BGM1004/L10 Sex in Genetics

Question 1

Give 2 advantages to asexual reproduction.

Answer 1

Fast cycle
Less energy required than sexual reproduction

Question 2

Give an advantage to sexual reproduction.

Answer 2

Gives new gene combinations

Question 3

Give 2 disadvantages to sexual reproduction.

Answer 3

Time & energy to find a mate
Potential of breaking apart favourable gene combinations

Question 4

What kind of reproduction drives natural selection?

Answer 4

Sexual reproduction

Question 5

What kind of reproduction gives an advantage in harsh environments?

Answer 5

Sexual reproduction

Question 6

What are the products of spermatogenesis according to the Protenor mode of sex determination?

Answer 6

7 chromosomes with 1X
6 chromosomes without X

Question 7

What is another name for the Protenor mode of sex determination?

Answer 7

XX/X0

Question 8

What are the products of spermatogenesis according to the Lygaeus mode of sex determination?

Answer 8

6 autosomes + X OR
6 autosomes + Y

Question 9

What is another name for the Lygaeus mode of sex determination?

Answer 9

XX/XY

Question 10

What is the term for the sex that produces unlike gametes? (In humans = male sex)

Answer 10

Heterogametic

Question 11

Give 2 species in which the female is the heterogametic sex.

Answer 11

Moths
Butterflies
Some fish
Most birds

Question 12

What nomenclature is commonly used to describe a heterogametic female?

Answer 12

ZW

Question 13

What nomenclature is commonly used to describe a homogametic male?

Answer 13

ZZ

Question 14

What was the outcome of the Tijo experiment (1956)?

Answer 14

Improved method of preparing human metaphase chromosomes (karyotyping)

Question 15

What results in variation in numbers of X chromosomes?

Answer 15

Nondisjunction (failure of X chromosomes to separate properly during meiosis)

Question 16

What genotypes result in Klinefelter syndrome?

Answer 16

47,XXY, 48,XXXY, 48,XXYY, 49,XXXXY and 49,XXXYY

Question 17

What genotypes result in Turner syndrome?

Answer 17

45,X0

Question 18

Give 3 symptoms of Klinefelter syndrome.

Answer 18

Tall stature
Slightly feminised physique
Tendency to lose chest hair
Breast development
Testicular atrophy
Female-type public hair pattern

Question 19

Give 3 symptoms of Turner syndrome.

Answer 19

Short stature
Small fingernails
Shortened metacarpal IV
No menstruation
Poor breast development
Rudimentary ovaries

Question 20

How did X and Y chromosomes likely begin their existence?

Answer 20

Ordinary autosomes

Question 21

How many proteins are encoded by the Y chromosome for male fertility?

Answer 21

At least 26

Question 22

What are PARs (pseudoautosomal regions)?

Answer 22

Regions that share homology with X chromosome

Question 23

What is MSY?

Answer 23

Male-specific region of Y that does not synapse with X chromosome

Question 24

What is SRY?

Answer 24

Sex-determining region Y, producing testis determining factor (TDF)

Question 25

In what species is sex determined by incubation temperature?

Answer 25

All crocodile Most turtles Some fish

Question 26

How does temperature determine sex in some species?

Answer 26

Activity of enzymes and inhibitors control production of steroid hormones such as oestrogen

Question 27

What is dosage compensation?

Answer 27

Mechanism to keep X-linked gene doses similar between males and females

Question 28

How is dosage compensation achieved?

Answer 28

X chromosome inactivation

Question 29

How many X chromosomes are active in a given organism?

Answer 29

All but 1

Question 30

What is the number of Barr Bodies in a given organism?

Answer 30

X(n-1)

Question 31

What is a Barr Body?

Answer 31

Condensed X chromosome with RNA attached

Question 32

What is the Lyon Hypothesis (1961)?

Answer 32

Inactivation is random at an early point in development Once inactivated, all progeny cells have the same X chromosome inactivated

Question 33

What is anhidrotic ectodermal dysplasia?

Answer 33

X-linked mutation causing absence of sweat glands

Question 34

How does anhidrotic ectodermal dysplasia present in men?

Answer 34

Men carrying dominant allele (D) have no sweat glands

Question 35

How does anhidrotic ectodermal dysplasia present in heterozygous females?

Answer 35

Mosaic of D and d sectors across the body

Question 36

Where is X chromosome inactivation initiated?

Answer 36

XIC (X-inactivation centre)

Question 37

What are the key products from the XIC? (2)

Answer 37

Xist Tsix

Question 38

What is the function of Xist?

Answer 38

Progressive coating of one X chromosome spreading outwards from XIC

Question 39

What does the coating of an X chromosome lead to?

Answer 39

Packaging into heterochromatin

Question 40

Approximately what percentage of genes escape inactivation?

Answer 40

15%