AP Bio Unit 5 Heredity

Gene

Unit of heredity that codes for a trait

Allele

Alternative form of a gene

Genotype

Genetic makeup of an organism

Phenotype

Observable traits

Homozygous

Two identical alleles

Heterozygous

Two different alleles

Dominant Allele

Allele expressed in heterozygotes

Recessive Allele

Allele masked by a dominant allele

Mendel

Scientist who established laws of inheritance

Law of Segregation

Allele pairs separate during gamete formation

Law of Independent Assortment

Genes assort independently if unlinked

Punnett Square

Diagram predicting genetic outcomes

Monohybrid Cross

Cross involving one trait

Dihybrid Cross

Cross involving two traits

Incomplete Dominance

Heterozygous phenotype is intermediate

Codominance

Both alleles fully expressed

Multiple Alleles

More than two alleles for a gene

Polygenic Trait

Trait controlled by multiple genes

Epistasis

Interaction where one gene affects another

Linked Genes

Genes located close together on a chromosome

Crossing Over

Exchange of genetic material during meiosis

Meiosis

Cell division producing gametes

Independent Assortment

Random distribution of chromosomes

Nondisjunction

Failure of chromosomes to separate

Aneuploidy

Abnormal chromosome number