Genetics and Inheritance

Chromosomal abnormalities

Changes in chromosome number or structure.

Polyploidy

Genome duplication.

Aneuploidy

The addition or deletion of a single chromosome.

Deletion

A type of structural change where a part of the chromosome is removed.

Duplication

A structural change where a part of the chromosome is replicated.

Translocation

A structural change where a segment of one chromosome is transferred to another chromosome.

Inversion

A structural change where a segment of a chromosome is reversed end to end.

Polygenetic inheritance

Multiple genes contribute to a single trait, producing continuous variation.

Pleiotropy

One gene affects multiple seemingly unrelated traits.

Epistasis

One gene masks or modifies the expression of another gene.

Sex-linked inheritance

The gene is located on the X or Y chromosome.

Novel phenotypes

A trait affected by two or more different genes that cooperate to produce a phenotype; neither could produce it alone.

Environment + Phenotype

Factors such as temperature can affect phenotype through sensitive enzymes.

Gene expression

Can be affected by other genes, environment, sunlight, and temperature.

Expressivity

Degree to which a genotype is expressed in the phenotype of an individual.

Penetrance

Proportion (frequency) of individuals with a particular genotype that show the described phenotype.

Chromosome theory of inheritance

Genes are localized to specific parts of chromosomes, and their genetic information determines the traits of an organism.

Particulate theory of inheritance

Parents pass on discrete heritable units (genes) that retain identities in offspring.

Law of Segregation

Two alleles for a heritable character segregate during gamete formation; each gamete carries only one allele.

Principle of Dominance

Dominant allele masks expression of the recessive allele.

Law of Independent Assortment

Pairs of traits for one character segregate independently of traits for another character.

Incomplete dominance

Neither allele is fully dominant, resulting in a blended phenotype.

Codominance

Both alleles are expressed simultaneously, showing both phenotypes at once.

Multiple alleles

More than two alleles exist for a particular gene within a population.

Dihybrid Cross

A genetic cross involving two traits, resulting in a 9:3:3:1 phenotypic ratio.

Alleles

Different versions of a gene that occur at a particular locus on homologous chromosomes.