Mendel’s Laws of Inheritance: Key Concepts and Practice for ATI TEAS 7

Gene

Segment of DNA that determines a trait

Allele

Different version of a gene

Trait

Observable characteristic

Dominant allele

Masks the recessive allele; shown with a capital letter

Recessive allele

Expressed only when two recessive alleles are present; lowercase letter

Genotype

Genetic makeup of an organism (AA, Aa, aa)

Phenotype

Physical expression of a trait

Homozygous dominant

Two dominant alleles (AA)

Homozygous recessive

Two recessive alleles (aa)

Heterozygous

One dominant and one recessive allele (Aa)

Law of Segregation

Allele pairs separate during gamete formation

Law of Independent Assortment

Different traits are inherited independently

Punnett square

Diagram used to predict offspring genotypes

Monohybrid cross

Punnett square showing one trait

Genotype ratio (Aa × Aa)

1 AA : 2 Aa : 1 aa

Phenotype ratio (Aa × Aa)

3 dominant : 1 recessive

Dihybrid cross

Punnett square involving two traits

Key concept of dihybrid cross

Traits assort independently

Incomplete dominance

Blended phenotype

Codominance

Both alleles expressed equally

Multiple alleles

More than two alleles for one trait

AB blood type

Example of codominance

Blood type system

Example of multiple alleles

Dominant does NOT mean

More common

Recessive traits

Can skip generations

Punnett squares predict

Probability, not certainty

Genotype memory tip

Geno = genes

Phenotype memory tip

Pheno = physical

Genotype of heterozygous individual

Aa

Trait expressed with one dominant allele

Dominant trait

Mendel inheritance summary

Traits are inherited through dominant and recessive alleles and predicted using Punnett squares