Chromosomes

Question 1

Where are genes located?

Answer 1

Chromosomes

Question 2

Why was chromosome theory contentious for so long?

Answer 2

Chromosomes are invisible for most of the cell cycle

Question 3

How was the behaviour of chromosomes found to be similar to that of mendel’s particles?

Answer 3

1. They are present in pairs
2. Segregate and are reformed during fertilisation
3. Different chromosomes segregate independently

Question 4

What did Thomas Hunt Morgan’s lab work with?

Answer 4

Drosophila

Question 5

Which experiment discovered sex linkage?

Answer 5

THM’s red-/white-eyed flies

Question 6

What did THM discover about red-/white-eyed flies?

Answer 6

Red female + white male –> all white F1
but
Red male + white female –> all red female, white male F1

Question 7

What resulted from the F1 cross of THM’s sex-linkage experiment?

Answer 7

From all red cross: all females red, males half/half in F2

From cross 2: half/half for both sexes in F2

Question 8

How does THM’s fruit fly experiment prove that genes are on chromosomes?

Answer 8

White eye allele in drosophila followed X chromosome exactly,

Question 9

What abnormality in THM’s drosophila crosses provided further proof of chromosome theory?

Answer 9

White female + red male –> all WHITE fem, RED male in F1

Question 10

Define aneuploidy

Answer 10

Abnormal chromosomes, different in number

Question 11

How is sex determined in drosophila?

Answer 11

By number of X chromosomes; 2 for female, 1 for male

Question 12

What other anomaly did THM find in his drosophila stock?

Answer 12

Attached X-stock

Question 13

How is sex determined in birds and butterflies?

Answer 13

WW for males, WZ for females

Question 14

Hoe do recessive alleles on the X chromosome act?

Answer 14

Transmitted mainly by females, expressed mainly my males

Question 15

What is one famous example of a recessive X-allele

Answer 15

Haemophilia

Question 16

Who was famous for spreading this allele across European royal families?

Answer 16

Vick

Question 17

Draw the pedigree of the Spanish Bourbon line starting with Philip V

Answer 17

Just kidding

Question 18

Does the royal line still carry haemophilia?

Answer 18

Probably not

Question 19

Was haemophilia present in the royal line before Victoria?

Answer 19

No, not really

Question 20

What are some other examples of sex-linked conditions?

Answer 20

Color-blindness, Lesch-Nyhan Syndrome (low IQ and self-mutilation), some rare X-linked dominants

Question 21

How many X chromosomes are ever used by either sex?

Answer 21

Just one

Question 22

What is the mechanism by which one X chromosome is inactivated in females?

Answer 22

X Chromosome Inactivation, Lyonisation

Question 23

Who discovered XCI?

Answer 23

Mary Lyon

Question 24

What is the Barr Body?

Answer 24

The inactivated X chromosome in female mammals

Question 25

What does XCI mean for the adult female?

Answer 25

She is a mosaic of cells, expressing either one X or the other

Question 26

Are Tortoise-Shelled cats an example of lyonisation?

Answer 26

Ye

Question 27

What is an example of this in humans?

Answer 27

Female heterozygous for color-blindness; normal vision, but have patches of color-blind cells in the retina

Question 28

Who is affected by most X-linked diseases?

Answer 28

Males, since they only need one copy

Question 29

Duchenne Muscular Dystrophy results from what mutation and in what phenotype?

Answer 29

Mutations of the dystrophin gene, results in great wasting away of the muscles

Question 30

Why are women generally not affected by this?

Answer 30

They would require two copies of the gene, and most affected males die before sexual maturity

Question 31

How is XCI controlled?

Answer 31

By a single gene

Question 32

What gene controls XCI?

Answer 32

Xist

Question 33

Now, back to fruit flies: how does drosophila ensure equality of action with sex-linked genes?

Answer 33

All x chromosomes are active, but in males the x chromosome works twice as much

Question 34

How is sex determined in alligators?

Answer 34

Temperature during egg incubation

Question 35

How is sex determined in fish?

Answer 35

Social pressure