allele
a version of a gene
chromosomal crossing over
a process in which chromosomes swap portions of their arms, resulting in the redistribution of genetic material
chromosome
a structure that contains DNA, the genetic material that is passed from one generation to the next
codominance
when two alleles are both expressed in the organism's phenotype
dominant allele
an allele whose expression masks that of another allele
epistasis
when one gene "activates" another one
first filial generation (F1)
the first generation offspring resulting from a parental cross
gene
a unit of heritable material that codes for a particular trait
genotype
the genetic makeup of an organism
Gregor Mendel
the scientist who discovered the principles underlying genes and inheritance
heterozygous
having two different alleles for a gene
homozygous
having two identical alleles for a gene
incomplete dominance
when two alleles are blended in the organism's phenotype
law of independent assortment
the principle that states alleles of different genes are sorted into gametes independently of one another
linked genes
genes that are frequently inherited together (more than 50% of the time)
meiosis
a process in cell division during which the number of chromosomes decreases to half the original number by two divisions of the nucleus, resulting in the production of gametes
Mendelian inheritance
patterns of inheritance that follow Mendel's laws of dominance and recessiveness, showing that some genes appear more often than others, and independent assortment, which suggests that genes are inherited randomly
non-Mendelian inheritance
patterns of inheritance that do not follow Mendelian patterns, such as codominance or polygenic inheritance
parent generation (P)
the original two organisms that are crossed to give offspring
phenotype
an observable characteristic of an organism that results from genetic and environmental influences
pleiotropy
when multiple phenotypes arise from a single gene
polygenic inheritance
when more than one gene codes for a single trait
Punnett square
a tool used to predict the possible genotypic outcomes of a cross between two individuals
recessive allele
an allele whose expression is masked by another allele
second filial generation (F2)
the offspring of a cross between individuals of the first generation
sex-linked trait
trait that is inherited on either the X or Y chromosome
trait
a characteristic determined by an organism's genes