Topic 11-2

Question 1

the cameo recissive mutation in female peacocks in a gene on the ______ leads to dull brown feathers

Answer 1

Z sex chr

Question 2

in a ZZ-ZW system, females inherit ____ chromosome from their mother and ____ chromosome from their father

Answer 2

W, Z

Question 3

in ZZ-ZW systems, traits that are dictated by the Y chr genes are called:

Answer 3

holandric traits

Question 4

three main characteristics of holandric traits are:

Answer 4

1) present only in males
2) always inherited from the father
3) if father has trait, then every son will have it

Question 5

human Y chr only have about ______ genes, and half of these encode for ______.

Answer 5

350, proteins

Question 6

how many palindromic sequences on the human Y chr?

Answer 6

eight

Question 7

can palindromic sequences on the human Y chr undergo recombination?

Answer 7

yes

Question 8

lack of recombination b/w chr (like X and Y) would lead to:

Answer 8

accumulation of mutations and loss of genetic material on Y

Question 9

what is intrachromosomal recombination?

Answer 9

occurs at the Y chr where arms of the Y chr crossover w/ each other. helps to prevent decay of the Y chr

Question 10

dosage compensation equalizes:

Answer 10

protein levels

Question 11

mechanisms to equalize the amount of protein produced by X-linked genes in males w/ respect to autosomal genes and X-linked genes in females

Answer 11

dosage compensation

Question 12

if there is no dosage compensation in males, they will produce:

Answer 12

insuficient levels of certain proteins

Question 13

in flies dosage compensation consists of:

Answer 13

increased expression of X-linked genes only in males

Question 14

in placental mammals dosage compensation consists of:

Answer 14

increasing X-linked genes in males AND females, BUT one X in females is inactivated

Question 15

who was the person who discovered what Barr bodies were?

Answer 15

Mary Lyon

Question 16

what is the Lyon hypothesis?

Answer 16

wihin each female (placental mammals), one of the two X chr is inactivated, producing Barr bodies (dark spots in nucleus)

Question 17

true or false: in placental mammal dosage compensation, the X chromosome that becomes inactivated is selected at random

Answer 17

true

Question 18

due to random X-inactivation, female placental mammals are functionally _______ at the cellular level so that 50% of cells express one allele, and 50% of cells express another

Answer 18

hemizygous

Question 19

random X-inactivation means that females are _____ for the expression of X-linked genes. and example of this is ______.

Answer 19

mosaics, calico cats

Question 20

all cells produced from mitosis from one cell will have:

Answer 20

the same X chr inactivated as the parent cell

Question 21

how does X-inactivation work w/ extra chr disorders?

Answer 21

if more than two chr, all but one X id inactivated and additional X’s become Barr bodies

Question 22

why doesn’t dosage compensation prevent disorders like triple X disorder (XXX)?

Answer 22

probably bc some X-linked genes escape X-inactivation.

Question 23

what are the two main steps for X-inactivation?

Answer 23

1) cell somehow counts how many X chr are present
2) one X chr is selected for inactivation

Question 24

what is the mechanism for random X-inactivation? (five steps)

Answer 24

1) a gene called Xist becomes active in X chr chosen to be inactive
2) Xist makes a very long RNA molecule
3) Xist RNA molecules coat the X chr
4) Xist RNA molecules recruit protein complexes that alter chromatic structure making Barr bodies
5) other genes on the chosen “active” X chr repress the transcription of Xist and prevent RNA coating

Question 25

is dosage compensation universal?

Answer 25

no!