Variation and Sexual Reproduction Flashcards
What are the costs of sexual reproduction?
Males are unable to produce offspring, only half of each parent’s gamete is passed onto offspring, and it disrupts successful parental genomes.
What are the benefits of sexual reproduction
There’s an increase in genetic variation.
What does genetic variation provide
Genetic variation provides the raw material required for adaptation, giving sexually reproducing organisms a better chance of survival under changing selection pressures.
Use the Red Queen Hypothesis to explain the persistence of sexual reproduction.
Without such genetic variety, the Red Queen Arms race would stop. In other words, this variation can drive selection and evolution should the different genes and alleles provide the individual with an advantage and increased chance of survival.
What may select for sexually reproducing hosts
Co-evolutionary interactions between parasites and hosts may select for sexually reproducing hosts.
What does it mean for parasites when a host reproduces sexually
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.
In what niche is maintaining the genome of a parent an advantage
Maintaining the genome of the parent is an advantage in very narrow, stable niches or when re-colonizing disturbed habitats.
What are examples of asexual reproduction in eukaryotes
Vegetative cloning in plants and parthenogenesis in lower plants and animals that fertilise are examples of asexual reproduction in eukaryotes.
How often and how much offspring are produced during asexual reproduction
Offspring can be reproduced more often and in larger numbers with asexual reproduction.
Where is parthenogenesis more common
Parthenogenesis is more common in cooler climates, which are disadvantageous to parasites, or regions of low parasite density or diversity.
How can mutations help organisms and plants that reproduce asexually
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.
How do organisms that reproduce principally by asexual reproduction have variation
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.
What is meiosis
Meiosis is the division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte.
What do chromosomes appear as in diploid cells
In diploid cells, chromosomes typically appear as homologous pairs.
What happens in meiosis 1
The chromosomes, which have replicated prior to meiosis 1, each consist of two genetically identical chromatids attached to the centromere. The 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. The crossing over of DNA is random and produces genetically different recombinant chromosomes. Spindle fibres attach to the homologous pairs and line them up at the equator of the spindle. The orientation of the pairs of homologous chromosomes at the equator is random. The chromosomes of each homologous pair are separated and move towards opposite poles. Cytokinesis occurs and two daughter cells form.
What happens in meiosis 2
Each of the two cells produced in meiosis 1 undergoes a further division during which the sister chromatids of each chromosome are separated.
How is the sex of birds, mammals, and some insects determined
The sex of birds, mammals, and some insects is determined by the presence of sex chromosomes.
What does an SRY gene on the Y chromosome determine
In most mammals, the SRY gene on the Y chromosome determines the development of male characteristics.
Where do heterogametic males lack corresponding homologous alleles
Heterogametic males lack most of the corresponding homologous alleles on the shorter Y chromosome.
What does lack of corresponding homologous alleles result in
This can result in sex-linked patterns of inheritance as seen with carrier females and affected males.
What inactivates in early stages of development
In homogametic females, one of the two X chromosomes present in each cell is randomly inactivated at an early stage of development.
What does X chromosome inactivation prevent
X chromosome inactivation prevents a double dose of gene products, which could be harmful to cells.
Which organisms are less likely to be affected by any deleterious mutations on these X chromosomes
Carriers are less likely to be affected by any deleterious mutations on these X chromosomes.
How do half of the cells in any tissue have working copies of the gene in question
As the X chromosome inactivated in each cell is random, half of the cells in any tissue have a working copy of the gene in question.
What are hermaphrodites
Hermaphrodites are species that have functioning male and female reproductive organs in each individual.
What do hermaphrodites produce
They produce both male and female gametes and usually have a partner with which to exchange gametes.
What is the benefit 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.
What determines the sex and sex ratio
Environmental rather than genetic factors determine sex and sex ratio.
How can sex change
Sex can change within individuals of some species as a result of size, competition, or parasitic infection.
How else can the sex ratio of offspring be adjusted
In some species, the sex ratio of offspring can be adjusted in response to resource availability.
