Unit 2: Organisms and Evolution, Variation and Sexual reproduction Flashcards
What are the costs of sexual reproduction?
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 in sexual reproduction?
Benefits outweigh costs due to an increase in genetic variation in the population
What does genetic variation allow for?
Genetic variation provides the raw material required for adaptation, giving sexually reproducing organisms a better chance of survival under changing selection pressures.
How does genetic variation increase chances of survival?
If hosts reproduce sexually, the genetic variability in their offspring reduces the chances that all will be susceptible to
infection by parasites.
What are the benefits of asexual reproduction?
Asexual reproduction can be a successful reproductive strategy as whole genomes are passed on from parent to offspring.
Maintaining the genome of the parent is an advantage particularly in very narrow, stable niches or when re-colonising disturbed habitats.
In asexual reproduction, just one parent is needed
produce daughter cells and establish an unlimited colony size.
What is parthenogenesis?
Parthenogenesis is reproduction from a
female gamete without fertilisation.
In which type of environment is parthenogenesis most common in?
Parthenogenesis is more common in cooler climates, which are disadvantageous to parasites, or regions of low parasite density or diversity
How can organisms that reproduce asexually increase variation?
They have mechanisms for horizontal gene transfer between individuals to increase variation, for
example the plasmids of bacteria and yeasts. Also mutations can occur
What is meiosis?
Meiosis is the division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte
How are chromosomes presented in diploid cells?
In diploid cells, chromosomes typically appear as homologous pairs
What are homologous chromosomes?
Homologous chromosomes are chromosomes of the same size, same centromere position and with the same
sequence of genes at the same loci.
Describe the steps of Meiosis I
The chromosomes have replicated prior to meiosis I
These chromosomes consist of two genetically identical chromatids attached at the centromere
Chromosomes condense and the homologous chromosomes pair up
Chiasmata form at points of contact between the non-sister chromatids of a homologous pair and sections of DNA are exchanged.
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 form
What is independent assortment?
Each pair of homologous chromosomes is positioned independently of the other pairs, irrespective of their maternal and paternal origin.
Describe the steps of Meiosis II
Each of the two cells produced in meiosis I undergoes a further division during which the sister chromatids of each chromosome are separated.
A total of 4 haploid cells are produced.
What gene determines male characteristics in most mammals?
The SRY gene
Why is random X chromosome inactivation a benefit to cells?
Prevents a double dose of gene products which could potentially be harmful to cells
What is X chromosome inactivation and in who does it happen in?
In homogametic females (XX) one of the two X chromosomes present in each cell is randomly inactivated at an early stage of development
X chromosome inactivation is a process by which most of one X chromosome is inactivated.
What are hermaphrodites?
Hermaphrodites are species that have functioning male and female reproductive organs in each individual.
What is the advantage of being a hermaphrodite?
The benefit to the individual organism is that if the chance of encountering a partner is an uncommon event, there is no requirement for that partner to be of the opposite sex. for example when flowers can’t find pollen from other flowers, they can use their own.
What environmental factors can affect other species’ sex and sex ratio?
Environmental sex determination in reptiles is controlled by environmental temperature of egg incubation.
