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Heterogamy is a term applied to a variety of distinct phenomena in different scientific domains. Usually having to do with some kind of difference, "hetero", in reproduction, "gamy". See below for more specific senses.
In reproductive biology, heterogamy is the alternation of differently organized generations, applied to the alternation between parthenogenetic and a sexual generation. [1] [2] This type of heterogamy occurs for example in some aphids.
Alternately, heterogamy or heterogamous is often used as a synonym of heterogametic, meaning the presence of two unlike chromosomes in a sex. [3] [4] For example, XY males and ZW females are called the heterogamous sex.
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In cell biology, heterogamy is a synonym of anisogamy, the condition of having differently sized male and female gametes produced by different sexes or mating types in a species.
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In botany, a plant is heterogamous when it carries at least two different types of flowers in regard to their reproductive structures, for example male and female flowers or bisexual and female flowers. Stamens and carpels are not regularly present in each flower or floret.
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In sociology, heterogamy refers to a marriage between two individuals that differ in a certain criterion, and is contrasted with homogamy for a marriage or union between partners that match according to that criterion. For example, ethnic heterogamy refers to marriages involving individuals of different ethnic groups. Age heterogamy refers to marriages involving partners of significantly different ages. Heterogamy and homogamy are also used to describe marriage or union between people of unlike and like sex (or gender) respectively.
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the full set of genes of their single parent and thus the newly created individual is genetically and physically similar to the parent or an exact clone of the parent. Asexual reproduction is the primary form of reproduction for single-celled organisms such as archaea and bacteria. Many eukaryotic organisms including plants, animals, and fungi can also reproduce asexually. In vertebrates, the most common form of asexual reproduction is parthenogenesis, which is typically used as an alternative to sexual reproduction in times when reproductive opportunities are limited. Komodo dragons and some monitor lizards can reproduce asexually.
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. The name gamete was introduced by the German cytologist Eduard Strasburger.
Sex is the trait that determines whether a sexually reproducing organism produces male or female gametes. During sexual reproduction, a male and a female gamete fuse to form a zygote, which develops into an offspring that inherits traits from each parent. By convention, organisms that produce smaller, more mobile gametes are called male, while organisms that produce produce larger, non-mobile gametes are called female. An organism that produces both types of gamete is hermaphrodite.
Sexual dimorphism is the condition where sexes of the same species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most dioecious species, which consist of most animals and some plants. Differences may include secondary sex characteristics, size, weight, color, markings, or behavioral or cognitive traits. Male-male reproductive competition has evolved a diverse array of sexually dimorphic traits. Aggressive utility traits such as "battle" teeth and blunt heads reinforced as battering rams are used as weapons in aggressive interactions between rivals. Passive displays such as ornamental feathering or song-calling have also evolved mainly through sexual selection. These differences may be subtle or exaggerated and may be subjected to sexual selection and natural selection. The opposite of dimorphism is monomorphism, when both biological sexes are phenotypically indistinguishable from each other.
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.
Assortative mating is a mating pattern and a form of sexual selection in which individuals with similar phenotypes or genotypes mate with one another more frequently than would be expected under a random mating pattern. A majority of the phenotypes that are subject to assortative mating are body size, visual signals, and sexually selected traits such as crest size. The opposite of assortative is disassortative mating.
In biology, gonochorism is a sexual system where there are two sexes and each individual organism is either male or female. The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric.
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.
Sequential hermaphroditism is one of the two types of hermaphroditism, the other type being simultaneous hermaphroditism. It occurs when the organism's sex changes at some point in its life. In particular, a sequential hermaphrodite produces eggs and sperm at different stages in life. Sequential hermaphroditism occurs in many fish, gastropods, and plants. Species that can undergo these changes do so as a normal event within their reproductive cycle, usually cued by either social structure or the achievement of a certain age or size. In some species of fish, sequential hermaphroditism is much more common than simultaneous hermaphroditism.
Male is the sex of an organism that produces the gamete known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilisation. A male organism cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. Most male mammals, including male humans, have a Y chromosome, which codes for the production of larger amounts of testosterone to develop male reproductive organs.
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.
The heterogametic sex is the sex of a species where an individual's gametes have non-matching sex chromosomes. In humans, the heterogametic sex is the male sex, where each gamete's sex chromosomes are X and Y. This is in contrast to the female sex, where each gamete's sex chromosomes are X and X. This arrangement is understood within the XY sex-determination system.
Parthenogenesis is a natural form of asexual reproduction in which growth and development of an embryo occur directly from an egg, without need for fertilisation. In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. In plants, parthenogenesis is a component process of apomixis. In algae, parthenogenesis can mean the development of an embryo from either an individual sperm or an individual egg.
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete with a single set of chromosomes combines with another gamete to produce a zygote that develops into an organism composed of cells with two sets of chromosomes (diploid). This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes.
Automixis is the fusion of nuclei or gametes derived from the same individual. The term covers several reproductive mechanisms, some of which are parthenogenetic.
Intralocus sexual conflict is a type of sexual conflict that occurs when a genetic locus harbours alleles which have opposing effects on the fitness of each sex, such that one allele improves the fitness of males, while the alternative allele improves the fitness of females. Such "sexually antagonistic" polymorphisms are ultimately generated by two forces: (i) the divergent reproductive roles of each sex, such as conflicts over optimal mating strategy, and (ii) the shared genome of both sexes, which generates positive between-sex genetic correlations for most traits. In the long term, intralocus sexual conflict is resolved when genetic mechanisms evolve that decouple the between-sex genetic correlations between traits. This can be achieved, for example, via the evolution of sex-biased or sex-limited genes.
Homogamy is marriage between individuals who are, in some culturally important way, similar to each other. It is a form of assortative mating. The union may be based on socioeconomic status, class, gender, caste, ethnicity, or religion, or age in the case of the so-called age homogamy.
Homogamy is used in biology in four separate senses:
David Pafford Crews is the Ashbel Smith Professor of Zoology and Psychology at the University of Texas at Austin. He has been a pioneer in several areas of reproductive biology, including evolution of sexual behavior and differentiation, neural and phenotypic plasticity, and the role of endocrine disruptors on brain and behavior.
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.
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