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More Complex Inheritance Patterns: Sex-Linked Traits

More Complex Inheritance Patterns: Sex-Linked Traits. Autosomes v. Sex Chromosomes. Of the 23 pairs of chromosomes (46 total) in humans… 22 pairs = autosomes ♀ and ♂ autosomes are the same type 1 pair = sex chromosomes ♀ = XX, ♂ = XY. X.

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More Complex Inheritance Patterns: Sex-Linked Traits

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  1. More Complex Inheritance Patterns: Sex-Linked Traits

  2. Autosomes v. Sex Chromosomes • Of the 23 pairs of chromosomes (46 total) in humans… • 22 pairs = autosomes • ♀ and ♂ autosomes are the same type • 1 pair = sex chromosomes • ♀ = XX, ♂ = XY X X and Y chromosomes photographed by electron microscope Y What do you notice about the X and Y chromosomes?

  3. Punnett Squares with Sex Chromosomes • Sex is determined by the father of a child. • Why? • The father can give an X or Y but the mother can only give an X. • Every time a couple has a baby, there is a 50% chance of having a boy and a 50% chance of having a girl. X Y X XY XX XX XY X

  4. Sex-linked Traits • Sex chromosomes also control traits beyond what sex you are • Sex-linked traits = traits of genes located on sex chromosomes • Sex-linked traits are usually located on the X chromosome, tend to affect males more than females. WHY?? …What do you know about alleles and homologous chromosomes? ≈ 1,000 genes on X, ≈ 90 on Y

  5. Colorblindness is a sex-linked trait People with normal vision should see a light image of a red/brown sailboat.

  6. Sex-linked Traits in Humans • ♂ more likely to show sex-linked recessive traits because only one X chromosome …If he inherits a recessive allele (on X), there is no paired dominant allele to mask it • A carrier has the recessive allele, but it is not expressed …If she inherits a recessive allele (on X), she has a paired dominant X allele to mask it • ♂ cannot be a carrier of sex-linked trait – he will always express the trait • Example: color blindness More colorblindness test Color-blindness

  7. Other sex-linked traits • Baldness (some types) • Muscular Dystrophy • Hemophilia • Because the X chromosome carries alleles for sex-linked traits, X is used for the alleles • The traits are written as superscripts. • Ex: balding in humans- XB=not bald, Xb=bald

  8. Punnett Squares for Baldness bald dad x carrier mom Xb Y XB XB Y XB Xb Is your father bald? Will you be bald? • Does a son inherit baldness from his dad? • If mom is a carrier for baldness (XB Xb), son has a 50% chance of being bald! …So who should you look at to see if you will be bald? Xb Xb XbY Xb bald dad x homozygous non-bald mom Xb Y XB XB Y XB Xb XB Xb XBY XB

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