12: Mendel's Experiments and Heredity Flashcards
gene variations that arise by mutation and exist at the same relative locations on homologous chromosomes
allele
any of the non-sex chromosomes
autosomes
hypothetical inheritance pattern in which parental traits are blended together in the offspring to produce an intermediate physical appearance
blending theory of inheritance
in a heterozygote, complete and simultaneous expression of both alleles for the same characteristic
codominance
inheritance pattern in which a character shows a range of trait values with small gradations rather than large gaps between them
continuous variation
result of a cross between two true-breeding parents that express different traits for two characteristics
dihybrid
inheritance pattern in which traits are distinct and are transmitted independently of one another
discontinuous variation
trait which confers the same physical appearance whether an individual has two copies of the trait or one copy of the dominant trait and one copy of the recessive trait
dominant
inheritance pattern in which an allele is lethal both in the homozygote and the heterozygote; this allele can only be transmitted if the lethality phenotype occurs after reproductive age
dominant lethal
antagonistic interaction between genes such that one gene masks or interferes with the expression of another
epistasis
first filial generation in a cross; the offspring of the parental generation
F1
second filial generation produced when F1 individuals are self-crossed or fertilized with each other
F2
underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism
genotype
presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant
hemizygous
having two different alleles for a given gene on the homologous chromosome
heterozygous
having two identical alleles for a given gene on the homologous chromosome
homozygous
process of mating two individuals that differ
with the goal of achieving a certain characteristic in their offspring
hybridization
in a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype
incomplete dominance
in a heterozygote, one trait will conceal the presence of another trait for the same characteristic
law of dominance
genes do not influence each other with regard to sorting of alleles into gametes; every possible combination of alleles is equally likely to occur
law of independent assortment
paired unit factors (i.e., genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors
law of segregation
phenomenon in which alleles that are located in close proximity to each other on the same chromosome are more likely to be inherited together
linkage
species or biological system used to study a specific biological phenomenon to be applied to other different species
model system
result of a cross between two true-breeding parents that express different traits for only one characteristic
monohybrid
parental generation in a cross
P0
observable traits expressed by an organism
phenotype
probability of two independent events
occurring simultaneously can be calculated by multiplying the individual probabilities of each event occurring alone
product rule
visual representation of a cross between two individuals in which the gametes of each individual are denoted along the top and side of a grid, respectively, and the possible zygotic genotypes are recombined at each box in the grid
Punnett square
trait that appears “latent” or non-expressed when the individual also carries a dominant trait for that same characteristic; when present as two identical copies, the recessive trait is expressed
recessive
inheritance pattern in which an allele is only lethal in the homozygous form; the heterozygote may be normal or have some altered, nonlethal phenotype
recessive lethal
paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross
reciprocal cross
any gene on a sex chromosome
sex-linked
probability of the occurrence of at least one of two mutually exclusive events is the sum of their individual probabilities
sum rule
cross between a dominant expressing individual with an unknown genotype and a homozygous recessive individual; the offspring phenotypes indicate whether the unknown parent is heterozygous or homozygous for the dominant trait
test cross
variation in the physical appearance of a heritable characteristic
trait
gene present on the X, but not the Y chromosome
X-linked
