A gamete is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual that produces the larger type of gamete—called an ovum— and a male produces the smaller type—called a sperm. Sperm cells or spermatozoa are small and motile due to the flagellum, a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell or ovum is relatively large and non-motile. In short a gamete is an egg cell or a sperm. In animals, ova mature in the ovaries of females and sperm develop in the testes of males. During fertilization, a spermatozoon and ovum unite to form a new diploid organism. Gametes carry half the genetic information of an individual, one ploidy of each type, and are created through meiosis, in which a germ cell undergoes two fissions, resulting in the production of four gametes. In biology, the type of gamete an organism produces determines the classification of its sex.
Sex is the trait that determines whether a sexually reproducing organism produces male or female gametes. Male plants and animals produce small mobile gametes, while females produce larger, non-motile ones. Organisms that produce both types of gametes are called hermaphrodites. During sexual reproduction, male and female gametes fuse to form zygotes, which develop into offspring that inherit traits from each parent.
The XY sex-determination system is a sex-determination system used to classify many mammals, including humans, some insects (Drosophila), some snakes, some fish (guppies), and some plants. In this system, the sex of an individual is determined by a pair of sex chromosomes. In most cases, females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males have two different kinds of sex chromosomes (XY), and are called the heterogametic sex.
A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two common sexes and a few less common intersex variations.
Silene is a genus of flowering plants in the family Caryophyllaceae. Containing nearly 900 species, it is the largest genus in the family. Common names include campion and catchfly. Many Silene species are widely distributed, particularly in the northern hemisphere.
The Y chromosome is one of two sex chromosomes in therian mammals and other organisms. The other sex chromosome is the X chromosome. Y is normally the sex-determining chromosome in many species, since it is the presence or absence of Y that determines the male or female sex of offspring produced in sexual reproduction. In mammals, the Y chromosome contains the gene SRY, which triggers male development. The DNA in the human Y chromosome is composed of about 62 million base pairs, making it similar in size to chromosome 19. The Y chromosome is passed only from father to son. With a 30% difference between humans and chimpanzees, the Y chromosome is one of the fastest-evolving parts of the human genome. The human Y chromosome carries 693 genes, with 107 of these being protein-coding, but some genes are repeated and that makes the number of exclusive protein-coding genes just 42, the numbers are given for telomere-to-telomere CHM13. The Consensus Coding Sequence (CCDS) Project only classified 63 out of 107. All single-copy Y-linked genes are hemizygous except in cases of aneuploidy such as XYY syndrome or XXYY syndrome. Because of fake gaps inserted in GRCh38 it may be not obvious that CHM13 added 30 million base pairs into the Y chromosome, which is almost half of it that was unknown before 2022.
Haldane's rule is an observation about the early stage of speciation, formulated in 1922 by the British evolutionary biologist J. B. S. Haldane, that states that if — in a species hybrid — only one sex is inviable or sterile, that sex is more likely to be the heterogametic sex. The heterogametic sex is the one with two different sex chromosomes; in therian mammals, for example, this is the male.
Dosage compensation is the process by which organisms equalize the expression of genes between members of different biological sexes. Across species, different sexes are often characterized by different types and numbers of sex chromosomes. In order to neutralize the large difference in gene dosage produced by differing numbers of sex chromosomes among the sexes, various evolutionary branches have acquired various methods to equalize gene expression among the sexes. Because sex chromosomes contain different numbers of genes, different species of organisms have developed different mechanisms to cope with this inequality. Replicating the actual gene is impossible; thus organisms instead equalize the expression from each gene. For example, in humans, female (XX) cells randomly silence the transcription of one X chromosome, and transcribe all information from the other, expressed X chromosome. Thus, human females have the same number of expressed X-linked genes per cell as do human males (XY), both sexes having essentially one X chromosome per cell, from which to transcribe and express genes.
Dioecy is a characteristic of certain species that have distinct unisexual individuals, each producing either male or female gametes, either directly or indirectly. Dioecious reproduction is biparental reproduction. Dioecy has costs, since only the female part of the population directly produces offspring. It is one method for excluding self-fertilization and promoting allogamy (outcrossing), and thus tends to reduce the expression of recessive deleterious mutations present in a population. Plants have several other methods of preventing self-fertilization including, for example, dichogamy, herkogamy, and self-incompatibility.
Silene latifolia subsp. alba, the white campion is a dioecious flowering plant in the family Caryophyllaceae, native to most of Europe, Western Asia and Northern Africa. It is a herbaceous annual, occasionally biennial or a short-lived perennial plant, growing to between 40–80 centimetres tall. It is also known in the US as bladder campion but should not be confused with Silene vulgaris, which is more generally called bladder campion.
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, the schistosome family of flatworms, and some reptiles, e.g. majority of snakes, lacertid lizards and monitors including Komodo dragons. It is also used in some plants where it has probably evolved independently on several occasions. The letters Z and W are used to distinguish this system from the XY sex-determination system. In the ZW system, females have a pair of dissimilar ZW chromosomes, and males have two similar ZZ chromosomes.
The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring are sterile. These barriers maintain the integrity of a species by reducing gene flow between related species.
A sex chromosome is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical pair of mammal allosomes, determine the sex of an individual created in sexual reproduction. Autosomes differ from allosomes because autosomes appear in pairs whose members have the same form but differ from other pairs in a diploid cell, whereas members of an allosome pair may differ from one another and thereby determine sex.
Sexual differentiation in humans is the process of development of sex differences in humans. It is defined as the development of phenotypic structures consequent to the action of hormones produced following gonadal determination. Sexual differentiation includes development of different genitalia and the internal genital tracts and body hair plays a role in sex identification.
Androdioecy is a reproductive system characterized by the coexistence of males and hermaphrodites. Androdioecy is rare in comparison with the other major reproductive systems: dioecy, gynodioecy and hermaphroditism. In animals, androdioecy has been considered a stepping stone in the transition from dioecy to hermaphroditism, and vice versa.
A hermaphrodite is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are of different sexes, either male or female but not both, are gonochoric, which is the opposite of hermaphroditic.
An organism's sex is female if it produces the ovum, the type of gamete that fuses with the male gamete during sexual reproduction.
Gynodioecy is a rare breeding system that is found in certain flowering plant species in which female and hermaphroditic plants coexist within a population. Gynodioecy is the evolutionary intermediate between hermaphroditism and dioecy.
The ZO sex-determination system is a system that determines the sex of offspring in several moths. In those species, there is one sex chromosome, Z. Males have two Z chromosomes, whereas females have one Z. Males are ZZ, while females are ZO.
A sexual system is a pattern of sex allocation or a distribution of male and female function across organisms in a species. Terms like reproductive system and mating system have also been used as synonyms.
