Organisms and Evolution - Variation and Sexual Reproduction Flashcards
What are the costs of sexual reproduction?
Males unable to produce offspring;
Only half of each parent’s genome passed onto offspring,
Disrupting successful parental genomes
Why do the benefits of sexual reproduction outweigh the costs?
Due to an increase in genetic variation in the population
What does genetic variation provide?
The raw material required for adaptation, giving sexually
reproducing organisms a better chance of survival under changing selection pressures
Why may co-evolutionary interactions between parasites and hosts select for sexually reproducing hosts?
Hosts better able to resist and tolerate parasitism have greater fitness. Parasites better able to feed, reproduce and find new hosts have greater fitness
What happens if hosts reproduce sexually?
The genetic variability in their offspring reduces the
chances that all will be susceptible to infection by parasites
How can asexual reproduction be a successful reproduction strategy?
Whole genomes are passed on from parent to offspring.
Just one parent can produce daughter cells and establish a colony of virtually unlimited size over time
When is maintaining the genome of a parent an advanatage?
Particularly in very narrow, stable niches or when re-colonising disturbed habitats
Give examples of asexual reproduction in eukaryotes?
Vegetative cloning in plants and parthenogenesis in lower plants and animals that lack fertilisation
What is parthenogenesis?
Reproduction from a female gamete without fertilisation
In what reproductive strategy can offspring be reproduced more often and in larger numbers?
Asexual reproduction
Where is parthenogenesis more common?
In cooler climates, which are disadvantageous to parasites, or regions of low parasite density or diversity
Describe asexually reproducing populations?
They 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
What do organisms that reproduce principally by
asexual reproduction also often have?
Mechanisms for horizontal gene transfer between individuals to increase variation, for example the plasmids of bacteria and yeasts
How can prokaryotes exchange genetic material?
Horizontally, resulting in faster evolutionary change than in organisms that only use vertical transfer
What is meiosis?
The division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte
How do chromosomes typically appear in diploid cells?
As homologous chromosomes
What are homologous chromosomes?
Chromosomes of the same size, same centromere position and with the same sequence of genes at the same loci
