Part H: Lecture 19

Question 1

sex chromosomes discovery

Answer 1

Nettie Stevens while studying beetle chromosomes

Question 2

sex chromosomes examples

Answer 2

X
Y
Z
W

Question 3

how did sex chromosomes get their names?

Answer 3

they were unknown (not their shape)

Question 4

evolution of X and Y system

Answer 4

X and Y chromosome were identical before than Y lost most of its genes while X kept its genes

Question 5

why do X an Y chromosomes pair during mitosis

Answer 5

they were homologous chromosomes millions of years ago

Question 6

evolution of Z and W system

Answer 6

Two Z identical chromosomes then one Z became W after millions of years

Question 7

Z is similar to ___ and W is similar to ___

Answer 7

-X
-Y

Question 8

in some species(drosophila), length of X/Y chromosomes?

Answer 8

Y is longer than X

Question 9

sex determination in drosophila system

Answer 9

sis gene on X chromosome
two sis+ genes = female
one sis+ gene = male

Question 10

drosophila system is dependent on ____

Answer 10

X chromosome
one X = male
two X = female

Question 11

meiosis in drosophila (female)

Answer 11

normal crossovers in prophase I

Question 12

meiosis in drosophila (male)

Answer 12

no crossovers at all because no crossover possible between X and Y

Question 13

Dosage compensation in Drosophila

Answer 13

increase X-linked gene expression in males (1 X) with positive TFs = MSL transcription factors

Question 14

sex chromosomes in mammals

Answer 14

X- has lots of genes
Y- mostly no genes
X and Y have a pseudo-autosomal region with regular genes (homologous region)

Question 15

meiosis in mammals (female)

Answer 15

normal crossovers in prophase I

Question 16

meiosis in mammals (male)

Answer 16

slightly unusual
crossovers on autosomes and at pseudo-autosomal region on sex chromosomes

Question 17

sex determination in mammals system

Answer 17

SRY gene on Y chromosome
SRY+ gene = male
no SRY+ gene =female

Question 18

mammals system dependent on ____

Answer 18

Y chromosome
Y = male
no Y = female

Question 19

mammals sex determination steps

Answer 19

1) gonads in embryo becomes ovaries (TF) or testes (TF & SRY+)
2)ovaries and testes synthesize sex hormones and do meiosis
3) sex hormones travel to other cells
4) sex hormones enter cells and bind to receptors
5) sex hormones activate transcription factors which turn on target gene

Question 20

SRY gene at ___

Answer 20

Yp11.3

Question 21

ovary sex hormone

Answer 21

estrogen

Question 22

testis sex hormone

Answer 22

testosterone

Question 23

sex hormone receptors in cell (male)

Answer 23

estrogen & testosterone

Question 24

sex hormone receptors in cell (female)

Answer 24

estrogen & testosterone

Question 25

sex hormone + receptors =

Answer 25

transcription factor

Question 26

Dosage compensation in mammals

Answer 26

decrease X-linked gene expression in females

Question 27

Dosage compensation in mammals steps

Answer 27

1) Count the X chr in human embryo at 2 weeks old (500-1000 cells)
2)Turn off all but one - permanent random decision (paternal or maternal X) - Xi is marked

Question 28

Xa is ____

Answer 28

active X chromosome

Question 29

Xi is ____

Answer 29

inactive chromosome

Question 30

Xa decondenses after mitosis?

Answer 30

yes

Question 31

Xi decondenses after mitosis?

Answer 31

no

Question 32

Xa replicated during S phase?

Answer 32

yes

Question 33

Xi replicated during S phase?

Answer 33

yes

Question 34

Xa in interphase/metaphase

Answer 34

decondensed
condensed

Question 35

Xi in interphase/metaphase

Answer 35

condensed
condensed

Question 36

Xi in an interphase nucleus is called ___

Answer 36

Barr body (small condensed DNA dot)

Question 37

dosage compensation is _____ from sex determination in mammals

Answer 37

independent of

Question 38

dosage compensation occurs in which type of cell?

Answer 38

somatic cells

Question 39

dosage compensation does not occurs in which type of cell? why?

Answer 39

germline cells; so the egg will always get an active X