2.3 Organisms and Evolution: Variation and Sexual Reproduction Flashcards
2.3 (41 cards)
compared to asexual reproduction, sexual reproduction has two disadvantages, what are they?
half the population are unable to reproduce (males)
each parent is only able to pass on half of their genetic material
why do the benefits outweigh the costs in terms of sexual reproduction?
due to an increase in genetic variation in the population
what does genetic variation provide?
raw material required for adaptation, giving sexually reproducing organisms a better chance of survival under changing selection pressures
use the The Red Queen’s hypothesis to explain the persistence of sexual reproduction:
this variation can drive selection and evolution should the different genes and alleles provide the individual with an advantage and, therefore, an increased chance of survival
if a host reproduces sexually, how does that impact the offspring?
the genetic variability decreases the chance that all the individuals will be susceptible to infection by the parasites, this means the host will be able to resist and tolerate the parasitism and therefore shows greater fitness
where can asexual reproduction be successful?
in narrow, stable niches
what is asexual reproduction in eukaryotic plants?
vegetative propagation
why is asexual reproduction a successful reproductive method?
whole genomes are passed on from parent to offspring
what is asexual reproduction in animals?
parthenogenesis
where parthenogenesis most common?
in cooler climates with low parasite density
what is another benefit to asexual reproduction?
offspring can be produced more often and in larger numbers
what is the result of the offspring produced by parthenogenesis?
they are haploid
what is meiosis?
is the division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte
where does meiosis occur in animals?
in testes and ovaries
where does meiosis occur in plants?
in ovaries and anthers
what are homologous chromosomes?
chromosomes of the same;
size
centromere position
same genes at same loci
how may the alleles of the genes of the homologous chromosomes be slightly different?
each homologous chromosome is inherited from a different parent
where does crossing over occur?
at the chiasmata
what is crossing over?
when sections of DNA get swapped, shuffling sections of DNA between the homologous pairs, allowing recombination of new alleles to occur
what process results in variation between gametes?
independent assortment
what is independent assortment?
takes place during meiosis 1 when homologous chromosomes line up along the equator, the final position of one pair is completely random to relative to every other pair
what else results in variation between gametes?
crossing over of DNA is random and produces genetically different recombinant chromosomes
what can be said about the crossing over of DNA?
a random process and produces genetically different recombinant chromosomes
describe the process of meiosis 1:
chromosome, which have been separated prior to meiosis 1, consist of two genetically identical chromatids attached at the centromere, the chromosomes condense and homologous chromosomes pair up, chiasmata forms at points of contact between non-sister chromatids and sections of DNA are exchanged, the process of crossing over is random and produces genetically different recombinant chromosomes, spindle fibres attach to homologous pairs and line them up at the equator of the spindle, the orientation is random, the chromosome of each homologous pair is separated and moves to opposite poles, cytokinesis occurs and two daughter cells are produced
