AP Biology - Unit 5

Character

an observable feature that may vary among individuals

Trait

one of two or more detectable variants in a genetic character

true breeding

organisms that produce the same variety over many generations of self-pollination

Hybridization

the mating/crossing of two true-breeding varieties

P generation

Parental generation, the first two individuals that mate in a genetic cross

F1 generation

the first generation of offspring obtained from an experimental cross of two organisms

F2 generation

offspring of the F1 generation

Allele

any of the alternate versions of a gene that may produce distinguishable phenotypic effects

Law of segregation

the two alleles for a heritable character segregate during gamete formation and end up in different gametes

homozygote

an organism with two similar alleles for a gene

heteroygote

an organism with two different alleles for a gene

phenotype

observable traits

genotype

genetic makeup of an organism

Test cross

breeding of an unknown genotype with recessive to determine unknown genotype

Monohybrids

heterozygous for one particular trait

Monohybrid cross

A cross between two individuals, concentrating on only one definable trait

Dihybrids

heterozygous for two traits

Dihybrid cross

A cross between individuals that have different alleles for the same gene

Law of independent assortment

the alleles of two (or more) different genes get sorted into gametes independently of one another

Complete dominance

phenotypes of heterozygote and dominant homozygote are indistinguishable

incomplete dominacne

heterozygotes is intermediate between the phenotypes of individual homozygotes

codominance

two alleles each affect the phenotype in separate, distinguishable ways

pleitropy

single gene having multiple effects

epistasis

phenotypic expression of a gene t one locus alters that of a gene at a second locus

quantitative characters

a heritable feature that varies continuously over a range rather than in an either or fashion

polygenic inheritance

an additive effect of two or more groups on a single phenotypic character

multifactorial

many factors, both genetic and environmental, collectively influence phenotype

pedigree

a diagram of a family tree with conventional symbols, showing the occurrence of a heritable character in parents and offspring over multiple generations

carriers

heterozygotes transmitting a recessive allele

chromosome theory of inheritance

Mandelian genes have specific sites along chromosomes and it is the chromosomes that undergo segregation

Wild type

phenotype most commonly observed in natural populations

Mutant phenotypes

alleles assumed to be changes or mutations

sex-linked gene

gene located on either sex chromosome

X-linked gene

gene on X chromosome

Y-linked gene

gene on Y chromosome

Barr body

inactive condensed X chromosome

linked genes

genes located near each other on the same chromosome that tend to be inherited together

genetic recombination

the production of offspring with combinations of traits that differ from those found in either P generation parent

parental types

offspring with phenotype that matches the true-breeding parent

recombinant types

offspring with new variations

genetic map

an ordered list of genetic loci along a particular chromosome

linkage map

genetic map based on recombination frequencies

map unit

distance between genes

nondisjunction

members of homologs do not move apart properly during meiosis I

aneuploidy

when one or more chromosomes are absent or present in excess

polypoidy

have more than two complete chromosome sets in all somatic cells

deletion

a chromosomal fragment is lost

duplication

a broken fragment becoming reattached as an extra segment

inversion

fragment reattaching in reverse

translocation

fragment joining a nonhomologous chromosome

genetic imprinting

expression of an allele depends upon which parent passed it on