1. Sex-Linked Traits

2. What do you think the term sex-linked traits means?
Journal
What do you think the term sex-linked traits means?

3. Humans
22 pair of autosomal chromosomes
1 pair of sex chromosomes

4. Sex Chromosomes
Females XX
Males XY

5. The genes located on the X and Y chromosomes show a pattern of inheritance called sex-linked.
A sex-linked gene is a gene located on a sex chromosome.
Genes on the Y chromosome are found only in males and are passed directly from father to son.
Genes located on the X chromosome are found in both sexes, but the fact that men have just one X chromosome leads to some interesting consequences.
In humans the X-chromosome is much larger than the Y chromosome and contains thousands of genes more than the Y chromosome.

6. Sex-linked traits are those carried on the X or Y chromosome.
A normal female has two X chromosomes.
One from each parent
A normal male inherits an X chromosome from the mother and a Y chromosome from the father. Therefore, normal males inherit sex-linked traits only from their mothers.

7. For each of the genes that are exclusively on the X chromosome:
females, who are XX, would obviously have two alleles
Males, who are XY, would have only one allele.
Therefore, females with one recessive allele and one dominant allele for a gene that is unique to the X chromosome will display the dominant phenotype.
A male with a recessive allele for a gene unique to the X chromosome will always exhibit that recessive trait because there is no other corresponding allele on the Y chromosome.

8. Colorblindness
For example, humans have three genes responsible for color vision, all located on the X chromosome.
In males, a defective allele for any of these genes results in colorblindness, an inability to distinguish certain colors. The most common form, red-green colorblindness, occurs in about 1 in 12 males.
Among females, however, colorblindness affects only about 1 in 200. In order for a recessive allele, like colorblindness, to be expressed in females, it must be present in two copies—one on each of the X chromosomes.
The recessive phenotype of a sex-linked genetic disorder tends to be much more common among males than among females.

9. Duchenne Muscular Dystrophy
Sex-Linked Disorders
Hemophilia
Colorblindness
Duchenne Muscular Dystrophy

10. Hemophilia A disorder affecting human blood clotting
Defective allele prevents the synthesis of a factor needed for blood clotting

11. Colorblindness
Prevents humans from distinguishing between different colors

12. Duchenne Muscular Dystrophy
Condition in which muscles begin to degenerate in childhood

13. XHXH Chromosome with normal dominant allele female Non-hemophilia
Normal types—wild type

14. XhXh
Chromosome with recessive hemophilia allele
female

15. XHXh Chromosome with heterozygous allele female; carrier
Non-hemophilia

16. XHY Chromosome with normal dominant allele male Non-hemophilia
Wild type (normal)

17. XhY
Chromosome with recessive hemophilia allele, male