Transcript Part 1 – Sex-Linked Traits

Chapter 7.1 & 7.2
 Mendel’s
rules of inheritance apply to autosomal
genetic disorders.
– We have learned about alleles carried on the
autosomes
– A heterozygote for a recessive disorder is a carrier.
– Disorders caused by dominant alleles are uncommon.
(dominant)
• Sex Chromosomes
– Females are XX
– Males are XY
• Some traits can be
carried on the sex
chromosomes
• Some are on the X,
others on are the Y
• These are known as
Sex-Linked Traits
• When writing Genotypes, must include the
sex chromosomes
B = Normal
b= bald
Reading Genotypes
XBXB
Normal Female
XBXb
Normal Female
XbY
Bald Male
XBXb x XbY
B = Normal
b= Colorblind
XB
b
X
Xb XBXb X b Xb
Y
B
X Y
XbY
 What
is the probability their babies will be bald?
XB
b
X
X b XBXb Xb Xb
Y
B
X Y
Xb Y
• Girls 50%
• Boys 50%
Colorblind – Sex-linked recessive
Baldness – Sex-linked recessive
Why are calico cats always female?