 | Term | Definition |
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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. |
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gene |
A distinct unit of hereditary material found in chromosomes; a sequence of nucleotides in DNA that codes for a particular tRNA, rRNA, or polypeptide. |
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allele |
one of two alternate forms of a gene that can have the same locus on homologous chromosomes and are responsible for alternative traits |
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locus |
The specific location of a gene or DNA sequence on a chromosime. |
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homologous pair |
a pair of chromosomes, one from each parent, that have relatively similar structures and gene values |
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dominant |
the allele in a heterozygote that determines the phenotype |
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recessive |
describes a trait or an allele that is expressed only when two recessive alleles for the same characteristic are inherited |
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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 |
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homozygous recessive |
An organism that has two recessive alleles for a gene |
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phenotype |
an organism’s appearance or other detectable characteristic that results from the organism’s genotype and the environment |
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law of segregation |
The genetic principle stating that the alleles of a gene occur in pairs and are separated from each other during meiosis and are recombined at fertilization. |
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law of independent assortment |
Mendel's second law. States that genes found on different chromosomes, or genes found very far apart on the same chromosome (i.e., unlinked genes) sort independently of one another during gamete formation (meiosis). |
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hybrids |
an organism that has two different alleles for a trait ; an organism that is heterozygous for a particular trait |
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monohybrid cross |
An organism that is heterozygous with respect to a single gene of interest. all the offspring from a cross between parents homozgous for different alleles are monohybrids. For example, parents of genotypes AA and aa produce a genotype of Aa. |
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p generation |
parental generation, the first two individuals that mate in a generic cross |
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F1 generation |
These are the offspring from a cross of a homozygous dominant and homozygous recessive P1 |
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f2 generation |
the second generation of offspring, obtained from an experimental cross of two organisms; the offspring of the F1 generation |
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test cross |
A genetic cross in which a test organism showing the dominant trait is crossed with one showing the recessive trait; used to determine whether the test organism is homozygous dominant or heterozygous. |
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dihybrid cross |
A cross between two individuals identically heterozygous at two loci for example, AaBb/AaBb |
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incomplete dominance |
neither allele is dominant, produces intermediate phenotype, possible cause:loss of function mutation |
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codominance |
A type of inheritance in which two dominant alleles are expressed at the same time without blending of traits. |
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epistasis |
interaction between genes in which the presence of a particular allele of one gene determines whether another gene will be expressed |
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pleiotropy |
when a gene has more than one effect or phenotype e.g: sickle-cell |
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continuous variation |
Variation measured on a continuum rather than in discrete units or categories (eg height in human beings). |
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polygenic inheritance |
occurs when a group of gene pairs acts together and produces a specific trait, such as human eye color, skin color, or height |
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linked genes |
Located on same Chromosomes and tend to be inherited together in genetic crosses. |
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sex chromosomes |
one of the 23 pairs of chromosomes in the human, contains genes that will determine the sex of the individual |
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autosomes |
All chromosomes except the sex chromosomes |
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sex-linked |
(of a gene or heritable characteristic) carried by a sex chromosome. |
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x-inactivation |
locus on the x chromosome in mammals at which inactivation is initiated |
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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 |
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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 none to the other. |
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deletion |
A type of chromosomal alteration in which a portion of a chromosome and the genes it contains is lost. |
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duplication |
More than one copy of a particular chromosomal segment in a chromosome set. Duplications supply genetic material capable of evolving new functions. |
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translocation |
the movement of a segment of DNA from one chromosome to another, which results in a change in the position of the segment; also the movement of soluble nutrients from one part of a plant to another |
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inversion |
a kind of mutation in which the order of the genes in a section of a chromosome is reversed |
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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 |
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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 |
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tay-sachs disease |
autosomal recessive disease: inability to properly break down certain lipids. Accumulation of the lipids in brain cells cause progressive nervous system dysfunction and is usually fatal by age 4 |
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huntington's disease |
autosomal dominant disease: is caused by a dominant allele located on an autosome and is therefore said to show an autosomal-dominant pattern of inheritance |
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hemophilia |
a sex-linked recessive disorder defined by the absence of one or more of the proteins required for blood clotting |
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red-green color blindness |
sex-linked recessive disease; inability to distinguish red from green |
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duchenne's muscular atrophy |
sex-linked odminant disease: absence of essential muscle protein which results in dystrophy deteriorating muscles and loss of coordination |
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down syndrome |
a disorder caused by an extra twenty-first chromosome and characterized by a number of physcial and mental abnormalities, non-disjunction of chromosone 21 disease: Trisomy 21 (3 copies of chromosone 21). Physical abnormalities, mental retardation |
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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 |
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klinefelter syndrome |
non-disjunction of sex chromosones disease: XXY and male. Union of XX gamete and normal Y gamete. Sterile and often mentally retarded |
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cri du chat syndrome |
deletion of chromosome 5 disease: physical and mental retardation and catlike cry (cri du chat is French for "cry of the cat") |
