Genetics Quiz 1 Terms

Genes

basic units of biological information; a region of DNA that specifies a protein or RNA

Heredity

the way genes transmit from parents to offspring

Genome

all genes an individual possesses

Genetics

the science of heredity

Sickle cell disease

genetic condition in which the hemoglobin molecule found in red blood cells is defective

Mendel’s genetic laws

patterns that determine inheritance

Artificial selection

selective breeding of domesticated plants and animals with desired characteristics

Self fertilization

egg and pollen/sperm come from the same organism

Cross fertilization

fertilizing an egg with sperm from another organism

Discrete trait

clear cut alternatives for a particular trait with no intermediate forms

Continuous trait

traits that can have intermediate forms

True/pure breeding lines

genetic lines that produce offspring that carry specific parental characteristics that remain constant from generation to generation (aka inbred)

Hybrids

offspring of genetically dissimilar parents

Antagonistic pairs

what Mendel called constant but mutually exclusive alternatives to a trait (aka differing alleles)

Reciprocal crosses

reversing the characteristics of the male and female parents transmitted via the egg or sperm

Monohybrid cross

crosses between parents that only differ in one trait

Dominant trait

the trait that appears in the F1 hybrids resulting from a mating between pure breeding parental strains showing antagonistic phenotypes

Recessive trait

a trait that remains hidden in F1 hybrids but usually reappears in the F2 generation

Genes (to Mendel)

units of inheritance for each trait, one received from each parent

Alleles (to Mendel)

alternative forms of genes, combinations of which determine contrastic characteristics

Monohybrids

individuals having two different alleles of a single gene

Gametes

specialized cells (eggs/sperm) that carry genes between generations

Zygote

fertilized egg

Law of segregation

the two alleles of a each gene separate during gamete formation and then unite at random, one from each parent, at fertilization

The product rule

the probability of two or more independent events occurring together is the product of the probabilities that each event will occur by itself

The sum rule

the probability of two mutually exclusive events occuring is the sum of their individual probabilities

Phenotype

an observable characteristic

Genotype

the pair of alleles present in an individual

Homozygous

YY or yy genotype

Heterozygous

Yy genotype (aka hybrid)

Dihybrid

an organism that is heterozygous for two genes at the same time

Parental types

progeny that share both characteristics from a dihybrid cross with one of the two parents

Recombinant types

progeny that share one characteristic with each parent in a dihybrid cross

Independent assortment

shuffling of gene pairs during gamete formation

The Law of Independent Assortment

During gamete formation, different pairs of alleles segregate independently of each other

Multihybrid crosses

matings between F1 progeny of pure breeding parents that differ in three or more traits

Pedigree

diagram of a family’s relevant genetic features, extending through many generations

Consanguineous mating

a mating between close relatives

Late-onset genetic trait

symptoms are not present at birth, but manifest themselves later in life

Carriers

heterozygous individuals of normal phenotype that have a recessive allele for a trait

Complex traits

traits controlled by multiple genes and often also by environmental factors

Incomplete dominance

the relationship between two alleles of a gene where the heterozygote has a phenotype intermediate between that of the two homozygotes

Codominant

the relationship between two alleles of a gene where the heterozygote has the characteristics of both homozygotes

Dominance series

the dominance relations of all possible pairs of alleles arranged in linear order

Mutations

spontaneous, heritable alterations in DNA sequences that occur at low frequencies

Allele frequency

the proportion of all copies of a gene in a population that are of a given allele type

Wild type alleles

an allele whose frequency is more than 1% in a population; an allele that dictates the most frequently observed phenotype in a population

Mutant allele

an allele that causes a phenotype seen only rarely in a population (less than 1%)

Monomorphic

a gene with only one wild type allele

Polymorphic

a locus with two or more common alleles in a population

Common variants

high frequency alleles of a polymorphic gene or other chromosomal locus

Pleitropy

phenomenon in which a single gene determines a number of distinct and seemingly unrelated characteristics

Syndrome

a group of symptoms that appear together consistently

Recessive lethal allele

an allele that prevents survival of homozygotes, though heterozygotes carrying the allele survive

Delayed lethality

when homozygotes of some mutations live past birth only to die later in life from consequences of the deleterious mutation

Genotypic classes

a grouping defined by a set of related genotypes that will produce a particular phenotype

Recessive epistasis

a gene interaction in which the effects of recessive alleles at one gene hide the effects of alleles at another gene

Dominant epistasis

a phenomenon where the effects of a dominant allele at one gene hide the effects of alleles at another gene

Reciprocal dominant epistasis

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Redundant gene action

a phenomenon where dominant, functional alleles of either one or the other of two genes is required in a pathway

Heterogenous trait

a characteristic caused by a mutation in any one number of different genes

Locus heterogeneity

describes a trait where mutations in any one of two or more genes results in the same mutant phenotype

Complementation test

method of discovering whether two mutations are in the same or seperate genes

Complementation

the process in which heterozygosity for loss-of-function mutant recessive alleles for two different genes produces a normal phenotype

Complex traits

traits controlled by multiple genes and also by environmental factors (can be discrete or continuous)

Penetrance

in a population, the fraction of individuals with a particular genotype that show the associated phenotype (can be complete or incomplete)

Expressivity

the degree or intensity with which a particular genotype is expressed as a phenotype

Modifier genes

genes that produce a subtle, secondary effect on phenotype

Genetic backgrond

all the alleles of genes in an organism’s genome; the set of unknown modifier genes that influence the action of the known genes that control specific aspects of phenotype

Temperature sensitive

describes an allele whose function depends on the environmental temperature

Conditional lethal

an allele that is lethal only under certain conditions

Permissive conditions

an environmental condition that prevents the survival of an individual with a conditional lethal allele

Restrictive conditions

an environmental condition that prevents the survival of an individual with a conditional lethal allele

Phenocopy

a change in phenotype arising from environmental agents that mimics the effects of a mutation in a gene

Discontinuous/discrete trait

an inherited trait that exhibits and either/or status (ie. purple or white)

Continuous/quantitative trait

inherited trait that is controlled by many different genes and sometimes also environmental factors

Polygenic

trait controlled by multiple genes