altitudinal contact zone (ACZ)
n. Geographic contact between two populations along a certain line of elevation, in which one population occurs above that line, and the other, below it.
n. Cellular death and disintegration. Apoptosis is generally thought of as occurring as an aspect of development or maintenance of the body (as opposed to death caused by external causes such as trauma). High levels of germ cell apoptosis are, however, common in, or even characteristic of hybrids, particularly those derived from parents with different karyotypes.
adj. Not producing, or unable to produce sperm.
n. A chromosome not involved in sex determination. Such chromosomes exist as homolog pairs. — autosomal
(1) n. Mating between a hybrid and one of the two parents (or two parental types) that originally crossed to produce it; (2) n. a hybrid individual produced by such a cross; (3) v. to produce such a cross.
n. Hybridization that occurs in captivity.
n. A population composed of individuals with a particular karyotype.
n. A physically discrete portion of the genome carrying many genes. A chromosome is composed of chromatin. Prokaryotic chromosomes are single and circular. Eukaryotic chromosomes are multiple and linear.
chromosome number (also chromosome count) /KRŌM-ə-zōm/
n. The number of chromosomes in a eukaryotic cell. Each eukaryote has a characteristic chromosome number, which is the typical number of chromosomes found in each of its cells.
n. The type of organism defined in terms of a particular karyotype.
v. To engage in sexual intercourse — copulation /kawp-yə-LAY-shən/
n. (1) an instance of a particular type of hybridization; (2) a hybrid.
v. To hybridize.
adj. (1) adj. in the case of a single-celled eukaryotic organism, having two complete sets of chromosomes; (2) adj. in the case of a multicellular eukaryotic organism, having two complete sets of chromosomes in each somatic cell. ; (3) n. a haploid individual. See also: haploid.
n. The earliest of stage of development of a plant or animal. In humans, embryo is used up to the third month of pregnancy. Thereafter, once the basic body shape has formed, the term fetus is employed.
n. A hormone, produced by the ovaries, that prepares the uterus for embryo implantation.
n. Causing estrus.
estrus (also estrum) /ES-trəs, ES-trəm/
n. In many female mammals, the periodically recurrent state of sexual receptivity (“heat”). In heat: In a state of estrus (“The animal is in heat.”)
n. An organism with cells that have membrane-bounded nucleus. Cells of this type are found in protoctists, plants, fungi, and animals. Humans are eukaryotes, as are oak trees, mushrooms, and amoebas. Many, but not all, eukaryotic cells contain additional membrane-bounded organelles (e.g., mitochondria, chloroplasts, Golgi bodies, etc.). The name eukaryote is derived from Greek eu-, meaning true, and karyon, denoting nucleus. Eukaryotes compose one of the three primary divisions of cellular life. The other two, Archaea and Bacteria, are the prokaryotes, simple single-celled organisms. In general, eukaryotes have multiple, linear chromosomes, whereas a prokaryote has a single, circular chromosome not enclosed in a membrane — eukaryotic /you-kare-ee-AWT-ick/ adj.
n. See: First filial generation.
n. See: Second filial generation.
adj. Capable of producing offspring (by means of gamete production, as opposed to asexual reproduction).
/fert-əl-eye-ZAY-shən/ n. The union of a male and a female gamete to form a zygote.
v. (1) in a male gamete: to join with a female gamete in fertilization; (2) in a male organism: to place male gametes within a female or on eggs.
first filial generation (FF₁ generation, or simply FF₁)
n. The generation produced by an initial cross between two distinct types of parents.
n. In a hybrid, capable of producing as many viable gametes as do either of the parental types that crossed to produce the hybrid.
n. Haploid reproductive cells. Two gametes, one of each sex, fuse during fertilization to produce a zygote during sexual reproduction. A female reproductive cell is an ovum (or egg) and a male reproductive cell is a spermatozoon.
n. Within the context of hybridization, a generation is the individual, or set of individuals, produced from a particular mating within a series of matings. For example, the first generation is the set of individuals produced from an initial cross or hybridization between two distinct types of organisms. The second generation is the set of offspring produced by the first generation, and so forth.
adj. (1) having a hereditary basis, as opposed to an environmental cause; (2) of, relating to, produced by, or being a gene or genes. — genetics /jə-NET-icks/n.
n. A sex gland (of either sex), a gland that produces gametes.
n. A hybrid (half-breed is an archaic term, not used in modern science, but that was formerly very common, especially in the literature of the 18th and 19th centuries).
(1) adj. in the case of a single-celled eukaryotic organism, having a single complete set of chromosomes; (2) adj. in the case of a multicellular eukaryotic organism, having a single complete set of chromosomes in each somatic cell; (3) n. a haploid individual. See also: diploid.
n. The collective genotype of a set of linked loci.
adj. Producing two types of gametes. In mammals, the heterogametic sex is the male, because that sex produces both XX gametes (gametes containing two X chromosomes) and XY gametes (gametes containing both an X chromosome and a Y chromosome), whereas the female produces only XX gametes.
adj. In a diploid organism: having two different alleles at the locus in question.
adj. In a diploid organism, having two identical alleles at the locus in question.
homologs /HŌM-ə-lawgz/ (also homologous chromosomes /hə-MALL-ə-gəs/)
n. (1) chromosomes having the same loci, in the same order (a diploid cell has two copies of each homolog, one derived from each parent), also called homologous chromosomes; a “chromosome pair” is a pair of homologs (2) genes having the same origin.
adj. In a diploid organism, having two identical alleles at the locus in question.
n. An organism produced by a mating between two organisms of different types.
hybrid zone /HĪ-brid/
n. A geographic region where hybridization occurs on an ongoing basis.
v. The production of an offspring from matings between organisms of two different types.
v. To produce offspring from matings between organisms of two different types. Another word for hybridize: interbreed
interbreedv. See: hybridize.
intergradationn. Another word for hybridization, but generally used in connection with populations treated as conspecific.
introgressionn. See the discussion of this word here — introgress v.
adj. In between, having the characters of both.
n. A hybrid.
n. (1) a photomicrograph of the chromosomes present in an individual's somatic cells, often arranged in a standard format showing the number, size, and shape of each type of chromosome; (2) the set of chromosomes present in a particular type of organism, viewed in terms of their characteristic size and structure. More precisely, a karyotype is a set of chromosomes in which a particular set of loci is distributed onto particular chromosomes in a particular order and relative orientation (the DNA segments between the loci also are distributed in a particular order and orientation). Often, when organisms with different karyotypes mate, they produce infertile hybrids.— karyotypic adj.
meiosis /my-Ō-səs, -sis/
n. The process of two consecutive cell divisions that produces haploid sex cells and spores from diploid progenitor cells. Meiosis results in four daughter cells, each with a haploid set of unreplicated chromosomes — meiotic adj.
mitochondrial DNA (mtDNA) /MY-tŌ-KAWN-dree-əl/
n. The DNA found in mitochondria, the organelles that generate energy for the cell.
mitochondria (sing mitochondrion) /MY-toe-kawn-dree-ə (sing MY-toe-KAWN-dree-ən)/
n. Organelles that are the site of respiration in eukaryotic cells.
offspring (pl offspring)
n. the product of the reproductive processes of an animal or plant. The offspring of a human are the children of a parent, in cattle, the offspring of a cow is the calf. Other words with the same meaning as offspring, and also used only in the singular: young (animals only), progeny, issue
n. (1) in animals: a female gonad; (2) in plants: the portion of a carpel containing the ovules.
ovum (pl ova) /Ō-vəm, pl: Ō-və/
n. An unfertilized egg; a female gamete.
parapatric contact zone
n. A line of contact where two populations meet without significant geographic overlap.
adj. In a hybrid, capable of producing viable gametes, but not in as great numbers as do either of the parental types that crossed to produce the hybrid.
n. See: offspring.
n. A hybrid cross occurring between the same two types of organisms, but with the sexes of the parents reversed.
n. A hybrid cross for which both reciprocal crosses occur.
second filial generation (F₂ generation, or simply F₂)
n. The second filial generation, the generation produced by interbreeding of individuals belonging to the F₁ generation. In general, the Fn generation is produced by interbreeding of individuals belonging to the Fn-1 generation.
n. The normal biological process whereby the the chromatids of each chromosome pair are separated during meiosis and randomly distributed to the germ cells.
n. Chromosomes that determine the sex of an individual. There are two sex chromosome systems (1) the XX/XY system, where XY individuals are male, and XX individuals are female (the usual system, for example, in mammals and butterflies); and (2) the WW/WZ system; where WW individuals are male, and WZ individuals are female (the normal system in birds, for example). In humans the sex chromosomes comprise the 23rd chromosome pair. See also: autosome.
n. A population defined in terms of a set of morphological traits.
n. A type of organism defined in terms of a set of morphological traits.
n. (1) spermatozoa; (2) semen; (3) a spermatozoon.
n. /sper-MAWD-ə-site/ n. Either of two types of cells that originate from the spermatogonium during spermatogenesis and that develop, via division into spermatids. The first of these two types is the primary spermatocyte, which is a mature sex cell that develops from the spermatogonium without division. The second is the secondary spermatocyte, which is produced from the primary spermatocyte by division.
spermatogonium (pl spermatogonia) /sper-mawd-ə-GŌ-nee-əm, pl -nee-ə/
n. During spermatogenesis, one of the primordial, undifferentiated sex cells that give rise, via maturation and growth, first to a primary spermatocyte, then via division, to two secondary spermatocytes that in turn divide to form four spermatids, which then mature without further division into four fully functional spermatozoa.
spermatozoon (pl spermatozoa) /sper-mawd-ə-ZŌ-ən; pl: -ZŌ-ə/
n. A mature male haploid gamete capable of active movement by means of a undulipodium. During spermatogenesis, spermatozoa form in huge quantities within the seminiferous tubules of the testes. In shape, a spermatozoon resembles a tadpole. It has an oval, flattened head containing a haploid nucleus. A human spermatozoon is about 0.005 mm (0.002 in) in length. When a spermatozoon pierces an ovum it loses its tail as the two cell fuse.
adj. Incapable of producing offspring (by means of gamete production, as opposed to asexual reproduction).
v. To join or fuse; within the context of biology this term is used primarily with regard to meiotic synapsis. See: synapsis.
n. The pairing of homologous chromosomes during prophase I of meiosis.
synaptonemal complex (SC)
n. The interface formed between two homologs when they unite during meiosis.
testis (pl testes) /TES-tiss, pl TES-teez/
uterus /YOO-ter-əs, YOO-trəs/
n. The organ of gestation, present only in females, commonly known as the womb. It holds and nourishes the developing embryo and fetus — uterine /YOO-ter-ən, -in/ adj. Of, pertaining to, or in the uterus.
n. See: offspring.
n. A fertilized egg, produced by the union of a male and female gamete. A zygote goes on to develop into a multicellular organism by repeated cell division (mitosis). — zygotic /zī-GAWT-ik/ adj.
Human Origins: Are we hybrids?
On the Origins of New Forms of Life
Cat-rabbit Hybrids: Fact or fiction?
Georges Cuvier: A Biography
Prothero: A Rebuttal
Branches of Biology