    of the dominant allele on an X chromosome
  – Ex.
• X-linked Recessive:
  – Males and females are affected but only females can
    carry the trait.
  – See the trait when females have two copies of the
    recessive allele and males have one copy.
  – Ex. Hemophilia, Colorblindness
WRITE THESE IN ORDER ON
      YOUR PAPER!
 – Y-LINKED: ALL MALES
 – AUTOSOMAL DOMINANT: NO
   CARRIERS
 – X-LINKED RECESSIVE: ONLY FEMALE
   CARRIERS
 – AUTOSOMAL RECESSIVE

				
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posted:8/10/2011
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