2.8

Question 1

Human cells contain how many chromosomes?

Answer 1

46

Question 2

There are 23 different chromosomes, but we have one set of chromosomes from our mother and one from our

Answer 2

father

Question 3

Chromosomes are arranged in

Answer 3

homologous pairs

Question 4

The chromosomes of a homologous pair look identical to each other, except for one pair:

Answer 4

sex chromosomes

Question 5

The X chromosome is much larger than the

Answer 5

Y chromosome

Question 6

Females have

Answer 6

XX

Question 7

Males have

Answer 7

XY

Question 8

The DNA in the human Y chromosome is 58 million base pairs long, but represents only about…

Answer 8

0.4% of the total DNA in a human cell

Question 9

Y chromosome contains very few genes, one it does contain is known as

Answer 9

SRY

Question 10

SRY is the gene that triggers an embryo to

Answer 10

develop as a male

Question 11

Other genes on the Y chromosome are needed for

Answer 11

normal sperm production

Question 12

Because females have two X chromosomes, every gamete they produce will contain a

Answer 12

single X chromosome

Question 13

The gametes produced by a male will differ from each other. Half will contain X and half will contain a

Answer 13

Y chromosome

Question 14

The sex of the offspring will be determined by whether the sperm that fertilised the oocyte contains an

Answer 14

X or Y chromosome

Question 15

Genes found on the sex chromosome are said to be

Answer 15

sex linked

Question 16

There are very few genes on the human Y chromosome, so sex linked genes are usually found on the

Answer 16

X chromosome

Question 17

An example of a sex-linked characteristic is Duchenne Muscular Dystrophy (DMD) this is a genetic disorder caused by an error in the

Answer 17

dystrophin gene

Question 18

(SEX-LINKED GENES) Dystrophin is an important protein in muscle tissue. The condition causes

Answer 18

-Progressive muscle weakness as the muscle cells break down and die

Question 19

(SEX-LINKED GENES) Symptoms usually appear in boys under the age of 6. The first signs are a

Answer 19

loss of muscle tissue and weakness of the arms and pelvis

Question 20

(SEX-LINKED GENES) Children with the condition DMD have have progressive difficulties with mobility, and usually need a wheelchair from the age of about 11. By the time the child has reached his late teens or early twenties, the breathing muscles become affected and the conditions become

Answer 20

life-threatening

Question 21

(SEX-LINKED GENES) DMD usually only affects

Answer 21

boys

Question 22

(SEX-LINKED GENES) DMD is caused by a

Answer 22

recessive allele on the X chromosome

Question 23

(SEX-LINKED GENES) A woman who carries the allele for DMD does not usually show any symptoms of the condition, since she has a second X chromosome with a

Answer 23

normal allele on it

Question 24

(SEX-LINKED GENES) We can use the symbol XD for the normal (dominant) allele and Xd for the

Answer 24

recessive DMD allele