Ch. 12 Genetics

Allele

Alternative forms of a gene for each variation of a trait of an organism.

Codominance

situation in which both alleles of a gene contribute to the phenotype of the organism

Crossing Over

the exchange of genes between homologous chromosomes

Diploid

Cell with two copies of each chromosome; or 2n, number of chromosomes.

Dominant

Observed trait of an organism that masks the other form of a trait.

Fertilization

Process in sexual reproduction in which male and female reproductive cells join to form a new cell

Gamete

Male and female sex cells; sperm and eggs.

Gene

unit that controls the traits that are passed from one generation to the next.

Genetics

Branch of biology that studies heredity.

Genotype

Combination of genes in an organism.

Genotype

genetic makeup of an organism

Haploid

Cell with one copy of each chromosome; is n, number of chromosomes.

Heterozygous

When there are two different alleles for a trait.

Homologous

term used to refer to chromosomes in which one set comes from the male parent and one set comes from the female parent

Homozygous

When there are two identical alleles for a trait.

Hybrid

organism that is heterozygous for a specific traits

incomplete dominance

Situation in which one allele is not completely dominant over another allele

independent assortment

One of Mendel's principles that states that genes for different traits can segregate independently during the formation of gametes

Law of independent assortment

Mendelian law stating that genes for different traits are inherited randomly during the formation of gametes.

Law of segregation

Mendelian law stating that two alleles for each trait separate during meiosis

Meiosis

Cell division that produces reproductive cells in sexually reproducing organisms

multiple alleles

A gene that has more than two alleles

Phenotype

An organism's physical appearance, or visible traits.

Phenotype

Outward appearance of an organism, regardless of its genes.

polygenic trait

trait controlled by two or more genes

polyploidy

having one or more extra sets of chromosomes

Principle of Dominance

states that some alleles are dominant and others are recessive

Probability

likelihood that a particular event will occur

Punnett Square

A chart that shows all the possible combinations of alleles that can result from a genetic cross

Recessive

Trait of an organism that can be masked

Segregation

Separation of alleles during gamete formation

Tetrad

structure containing 4 chromatids that forms during meiosis

Trait

A characteristic that an organism can pass on to its offspring through its genes.