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