Download Sex Determination and Sex

Sex Determination and SexLinked Traits
Chapter 4
Outline
• Sex Determination
• Different Karyotypes
• sry gene and maleness
• Sex Linked Traits
• Barr Bodies
1. Chromosomal Sex determination Systems
• XX-XO
• XX-XY
• ZZ-ZW
• Haplodiploidy
A closer look at 2 different systems of sex
determination
2. Genetic Sex Determining
Systems
• Genic Balance Sex
Determination
drosophila
• Environmental Sex
Determination
Slipper limpet
Drosophila: genic balance
Sex
chromosome
Autosome*
complement
X:A
ratio
Phenotype
XX and AA
1.0
female
Xy and AA
0.5
male
XXY and AA
1.0
female
XXX and AAA
0.67
intersex
* autosome= any non-sex chromosome
Human Karyotypes
Klinefelter Syndrome
Non-disjunction
NORMAL
Turner Syndrome
Maleness
• Determination of maleness is due to sry
gene of Y chromosome
• Expression of gender is more complex
than just sry gene.
• Example: androgen insensitivity
– Xy genotype
– Many female characteristics!
Sex Linked (X-linked) Traits (3 examples)
• Human Color Blindness
Sex Linked (X-linked) Traits
• White eye Drosophila
Hemophilia
XhY
x
XHXh
Pedigree of hemophilia
½ XH
½ Xh
½ Xh ¼ XHXh ¼ XhXh
½Y
¼ XHY
¼ XhY
Barr Bodies & X-Inactivation
• What are they?
• Why does it occur?
Number of Barr Bodies in Human
Cells
X-Inactivation in cats
Tortoiseshell Color
Y-Linked Inheritance
• Few genes on Y chromosomes
• Few examples of known Y linked traits to date
The End