Life: Science Of Biology - Ch 2

Front 1

Allele (a leel´) [Gr. allos: other]

Back 1

alternate forms of a genetic character found at a given locus on a chromosome.

Front 2

Autosome

Back 2

chromosome (in a eukaryote) other than a sex chromosome.

Front 3

Codominance

Back 3

ondition in which two alleles at a locus produce different phenotypic effects and both effects appear in heterozygotes.

Front 4

Dihybrid cross

Back 4

ating in which the parents differ with respect to the alleles of two loci of interest.

Front 5

Dominance

Back 5

genetics, the ability of one allelic form of a gene to determine the phenotype of a heterozygous individual, in which the homologous chromosomes carries both it and a different (recessive) allele. (Contrast with recessive.)

Front 6

Epistasis

Back 6

eraction between genes in which the presence of a particular allele of one gene determines whether another gene will be expressed.

Front 7

Expressivity

Back 7

degree to which a genotype is expressed in the phenotype

Front 8

F1 (first filial generation)

Back 8

immediate progeny of a parental (P) mating.

Front 9

Gene [Gr. genes: to produce]

Back 9

nit of heredity. Used here as the unit of genetic function which carries the information for a single polypeptide or RNA.

Front 10

Genotype (jean´ oh type) [Gr. gen: to produce + typos: impression]

Back 10

exact description of the genetic constitution of an individual, either with respect to a single trait or with respect to a larger set of traits. (Contrast with phenotype.)

Front 11

Hemizygous (hem´ ee zie´ gus) [Gr. hemi: half + zygotos: joined]

Back 11

a diploid organism, having only one allele for a given trait, typically the case for X-linked genes in male mammals and Z-linked genes in female birds. (Contrast with homozygous, heterozygous.)

Front 12

Heritable

Back 12

e to be inherited

Front 13

Heterosis

Back 13

uation in which heterozygous genotypes are superior to homozygous genotypes with respect to growth, survival, or fertility. Also called hybrid vigor.

Front 14

Heterozygous (het´ er oh zie´ gus) [Gr. heteros: different + zygotos: joined]

Back 14

a diploid organism having different alleles of a given gene on the pair of homologues carrying that gene. (Contrast with homozygous.)

Front 15

Homozygous (home´ oh zie´ gus) [Gr. homos: same + zygotos: joined]

Back 15

a diploid organism, having identical alleles of a given gene on both homologous chromosomes. An individual may be a homozygote with respect to one gene and a heterozygote with respect to another. (Contrast with heterozygous.)

Front 16

Incomplete dominance

Back 16

dition in which the heterozygous phenotype is intermediate between the two homozygous phenotypes.

Front 17

Independent assortment

Back 17

ing meiosis, the random separation of genes carried on nonhomologous chromosomes. Articulated by Mendel as his second law.

Front 18

Locus

Back 18

genetics, a specific location on a chromosome. May be considered to be synonymous with gene.

Front 19

Monohybrid cross

Back 19

ating in which the parents differ with respect to the alleles of only one locus of interest.

Front 20

Mutation

Back 20

etectable, heritable change in the genetic material not caused by recombination.

Front 21

P generation

Back 21

ental generation. The individuals that mate in a genetic cross. Their immediate offspring are the F1 generation.

Front 22

Pedigree

Back 22

pattern of transmission of a genetic trait within a family.

Front 23

Penetrance

Back 23

a genotype, the proportion of individuals with that genotype who show the expected phenotype.

Front 24

Phenotype (fee´ no type) [Gr. phanein: to show]

Back 24

observable properties of an individual resulting from both genetic and environmental factors. (Contrast with genotype.)

Front 25

Pleiotropy (plee´ a tro pee) [Gr. pleion: more]

Back 25

determination of more than one character by a single gene.

Front 26

Polymorphism (pol´ lee mor´ fiz um) [Gr. poly: many + morphe: form, shape]

Back 26

genetics, the coexistence in the same population of two distinct hereditary types based on different alleles.

Front 27

Recessive

Back 27

genetics, an allele that does not determine phenotype in the presence of a dominant allele. Contrast with dominance.

Front 28

Reciprocal crosses

Back 28

air of crosses, in one of which a female of genotype A mates with a male of genotype B and in the other of which a female of genotype B mates with a male of genotype A.

Front 29

Recombinant

Back 29

individual, meiotic product, or single chromosome in which genetic materials originally present in two individuals end up in the same haploid complement of genes. The reshuffling of genes can be either by independent segregation, or by crossing over between homologous chromosomes.

Front 30

F2 (second filial generation)

Back 30

immediate progeny of a mating between members of the F1 generation.

Front 31

Segregation

Back 31

genetics, the separation of alleles, or of homologous chromosomes, from one another during meiosis so that each of the haploid daughter nuclei produced by meiosis contains one or the other member of the pair found in the diploid mother cell, but never both. This principle was articulated by Mendel as his "first law."

Front 32

Sex chromosome

Back 32

organisms with a chromosomal mechanism of sex determination, one of the chromosomes involved in sex determination.

Front 33

Sex linkage

Back 33

pattern of inheritance characteristic of genes located on the sex chromosomes of organisms having a chromosomal mechanism for sex determination.

Front 34

Test cross

Back 34

ross of a dominant-phenotype individual (which may be either heterozygous or homozygous) with a homozygous-recessive individual.

Front 35

Trait

Back 35

form of a character: Eye color is a character

Front 36

Wild type

Back 36

eticists' term for standard or reference type. Deviants from this standard, even if the deviants are found in the wild, are said to be mutant.