multiplication rule
The act or process of multiplying, or of increasing in number; the state of being multiplied; as, the multiplication of the human species by natural generation.
gene
A basic unit of hereditary material; an ordered sequence of nucleotide bases that encodes a product (this product could be just RNA like rRNA or finally coding for a protein). The gene includes, however, regions preceding and following the coding region (
allele
Any one of the alternative forms of a given gene (e.g. the ABO gene has three major word here: A, B and O word here). One of two slightly different versions of a gene that code for different forms of the same trait.
locus
The position of a gene, DNA marker or genetic marker on a chromosome.
homologous pair
a pair of chromosomes, one from each parent, that have relatively similar structures and gene values
dominant
An allele that determines phenotype even when heterozygous. Also the trait controlled by that allele
recessive
An allele that is not expressed in the heterozygous condition. Also the phenotype of the homozygote of a (word here) allele
homozygous dominant
in a diploid organism, characterized by both alleles being the same at a specific locus An allele that determines phenotype even when heterozygous. Also the trait controlled by that allele
homozygous recessive
in a diploid organism, characterized by both alleles being the same at a specific locus An allele that is not expressed in the heterozygous condition. Also the phenotype of the homozygote of a (word here) allele
phenotype
(1) The detectable outward manifestations of a specific genotype. (2) The observable attributes of an organism. (3) The physical characteristics of a living object.
law of segregation
allele pairs separate or segregate during gamete formation, and randomly unite at fertilization.
law of independent assortment
states that allele pairs separate independently during the formation of gametes. This means that traits are transmitted to offspring independently of one another.
hybrids
(1) A heterozygote.(2) A progeny individual from any cross involving parents of differing genotypes. Offspring of unlike parents. 3) A duplex polynucleotide, formed by hybridization of two single stranded polynucleotides of different origin.
monohybrid cross
A cross between two individuals identically heterozygous at one gene pair for example, Aa x Aa
P generation
The parental generation in the cross pollination between two true-breeding plants that differ in a particular trait.
F1 generation
The first filial generation, produced by crossing two parental lines
F2 generation
The second filial generation, produced by selfing or intercrossing the F1.
Test cross
A cross between an individual of unknown genotype or a heterozygote (or a multiple heterozygote) to a homozygous recessive individual (tester).
dihybrid cross
A cross between two individuals identically heterozygous at two loci for example, AaBb/AaBb
incomplete dominance
The situation in which both alleles of a heterozygote influence the phenotype. The phenotype is usually intermediate between the two homozygous phenotypes. The situation in which a heterozygote shows a phenotype somewhere (but not exactly half-way) interm
codominance
Variation measured on a continuum rather than in discrete units or categories (eg height in human beings).
epistasis
The masking of the phenotypic effect of alleles at one gene by alleles of another gene. A gene is said to be epistatic when its presence suppresses the effect of a gene at another locus. Epistatic genes are sometimes called inhibiting genes because of the
pleiotropy
The phenomenon whereby a single mutation affects several apparently unrelated aspects of the phenotype.
continuous variation
Variation measured on a continuum rather than in discrete units or categories (eg height in human beings).
polygenic inheritance
An additive effect of two or more gene loci on a single phenotypic character
linked genes
Genes which control more that one trait between themselves
sex chromosones
A chromosome whose presence or absence is correlated with the sex of the bearer; a chromosome that plays a role in sex determination. Heteromorphic (different shaped, e.g. X and Y) chromosomes whose distribution in a zygote determines the sex of the organ
autosomes
Any chromosome that is not a sex chromosome
sex-linked
The inheritance pattern of loci located on the sex chromosomes (usually the X chromosome in XY species); also refers to the loci themselves
x-inactivation
locus on the X chromosome in mammals at which inactivation is initiated.
barr body
A densely staining mass that represents an inactivated X chromosome. Heterochromatic body found in the nuclei of normal females but absent in the nuclei of normal males
nondisjunction
The failure of a pair of homologous chromosomes to separate properly during meiosis. The failure of homologues (at meiosis) or sister chromatids (at mitosis) to separate properly to opposite poles, that is two chromosomes or chromatids go to one pole and
deletion
Loss of a DNA (chromosome) segment from a chromosome. Deletions are recognised genetically by:
duplication
More than one copy of a particular chromosomal segment in a chromosome set. Duplications supply genetic material capable of evolving new functions.
translocation
1. The relocation of a chromosomal segment in a different position in the genome. A chromosomal configuration in which part of a chromosome becomes attached to a different chromosome.
inversion
A chromosomal mutation involving the removal of a chromosome segment, its rotation through l80 degrees, and its reinsertion in the same location. The replacement of a section of a chromosome in the reverse orientation.
Phenylketonuria
autosomal recessive disease: inability to break down amino acid- phenylalanine. Accumulation of phenylalanine in untreated children causes mental retardation. Symptoms can be avoided with diets low in phenylalanine
sickle-cell anemia
autosomal recessive disease: abnormal hemoglobin. Red blood cells of individuals with this defect are unable to effectively transport oxygen throughout the body
tay-sachs disease
autosomal recessive disease: inability to properly break down certain lipids. Accumulation of the lipids in brain cells causes progressive nervous system dysfunction and is usually fatal by age four
huntington's disease
autosomal dominant disease: expression begins in middle age with mild mental illness and loss of motor control progressing to total physical and mental incapability
hemophilia
sex-linked recessive disease: inability to code for a clotting factor required to form normal blood cells
red-green color blindness
sex-linked recessive disease: inability to distinguish red from green
duchenne's muscular atrophy
sex-linked dominant disease: absence of an essential muscle protein. Results in dystrophy deteriorating muscles and loss of coordination
down syndrome
non-disjunction of chromosone 21 disease: Trisomy 21 (3 copies of chromosone 21). Physical abnormalities, mental retardation
turner syndrome
non-disjunction of sex chromosones disease: XO and female. Union of a gamete missing the sex chromosone with a normal egg or sperm bearing an x chromosone
klinefelter syndrome
non-disjunction of sex chromosones disease: XXY and male. Union of XX gamete and normal Y gamete. Sterile and often mentally retarded
Cri du chat syndrome
de;etion of chrmosone 5 disease: physical and mental retardation and catlike cry (cri du chat is French for "cry of the cat")