cap 4

mendelian inheritance

inheritance that obeys two laws: the law of segregation and the law of independent assortment.

simple mendelian inheritance

inheritance in which traits are affected by a single gene that is found in two different alleles. In these cases, one allele is dominant over the other.

incomplete penetrance

a type of inheritance pattern that in the case of dominant traits, this pattern occurs when a dominant phenotype is not expressed even though an individual carries a dominant allele.In the case of recessive traits, this pattern occurs when a homozygote carrying both recessive alleles does not exhibit the trait.

incomplete dominance

a type of inheritance pattern that occurs when the heterozygote has a phenotype that is intermediate between either corresponding homozygote.

heterozygote advantage

a type of inheritance pattern that occurs when the heterozygote has a trait that confers a greater level of reproductive success than either homozygote has.

codominance

a type of inheritance pattern that occurs when the heterozygote expresses both alleles simultaneously without forming an intermediate phenotype

x linked inheritance

a type of inheritance pattern that involves the inheritance of genes that are located on the X chromosome

sex influenced inheritance

a type of inheritance pattern that refers to the effect of sex on the phenotype of the individual

• the phenomenon in which an allele is dominant in

  one sex but recessive in the other sex

sex limited inheritance

a type of inheritance pattern in which a trait occurs in only one sex

lethal alleles

an allele that has the potential of causing the death of an organism.

wild type alleles

prevalent alleles in a natural population

genetic polymorphism

a phenomenon in which more than one wild-type allele may occur

mutant alleles

Random mutations that occur in populations and alter preexisting alleles

loss of function alles

mutant alleles that are defective in their ability to express a functional protein

gain of function mutation

a mutation that changes the gene or the protein coded by a gene so that it gains a new or abnormal function

dominant negative mutations

a mutation that changes a protein such that the mutant protein acts antagonistically to the normal protein

haploinsufficiency

a mutation in which the dominant mutant allele is a loss-of-function allele

expressivity

a term used to describe the outcome of traits that explains the degree to which the trait is expressed

temperature sensitive allele

The phenotypic effects of an allele are dependent on the temperature

norm of reaction

refers to the effects of environmental variation on a phenotype

heterozygote advantage

The phenomenon in which a heterozygote has greater reproductive success compared with either of the corresponding homozygotes

dimer

A protein composed of two subunits

homodimer

a protein that both subunits are coded by

the same gene

antigens

molecular structures that are recognized by antibodies produced by the immune system

codominance

The phenomenon in which two alleles are both expressed in the heterozygous individual

sex chromosomes

chromosomes that differ between males and females

x linked inheritance

When a gene is located on the X chromosome but not on the Y chromosome

hemizygous

indicate that males have a single copy of an X-linked gene.

x linked recessive

the allele causing the disease is recessive and located on the X chromosome.

reciprocal cross

a second cross in which the sexes and

phenotypes are reversed.

sex linked gene

refers to a gene that is found on one of the two types of sex chromosomes but not on both.

x linked genes

genes that are only found on the X chromosome

y linked genes

genes that are only found on the Y chromosome

sex limited inheritance

a trait that occurs in only one sex

sexual dimosphism

the sexes in a particular species have different morphological features.

essential gene

a gene that must be present for survival.

nonessential gene

a gene that is not absolutely required for survival

conditional lethal alleles

lethal alleles that may kill an organism only when certain environmental conditions prevail

temperature sensitive lethal alleles

conditional lethal alleles that may cause an organism to die only in a particular temperature range

semilethal alleles

lethal alleles that act only in some individuals

age of onsent

the age when lethal alleles exert their effects

pleitropy

The multiple effects of a single gene on the phenotype of an organism

gene interaction

a phenomenon in which the allelic variants of two different genes affect a single trait

epistasis

a phenomenon in which the alleles of one gene mask the phenotypic effects of the alleles of another gene

complementation

the production of offspring with a wild-type phenotype by

parents that both display the same or similar recessive phenotype

gene modification

the phenomenon in which an allele of one gene modifies the phenotypic outcome of the alleles of a different gene.

gene knockout

When a geneticist abolishes gene function by creating an organism that is homozygous for a loss-of-function allele

gene recundancy

the phenomenon in which one gene compensates for the loss of function of another gene

paralogs

genes that have been duplicated during evolution, so a species may have two or more copies of similar genes.