Inheritance of Sex and SexLinked or Influenced Traits

Inheritance of Sex and Sex-Linked or Influenced Traits

Sex Determination n Sex chromosomes determined at fertilization _____ = female ¨ _____= male ¨ n Sperm determines sex Females only make ___ eggs ¨ Males make ____ sperm ¨

Can We Influence the Sex? n Historical Views ¨ Thought _____ determined the sex ¨ Thought the _________ determined the sex n Some Current Theories ¨ Chemical environment of female reproductive tract ¨ Timing of sex around ________

Comparing the Chromosomes n X chromosome ¨ ______ n genes Y chromosome ¨ ______ genes ¨ Sex-determining region of the Y (_______ gene)- gene that codes for maleness

Looking Closer at the Y n n Very small Tips are called pseudoautosomal regions ¨ Genes similar to genes on X ¨ Can recombine with X n Middle section called male-specific region (MSY) ¨ Genes essential to fertility including SRY ¨ Genes nearly identical to X ¨ Amplicons- regions of palindromes

Sex Development n During fifth week of development ¨ Unspecified gonads form ¨ Two duct systems form Mullerian ducts- will develop into ____ structures n Wolffian ducts- will develop into ____ structures n ¨ During sixth week n In males- SRY gene is activated n In females- no SRY gene, other genes control development

What does SRY do? n n 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 n Androgen insensitivity XY chromosomes ¨ Testosterone is produced but receptors are absent or faulty ¨ Phenotypic, but infertile, she ¨ n 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 n Y-linked Traits ¨ Rare because so few genes ¨ None currently well understood besides infertility ¨ Trait would be passed from _______ n X-linked Traits ¨ Can be recessive or dominant

Recessive X-Linked Traits n Expression Females___________ ¨ Males- only need one copy (_______) ¨ n Inheritance Fathers pass mutated allele to all ______ ¨ Mothers pass mutated allele to ________ ¨

Dominant X-Linked Trait n n n 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 n Mom on one side, Dad on other n Need to write it like this: ______ n Y does not have a letter n

Calico Cats

X Inactivation n n 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 n n n 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 n 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 n In _______ disorders ¨ Females have normal and abnormal tissues throughout body

Sex-Limited Traits can be inherited on autosomal or sex chromosome n Trait only affects _________ n ¨ For example Beard growth n Pregnancy- Preeclampsia n Milk production n

Sex-Influenced Trait May be inherited on autosomal or sex chromosome n Sex of individual _________ n ¨ May be dominant in one and recessive in the other

Genomic Imprinting n n 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