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Based on the Trivers-Willard model, Clutton-Brock hypothesized that the sex ratio of mammalian offspring may change according to maternal condition, where high-ranked females should produce more male offspring and low-ranked females should produce more female offspring. [19] This is based on the assumption that high-ranked females are in better ...
Fisher was aware that in humans, more boys are born, but boys are also more likely to die in infancy. As a consequence, he reasoned that because parents tend to invest less in boys – because more boys die before the end of the period of parental care – there is a higher rate of male births to equalise parental investment in each sex.
This is an example of indirect genetic benefits received by the choosy sex, because mating with such individuals will result in high-quality offspring. The indicator traits hypothesis is split into three highly related subtopics: the handicap theory of sexual selection, the good genes hypothesis, and the Hamilton–Zuk hypothesis.
Some chromosomal sex determination systems in animals A sex-determination system is a biological system that determines the development of sexual characteristics in an organism . [ 1 ] Most organisms that create their offspring using sexual reproduction have two common sexes, males and females , and in other species, there are hermaphrodites ...
The distinction between chromosomal sex-determination systems and TSD is often blurred because the sex of some species – such as the three-lined skink Bassiana duperreyi and the central bearded dragon Pogona vitticeps – is determined by sex chromosomes, but this is over-ridden by temperatures that are tolerable but extreme. Also ...
Therefore, he inferred the number of involved mates based on the number of offspring that were later found to have mutations from both a male and a female. The difficulty that arose was that if a female Drosophila had copulated with five males and only one larva survived, Bateman would not be able to account for the other four copulations.
Therefore, the sperms are not identical, because in each chromosome of a pair there will be different alleles at many of the loci. But when the father is haploid all the sperms are identical (except for a small number where gene mutations have taken place in the germ line). So, all female offspring inherit the male's chromosomes 100% intact.
[9] [10] [11] In some harem-forming species, when a dominant male vacates his harem (due to death, defection to another harem, or usurpation) the incoming male sometimes commits infanticide of the offspring. [12] Because time and resources are no longer being devoted to the offspring, infanticide often stimulates the female to return to sexual ...