AH Biology - Unit 2 - KA3(a) - Variation and Sexual Reproduction

What is sexual reproduction?

Sexual reproduction is when offspring are produced by combining genetic information from two individuals of different sexes.

What are costs of sexual reproduction?

Costs of sexual reproduction are:

• Only half of the population can produce offspring, since males can’t, so population growth is slower.

• Each parents successful genome is disrupted as only half of each parents genome is passed on.

What is a benefit of sexual reproduction?

A benefit of sexual reproduction is that it maintains greater genetic variation which provides the raw material required for an adaptation. This gives sexually reproducing offspring a better chance of survival when selection pressures change.

What is it thought that the parasitic co-evolution between parasites and hosts selects for?

It is thought that the parasitic co-evolution between parasites and hosts selects for sexually reproducing hosts.

What does sexual reproduction in hosts increase and reduce, and what does this mean for the host and parasite.

Sexual reproduction in hosts increases their offsprings genetic variability and reduces the chances that all offspring will be susceptible to infection. This variation means that hosts better able to resist and tolerate parasitism have a greater fitness and parasites better able to feed, reproduce, and find a new host have a greater fitness.

What is asexual reproduction?

Asexual reproduction is when offspring arise from a single parent and inherit genes from that parent alone.

What is a benefit of asexual reproduction?

A benefit of asexual reproduction is that in very narrow, stable niches and when recolonising a disturbed habitat, asexual reproduction can be a very successful strategy because:

• Just one parent can produce a daughter cell colony rapidly and of a virtually unlimited size.

• The successful whole genome of the parent is passed on from parent to offspring, so the offspring are already well adapted to their habitat.

What are costs of asexual reproduction?

Costs of asexual reproduction are:

• There is very little, if any, genetic variation in the population, so they cannot adapt to changing selection pressures easily. (Mutations can give rise to some variation.)

• Some organisms that can reproduce asexually have mechanisms for horizontal gene transfer between organisms of the same generation, such as prokaryotes and yeasts, which can transfer genetic information horizontally in the form of plasmids. This increases variation and can result in faster evolutionary change. THIS MIGHT NOT BE A COST?

What are examples of asexual reproduction?

Examples of asexual reproduction are:

• Vegetative cloning in plants. Examples of vegetative cloning are bulbs, runners, and tubers.

• Parthenogenesis in lower plants and animals, such as the brahminy blind snake (Indotyphlops braminus). They are the only obligate parthenogenetic snake species.

What is parthenogenesis?

Parthenogenesis is reproduction from a female gamete without fertilisation, for example an unfertilised egg.

Where is parthenogenesis more common?

Parthenogenesis is more common in:

• Cooler climates, which are disadvantageous to parasites

• Regions of low parasite density or diversity