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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
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
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