Lecture 10: Dosage Compensation File

Question 1

What is trisomy ?

Answer 1

when someone has an extra chromosome

Question 2

What type of trisomy is pataus syndrome ?

Answer 2

trisomy 13 (dont survive a year)

Question 3

What type of trisomy is edwards syndrome ?

Answer 3

trisomy 18 (dont survive a year)

Question 4

What type of trisomy is downs syndrome ?

Answer 4

trisomy 21

Question 5

How do females have double the number of X chromosomes compared to males ?

Answer 5

Females swithc off one X chromosome and it forms an inactive barr body

Question 6

What is a barr body ?

Answer 6

Inactivated X chromosome that is condensed. Appears as a dark stain attached to edge of nuclear membrane

Question 7

Are females of males genetic mosaic ?

Answer 7

Females

Question 8

Who has no barr bodies ?

Answer 8

males and XO turners syndrome patients

Question 9

Who has barr bodies

Answer 9

females and XXY kleinfelters patients

Question 10

How do flies overcome the dosage compensation problem ?

Answer 10

either :

1. express two X chromosomes in a female at half the normal rate
2. express the one X chromosome in a male at twice the normal rate

Question 11

Mutant flies for dosage compensation are either ..

Answer 11

1. lethal to mutant females becasue they over express all x-linked genes
2. lethal to mutant males because they under express all x-linked genes

Question 12

What is ‘maleless’ and what chromosome does it map to ?

Answer 12

male-lethal mutation, maps to 2nd chromosome

Question 13

How does maleless affect each fly gender ?

Answer 13

Male mutants = die aas embryos

female mutants= completely unaffected

Question 14

What does maleless actually do ?

Answer 14

encodes a binding protein that binds to control regions of x-chromosome genes and doubles transcription rate (X chromosomes work twice as hard)

Question 15

X-linked conditions generate what phenotype in each gender ?

Answer 15

males = mutant phenotype

heterozygous females= generate mosaic tissues

Question 16

what type of condition is retts syndrome ?

Answer 16

X linked dominant, caused by mutation in MeCP2 gene (a transcriptional repressor)

Question 17

How does retts affect mosaic females ?

Answer 17

90% normal chromosome inactivated = severe

10% normal chromosome inactivated = mild (okay)

Question 18

What determines the severity of DMD in heterozygous females ?

Answer 18

relative rates of random X inactivation (same as retts)

Question 19

Why do all relatives with DMD show the same chromosomal break point ?

Answer 19

the common breakpoint interrupts the Duchenne gene , normal X chromosome is ALWAYSinactivated

Question 20

What is the tortoiseshell orange and black fur pattern due to ?

Answer 20

random x activation of the ‘orange’ gene with has two alleles (orange and black)

Question 21

Why would cloning a toroiseshell cat be a bad idea?

Answer 21

Coat would be unique to that of original cat as x-inactivation is totally random process