Inheritance of Sex and Sex-Linked or Influenced Traits
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Transcript of Inheritance of Sex and Sex-Linked or Influenced Traits
Inheritance of Sex and Sex-Linked or Influenced Traits
Sex Determination
Sex chromosomes determined at fertilization _____ = female _____= male
Sperm determines sex Females only make ___
eggs Males make ________
sperm
Can We Influence the Sex?
Historical ViewsThought __________ determined the sexThought the __________________
determined the sex Some Current Theories
Chemical environment of female reproductive tract
Timing of sex around _______________
Comparing the Chromosomes
X chromosome ____________ genes
Y chromosome ___________ genes Sex-determining region of the Y
(_______ gene)- gene that codes for maleness
Looking Closer at the Y
Very small Tips are called pseudoautosomal regions
Genes similar to genes on X Can recombine with X
Middle section called male-specific region (MSY) Genes essential to fertility including SRY Genes nearly identical to X Amplicons- regions of palindromes
Sex Development
During fifth week of developmentUnspecified gonads formTwo duct systems form
Mullerian ducts- will develop into ________ structures Wolffian ducts- will develop into ________ structures
During sixth week In males- SRY gene is activated In females- no SRY gene, other genes control
development
What does SRY do?
Codes for a __________________that activates other genes controlling male development
Indifferent gonads develop into testes Secrete anti-Mullerian hormones which causes these
ducts to degenerate Secrete testosterone to stimulate some internal male
structures to develop Some testosterone is converted to
dihydrotestosterone (DHT) which cause external and some internal male structures to develop
When Things Go Wrong
Androgen insensitivity XY chromosomes Testosterone is produced but receptors are absent or faulty Phenotypic, but infertile, she
Male pseudohermaphroditism XY chromosome Block in testosterone production Phenotypic she at birth At puberty, other sources of testosterone are produced and male
characteristics start to develop
Severe Combined Immune Deficiency Syndrome
Sex-Linked Traits
Y-linked TraitsRare because so few genesNone currently well understood besides
infertilityTrait would be passed from ______________
X-linked TraitsCan be recessive or dominant
Recessive X-Linked Traits
Expression Females-
______________________
Males- only need one copy (_____________)
Inheritance Fathers pass mutated
allele to all ___________ Mothers pass mutated
allele to _______________
Dominant X-Linked Trait
Both females and males only need one copy
Females are usually less severely affected because one X is still ok
Some disorders are _________ in males
Sex-Linked Punnett Squares
Same as other Punnett squares
Mom on one side, Dad on other
Need to write it like this: ___________
Y does not have a letter
Calico Cats
X Inactivation
Occurs during early embryonic development
Each cell inactivated about ______ of one of the X chromosomes
Which X is chosen at random
All cells in that lineage will have the same inactivation
Barr Bodies
X chromosome is inactivated by attaching __________(epigenetics)
Inactive X chromosomes absorb more stain creating a Barr body in the cell
Males do not have a Barr body
Consequences of Inactivation
In _____________ disorders Females can have patches of tissue that express
mutant allele Most of the time enough parts are normal to not have
the effects of the disorder Manifesting heterozygote- female who expresses mild
form of disorder because of inactivation In _____________ disorders
Females have normal and abnormal tissues throughout body
Sex-Limited Traits
Traits can be inherited on autosomal or sex chromosome
Trait only affects __________________For example
Beard growth Pregnancy- Preeclampsia Milk production
Sex-Influenced Trait
May be inherited on autosomal or sex chromosome
Sex of individual __________________May be dominant in one and recessive in the
other
Genomic Imprinting
Another form of epigenetics Gene from specific parent is
silenced in each generation using attached methyl groups
Methyl group are removed during meiosis and replaced once new embryo forms
Most seem to control early embryonic development