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Genetic Variation

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Title: Genetic Variation


1
Genetic Variation
2
The Law of Segregation
  • Mendels 1st Law
  • The 2 alleles of each gene pair separate into
    different gametes (egg or sperm) during meiosis.

3
The Law of Independent Assortment
  • Mendels 2nd Law
  • Independent Assortment
  • Genes that are inherited separately Do NOT
    influence the inheritance of others
  • Alleles segregate independently during meiosis
  • Some ALLELES go to one gamete and some to another

4
INCOMPLETE DOMINANCE
  • Incompletely dominance
  • Genes are neither dominant nor recessive they
    mix!!!
  • Genotype is heterozygous (hybrid--Hh)
  • Phenotype is between two parents
  • Dominant gene cannot fully mask the recessive
  • Ex white flower x red flower pink flowers

5
CODOMINANCE
  • Codominance
  • Offspring shows phenotype of neither parent
  • Both alleles are DOMINANT!!!
  • Ex black chicken x white chicken checkered
    chicken

6
MULTIPLE ALLELES
  • Multiple alleles (Polygenic Traits
  • Two OR More alleles control a trait
  • You still will only have two of these alleles. 
  • Ex height, hair color, eye color and blood type
     
  • There are 3 different alleles for blood 
  • IA (Type A) IA IA or IA i
  • IB (Type B) IB IB or IB I
  • IA IB (Type AB) IA IB
  • ii (Type O) ii

7
Sex-Linked Alleles
  • Sex-linked alleles
  • controlled by genes located on sex chromosomes
    (XX or XY)
  • Usually carried on X chromosome
  • Since females are XX, they are usually carriers
    of the trait
  • Since males are XY, they have a higher tendency
    for inheritance of trait

8
  • If trait is X-linked, MALES
  • pass it to all daughters
  • none to sons
  • If trait is X-linked, MOTHERS
  • have 50/50 chance of passing it to all of their
    children
  • Ex colorblindness, hemophilia, male pattern
    baldness

9
Mutations
  • Mutation
  • Any mistake or change in the DNA sequence
  • Point mutation
  • Change in one nitrogen base inDNA
  • Ex albinism

10
Chromosomal Mutation
  • Changes in chromosome structure
  • 1) INVERSION
  • the order of genes on a chromosome is inverted
  • 2) TRANSLOCATION
  • the movement of a chromosome fragment to a
    nonhomologus chromosome

11
  • 3. DELETION
  • Loss of a few bases
  • Loss of large regions of a chromosome
  • 4. DUPLICATION
  • Duplication of a few bases
  • Duplication of large regions of a chromosome

12
Crossing Over
  • Occurs when chromosomes exchange genes.
  • 2 chromosomes overlap.
  • Some genes cross over and switch places

13
NONDISJUNCTION
  • Nondisjunction
  • chromosome pair fails to separate properly during
    meiosis
  • Monosomy
  • gamete has 1 less chromosome than it should
  • 45 chromosomes is the result
  • Ex Turner syndrome
  • Missing a sex chromosome

14
  • Trisomy
  • Gamete has 1 more chromosome than it should
  • Result is 47 chromosomes
  • Ex Downs Syndrome
  • Extra 21 chromosome

15
Methods of Detection
  • Chorion villi sampling
  • Take sample of the chorion
  • (membrane surrounding fetus)
  • Chemical tests and Karyotyping performed
  • Ultrasound
  • Sound waves are used to generate an image of the
    unborn child.
  • Used to detect abnormalities of limbs, organs,
    etc.
  • Amniocentesis
  • Fluid surrounding the fetus is drawn out by
    needle
  • Fetal cells are collected and grown in a lab.
  • Chromosomes can be then Karyotyped
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