Variation and Sexual Reproduction Flashcards
1
Q
What are the disadvantages of sexual reproduction?
A
- Half of the population (males) are unable to produce offspring;
- Only half of each parent’s genome is passed onto offspring, disrupting successful parental genomes.
2
Q
What are the advantages of sexual reproduction?
A
- An increase in genetic variation in the population.
- It provides the raw materials required for adaptation, giving sexually reproducing organisms a better chance of surviving under changing selection pressures.
3
Q
How does sexual reproduction favour parasite affected organisms?
A
- Co-evolutionary interactions between parasites and hosts may select for sexually reproducing hosts.
- If hosts reproduce sexually, the genetic variability in their offspring reduces the chances that all will be susceptible to infection by parasites.
4
Q
What are the advantages of asexual reproduction?
A
- In asexual reproduction, just one parent can produce daughter cells and establish a colony of virtually unlimited size over time.
- Maintaining the genome of the parent is an advantage particularly in very narrow, stable niches or when re-colonising disturbed habitats.
- Organisms that reproduce principally by asexual reproduction also often have mechanisms for horizontal gene transfer between individuals to increase variation.
5
Q
What is vegatitive propagation?
A
- All offspring will be genetically identical to the original parent plants.
- This includes bulbs (onions and daffodils) and runners (spider plants and strawberries).
6
Q
What is parthenogenesis?
A
- Parthenogenesis is reproduction from a female gamete without fertilisation.
- Embryos result from unfertilised eggs and, therefore the resulting offspring would be haploid.
- Parthenogenesis is more common in cooler climates that are disadvantageous to parasites or regions of low parasite density/diversity.
7
Q
What are the disadvantages of asexual reproduction?
A
- Asexually reproducing populations are not able to adapt easily to changes in their environment.
- But mutations can occur that provide some degree of variation and enable some natural selection and evolution to occur.
8
Q
What is meosis?
A
- The process of gamete production in the reproductive organs.
- Is the division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte (germline cell).
- Meiosis has two divisions and results in variable gametes so increases variation within a species.
- Division 1 = meiosis I and division 2 = meiosis II.
9
Q
Describe homologous chromosomes.
A
- In diploid cells, chromosomes typically appear as homologous pairs.
- Homologous chromosomes are chromosomes of the same size, same centromere position and with the same sequence of genes at the same loci.
10
Q
What happens in meiosis 1?
A
The chromosomes replicate. Each consist of two genetically identical chromatids attached at the centromere.
11
Q
Meiosis I 1
A
The chromosomes condense and the homologous chromosomes pair up.
12
Q
Meiosis I 2
A
- Chiasmata forms at points of contact between the non-sister chromatids of a homologous pair and sections of DNA are exchanged.
- Linked genes are those on the same chromosome.
- Crossing over can result in new combinations of the alleles of these genes.
- This crossing over of DNA is random and produces genetically different recombinant chromosomes.
13
Q
Meiosis I 3
A
- Spindle fibres attach to the homologous pairs and line them up at the equator of the cell.
- The orientation of the pairs of homologous chromosomes at the equator is random.
- Each pair of homologous chromosomes is positioned independently of the other pairs, irrespective of their maternal and paternal origin.
- This is known as independent assortment.
- This is another mechanism which brings around variation.
14
Q
Meiosis I 4
A
Homologous chromosomes are separated by spindle fibres and move towards opposite poles.
15
Q
Meiosis I 5
A
Cytokinesis occurs and two daughter cells form.
