2.3 Sexual reproduction

Question 1

Describe the costs and benefits of sexual reproduction.

Answer 1

Males cannot produce offspring and generally make up half of the species population.
There can be disruption of successful parental genomes.
However, genetic variation within a population provides the raw materials for adaptation, which allows for survival and reproduction.

Question 2

Explain how the Red Queen Hypothesis can be used in the persistence of sexual reproduction?

Answer 2

1. Hosts are better able to resist and have greater fitness.
2. If hosts reproduce sexually it reduces chance that all will be susceptible to infection.
3. Parasites with increased turbulence better able to feed.

Question 3

Explain why asexual reproduction can be a successful reproductive strategy.

Answer 3

1. Offspring are genetic clones of the parents.
2. Narrow stable niches.
3. Offspring develop rapidly.

Question 4

What are the costs of asexual reproduction?

Answer 4

Not able to adapt easily to changes.

Question 5

Explain what is meant by horizontal gene transfer and its benefits to prokaryotes.

Answer 5

The inheritance of genes horizontally.
Can result in faster evolutionary change then species who transfer vertically.

Question 6

Give a brief description of tow examples of asexual reproduction in eukaryotes, with an example for each.

Answer 6

Vegetative cloning and parthenogenesis.
Vegetative cloning - bulbs
Parthenogenesis - Komodo Dragon.

Question 7

Describe homologous chromosomes.

Answer 7

Homologous chromosomes are sets of genetic information of the same size, position of centromere and same genes at the same loci.

Question 8

Explain how chiasmata formation between paired homologous chromosomes leads to variation in gametes.

Answer 8

Chiasmata are points where genetic information is exchanged randomly between non-sister chromatids.

Question 9

Explain how independent assortment of chromosomes during meiosis I leads to variation.

Answer 9

This is the randomisation of chromosomes orientation at the equator. This separates maternal and paternal genetic information.

Question 10

Describe the main events of meiosis I.

Answer 10

Prophase - Chromosomes shorten and condense, becoming visible under microscope. Non-sister chromatids exchange genetic information at the chiasmata, creating variation.
Metaphase - Spindle fibres attach at the centromere and homologous pairs align at the equator randomly.
Anaphase - Chromosomes are separated as units of spindle fibre are removed by depolymerisation.
Telophase - Chromatids become chromosomes as nucleic acids begins to rebuild and cytokinesis occurs.

Question 11

Describe Meiosis II.

Answer 11

4 haploid daughter cells are produced, as diploid cells divide further.

Question 12

Describe how genetic control determines the sex in mammals.

Answer 12

XX chromosomes in females, and XY in males.

Question 13

Describe the function of the SRY gene.

Answer 13

The SRY gene expresses the TDF protein, which causes male characteristics.

Question 14

Explain why males are heterogematic.

Answer 14

Because they have both an ‘X’ and a ‘Y’ chromosome.

Question 15

Explain the significance of heterogametic males in relation to sex-linked patterns of inheritance.

Answer 15

Sex-linked alleles are only carried on the X chromosome and not on the Y; carrier females have two alleles for characteristics.

Question 16

Explain the importance of X chromosome inactivation and why female carriers are less likely to be affected by any deleterious mutations on these X chromosomes.

Answer 16

X chromosone inactivation prevents a double dosage of a harmful gene, and inactivation is random in each cell.