X link inheritance

Question 1

X inactivation

Answer 1

To equalize the amount of X gene product in females dosage compensation occurs in which X chromosome from father is inactivated in some cells while one of the X received from mother is inactivated in some cells via random inactivation. This leads to mosaic in females and as men only has one X chromosome they are hemizygote.

Question 2

What is Barr body?

Answer 2

Barr bodies are condensed form of inactive X chromosomes seen only in the cells with two X chromosomes. Only occurs in somatic cells.

Question 3

Number of Barr bodies and presence in different conditions

Answer 3

No. of barr bodies are always one less than the number of X chromosomes.
1. in normal somatic cells of females - no. of barr bodies is one
2. in female with turner syndrome have no barr bodies (bcz only one X chromosome)
3. in males no barr bodies present.

Question 4

What is XIST Gene

Answer 4

XIST gene is required for X inactivation and present in X inactivation centre

Question 5

X link recessive disease characteristics

Answer 5

• common among males than females bcz males have only one X
• Father to son transmission is not seen
• skip generation is present
• Female can be heterozygote carrier, homozygote normal and homozygote affected

Question 6

X link dominant disease characteristics

Answer 6

• Twice as common in females than males (due to two XX)
• Father to son transmission is not seen
• Skip generation is not seen

Question 7

Mitochondrial mutation

Answer 7

• none of the off springs of affected father will have the disease
• all of the off springs of affected mother will have the disease

Question 8

Anticipation

Answer 8

When hereditary trait or genetic diseases seem to display an earlier age of onset and/or more severe expression in the more recent generations of a pedigree. This pattern is termed anticipation