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heredity
the transmission of traits from one generation to the next
genes
DNA segments that serve as the key functional units in hereditary transmission
mutations
a random error in gene replication that leads to a change
homologous chromosomes
a pair of chromosomes (same size, length, centromere position) that carry the same genetic information (each from both parents)
asexual reproduction
a reproductive process that involves only one parent and produces offspring that are identical to the parent
sexual reproduction
a reproductive process that involves two parents that combine their genetic material to produce a new organism, which differs from both parents
karyotype
a display of the chromosome pairs of a cell arranged by size and length
somatic cell
body cell (diploid)
gametic cell
sex cell (haploid)
diploid
(2n) two complete sets of each chromosome
haploid
(n) one set of each chromosome
autosome
chromosomes that do not determine sex
sex chromosome
chromosomes that determine the sex of an individual (X & Y)
life cycle
sequence of stages in the reproductive history of an organism from conception to its own reproduction
zygote
fertilized egg (diploid)
genetics
the study of heredity and hereditary variation
clones
identical genetic copies
meiosis
a process that creates haploid gamete cells in sexually reproducing diploid organisms
synapsis
homologous chromosomes pair up and physically connect to each other forming a tetrad
tetrad
structure containing four chromatids that forms during meiosis (two pairs of homologous chromosomes)
chiasmata
site of crossing over
crossing over
the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring
independent assortment
independent and random orientation of tetrads at the metaphase plate during metaphase I
be able to define each stage of meiosis
interphase: cells go through G1, S (DNA copy), and G2
prophase 1: synapsis and crossing over
metaphase 1: independent orientation (tetrads in middle)
anaphase 1: homologous pairs separate
telophase/cytokinesis 1: cell division. now 2 haploid cells
prophase 2: no crossing over, spindle forms
metaphase 2: chromosomes line up at metaphase plate
anaphase 2: chromatids separate
telophase/cytokinesis 2: 4 haploid cells now
true breeding
organisms that produce offspring of the same variety over many generations of self pollination
p generation
true breeding parental generation
f1 generation
(first filial) hybrid offspring of p generation
f2 generation
(second filial) offspring of the f1 generation
punnett squares
diagrams used to predict the allele combinations of offspring from a cross with known genetic compositions
monohybrid cross
cross between f1 hybrids
dihybrid cross
cross between f1 dihybrids
phenotype
an organism's appearance, which is determined by the genotype
genotype
the genetic makeup (alleles) of an organism
the multiplication rule
the probability that two or more independent events will occur together in some specific combination is the product of their individual probabilities
the addition rule
the probability that two or more mutually exclusive events will occur is the sum of their individual probabilities
law of segregation
the two alleles for the same trait separate during gamete formation and end up in different gametes
law of independent assortment
genes for one trait are not inherited with genes of another trait
recessive
an allele that is masked when a dominant allele is present
dominant
describes a trait that covers over, or dominates, another form of that trait
alleles
different versions of a gene
heterozygous
having two different alleles for a trait
homozygous
having two identical alleles for a trait
pedigrees
family trees that give a visual of inheritance patterns of particular traits
incomplete dominance
neither allele is fully dominant
codominance
two alleles that affect phenotype are both expressed
polygenic inheritance
the effect of 2 or more genes acting on a single phenotype
multiple alleles
genes that exist in forms with more than two allels
epistasis
the phenotypic expression of a gene at one locus alters that of a gene at another locus
x-linked
genes found on the x-chromosome
y-linked
genes specifically found on the y chromosome
hemizygous
the presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant
barr body
a dense body formed from a deactivated X chromosome
recombinants
offspring whose phenotype differs from that of the parents
linkage map
genetic map that is based on recombinant frequencies
chi square
a form of statistical analysis used to compare the actual results (observed) with the expected results
phenotypic plasticity
the ability of an organism to change its phenotype in response to changes in the environment
nondisjuction
chromosomes fail to separate properly during meiosis I or meiosis II
