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The ZW sex-determination system is a chromosomal system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects (including butterflies and moths), the schistosome family of flatworms, and some reptiles, e.g. majority of snakes, lacertid lizards and monitors, including Komodo dragons.
The biologist Thierry Lodé proposed (2001, 2012) five modes of reproduction based on the relationship between the zygote (fertilised egg) and the parents: [1] [2] Ovuliparity: fertilisation is external, the oocytes being released into the environment and fertilised outside the body by the male. [1]
The word is most often used for the offspring of mammals, but can be used for any animal that gives birth to multiple young. In comparison, a group of eggs and the offspring that hatch from them are frequently called a clutch, while young birds are often called a brood. Animals from the same litter are referred to as littermates.
In species that use the XY sex-determination system, parthenogenetic offspring have two X chromosomes and are female. In species that use the ZW sex-determination system the offspring genotype may be one of ZW (female), [30] [31] ZZ (male), or WW (non-viable in most species, [33] but a fertile, [dubious – discuss] viable female in a few, e.g ...
Many animal species have specific mating (or breeding) periods e.g. (seasonal breeding) so that offspring are born or hatch at an optimal time. In marine species with limited mobility and external fertilisation like corals , sea urchins and clams , the timing of the common spawning is the only externally visible form of sexual behaviour.
Extra-pair copulation in men has been explained as being partly due to parental investment. [7] Research has suggested that copulation poses more of a risk to future investment for women, as they have the potential of becoming pregnant, and consequently require a large parental investment of the gestation period, and then further rearing of the offspring. [7]
The offspring of males with larger eyespots on their ornamented tails have been shown to weigh more and were more likely to be alive after 2 years than the progeny of males with fewer eyespots. [19] Ornaments that play a role in reproduction develop under the influence of two series of genes. [21]
Bird's nest in grass. Nesting behavior is an instinct in animals during reproduction where they prepare a place with optimal conditions to nurture their offspring. [1] The nesting place provides protection against predators and competitors that mean to exploit or kill offspring. [2] It also provides protection against the physical environment. [1]