Transcript Sex Linked Traits - South Kingstown High School Home Page

Sex Linked Traits
• Genes located on the X or Y chromosome.
• Genes found on the Y are related to sex
determination (these genes make an
embryo develop into a male)
Sex Linked Traits
• Several thousand genes are found on the
X chromosome, and only a few are related
to the sex of an individual
Sex Linked Genes on X
Chromosome
• Examples are:
– Red/Green Colorblindness
– Hemophilia – the Bleeding Disease
– Duchenne’s Muscular Dystrophy
Symbols
• Sex linked genes are noted by writing the
sex chromosomes and adding the gene
(dominant or recessive) as an exponent.
• XH
• Xh
•Y
= X-chromosome with dominant gene.
= X-chromosome with recessive gene
= Y-chromosome without a gene for
the trait
Worksheet - Figure 1
• Woman carrier crossed with Normal Male
XN
XN
Y
XNXN
XNY
Xn
XNXn
X nY
Probabilities
•
•
•
•
•
O%
Color blind daughter_________________
5O%
Carrier daughter____________________
Normal vision daughter non-carrier_____
5O%
5O%
Color blind son_____________________
5O%
Normal vision son___________________
Figure 2
• Normal woman crossed with color blind
Male
XN
XN
Xn
Y
XN Xn
XNY
XNXn
XNY
Probabilities
•
•
•
•
•
O%
Color blind daughter_________________
100%
Carrier daughter____________________
Normal vision daughter non-carrier_____
O%
O%
Color blind son_____________________
10O%
Normal vision son___________________
Figure 3
• Woman carrier crossed with Color Blind
Male
XN
Xn
Xn
Y
XNXn
XnXn
XNY
X nY
Probabilities
5O%
• Normal vision daughter _____
5O%
• Normal vision son___________________
John Taylor’s Family
• Begin with the information you are given.
NY
X
– What is John’s genotype?____________
XnY
– What is his brother’s genotype?_______
– What is his father’s genotype?________
XnY
John Taylor’s Parents
XN
Xn
Y
Xn
XNXn
XnXn
XNY
X nY
John Taylor’s Family
• From which parent(s) did John’s brother
inherit a gene for color blindness?
– __________________________________
mother
• From which parent(s) did John’s sister
inherit a gene for color blindness?
father
– __________________________________
John and Susie Taylor
• Is it likely that they their son is colorblind?
NO
• Why or why not?