ap bio ch. 14

character

heritable feature that varies among individuals (ex: flower color)

trait

each variant for a character (ex: purple or white color for flowers)

hybridization

Mendel mated two contrasting, true-breeding varieties

P generation

true-breeding parents

F1 generation

hybrid offspring of the P generation

F2 generation

produced when F1 individuals self-pollinate or cross- pollinate with other F1 hybrids

law of segregation

true-breeding white & purple plants → all F1 hybrids were purple. F1 hybrids cross: 3:1 ratio of purple to white flowers in F2 generation

Mendel’s model

hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring; (1) alternative versions of genes account for variations in inherited characters (gene for flower color in pea plants exists in two versions: purple/white). (2) for each character, an organism inherits two alleles (may be identical or differ), one from each parent; Mendel made this deduction w/o knowing abt chromosomes. (3) if two alleles at a locus differ, dominant allele determines the organism’s appearance, & recessive allele has no noticeable effect on appearance. (4) law of segregation: two alleles for a heritable character separate (segregate) during gamete formation & end up in diff gametes; egg/sperm only gets ½ alleles

alleles

alternative versions of a gene

locus

each gene resides at a specific locus on a specific chromosome

punnett square

shows possible combinations of sperm & egg, capital = dominant, lowercase = recessive

testcross

breeding the mystery individual w/ a homozygous recessive individual. If any offspring display the recessive phenotype, the mystery parent must be heterozygous

monohybrids

heterozygous for one character

monohybrid cross

cross btwn such heterozygotes

dihybrids

heterozygous for both characters (two true-breeding parents differing in two characters)

dihybrid cross

cross btwn F1 dihybrids, can determine whether two characters are transmitted to offspring as a package or independently

law of independent assortment

each pair of alleles segregates independently of each other pair of alleles during gamete formation; dev. when Mendel used dihybrid cross. Applies only to genes on diff, nonhomologous chromosomes or those far apart on the same chromosome; genes located near each other on the same chromosome tend to be inherited together

multi character cross

equivalent to two or more independent monohybrid crosses occurring simultaneously