Sex-Linked Genes

Anchoring Phenomenon: Why are calico cats always female? Why would a cloned calico cat not resemble the original?

Some genes are located on the sex chromosomes.

There are 22 pairs of autosomes and 1 pair of sex chromosomes in a typical human.

The Y chromosome is small and contains few genes. (Think: Y is WIMPY!)

The X chromosome is associated with several disorders:

Sex Linked Disorders

• Color Blindness (red-green)
• Hemophilia ("bleeders disease)
• Duchenne Muscular Dystrophy (weakening/loss of skeletal muscles)

 

 

How Coat Color in Inherited in Cats

Black and orange is sex linked, and codominant.

Show the cross between a black female and an orange male.

 

 

X Inactivation

-occurs when one copy of the X chromosome is inactivated
-prevents females from having too many gene products
-which X becomes inactive is random

*This is why some patches of the female cat display orange color, and other patches are black.

Why is CC (cloned cat) different color than her mother, whom she was cloned from?

 

 

Human Sex Linked Traits

Colorblindness - inability to distinguish certain colors, most common is red-green

Hemophilia - inabiliy of the blood to clot, wounds will bleed uncontrollably (can be deadly)

Duchenne Muscular Dystrophy - muscles become weak over time

Rett Syndrome - caused by a mutation on the X chromosome, not inherited, only affects girls

 

Example: Genetic Crosses with Sex Linked Traits

How hemophilia is inherited from a female who is a carrier.
Note: males cannot be carriers.