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A female produces an ovum with a full set (two sets of genes) provided solely by the mother. Thus, a male is not needed to provide sperm to fertilize the egg. This form of asexual reproduction is thought in some cases to be a serious threat to biodiversity for the subsequent lack of gene variation and potentially decreased fitness of the offspring.
In the absence of a Y chromosome, the fetus will undergo female development. This is because of the presence of the sex-determining region of the Y chromosome, also known as the SRY gene. [5] Thus, male mammals typically have an X and a Y chromosome (XY), while female mammals typically have two X chromosomes (XX).
In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively. Hormone levels in the male parent affect the sex ratio of sperm in humans. [25]
Parthenogenesis is a mode of asexual reproduction in which offspring are produced by females without the genetic contribution of a male. Among all the sexual vertebrates, the only examples of true parthenogenesis, in which all-female populations reproduce without the involvement of males, are found in squamate reptiles (snakes and lizards). [1]
The female boa could have chosen any number of male partners (and had successfully in the past) but on this occasion she reproduced asexually, creating 22 female babies with WW sex-chromosomes. Polyembryony is a widespread form of asexual reproduction in animals, whereby the fertilized egg or a later stage of embryonic development splits to ...
When meiosis occurs in the sporophyte generation of the life cycle, the sex chromosomes known as U and V assort in spores that carry either the U chromosome and give rise to female gametophytes, or the V chromosome and give rise to male gametophytes. [33] [34]
Sexual differentiation is the process of development of the sex differences between males and females from an undifferentiated zygote. [1] [2] Sex determination is often distinct from sex differentiation; sex determination is the designation for the development stage towards either male or female, while sex differentiation is the pathway towards the development of the phenotype.
The male reproductive system contains two main divisions: the testicles where sperm are produced, and the penis where semen is ejaculated through the urethra. In humans, both of these organs are outside the abdominal cavity. Having the testicles outside the abdomen facilitates temperature regulation of the sperm, which require specific ...