Genetics: Mendel's Laws, Inheritance Patterns, and Human Disorders

True-breeding

Organisms that produce offspring of the same variety after many generations of self-pollination.

Hybridization

The mating of two true-breeding varieties.

Monohybrid cross

A cross between two organisms differing in a single trait.

P generation

The parental generation used to start an experiment.

F1 generation

The first generation produced from crossing true-breeding parents.

F2 generation

The second generation produced by crossing F1 individuals.

Mendel's 4 components of inheritance

1. Alternative versions of genes cause variations. 2. Each organism inherits two alleles per gene. 3. Dominant alleles mask recessive ones. 4. Alleles separate during gamete formation (Law of Segregation).

Law of Segregation

Two alleles for a heritable trait separate during gamete formation and end up in different gametes.

Law of Independent Assortment

Each pair of alleles segregates independently of other allele pairs during gamete formation.

Dominant vs. Recessive

Dominant shows if one allele is present; recessive only shows if both are present.

Heterozygous vs. Homozygous

Heterozygous = two different alleles; Homozygous = two identical alleles.

Genotype vs. Phenotype

Genotype = genetic makeup; Phenotype = physical expression.

Incomplete dominance

Heterozygote phenotype is intermediate between the two parental varieties.

Complete dominance

Heterozygote and dominant homozygote have the same phenotype.

Codominance

Both alleles are expressed equally and distinctly in the phenotype.

ABO blood system

IA and IB alleles are codominant; i is recessive. Type AB expresses both A and B antigens.

Pleiotropy

One gene affects multiple traits (e.g., sickle-cell disease).

Epistasis

One gene alters or masks the expression of another gene.

Polygenic inheritance

Multiple genes affect a single trait, producing continuous variation (e.g., skin color).

Albinism

Recessive condition causing lack of pigmentation due to homozygous recessive alleles.

Cystic Fibrosis

Recessive disorder causing mucus buildup in lungs and digestive tract.

Tay-Sachs Disease

Recessive disorder leading to accumulation of lipids in brain cells; fatal in early childhood.

Sickle-Cell Anemia

Recessive disorder causing misshapen red blood cells; heterozygotes show resistance to malaria.

Achondroplasia

Dominant form of dwarfism caused by a rare dominant allele.

Huntington's Disease

Late-acting dominant disorder of the nervous system; symptoms appear after reproductive age.