Term
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Definition
| males and females differ in physical traits and behaviour. It is the male that shows extravagant secondary sexual characteristics |
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Term
| Theory of sexual selection |
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Definition
a)Male-male competition–males use these traits to compete with each other
b)Female choice–females prefer to mate with males with “attractive” phenotypes |
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Term
| Speed of evolution of traits involved in male reproduction |
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Definition
| Fast,show extensive changes between species. |
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Term
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Definition
| Sex-biased genes are those that are expressed at a higher level in one sex than in the other. The expression difference is usually determined by microarray or RNA-seq experiments |
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Term
| Sex-bias gene's cutoff for a statistical test |
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Definition
M/F > 2 = male-biased gene (MBG)
M/F < 0.5 = female-biased gene (FBG)
0.5 < M/F < 2 = unbiased gene (UBG) |
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Term
| Percentage of sex-biased genes in fly |
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Definition
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Term
| Which genes have a higher expression in fly? |
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Definition
| The average M/F for MBG = 6, while the average F/M for FBG = 2.5 |
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Term
| Why are MBG under -represented on the X? |
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Definition
a) Dosage: males have only 1 copy of the X, while females have 2 copies.There is mechanisms of dosage compensation:doubling the transcription of the male X.
b) X-inactivation:X is transcriptionally inactive in the male germline
c)Sexual conflict: expression of a MBG may have a deleterious effect on females. |
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Term
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Definition
| X is bad environment for MBG and there may be selective pressure for MBG to “escape” the X and move to an autosome by retrotransposition |
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Term
| Rates of evolution for sex-biased genes |
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Definition
In fly,MBG show greater divergence between sp
ecies than FBG and UBG. The biggest difference is at nonsynonymous sites.FBG evolve slightly faster than UBG. The strongest difference is in genes expressed in reproductive organs. |
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Term
| Why do male - biased genes evolve fast? |
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Definition
a) MBG genes are under less selective constraint.
b) MBG are subject to more positive (or sexual) selection |
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Term
| Correlation between evolutionary rate and recombination rate for MBG (Why do male-biased genes evolve fast?) |
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Definition
| Selection is more efficient in regions of high recombination:each mutation can be selected independently. If changes are due to positive selection, then positive correlation between divergence and recombination rate |
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Term
| How to test that male-biased genes evolve fast? |
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Definition
a) Correlation between evolutionary rate and recombination rate for MBG
b) Polymorphism within species
Tested with McDonald-Kreitman, ompares the ratio of divergence at nonsynonymous and synonymous sites (Dn/Ds) to polymorphism at nonsynonymous and synonymous sites (Pn/Ps). Excess of nonsynonymous divergence-> positive selection.Excess of nonsynonymous polymorphism-> balancing selection or weak
purifying selection.X-linked MBG show a stronger signal of positive selection than autosomal MBG. |
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