Studied by 6 people
alternation of generations
a life-cycle type in which the diploid and haploid stages alternate
chiasmata
(singular, chiasma) the structure that forms at the crossover points after genetic material is exchanged
cohesin
proteins that form a complex that seals sister chromatids together at their centromeres until anaphase II of meiosis
crossover
exchange of genetic material between non-sister chromatids resulting in chromosomes that incorporate genes from both parents of the organism
diploid-dominant
life-cycle type in which the multi-cellular diploid stage is prevalent
fertilization
union of two haploid cells from two individual organisms
gametophyte
a multicellular haploid life-cycle stage that produces gametes
germ cells
specialized cell line that produces gametes, such as eggs or sperm
haploid-dominant
a life-cycle type in which the multicellular haploid stage is prevalent
interkinesis
(also, interphase II) brief period of rest between meiosis I and meiosis II
life cycle
the sequence of events in the development of an organism and the production of cells that produce offspring
meiosis
a nuclear division process that results in four haploid cells
meiosis I
the first round of meiotic cell division; referred to as reduction division because the resulting cells are haploid
meiosis II
the second round of meiotic cell division following meiosis I; sister chromatids are separated from each other, and the result is four unique haploid cells
recombination nodules
protein assembles formed on the synaptonemal complex that mark the points of crossover events and mediate the multistep process of genetic recombination between non-sister chromatids
reduction division
a nuclear division that produces daughter nuclei each having one-half as many chromosome sets as the parental nucleus; meiosis I is a reduction division
somatic cell
all the cells of a multicellular organism except the gametes or reproductive cells
spore
haploid cell that can produce a haploid multicellular organism or can fuse with another spore to form a diploid cell
sporophyte
a multicellular diploid life-cycle stage that produces haploid spores by meiosis
synapsis
formation of a close association between homologous chromosomes during prophase I
synaptonemal complex
protein lattice that forms between homologous chromosomes during prophase I, supporting crossover
tetrad
two duplicated homologous chromosomes (four chromatids) bound together by chiasmata during prophase I
allele
gene variations that arise by mutation and exist at the same relative locations on homologous chromosomes
autosomes
any of the non-sex chromosomes
Blending Theory of Inheritance
hypothetical inheritance pattern in which parental traits are blended together in the offspring to produce an intermediate physical appearance
codominance
in a heterozygote, complete and simultaneous expression of both alleles for the same characteristic
continuous variation
inheritance pattern in which a character shows a range of trait values with small gradations rather than large gaps between them
dihybrid
the result of a cross between two true-breeding parents that express different traits for two characteristics
discontinuous variation
inheritance pattern in which traits are distinct and are transmitted independently of one another
dominant
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 lethal
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
epistasis
antagonistic interaction between genes such that one gene masks or interferes with the expression of another
F1
the first filial generation in a cross; the offspring of the parental generation
F2
the second filial generation produced when F1 individuals are self-crossed or fertilized with each other
genotype
the underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism
hemizygous
the presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant
heterozygous
having two different alleles for a given gene on the homologous chromosome
homozygous
having two identical alleles for a given gene on the homologous chromosome
hybridization
the process of mating two individuals that differ, with the goal of achieving a certain characteristic in their offspring
incomplete dominance
in a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype
law of dominance
in a heterozygote, one trait will conceal the presence of another trait for the same characteristic
law of independent assortment
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 segregation
paired unit factors (i.e., genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors
linkage
a phenomenon in which alleles that are located in close proximity to each other on the same chromosome are more likely to be inherited together
model system
a species or biological system used to study a specific biological phenomenon to be applied to other different species
monohybrid
the result of a cross between two true-breeding parents that express different traits for only one characteristic
P0
the parental generation in a cross
phenotype
observable traits expressed by an organism
product rule
probability of two independent events occurring simultaneously can be calculated by multiplying the individual probabilities of each event occurring alone
Punnett square
a 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
recessive
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 lethal
inheritance pattern in which an allele is only lethal in the homozygous form; the heterozygote may be normal or have some altered, non-lethal phenotype
reciprocal cross
a 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
sex-linked
any gene on a sex chromosome
sum rule
probability of the occurrence of at least one of two mutually exclusive events is the sum of their individual probabilities
test cross
a 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
trait
variation in the physical appearance of a heritable characteristic
X-linked
gene present on the X, but not the Y chromosome
aneuploid
an individual with an error in chromosome number; includes deletions and duplications of chromosome segments
autosome
any of the non-sex chromosomes
Centimorgan (cM)
(also, map unit) relative distance that corresponds to a recombination frequency of 0.01
Chromosomal Theory of Inheritance
theory proposing that chromosomes are the vehicles of genes and that their behavior during meiosis is the physical basis of the inheritance patterns that Mendel observed
chromosome inversion
the detachment, 180° rotation, and reinsertion of a chromosome arm
euploid
individual with the appropriate number of chromosomes for their species
homologous recombination
process by which homologous chromosomes undergo reciprocal physical exchanges at their arms, also known as crossing over
karyogram
the photographic image of a karyotype
karyotype
the number and appearance of an individuals chromosomes, including the size, banding patterns, and centromere position
monosomy
otherwise diploid genotype in which one chromosome is missing
nondisjunction
the failure of synapsed homologs to completely separate and migrate to separate poles during the first cell division of meiosis
nonparental (recombinant) type
progeny resulting from homologous recombination that exhibits a different allele combination compared with its parents
paracentric
inversion that occurs outside of the centromere
parental types
progeny that exhibits the same allelic combination as its parents
pericentric
inversion that involves the centromere
polyploid
individual with an incorrect number of chromosome sets
recombination frequency
average number of crossovers between two alleles; observed as the number of nonparental types in a population of progeny
translocation
the process by which one segment of a chromosome dissociates and reattaches to a different, nonhomologous chromosome
trisomy
otherwise diploid genotype in which one entire chromosome is duplicated
X inactivation
condensation of X chromosome into Barr bodies during embryonic development in females to compensate for the double genetic dose
Note 
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