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Crossing-over (genetics)

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Definition

Crossing-over (genetics)

The process whereby one or more gene alleles present in one chromosome may be exchanged with their alternative alleles on a homologous chromosome to produce a recombinant (crossover) chromosome which contains a combination of the alleles originally present on the two parental chromosomes.

Source: AccessScience, McGraw-Hill Education, 2019

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Crossing-over (genetics)

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Fungal genetics

The study of gene structure and function in fungi. Genetic research has provided important knowledge about genes, heredity, genetic mechanisms, metabolism, physiology, and development in fungi, and in higher organisms in general, because…

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Human genetics

A scientific discipline concerned with genetically determined resemblances and differences among human beings. Human genetics analyzes all aspects of inheritance occurring in humans. Although the mechanism by which heredity operates…

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Recombination (genetics)

The formation of new genetic sequences by piecing together segments of previously existing ones. Classical genetics is based on the transmission of traits, attributable to particular genetic determinants or genes, through sexual generations. The…

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DNA repair

The set of biochemical processes that fixes DNA molecules when they are damaged. The processes involved in deoxyribonucleic acid (DNA) repair are important because DNA (Fig. 1) is the genetic material that directs the production of all the proteins…

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Meiosis

The set of two successive cell divisions that serve to separate homologous chromosome pairs and thus reduce the total number of chromosomes by half. The process of meiosis (Fig. 1) includes two sequential nuclear divisions (meiosis I and II) that…

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Allele

Any of a number of alternative forms of a gene. Allele is a contraction of allelomorph, a term that William Bateson used to designate one of the alternative forms of a unit showing mendelian segregation. New alleles arise from existing ones by…

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Mosaicism

The condition in which more than one genetically distinct population of cells coexists within one individual. The term mosaic is used for an individual composed of two or more cell lines of different genetic or chromosomal constitutions, where the…

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Bdelloid rotifers

Bdelloid rotifers are microscopic freshwater invertebrate animals less than 1 mm in length. They are found in nearly every possible freshwater aquatic habitat, including those that remain wet for only a short period of time (Fig. 1). Originally…

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Gene discovery in Drosophila melanogaster

At an elementary level, the development and homeostasis of an organism are the result of the differential expression of thousands of genes, the basic heredity units. Each gene consists of a portion of the DNA that contains sequences that…

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Genetics of anxiety

The identification of genes that affect quantitative traits, or more specifically the identification of polymorphisms (multiple forms) within those genes that give rise to variation, is currently a central goal in biology and promises to advance the…

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Chromosome aberration

Any change (mutation) in the normal linear order of a chromosome or change in the typical chromosome number for a cell or organism. As genome sequencing is now revealing the linear order of chromosomes at the DNA level, even changes as small as the…

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Genetic mapping

The resolution of the elements of the genetic material of an organism into a linear array. Genetic mapping provides researchers with a graphic representation of the linear arrangement of genes on a chromosome (Fig. 1). Chromosomes are linear…

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Chromosome

A DNA–protein complex in the nucleus of eukaryotic cells. Chromosomes are linear (usually) or circular structures containing deoxyribonucleic acid (DNA) complexed with histone and nonhistone proteins, a centromere, and a telomere at each end, if…

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Nobel Prizes for 2007

The Nobel Prizes for 2007 included the following awards for scientific disciplines. Chemistry The chemistry prize was awarded to Gerhard Ertl of Fritz-Haber-Institut der Max-Planck-Gesellschaft (Fritz Haber Institute of the Max Planck Society),…

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Deoxyribonucleic acid (DNA)

A linear polymer made up of a specific sequence of deoxyribonucleotide repeating units linked by 3′,5′-phosphodiester bonds and acting as the carrier of genetic information. Deoxyribonucleic acid (DNA) [Fig. 1] is the common structure that forms the…

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Plant reproduction

The formation of a new plant that is either an exact copy or recombination of the genetic makeup of its parents. There are three types of plant reproduction considered here: (1) vegetative reproduction, in which a vegetative organ forms a clone of…

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Bioethics

A discipline concerned with the application of ethics to biological problems, especially in the field of medicine. Bioethics is a broad term that encompasses the environmental, ethical, legal, and social implications of agriculture, life sciences,…

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Sex-linked inheritance

The inheritance of a trait that is determined by a gene located on one of the sex chromosomes. Sex-linked inheritance is the transmission to successive generations of traits (phenotypes) that are the result of alleles (alternative gene forms) at…

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Parasexual cycle

A series of events, discovered in filamentous fungi, which lead to genetic recombination outside the standard sexual cycle.Until the 1940s the standard sexual cycle (an alternation of nuclear fusion and meiosis) was the only route to formal genetic…

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Genetic dominance

The expression of a heritable trait in both the homozygous and heterozygous conditions. Genetic dominance (Fig. 1) is a cornerstone of the basic laws of biological inheritance (also known as Mendelian inheritance or Mendelism). In particular,…

Biography

Morgan, Thomas Hunt (1866–1945)

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Cell lineage

A type of embryological study in which the history of individual blastomeres (cells formed during division of the zygote) or meristem cells is traced to their ultimate differentiation into tissues and organs. Animals The question of how the animal…

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Sex determination

The genetic mechanisms by which sex is determined in all living organisms. The nature of the genetic basis of sex determination varies a great deal, however, among the various forms of life.Forms of sexuality There are two aspects of sexuality: the…

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Lethal gene

A gene which brings about the death of the organism carrying it. Lethal genes constitute the most common class of gene changes (that is, mutations) and are reflections of the fact that the fundamental function of genes is the control of processes…

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Breeding the button mushroom (Agaricus bisporus)

The familiar button mushroom [Agaricus bisporus (J. Lange) Imbach (see illustration)], originally a forest-dwelling species, has been cultivated continuously for more than three centuries. Today, millions of tons of these mushrooms, with a farm gate…

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Plant breeding

The application of genetic principles to the improvement of cultivated plants. The science of plant breeding involves the controlled mating and selection of plants, often utilizing hybridization and genetic engineering techniques, to modify plant…

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Genetic exchange among bacteria

The transfer of genes is traditionally thought to occur in a vertical fashion, with genes being passed from parent cell to daughter cell or from parent to offspring through either sexual or asexual reproduction. In contrast, horizontal gene transfer…

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Human migration and population analysis

Before Christopher Columbus's famous voyage in 1492 and the beginning of modern transoceanic journeys, humans had established themselves on all habitable continents. This initial settlement of the continents by Homo sapiens originated approximately…

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Vernalization

The process by which plant flowering is promoted by prolonged exposure to the cold of a typical winter. Vernalization evolved in certain plants to ensure that flowering occurred at the proper time of year. In some plants, the requirement for…

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Plant hybrid vigor

The continued growth in the world population constantly increases the demand for food, feed, fiber, and fuel, which requires increased levels of growth and productivity of crops and plants. To increase plant productivity, a common agricultural…

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Speciation

The process by which new species of organisms evolve from preexisting species. It is part of the whole process of organic evolution. The modern period of its study began with the publication of Charles Darwin's and Alfred Russell Wallace's theory of…

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Engineered minichromosomes in plants

Chromosomes are physical carriers of genetic information that all organisms rely on as blueprints. The chromosome consists of deoxyribonucleic acid (DNA) and proteins. The DNA of the chromosome stores genetic information, with the content and the…

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Genetically modified crops

Commercially grown plants that have altered genetic material through artificial recombinant manipulation. Genetic modification is the latest scientific tool for developing improved crop varieties. Such genetically modified (GM) crops can help to…

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Oats

An agricultural crop of the genus Avena grown for its grain and straw in most countries of the temperate zones of the world. Oats (Fig. 1) belong to the order Poales (Cyperales), family Poaceae (Gramineae), and genus Avena. The most important crop…

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Rice

An annual cereal grass plant, Oryza sativa (family Poaceae), cultivated for its carbohydrate-rich grain. Rice is the major source of food for nearly one-half of the world's population. In China, Japan, Korea, the Philippines, India, and other…

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Paleoindian

The oldest archeological cultures of the New World, the ancestors of modern Native Americans. The Paleoindian colonizing populations of the Americas were Homo sapiens sapiens who arrived during the late Pleistocene (Ice Age) from Asia, though…

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Crustacea

An extremely diverse, species-rich group of arthropods that have inhabited marine environments since the beginning of the Cambrian Period. In some ways, they may be thought of as the marine equivalents of the insects. Within the marine realm, the…

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Stem cells

Cells that have the ability to self-replicate and to give rise to mature cells. The concept of stem cells (Fig. 1) was originally based on renewing tissues. Many adult tissues, including the skin, blood, and intestines, consist of mostly mature and…

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Fossil humans

All prehistoric skeletal remains of humans that are archeologically earlier than the Neolithic (necessarily an imprecise limit), regardless of degree of mineralization or fossilization of bone, and regardless of whether the remains may be classed…

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Crossing-over (genetics)

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Crossing-over (genetics)

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