Patterns of Inheritance: Mendel's Laws and Beyond

Gregor Mendel

Austrian monk who studied inheritance in pea plants.

Pisum sativa

Scientific name for garden pea used in Mendel's experiments.

P generation

Original parents in Mendel's breeding experiments.

F1 generation

First-generation offspring from P generation cross.

F2 generation

Second-generation offspring from F1 self-pollination.

Punnett Square

Diagram showing possible offspring genetic combinations.

Law of Segregation

Each trait's factors separate during gamete formation.

Testcross

Cross to determine if dominant phenotype is homozygous.

Alleles

Alternative forms of a gene located at gene locus.

Genotype

Alleles inherited by an individual at fertilization.

Phenotype

Observable traits expressed by an individual's genotype.

Homozygous

Two identical alleles for a trait (e.g., GG, gg).

Heterozygous

Two different alleles for a trait (e.g., Gg).

Independent Assortment

Factors segregate independently during gamete formation.

9:3:3:1 Ratio

Expected phenotypic ratio from a two-trait cross.

Chromosomal Theory

Chromosomes carry genetic information as discrete genes.

Gene Locus

Specific location of a gene on a chromosome.

Meiosis

Cell division explaining segregation of alleles.

True-breeding

Organisms that produce offspring identical to themselves.

Dominant Allele

Allele that masks the expression of a recessive allele.

Recessive Allele

Allele whose expression is masked by a dominant allele.

Drosophila melanogaster

Fruit fly used extensively in genetic research.

Vestigial Wings

Mutant trait in fruit flies indicating non-functional wings.

Ebony Body

Mutant trait in fruit flies with dark-colored bodies.

Dihybrid

Organism with two different traits.

Law of Independent Assortment

Genes for different traits segregate independently.

Rule of Multiplication

Probability of independent events occurring together.

Pedigree

Chart showing inheritance patterns in families.

Autosomal Recessive Disorder

Condition expressed only when both alleles are recessive.

Autosomal Dominant Disorder

Condition expressed with just one dominant allele.

Methemoglobinemia

Disorder causing bluish skin due to enzyme deficiency.

Cystic Fibrosis

Lethal disorder causing thick mucus due to ion defect.

Alkaptonuria

Disorder causing black urine due to acid accumulation.

Sickle-Cell Disease

Blood disorder causing sickle-shaped red blood cells.

Huntington Disease

Neurodegenerative disorder appearing in middle age.

Incomplete Dominance

Heterozygote shows intermediate phenotype.

Familial Hypercholesterolemia

Condition causing high cholesterol due to mutated allele.

Multiple Allele Traits

Traits controlled by more than two alleles.

ABO Blood Group

Blood type determined by three alleles.

Polygenic Inheritance

Trait influenced by multiple genes.

Multifactorial Traits

Traits affected by both genes and environment.

Pleiotropy

Single gene affects multiple traits.

Gene Linkage

Genes on the same chromosome do not assort independently.

Sex-Linked Inheritance

Traits associated with sex chromosomes.

X-Linked Recessive Disorder

Condition more common in males due to X chromosome.

Color Blindness

Common X-linked disorder affecting vision.

Duchenne Muscular Dystrophy

X-linked disorder causing muscle degeneration.