chapter 12 sex-linked traits
DESCRIPTION
CHAPTER 12 SEX-LINKED TRAITS. Karyotype: a picture of chromosomes. Body Cells vs. Sex Cells. Autosomes: the first 22 homologous pairs of chromosomes. Autosomes are the same for both males and females. Sex cells : Determine sex of offspring. Is it Male or Female? Explain. - PowerPoint PPT PresentationTRANSCRIPT
CHAPTER 12 SEX-LINKED TRAITS
Karyotype: a picture of chromosomes.
Body Cells vs. Sex Cells
Autosomes: the first 22 homologous pairs of chromosomes.
Autosomes are the same for both males and females.
Sex cells: Determine sex of offspring
Is it Male or Female? Explain
Sex chromosomes: determines the sex of the individual.
The sex chromosomes are the 23rd pair of chromosomes. XX =female
XY=male
Which parent determines the sex of an offspring?
DADWhy? All moms have the genotype XX.
When egg cells are made, they will all carry a single X chromosome.
All dads have the genotype XY. When sperm cells are made, 50% will have an X chromosome and 50% will have a Y chromosome.
Therefore, males and females are born in roughly a 50:50 ratio.
SEX-LINKED TRAITS
Those traits that are controlled by genes on the X or Y chromosomes.
NOTE: The Y chromosome is much smaller than the X chromosome and only contains a few genes. Most sex-linked traits are on the X chromosome.
In humans, hemophilia is a sex-linked trait. Having hemophilia is recessive (Xh) to being normal (XH). The heterozygous female is called a carrier. Cross a carrier female with a normal male.
mal
e__ XHXh __ X __ XHY ___
XH XH
XH Y Xh Y
XH Xh
XH
Y
XH Xh
Results:Genotypic ratio: 1 XHXH :1 XHXh : 1 XHY :1 Xh Y
XH XH
Normal Female
XH Y
Normal Male
Xh YMale w/
hemophilia
XH Xh
Normal FemaleXH
Y
XH XhPhenotypic ratio:2 normal females: 1normal male: 1 male with hemophilia
Now You Try
Cross a carrier female with a male with hemophilia.
__ XHXh __ X __ XhY ___
Results:Genotypic ratio: 1 XHXh :1 XhXh : 1 XHY :1 Xh Y
XH XH
Normal Female
XH Y
Normal Male
Xh YMale w/
hemophilia
Xh Xh
Female w/ hemophilia
XH
Y
XH XhPhenotypic ratio:1 normal female: 1 female w/ Hemopholia:1normal male: 1 male with hemophilia
Genetic Sex-Linked Disorders Color Blindness
Cause: x-linked recessive
1/10 males have, 1/100 females have. Why the difference?
Individuals are unable to distinguish shades of red-green.
Genetic Sex-Linked Disorders
2- Hemophilia A and B
Recessive disorders that affect 1 of 5,000 males. These interfere with normal blood clotting and occur on the X chromosome.
Polygenic Inheritance
Traits that are influenced by several Genes.
Show many degrees of variation.
Examples: Height Hair color Skin Color Eye Color