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

Autosomal Traits

● Some disorders are caused by dominant alleles○ just one dominant allele = disorder

● Less common than recessive disorders● ex) Huntington disease, Marfan syndrome

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 XB = allele for normal vision, and

Xb = allele for colorblindness, what are the possible phenotypes for a woman homozygous for normal vision and a man with normal vision?

● dad = XBY

● mom = XBXB

XB XB XBY

XB XB XBY

XB Y

XB

XB

● Genotypes- 1 XB XB : 1 XBY● Phenotypes-

1 normal female : 1 normal male

Sex-Linked Traits

● If XB = allele for normal vision, and

Xb = allele for colorblindness, what are the possible phenotypes for a woman heterozygous for normal vision and a man with normal vision?

● dad = XBY

● mom = XBXb

XB XB XBY

XB Xb XbY

XB Y

XB

Xb

● Genotypes- 1 XB XB : 1 XBY :1 XB Xb : 1 XbY● Phenotypes-

1 normal female : 1 normal male : carrier female : 1 color blind male

Sex-Linked Traits

● If XB = allele for normal vision, and

Xb = allele for colorblindness, what are the possible phenotypes for a woman heterozygous for normal vision and a man with color blindness?

● dad = XbY

● mom = XBXb

XB Xb XBY

Xb Xb XbY

Xb Y

XB

Xb

● Genotypes- 1 XB Xb : 1 XBY :1 X b Xb : 1 XbY● 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

Brain-Melting Bonus! Sex-Linked, Codominant Traits

● If XO= orange fur, and XB = black fur, what would be the possible phenotypes between a calico female and black male cat?

● male= XBY● female= XOXB

XO XB XBXB

XO Y XBY

XO XB

XB

Y

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