Variation and sexual reproduction

Question 1

Costs of sexual reproduction?

Answer 1

• males unable to produce offspring
• only half of each parents genome passed onto offspring, disrupting successful parental genomes.

Question 2

In sexual reproduction benefits outweigh costs due to…

Answer 2

An increase in genetic variation in the population.

Question 3

What does genetic variation provide?

Answer 3

The raw material required for adaptation, giving sexually reproducing organisms a better chance of survival under changing selection pressures.

Question 4

Co-evolutionary interactions between parasites and hosts may select for?

Answer 4

Sexually reproducing hosts.

Question 5

Hosts that are better at … have greater fitness.

Answer 5

Resisting and tolerating parasitism

Question 6

Parasites that are better able at … have greater fitness

Answer 6

Feeding, reproducing and finding new hosts.

Question 7

Asexual reproduction can be a successful reproductive strategy as…

Answer 7

Whole genomes are passed on from parent to offspring

Question 8

In asexual reproduction just one parent can?

Answer 8

Produce daughter cells and establish a colony of virtually unlimited size over time.

Question 9

Maintaining the genome of the parent is an advantage particularly in…

Answer 9

Very narrow and stable niches or when recolonising disturbed habitats.

Question 10

Asexually reproducing populations are not able to … BUT …

Answer 10

Adapt easily to changes in their environment BUT mutations occur that provide some degree of variation and enable some natural selection and evolution to occur

Question 11

Examples of asexual reproduction in eukaryotes?

Answer 11

Vegative cloning and parthenogenesis in lower plants and animals that lack fertilisation.

Question 12

What is parthenogenesis?

Answer 12

Reproduction from a female gamete without fertilisation.

Question 13

Asexual reproduction and offspring?

Answer 13

Offspring can often be reproduced often and in larger numbers

Question 14

Where is parthenogenesis more common?

Answer 14

Cooler climates which are disadvantageous to parasites, or regions of low parasite density or diversity.

Question 15

Organisism that reproduce asexually and Horizontal gene transfer?

Answer 15

Organisms that reproduce principally by asexual reproduction also have mechanisms for horizontal gene transfer between individuals to increase variation.

Question 16

Prokaryotes can exchange genetic material horizontally, resulting in…

Answer 16

Faster evolutionary change than in organisms that only use vertical transfer

Question 17

What is meiosis?

Answer 17

The division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte

Question 18

In diploid cells chromosomes typically appear as?

Answer 18

homologous pairs

Question 19

Homologous chromosomes?

Answer 19

Chromosomes of the same size, same centromere position and with the same sequence of genes at the same loci

Question 20

The chromosomes which have replicated prior to meiosis I, each consist of…

Answer 20

2 genetically identical chromatids attached at the centromere

Question 21

Meiosis I step 1

Answer 21

Chromosomes condense and the homologous chromosomes pair up.

Question 22

Meiosis I step 2

Answer 22

Chiasmata form at points of contact between the non-sister chromatids of a homologous pair and sections of DNA are exchanged

Question 23

What are linked genes?

Answer 23

Those on the same chromosome. Crossing over can result in new combinations of the alleles of these genes.

Question 24

Crossing over?

Answer 24

Crossing over of DNA is random and produces genetically different recombinant chromosomes.

Question 25

Meiosis I step 3

Answer 25

Spindle fibres attach to the homologous pairs and line them up at the equator of the spindle.

Question 26

The orientation of the pairs of homologous chromosomes at the equator is ———

Answer 26

Random.

Question 27

Independent assortment?

Answer 27

Each pair of homologous chromosomes is positioned independently of the other pairs, irrespective of their maternal or paternal origin.

Question 28

Meiosis I step 4

Answer 28

The chromosomes of each homologous pair are separates and move towards opposite poles.

Question 29

Meiosis I step 5

Answer 29

Cytokinesis occurs and 2 daughter cells form.

Question 30

Meiosis II

Answer 30

Each of the 2 cells produced in meiosis I undergoes a further division during which the sister chromatids of each chromosome are seperated. A total of 4 haploid gametes are produced

Question 31

The sex of birds, mammals and some insects is determined by?

Answer 31

The presence of sex chromosomes.

Question 32

What determines the development of male characteristics in most mammals?

Answer 32

SRY gene on the Y chromosome.

Question 33

What do heterogametic (XY) males lack?

Answer 33

Most of the corresponding homologous alleles on the shorter (Y) chromosome.

Question 34

What does males lacking most of the corresponding homologous alleles on the shorter (Y) chromosome result in?

Answer 34

Sex linked patterns of inheritance as seen with carrier females (XBXb) and affected males (XbY)

Question 35

In homogametic females (XX) what happens to the X chromosomes at an early stage of development?

Answer 35

One of the 2 X chromosomes present in each cell is randomly inactivated.

Question 36

Define X chromosome inactivation?

Answer 36

The process by which most of one X chromosome is inactivated.

Question 37

What does X chromosome inactivation prevent?

Answer 37

Double dose of gene products which could be harmful to cells.

Question 38

Which type of chromosome is less likely to be affected by any deleterious mutations on X chromosomes?

Answer 38

Carriers

Question 39

As X chromosome inactivated in each cell is random…

Answer 39

Half of the cells in any tissue will have a working copy of the gene in question.

Question 40

What are hermaphrodites?

Answer 40

Species that have functioning male and female reproductive organs in each individual.

Question 41

What type of gametes do hermaphrodites produce?

Answer 41

Both male and female gametes and usually have a partner to exchange gametes.

Question 42

What is the benefit of hermaphroditism?

Answer 42

The chance of encountering a partner is often an uncommon event, there is no requirement for that partner to be of the opposite sex.

Question 43

What else can sometimes determine sex and sex ratio?

Answer 43

Environmental factors.

Question 44

Environmental sex determination in reptiles is controlled by?

Answer 44

Environmental temperature of egg incubation.

Question 45

Sex change can be as a result of?

Answer 45

Size, competition or parasitic infection.

Question 46

In some species, sex ratio of offspring can be adjusted in response to?

Answer 46

Resource availability.

Question 47

What is the sex of birds and mammals determined by?

Answer 47

The presence of sex chromosomes.