Unit 2.3c

Question 1

What determines whether an individual is male or female?

Answer 1

Sex chromosomes

Question 2

In humans animals, what are the two sex chromosomes?

Answer 2

X and Y

Question 3

Pair them up:

Female
Male
Heterogametic
Homogametic

Answer 3

Female = Homogametic

Male = Heterogametic

Question 4

What kind of chromosomes do females have?

Answer 4

They have two homologous X chromosomes

Question 5

What kind of chromosomes do males have?

Answer 5

They have an X and a Y chromosome

Question 6

On the Y chromosome, which gene determines the development of male characteristics?

Answer 6

The SRY gene found on the short arm

Question 7

What do you heterogametic males lack?

Answer 7

They lack most of the homologous alleles on the shorter Y chromosome

Question 8

Can males be sex linked pattern carriers?

Answer 8

No because the Y chromosome does not hold the genes necessary

Question 9

What are sex linked genes?

Answer 9

They are genes that can be found on the X chromosome, but have no homologous allele on the Y-chromosome

Question 10

In males, where do you sex linked gene show and why?

Answer 10

They show in the males phenotype as there a no genes on the Y chromosome to counteract them

Question 11

What are three sex linked disorders?

Answer 11

1. Duchenne muscular dystrophy
   - Characterised by progressive weakening of muscles and loss of coordination
2. Haemophilia.
   - Defined by lack of protein involved in blood clotting
3. Red/green colour blindness

Question 12

Are males or females more likely to have a sex linked characteristic?

Answer 12

Males as they only require one recessive gene, females need two

Question 13

Who do males inherit sex linked characteristics from?

Answer 13

Their mothers

Question 14

What is a phenotype?

Answer 14

The physical appearance caused by the alleles in the genes

Question 15

What is a genotype?

Answer 15

An organisms genetic information

Question 16

What happens to one of the homogametic females X chromosomes?

Answer 16

It is inactivated at an early stage

Question 17

Why in females is one of the X chromosomes inactivated?

Answer 17

To prevent a double dose of gene products (proteins) which could be potentially harmful to cells

Question 18

Are carriers more or less likely to be affected by deleterious mutations on the X chromosomes?

Answer 18

Carriers are less likely to be cells deleterious. Mutations as the X chromosome inactivation is done at random only half the cells in any tissue will have a working copy of the gene with the deleterious allele

Question 19

What is sexual dimorphism?

Answer 19

It’s one of the different sexes present different characteristics, i.e. peacocks

Question 20

What does it mean when an organism is a hermaphrodite?

Answer 20

It has both male and female reproductive structures

Question 21

What are the two different types of hermaphrodites?

Answer 21

Simultaneous and sequential

Question 22

What does it mean if an organism is a simultaneous hermaphrodite?

Answer 22

It has both male and female reproductive structures at the same time
Some can self-fertilise like banana slugs and others have mechanisms to avoid doing this, and must meet another individual to reproduce like earthworms

Question 23

What does it mean if an organism is a sequential hermaphrodite?

Answer 23

The organism is born one sex, but can change to another sex at some point throughout it’s life.
This usually happens if reproductive success is likely to be much greater by being the other sex.
It’s common in jellyfish and gastropods.

Question 24

Do you hermaphrodites produce both male and female gametes?

Answer 24

Yes but there is usually another partner who also exchanges gametes.

Question 25

Do you hermaphrodites have to meet the opposite sex to sexually reproduce?

Answer 25

No, if the chance of encountering a partner is uncommon, the partner can be of the same sex.

Question 26

What can determines sex and sex ratios?
(5 examples)

Answer 26

Environmental factors, such as:
Size
Competition
Parasitic infection
Temperature
Resource availability

Question 27

What is sex change influence by?

Answer 27

The balance of androgen and oestrogen hormones in a group

Question 28

What are two examples of sex changes?

Answer 28

Clownfish
- Small groups with a large, dominant female, a large male and small males. If female is removed largest male becomes female.

Bluehead wrasse
- One male in group of females, if male removed largest female grows twice its size and changes coloration and behaviour to become a male

Question 29

How does temperature-dependent sex determination work?

Answer 29

The embryos sex is determined during a temperature sensitive period of egg incubation

Question 30

What species does temperature-dependent sex determination usually occur in?

Answer 30

Reptiles, birds and fish

Question 31

At what temperature is do tortoises, terrapins and turtles, produce males and females?

Answer 31

Males = cool
Females = warm

Question 32

At what temperature do lizards and alligators produce males and females?

Answer 32

Males = warm
Females = cool

Question 33

What temperature do crocodiles and snapping turtles produce males and females?

Answer 33

Males = intermediate
Females = cool and warm