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