Ch. 7: Genetics and Inheritance

Genotype

The genetic makeup of an organism; the combination of alleles an individual has (e.g., AA, Aa, aa).

Phenotype

The observable physical or biochemical traits determined by the genotype and environment.

Relationship between genotype and phenotype

Genotype provides the genetic instructions; phenotype is how those instructions are expressed as traits.

Gregor Mendel

Father of genetics who studied inheritance patterns using pea plants.

Mendel's discoveries

Showed that traits are inherited as discrete units (genes) and follow predictable patterns.

Law of Segregation

Each pair of alleles separates during gamete formation; offspring receive one allele from each parent.

Law of Independent Assortment

Genes for different traits assort independently during gamete formation when on different chromosomes.

Monohybrid cross

Cross between two individuals differing in one trait; predicts genotype and phenotype ratios for a single gene.

Typical monohybrid ratio

3:1 phenotype ratio from Aa × Aa cross (dominant to recessive).

Dihybrid cross

Cross between two individuals differing in two traits; used to study two genes that assort independently.

Typical dihybrid ratio

9:3:3:1 phenotype ratio from AaBb × AaBb cross.

Mendelian trait

Trait controlled by one gene with simple dominant and recessive alleles (e.g., pea flower color, cystic fibrosis).

Complex trait

Trait influenced by multiple genes and/or environmental factors (e.g., height, skin color, diabetes).

Polygenic inheritance

Trait determined by two or more genes (e.g., eye color, height).

Gene-environment interaction

The environment can influence how genes are expressed, affecting the phenotype.

Example of gene-environment interaction

Identical twins may have different weights or personalities due to different environments.