2.3 Variation and Sexual Reproduction

Question 1

What is sexual reproduction?

Answer 1

The production of new living organisms by combining genetic information from two individuals of different sexes

Question 2

What is asexual reproduction?

Answer 2

A mode of reproduction by which offspring arise from a single organism, and inherit the genes of that parent only

Question 3

What are the disadvantages of sexual reproduction?

Answer 3

Only half the population are able to produce offspring,
Disrupting a successful genome and only passing half onto each offspring,
Large energy usage,
Increased predation risk during mating

Question 4

What are the benefits of sexual reproduction?

Answer 4

Greater genetic variation which allows a large gene pool to be maintained,
Cope with selection pressures and evolve to changing environmental conditions,
Provides raw material to keep running in RQH

Question 5

What is variation?

Answer 5

The differences that exist between individuals in a population determined by the alleles that are inherited

Question 6

What are the disadvantages of asexual reproduction?

Answer 6

Offspring are genetic clones and so lack variation,
Offspring experience high competition,
Unfavourable conditions can wipe out entire colonies

Question 7

What are mechanisms of asexual reproduction in eukaryotes?

Answer 7

Vegetative cloning (in plants e.g. bulb production) and parthenogenesis

Question 8

What is parthenogenesis?

Answer 8

Reproduction from a female gamete without fertilisation, it is more common in cooler climates or regions of low parasite density/diversity

Question 9

What is horizontal gene transfer used for?

Answer 9

Increase variation in organisms which reproduce asexually, this results in faster evolutionary change than vertical transfer, plasmids can be transferred between individuals

Question 10

What do sex chromosomes do?

Answer 10

Determine whether the individual is male or female

Question 11

What are the female sex chromosomes?

Answer 11

Two homologous X chromosomes

Question 12

What are the male sex chromosomes?

Answer 12

X and a Y chromosome

Question 13

What is another word for females?

Answer 13

The homogametic sex

Question 14

What is another word for males?

Answer 14

The heterogametic sex

Question 15

What is the SRY gene?

Answer 15

Located on the Y chromosome and determines development of male characteristics

Question 16

What are sex-linked genes?

Answer 16

Genes that are found on the X chromosome but have no homologous allele on the Y chromosome, they always show in the phenotype

Question 17

What are examples of sex-linked disorders?

Answer 17

Duchenne muscular dystrophy,
Haemophilia,
Red/green colour blindness

Question 18

Why are sex-linked characteristic more common in males?

Answer 18

Males only require 1 recessive gene while females need 2, males only inherit sex-linked characteristics from their mothers.

Question 19

What is X-inactivation in females?

Answer 19

One of the X chromosomes is randomly inactivated at an early stage of development, thus preventing a double dose of gene products (proteins) which could be potentially harmful to the cells

Question 20

What are hermaphroditic organisms?

Answer 20

They contain both male and female reproductive structures

Question 21

What are the 2 types of hermaphrodite?

Answer 21

Simultaneous= both male and female at the same time and some can self-fertilise
Sequential= born one sex and can change to the other at some point

Question 22

What can result in sex change?

Answer 22

Size, competition, parasitic infection or temperature e.g. reptile egg incubation temperature can control sex determination

Question 23

What is a diploid cell?

Answer 23

A cell in possession of two sets of chromosomes

Question 24

What is a haploid cell?

Answer 24

A cell in possession of a single set of chromosomes

Question 25

What does meiosis increase?

Answer 25

Increases variation

Question 26

What does meiosis produce?

Answer 26

Genetically variable haploid cells which develop into gametes

Question 27

What are gametocytes?

Answer 27

The only diploid cells capable of carrying out meiosis

Question 28

What are homologous chromosomes?

Answer 28

Pairs of chromosomes of the same size, same centromere position, and same genes at the same loci

Question 29

What are linked genes?

Answer 29

Genes that are found on the same chromosome

Question 30

Where do homologous chromosomes come from?

Answer 30

One from maternal parent one from paternal parent

Question 31

What occurs before meiosis?

Answer 31

Each chromosome replicates forming two identical chromatids held together at a centromere

Question 32

What occurs during the process of meiosis I?

Answer 32

1. Each chromosome undergoes DNA replication to become two identical chromatids 2. Chromosomes condense and homologous chromosomes pair up 3. Chiasmata form where non-sister chromatids touch and crossing over occurs and DNA exchanges between non-sister chromatids 4. Spindle fibres attach to the homologous pairs of chromosomes which lines them up at equator of spindle, this is random and called independent assortment 5. The chromosomes of each homologous pair are separated and move towards opposite poles 6. Cytokinesis occurs and 2 daughter cells are formed

Question 33

What is independent assortment?

Answer 33

The random pairing of homologous chromosomes at the equator of the spindle

Question 34

What is meiosis II?

Answer 34

Each of the two cells produced in meiosis I undergo further division, separating the sister chromatids of each chromosome, producing 4 haploid cells

Question 35

What is the process of meiosis II?

Answer 35

1. Nuclear membrane disintegrates 2. Chromosomes line up singly on equator 3. Sister chromatids separate and are randomly distributed to daughter cells/gametes 4. Cytoplasm divides/cytokinesis occurs 5. Four genetically different haploid gametes produced

Question 36

What does crossing over allow?

Answer 36

Shuffling of sections of DNA between homologous chromosomes

Question 37

What does independent assortment allow?

Answer 37

Many combinations of chromosomes of maternal and paternal origin in the gametes

Question 38

What does sexual reproduction allow?

Answer 38

Brings genetic information from two different parents together in one organism

Question 39

Where does meiosis occur?

Answer 39

Only occurs in testes and ovaries

Question 40

What does meiosis form?

Answer 40

four genetically different gamete cells