Ap Bio module 27-30 vocab

dominant

describes an allele or trait that is expressed in heterozygotes. only one dominant allele is needed to express the phenotype.

recessive

describes an allele or trait that is only expressed in homozygotes, and not expressed in heterozygotes. two recessive alleles are needed to express the phenotype.

allele

different forms of a gene, corresponding to different DNA sequences.

monohybrid cross

a cross between two individuals that are hybrids for a single gene, meaning they possess two different alleles.

law of segregation

the principle that half of the gametes receive one allele of a gene and half receive the other allele. this principle is explained by meiosis, in which the maternal and paternal homologous chromosomes separate during anaphase I.

homozygous

a condition in which an individual possesses two identical alleles for a given gene.

heterozygous

a condition in which an individual possesses two different alleles for a given gene.

probability

the likelihood of an event happening.

addition rule of probability

rule which states that the probability of two mutually exclusive events happening is the sum of their individual probabilities.

multiplication rule of probability

a rule which states that the probability of two independent events both happening is the product of their individual probabilities.

chi-square test

a statistical test that determines whether the number of observed events in different categories differs from an expected number of events.

law of independent assortment

the principle that segregation of one set of alleles for one gene is independent of the segregation of a second set of alleles for a different gene.

dihybrid cross

a mating in which hybrid individuals differ in two traits that are coded by two different genes.

pedigree

a visual mapping of phenotypes using ancestral relationships.

sex-linked genes

a gene that is only located on one of the two sex chromosomes.

linked genes

genes that are physically located near each other on the same chromosome.

recombination

a process in prophase I in meiosis when each chromatid can break at the chiasma and then connect to a non-sister chromatid.

maternal inheritance

a type of inheritance in which the organelles in the offspring cells derive from those in the mother.

paternal inheritance

a type of inheritance in which the organelles in the offspring cells derive from those in the father.

phenotypic plasticity

the ability of a single genotype to produce different phenotypes in different environments.

nondisjunction

the failure of a chromosome to separate during anaphase of cell division.

down syndrome

a condition in humans caused by an extra chromosome 21.

turner syndrome

a condition in humans in which females have only one X chromosome.