Chapter 4 Vocab

sex

refers to sexual phenotype; typically male or female

sex determination

specification of sex (male or female); mechanisms include chromosomal, genic, and environmental systems

sex chromosomes

chromosomes that differ in number or morphology in males and females

autosomes

chromosome that is the same in males and females; a nonsex chromosome

heterogametic sex

the sex that produces two types of gametes with respect to sex chromosomes; for example, in the XX-XY sex-determing system, the male produces both X-bearing and Y-bearing gametes

homogametic sex

the sex that produces gametes that are all alike with respect to sex chromosomes; for example, in the XX-XY sex-determining system, the female produces only X-bearing gametes

pseudoautosomal regions

small region of the X and Y chromosomes that contains homologous gene sequences

ZZ-ZW sex determination

the female is heterogametic (ZW and the male is homogametic; this system if found in birds, some reptiles, butterflies, some amphibians & fish

genic sex determination

the sexual phenotype is specified by genotypes at one or more loci, but there are no obvious differences in the chromosomes of males and females; this type of sex determination has been observed in some plants, fungi, protozoans, and fish

Turner syndrome

human condition in which cells contain a single X chromosome and no Y chromosome (XO); people with this are female in appearance and have underdeveloped female secondary sex characteristics; most are sterile but have normal intelligence

Klinefelter syndrome

human condition in which cells contain one or more Y chromosomes and multiple X chromosomes (most commonly XXY but can be XXXY, XXXXY, or XXYY); people with this are male in appearance but frequently have small testes and reduced facial and pubic hair; they are often taller than normal and sterile, and most have normal intelligence

triple-X syndrome

human condition in which cells contain 3 X chromosomes; a person with this has a female phenotype with no distinctive features other than a tendency to be tall and thin; a few such females are sterile, but many menstruate regularly and are fertile

sex-determining region Y (SRY) gene

the male-determing gene in mammals, located on the Y chromosome

sex linked characteristics

characteristic(s) determined by genes located on the sex chromosomes

X-linked characteristics

determined by a gene or genes on the X chromosome

Y-linked characteristics

determined by a gene or genes on the Y chromosome

Thomas Morgan Hunt

first person to provided an explanation for sex-linked inheritance; used fruit flies and eye color to investigate this

hemizygous

possession of a single allele at a locus; males of organisms with XX-XY sex determination are this for X-linked loci because their cells possess a single X chromosome

dosage compensation

a mechanism to equalize the amount of protein produced by X-linked genes and autosomal genes; in placental mammals, this is accomplished by the random inactivation of one X chromosome in the cells of females

Barr bodies

inactivated X chromosome that appears as a condensed, darkly staining body in the nuclei of most cells of female placental mammals

Lyon hypothesis

proposal by Mary Lyon in 1961 that on X chromosome in each female cell becomes inactivated (a Barr body), and that which of the X chromosomes is inactivated is random and varies from cell to cell

complete dominance

type of dominance in which the same phenotype is expressed in homozygotes (AA) and in heterozygotes (Aa); only the dominant allele is expressed in a heterozygote

incomplete dominance

type of dominance in which that phenotype of the heterozygote falls between the phenotypes of the two homozygotes

codominance

type of allelic interaction in which the heterozygote simultaneously expresses the phenotypes of both homozygotes

incomplete penetrance

the genotype does not always produce the expected phenotype

penetrance

percentage of individual organisms having a particular genotype that express the expected phenotype

expressivity

degree to which a trait is expressed

lethal allele

causes death at an early stage in development—often before birth—so that some genotypes do not appear among the progeny

multiple alleles

presence of more than two alleles within a group of organisms; however, each diploid member of the group has only two of the possible alleles

compound heterzygote

an individual that carries two different alleles at a locus that result in a recessive phenotype

gene interaction

interaction between genes at different loci that affect the same characteristic

epistasis

type of gene interaction in which a gene at one locus masks or supresses the effects of a gene at a different locus

epistatic gene

gene that masks or suppresses the effect of a gene at a different locus; may be recessive or dominant in their effects

hypostatic gene

gene that is masked or suppressed by the action of a gene at a different locus

complementation test

test designed to determine whether two different mutations are at the same locus (allelic) or at different loci (non-allelic)

complementation

manifestation of two different mutations in the heterozygous condition as the wild-type phenotype; indicates that the mutations are at different loci (non-allelic)

sex-influenced characteristics

characteristic encoded by autosomal genes that are more likely to be expressed in one sex vs the other

sex-limited characteristic

characteristic encoded by autosomal genes and expressed in only one sex

cytoplasmic inheritance

inheritance of characteristics encoded by genes located in the cytoplasm; because the cytoplasm is usually contributed entirely by one parents, most of these characteristics are inherited from only one parent

genetic maternal effect

genes are inherited from both parents, but the offspring’s phenotype is determined by the genotype of the mother

genomic imprinting

differential expression of a gene depending on whether it is inherited from the male or female parent

epigenetics

phenomena due to alterations in DNA that do not include changes in the base sequence; how environmental influences often affects the way in which DNA sequences are expressed in genes

temperature-sensitive allele

an allele that is functional only at certain temperatures (ex: himalayan allele, an enzyme necessary for the production of dark pigment is inactivated at higher temperatures)

phenocopy

phenotype produced by environmental factors alone that is the same as the phenotype produced by a genotype

discontinuous characteristics

characteristics that exhibits only a few easily distinguished phenotypes (ex: seed shape, where seeds are either round or wrinkled)

continuous characteristics

characteristics that displays a large number of possible phenotypes that are not easily distinguished (ex: human height)

quantitative characteristics

continuous characteristics; displays a large number of possible phenotypes or is encoded by multiple genetic factors

polygenic characteristics

characteristics encoded by genes at many loci

pleiotropy

ability of one gene to affect multiple characteristics

multifactorial characteristics

characteristics determined by multiple genes and environmental factors

incomplete dominance produces

a blend of the parents' traits in the offspring

codominance produces

results in traits from both parents being expressed in the offspring simultaneously