Maternal influence on sex determination
Encyclopedia
In humans and several other species of animals, the father
determines the sex
of the child. 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.
Recent findings indicate that maternal influences may impact which sperm are more likely to achieve conception
and that there may be mechanisms by which the mother selectively encourages or discourages sperm with particular characteristics.
Human ova, like those of other mammals, are covered with a thick translucent layer called the zona pellucida
, which the sperm must penetrate to fertilize the egg. Once viewed simply as an impediment to fertilization, recent research indicates the zona pellucida may instead function as a sophisticated biological security system that chemically controls the entry of the sperm into the egg and protects the fertilized egg from additional sperm.
Recent research indicates that human ova may produce a chemical which appears to attract sperm and influence their swimming motion. However, not all sperm are positively impacted; some appear to remain uninfluenced and some actually move away from the egg.
Maternal influences may also be possible that affect sex determination in such a way as to produce fraternal twins equally weighted between one male and one female.
Father
A father, Pop, Dad, or Papa, is defined as a male parent of any type of offspring. The adjective "paternal" refers to father, parallel to "maternal" for mother...
determines the sex
Sex
In biology, sex is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety . Sexual reproduction involves combining specialized cells to form offspring that inherit traits from both parents...
of the child. In the XY sex-determination system
XY sex-determination system
The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects and some plants . In this system, females have two of the same kind of sex chromosome , and are called the homogametic sex. Males have two distinct sex chromosomes , and are called...
, the female-provided ovum
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
contributes an X chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
and the male-provided sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively.
Recent findings indicate that maternal influences may impact which sperm are more likely to achieve conception
Conception
Conception, or a concept, is an abstract idea or a mental symbol.Conception may also refer to:* Conception, or fertilisation, the fusion of gametes to produce a new organism.* Conception , an album by Miles Davis...
and that there may be mechanisms by which the mother selectively encourages or discourages sperm with particular characteristics.
Human ova, like those of other mammals, are covered with a thick translucent layer called the zona pellucida
Zona pellucida
The zona pellucida is a glycoprotein membrane surrounding the plasma membrane of an oocyte. It is a vital constitutive part of the latter, external but of essential importance to it...
, which the sperm must penetrate to fertilize the egg. Once viewed simply as an impediment to fertilization, recent research indicates the zona pellucida may instead function as a sophisticated biological security system that chemically controls the entry of the sperm into the egg and protects the fertilized egg from additional sperm.
Recent research indicates that human ova may produce a chemical which appears to attract sperm and influence their swimming motion. However, not all sperm are positively impacted; some appear to remain uninfluenced and some actually move away from the egg.
Maternal influences may also be possible that affect sex determination in such a way as to produce fraternal twins equally weighted between one male and one female.