ATI TEAS Mendel's Law of Inheritance

Inheritance

The process by which traits are passed from parents to offspring

Gregor Mendel

Scientist who developed the basic laws of inheritance using pea plants

Mendelian inheritance

Patterns of inheritance discovered by Mendel

Gene

A unit of heredity that determines a trait

Allele

Different forms of a gene

Dominant allele

An allele that is always expressed if present

Recessive allele

An allele only expressed when two copies are present

Genotype

The genetic makeup of an organism (e.g., PP, Pp, pp)

Phenotype

The physical expression of a trait

Homozygous

Having two identical alleles (PP or pp)

Heterozygous

Having two different alleles (Pp)

Alleles inherited

Offspring receive one allele from each parent

Gametes

Sex cells (sperm and egg) that carry one allele per gene

Fertilization

The fusion of gametes to form a zygote

Meiosis

Cell division that produces gametes with half the chromosomes

Genetic variation in meiosis

Caused by crossing over and random assortment

Punnett square

A chart used to predict offspring genotypes and phenotypes

Capital letters in Punnett square

Represent dominant alleles

Lowercase letters in Punnett square

Represent recessive alleles

Genotypic ratio of Pp x Pp

1 PP : 2 Pp : 1 pp

Phenotypic ratio of Pp x Pp

3 dominant : 1 recessive

Law of Dominance

Dominant alleles mask recessive alleles

Law of Segregation

Alleles separate during meiosis

Law of Independent Assortment

Genes for different traits are inherited independently

Dihybrid cross

A cross that examines two traits at once

Dihybrid phenotypic ratio

9 : 3 : 3 : 1

Non-Mendelian inheritance

Inheritance patterns that do not follow simple dominant/recessive rules

Incomplete dominance

A blend of traits (e.g., red + white = pink)

Codominance

Both alleles are fully expressed (e.g., AB blood type)

Multiple alleles

More than two allele options for a gene

Sex-linked traits

Traits carried on X or Y chromosomes

Non-Mendelian indicator

Ratios different from 3:1 or 9:3:3:1