Variation and Sexual Reproduction Flashcards
State 2 costs of sexual reproduction
males are unable to produce offspring
only half of each parent’s genome is passed to offspring, disrupting successful parental genomes
Why do the benefits of sexual reproduction outweigh the costs
Due to the increase in genetic variation in the population
Why is genetic variation in offspring beneficial?
It provides the raw material required for adaptation, giving sexually reproducing organisms a better chance of survival under changing selection pressures
What would a host with a good fitness be able to do
They would be better at resisting and tolerating a parasite
What would a parasite with a good fitness be able to do
Those that are able to feed, reproduce and find new hosts
What makes asexual reproduction successful
Whole genomes are passed to offspring
Just one parent can produce daughter cells and establish a colony of virtually any size over time
In what situation/environment would asexual reproduction be beneficial
In very narrow and stable niches or when re-colonising disturbed habitats
What is parthenogenesis
Reproduction from a female gamete without fertilisation
State 2 examples of organisms that use parthenogenesis
Animals that lack fertilisation
Lower plants
In what conditions is parthenogenesis most common
In cooler climates (disadvantageous to parasites)
Regions of low parasite density
Can natural selection or evolution occur in asexually producing organisms and why?
Yes it can and this is possible due to mutation which provides a small degree of variation
What is another mechanism for increasing variation in asexually reproducing organisms and give two examples where this is possible
Horizontal gene transfer in bacteria and yeast
Why can prokaryotes evolve fast
They can exchange genetic material horizontally instead of vertically
What is meiosis
The division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte
State the 3 features of homologous chromosomes
They are the same size
Same centromere position
Have the same sequence of genes at the same loci
Describe meiosis I (5 points)
- Chromosomes condense and homologous chromosomes pair up
- Chiasmata form at points of contact between non-sister chromatids of a homologous pair and sections of DNA are exchanged. (Producing different recombinant chromosomes)
- Spindle fibres attach to the homologous pairs and line them up at the equator of the spindle
- The chromosomes of each homologous pair are separated and move towards opposite poles
- Cytokinesis occurs and two daughter cells are produced
What is the independent assortment
When each pair of homologous chromosomes is positioned independently of the other pairs, irrespective of their maternal and paternal origin
Describe meiosis II
Each of the two cells produced in meiosis I undergoes a further division during which the sister chromatids of each chromatids of each chromosome are separated
What determines the sex of birds, mammals and some insects
The presence of sex chromosomes
In most mammals, which gene determines the development of male characteristics
The SRY gene on the Y chromosome
What do heterogametic males lack
most of the corresponding homologous alleles on the shorter Y chromosome
Explain X chromosome inactivation
In heterogametic females one of the two X chromosomes present in each cell is randomly inactivated at an early stage of development
What is the effect of X chromosome inactivation
It prevents a double dose of gene products which could be harmful to cells. This means carriers are less likely to be affected by any deleterious mutations on these X chromosomes
How many cells within some tissue will have their X chromosomes inactivated
Half
What are hermaphrodites
Species that have functioning male and female reproductive organs in each individual. They usually have a partner with which to exchange gametes
What type of gametes do hermaphrodites produce
Both male and female gametes
What is beneficial about hermaphrodites
If encountering a parter is an uncommon event, there is no requirement for that partner to be of the opposite sex
What determines the sex in reptiles
The environmental temperature of egg incubation
Name 3 factors that can cause sex change
Size
Competition
Parasitic infection
What can influence the sex ratio of offspring
Resource availability
