Sex%20Chromosomes - PowerPoint PPT Presentation

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Sex%20Chromosomes

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Title: Sex%20Chromosomes


1
Sex Chromosomes
2
Sex Chromosomes
3
X-linked Traits
  • Possible genotypes
  • XY ? Hemizygous wild type male
  • XmY? Hemizygous mutant male
  • XX ? Homozyogus wild female
  • XXm ? Heterozygous female carrier
  • XmXm ? Homozygous mutant female

4
X-linked Recessive Inheritance
  • Always expressed in hemizygous males
  • Female homozygotes show the trait but female
    heterozygotes do not
  • Affected males Inherited from affected or
    heterozygous mother
  • Affected females affected fathers and affected
    or heterozygous mothers

5
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6
X-linked Dominant Inheritance
  • Expressed with one copy
  • Males are often more severely affected
  • Typically associated with miscarriage or
    lethality in males
  • Passed from father to all his daughters but none
    of his sons

7
X-linked Dominant Inheritance Congenital
Generalized Hypertrichosis
Figure 6.10
8
Sex-limited traits
  • A trait that affects a structure or function of
    the body that is present in only one of the
    sexes.
  • May be X-linked or autosomal
  • Example A gene affecting milk production will
    not have an effect in males. However, males can
    carry and pass on the trait.
  • Why do men have nipples anyway???

9
Sex-influenced traits
  • An allele is dominant in one sex but recessive in
    the other sex.
  • May be X-linked or autosomal
  • Due to hormonal interactions
  • Men have testosterone
  • Women have estrogen

10
X-inactivation
  • Females turn off one of their X chromosomes in
    each cell
  • In order to be more equal to males who only have
    one X chromosome
  • The X chromosome turned off in each cell is random

11
X Chromosome Inactivation
12
Fur Color in Tortoiseshell Cats
Orange fur
Black fur
13
Manifesting Heterozygote
  • A carrier of an X-linked trait who expresses the
    phenotype
  • If a female is heterozygous for a recessive
    trait, the dominant allele will usually mask the
    recessive allele
  • Unless the dominant allele is on the X chromosome
    that was inactivated
  • Some cells will express the trait and others will
    not, depending on which X chromosome is
    inactivated

14
Multifactorial Traits
  • Genes and the Environment

15
Polygenic Traits
  • A trait is influenced by more than one gene
  • May be multifactorial (influenced by environment)

16
Polygenic Traits are Continuously Varying
  • Each gene in the polygenic trait contributes to
    the phenotype to a varying degree
  • Example Height
  • Polygenic (influenced by multiple genes)
  • Continuous

17
Pure Polygenic Trait -Eye Color
Figure 7.3
  • The number of human eye color genes is unknown
  • Analysis will probably reveal many genes
  • Mice have more than 60 eye color genes

18
Analyzing Multifactorial Traits
  • Difficult, requires multiple techniques
  • Use human genome sequences, population, and
    family studies
  • The frequency in a specific population
    Empiric risk
  • The amount of inheritance due to genes
    Heritability

19
Separating Genes and Environment
  • Dizygotic twins Shared environment
  • and 50 of genes
  • Monozygotic twins Identical genotype, and
  • shared environment
  • Twins raised apart Shared genotype but
  • not environment
  • Adopted individuals Shared environment
  • but not genes

20
Concordance
  • The percentage of pairs in which both twins
    express the trait
  • Used to determine heritability
  • Assumes both types of twins share similar
    environments
  • MZ twins often share more similar environments

21
Review
22
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