Genetics: Mendel's Principles, Inheritance, and Blood Types

Inheritance

The passing of traits from parents to offspring.

Traits

Characteristics or features of an organism that can be inherited, such as eye color or height.

Gametes

Sex cells (sperm and egg) that carry half the genetic material of an organism.

Blending Theory of Inheritance

An early (incorrect) theory that offspring are a smooth blend of their parents' traits.

Charles Darwin

Proposed the theory of evolution by natural selection but did not know the mechanism of inheritance.

Gregor Mendel

The "Father of Genetics"; discovered basic principles of heredity using pea plants.

Monohybrid Cross

A genetic cross that examines the inheritance of a single trait.

Purebred

An organism that always produces offspring with the same form of a trait; homozygous.

True Breeding

Another term for purebred; consistently passes down specific traits to offspring.

Parent Generation (P)

The original generation in a breeding experiment.

Filial Generation (F1, F2, etc.)

The offspring of the parent generation (F1) and subsequent generations (F2, etc.).

Hybrid

An organism with two different alleles for a trait (heterozygous).

Dominant

An allele that masks the expression of another allele; expressed when present.

Recessive

An allele that is masked by a dominant allele; expressed only when homozygous.

Latent Characteristic

A trait that is hidden in one generation but may appear in the next; same as recessive.

Principle of Dominance

Some alleles are dominant and mask the effects of recessive alleles.

Law of Segregation

Allele pairs separate during gamete formation, so each gamete carries only one allele for each gene.

Mendelian Ratio

Typical ratio of offspring phenotypes from Mendelian crosses (e.g., 3:1 in monohybrid crosses).

Genes

Segments of DNA that code for specific traits or proteins.

Alleles

Different forms of a gene found at the same locus on homologous chromosomes.

Homozygous

Having two identical alleles for a particular trait (AA or aa).

Heterozygous

Having two different alleles for a trait (Aa).

Punnett Square

A diagram used to predict the genotypes and phenotypes of offspring.

Genotype

The genetic makeup of an organism (the alleles it has).

Phenotype

The physical appearance or expression of a trait.

Dihybrid Cross

A cross involving two different traits, each controlled by different genes.

Law of Independent Assortment

The inheritance of one trait's alleles does not affect the inheritance of another trait's alleles.

Complete Dominance

One allele completely masks the other; only the dominant trait is expressed.

Incomplete Dominance

Neither allele completely masks the other; the result is an intermediate or blended phenotype.

Familial Hypercholesterolemia (FH)

An incomplete dominance disorder caused by a defective allele for cholesterol uptake receptors.

Codominance

Both alleles are fully expressed; results show traits of both alleles side by side.

Sickle Cell Anemia (SCA)

A codominance disorder where red blood cells have an abnormal sickle shape, leading to clotting and oxygen issues.

Multiple Alleles

A gene that has more than two possible alleles.

Human Blood Type

An example of multiple alleles and codominance; blood types (A, B, AB, O) are determined by glycoproteins on red blood cells.