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During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed sister chromatid separation during meiosis II. In some species, notably plants, nondisjunction can result in an organism with an entire additional set of chromosomes, which is called polyploidy. In humans, nondisjunction can occur during male or female gametogenesis and the resulting gametes possess one too many or one too few chromosomes.
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Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate correctly and move to the opposite poles of the cells. This produces daughter cells with abnormal chromosome numbers.  Nondisjunction is common during anaphase I or anaphase II of meiosis.  Mutations in synaptonemal complex proteins that attach homologous chromosomes increase the chances of nondisjunction in anaphase I of meiosis I. In contrast, mutations in topoisomerases and condensins that hold...
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Manipulation of Ploidy in Caenorhabditis elegans
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Sibling quality and the haplodiploidy hypothesis.

P Kennedy1, A N Radford1

  • 1School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.

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|March 19, 2020
PubMed
Summary

Haplodiploidy in insects may favor altruism without requiring sex discrimination. Focusing on female fitness benefits, particularly in nest-founding species, explains the evolution of helping behaviors in supersisters.

Keywords:
altruismeusocialityhaplodiploidy

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Area of Science:

  • Evolutionary Biology
  • Behavioral Ecology
  • Genetics

Background:

  • Haplodiploidy is hypothesized to promote altruism in social insects like bees and ants due to relatedness asymmetries.
  • Existing theories require workers to discriminate between sexes or exhibit sex-ratio biases to drive eusociality.

Purpose of the Study:

  • To investigate if insect biology, independent of sex discrimination, can explain the evolution of altruism in haplodiploids.
  • To model the conditions under which relatedness asymmetry drives worker origins without pre-existing biases.

Main Methods:

  • A kin selection model was developed to simulate the evolution of altruism.
  • The model incorporated varying influences of body quality on female versus male fitness.

Main Results:

  • Altruism can promote worker origins in haplodiploids without necessitating sex-ratio biases or brood discrimination.
  • When female fitness is strongly linked to body quality, sisters disproportionately benefit from altruistic aid.
  • This effect holds even when altruists cannot distinguish sibling sexes.

Conclusions:

  • Female-biased benefits from altruism, driven by quality-dependent fitness, can explain the evolution of helping behavior in haplodiploid insects.
  • This mechanism offers an alternative pathway to eusociality, broadening our understanding of social evolution in insects.