Question

A few species of insects, fish, and crustaceans can reproduce sexually and asexually

a. How can the populations shift towards only asexually? (Explain describing factors that may occur)

b. Why are asexual, parthenogenetic species found at the tips of trees while their closest relatives reproduce sexually?

(Explain why this pattern occurs)

c. Normally, one would infer that lower-variation should be found with asexually-reproducing species. However, lizards that have only females and parthenogenetic species of plants have higher-variation. Explain why this is and how the variability is maintained (with examples)

Answer 1

1. A population can shift towards only asexual reproduction because of following reasons-

# large numbers of offsprings are reproduced very quickly from only one parent when conditions are favourable.
# large colonies can form that can compete other for nutrients and water.
# large number of organisms mean that species may survive when conditions or the number of Predator change.

2. Asexual, parthenogenetic species are found at the tip of the tree because of the favourable conditions present in the atmosphere which supports the growth of organisms produced through a sexual reproduction. Because of less variation and less adaptation to the changes the organism produced through asexual reproduction die rapidly that's why the closest relatives turn to sexual reproduction.

3. Females can produce full clones of themselves through a modification of the normal meiosis process used to produce haploid egg cells for sexual reproduction.
The females germ cells undergo a process of premeiotic genome doubling, so that two consecutive division cycles in the process of meiosis result in a diploid genome.
Whereas homologous chromosomes pair and separate during meiosis 1 in sexual species, identical duplicate sister chromosomes, produced through premeiotic replication, pair and separate during meiosis 1 in true parthenotes.
Pairing of identical sister chromosomes, in comparison to the alternative of pairing homologous chromosomes., maintains heterozygosity, which causes variation.