Sex Determination

Question 1

What are autosomes?

Answer 1

These are the 44 out of 46 chromosomes in a human somatic cell that are non-sex chromosomes

Question 2

How many chromosomes out of the 46 in a human somatic cell are non-sex chromosomes?

Answer 2

44

Question 3

How many chromosomes out of the 46 in a human somatic cell are sex-chromosomes?

Answer 3

2 `

Question 4

What features are controlled by autosomes?

Answer 4

Features that are independent of whether a person is male or female

Question 5

Give some examples of gender-neutral features that are controlled by autosomes
(4)

Answer 5

Skin colour
Number of arms
Production of saliva
Digestive enzymes

Question 6

What are the names of the two human sex chromosomes?

Answer 6

X and Y

Question 7

What genes are contained in the X and Y sex chromosomes?

Answer 7

They contain genes that control gender

Question 8

Which chromosome, X or Y, is the largest?

Answer 8

The X chromosome is the longest

Question 9

What chromosomes should be found in the nucleus of every single somatic cell of a human?

Answer 9

Every single somatic cell nucleus should have two sex chromosomes

Question 10

Every somatic human cell has a pair of two sex chromosomes present, what combinations can there be?

Answer 10

XY

XX

Question 11

What does a combination of XY genes mean?

Answer 11

This means the human is male

Question 12

What does a combination of XX genes mean?

Answer 12

This means the human is female

Question 13

Does the male or female determine the sex of the offspring?

Answer 13

The male determines the sex of the child

Question 14

Why can it be said that the ratio of male to female births should be equal (1:1)?
(3)

Answer 14

This is because the male (father) has two different sex chromosomes (X and Y) while the mother has two X chromosomes

The father produces equal amounts of sperm containing the X chromosome as the Y chromosome

During fertilisation either the X or the Y chromosome but not both from the father will combine with one of the mother’s X chromosomes

Therefore there is a fifty percent chance of the Y chromosome from the father being passed on and a fifty percent chance of him passing on an X chromosome

Question 15

Give an example of an organism where the determination of sex is the reverse of that in humans?

Answer 15

Birds, butterflies and moths have the reverse sex-determining chromosomes to humans i.e. XX results in a male while XY results in a female