Variation and Reproduction Flashcards
What is meiosis?
the division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte.
In diploid cells, what do chromosomes typically appear as?
homologous pairs.
What are homologous chromosomes?
chromosomes of the same size, same centromere position and with the same sequence of genes at the same loci.
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 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 do 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 to genetic variability if hosts reproduce sexually?
the genetic variability in their offspring reduces the chances that all will be susceptible to infection by parasites
What is asexual reproduction and why can it be successful?
In asexual reproduction, just one parent can produce daughter cells and establish a colony of virtually unlimited size over time. Asexual reproduction can be a successful reproductive strategy as whole genomes are passed on from parent to offspring.
When is maintain the genome of a parent an advantage?
Maintaining the genome of the parent is an advantage particularly in very narrow, stable niches or when re-colonising disturbed habitats
What is an example of asexual reproduction in eukaryotes?
Vegetative cloning in plants and parthenogenesis in lower plants and animals that lack fertilisation are examples of asexual reproduction in eukaryotes
How is the sex of birds, mammals and some insects determined?
By the presence of sex chromosomes
What determines the development of male characteristics?
In most mammals the SRY gene on the Y chromosome
What do heterogametic(XY) males lack and what does this result in?
most of the corresponding homologous alleles on the shorter (Y) chromosome. This can result in sex-linked patterns of inheritance as seen with carrier females (XBXb ) and affected males (Xb Y).
What happens in homogametic(XX) females?
One of the two X chromosomes present in each cell is randomly inactivated at an early stage of development
What is X chromosome inactivation?
a process by which most of one X chromosome is inactivated. X chromosome inactivation prevents a double dose of gene products, which could be harmful to cells.
Why are carriers less likely to be affected by any deleterious mutations on these X chromosomes?
As the X chromosome inactivated in each cell is random, half of the cells in any tissue will have a working copy of the gene in question
What are hermaphrodites?
species that have functioning male and female reproductive organs in each individual. They produce both male and female gametes and usually have a partner with which to exchange gametes
What is the benefit of being hermaphroditic?
if the chance of encountering a partner is an uncommon event, there is no requirement for that partner to be of the opposite sex
What is an example of environmental sex determination?
Environmental sex determination in reptiles is controlled by environmental temperature of egg incubation.
What can sex change be a result of?
size, competition, or parasitic infection
