Sex-Linked Traits, Lecture notes of Genetics

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Sex-Linked Traits

Autosomal Traits

● Most traits and disorders are found on autosomes ○ autosome- a body chromosome (44 in humans) ● Some disorders are caused by recessive alleles ○ homozygous recessive (dd) = recessive disorder ○ homozygous dominant (DD) = healthy ○ heterozygous (Dd) = healthy, but carrier ● ex) cystic fibrosis, sickle-cell anemia

Sex Chromosomes

● Our cells have 2 sex chromosomes ○ X- contains gender info and some autosomal traits ○ Y- contains only gender info ● XX = female ● XY = male ● Each parent donates one sex chromosome to offspring

Sex-Linked Traits

● Some genetic information for non-gender traits are found on the X chromosome ○ For males, X chromosome comes from their mother ■ all body traits on the X are automatically shown, even recessive ○ For females, one X comes from mom and another from dad ■ standard hereditary rules apply ● ex) color blindness, male pattern baldness, hemophilia

Sex-Linked Traits

● If X B^ = allele for normal vision, and X b^ = allele for colorblindness, what are the possible phenotypes for a woman homozygous for normal vision and a man with normal vision? ● dad = X BY ● mom = X BX B

X B^ X B^ X BY

X B^ X B^ X BY

X B^ Y

X B

X B

● Genotypes- 1 XB^ XB^ : 1 XB^ Y ● Phenotypes- 1 normal female : 1 normal male

Sex-Linked Traits

● If X B^ = allele for normal vision, and X b^ = allele for colorblindness, what are the possible phenotypes for a woman heterozygous for normal vision and a man with color blindness? ● dad = X bY ● mom = X BX b

X B^ X b^ X BY

X b^ X b^ X bY

X b^ Y X B

X b

● Genotypes- 1 XB^ Xb^ : 1 XB^ Y :1 X b^ Xb^ : 1 Xb^ Y ● Phenotypes- 1 carrier female : 1 normal male : color blind female : 1 color blind male

Brain-Melting Bonus! Sex-Linked, Codominant Traits

● In some cats, hair color is found on the X chromosome ○ Orange and black hair are codominant traits ● Calico cats have orange, black, and white hair ○ Females have an orange allele on one X, and a black allele on the other X ■ show up as patches due to X-gene inactivation ○ Since males only have one X, they cannot be calico ■ exception- a cat with XXY

Brain-Melting Bonus! Sex-Linked, Codominant Traits

● If X O= orange fur, and X B^ = black fur, what would be the possible phenotypes between a calico female and black male cat? ● male= X BY ● female= X OX B

X O^ X B^ X BX B

X O^ Y X BY

X O^ X B

X B

Y

● Phenotypes- 1 calico female: 1 black female: 1 orange male: 1 black male