Soru

Zorluk: Çok zorModern Evolutionary Theory and Genetic Basis of Evolution

Match each microevolutionary genetic phenomenon on the left with its corresponding population genetics mechanism or outcome on the right.

  • Persistent retention of a deleterious or lethal recessive allele in a gene pool despite strong negative selection against homozygotesBalancing selection via heterozygote advantage
  • Stochastic shifts in allele frequencies resulting from a severe, non-selective reduction in population sizeGenetic drift via the bottleneck effect
  • Bimodal distribution of phenotypic traits caused by simultaneous selection against intermediate heterozygous or median phenotypesDisruptive selection
  • Alteration of allele frequencies and reduction of genetic divergence between sub-populations caused by inter-population movement of fertile individualsGene flow via migration

Cevap

The phenomenon of retaining a deleterious recessive allele corresponds to balancing selection via heterozygote advantage. Stochastic allele frequency shifts after population reduction correspond to genetic drift via the bottleneck effect. Bimodal distribution of traits corresponds to disruptive selection. The movement of individuals reducing divergence between populations corresponds to gene flow via migration.
The retention of deleterious alleles occurs through balancing selection because heterozygous carriers gain a survival advantage (e.g., malaria resistance in sickle-cell heterozygotes). Sudden random allele changes following a drastic population drop constitute genetic drift operating through the bottleneck effect. Selection favoring both extreme phenotypes while penalizing intermediate forms defines disruptive selection. The exchange of genetic material between distinct populations through migration defines gene flow.

Adım Adım Çözüm

1
Analyze the retention of lethal recessive alleles in a population.
Identify that when heterozygous individuals possess higher fitness than either homozygous form, the recessive allele is preserved in the population (balancing selection / heterozygote superiority).
This explains why negative selection against homozygotes fails to eliminate harmful recessive alleles.
2
Examine random frequency changes due to catastrophic size reduction.
Map non-selective population drop to sampling error and random allele loss/fixation known as genetic drift (bottleneck effect).
When population size drops precipitously, survival is stochastic rather than fitness-based.
3
Evaluate the mechanism generating a bimodal phenotypic distribution.
Pair selective pressure against intermediate phenotypes with disruptive selection.
Disruptive selection acts against average phenotypes, favoring both extreme tail traits.
4
Determine the effect of inter-population movement of individuals.
Connect movement of gametes or breeding individuals between populations to gene flow.
Gene flow introduces new alleles and homogenizes gene pools across geographic regions.

Anahtar Kavram

Mechanisms of Microevolution and Population Genetics
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