Topic 2: Mendelian Genetics

Blended inheritance

Incorrect theory that traits mix permanently in offspring.

Inheritance of acquired characteristics

Incorrect idea that traits gained during life are inherited.

Particulate theory of heredity

Correct idea that genes are discrete units passed from parents to offspring.

Gregor Mendel

Scientist who discovered basic laws of inheritance using pea plants.

Mendelian genetics

Study of inheritance patterns based on Mendel’s principles.

True-breeding

Organisms that produce identical offspring when self-fertilized

Monohybrid cross

Cross tracking one trait (typically between two heterozygotes).

Dihybrid cross

Cross tracking two traits at the same time.

Test cross

Cross between an individual of unknown genotype and a homozygous recessive individual.

Homozygous

2 alleles that are the same in a diploid organism

Heterozygous

2 alleles that are different in a diploid organism

Dominant

Allele that is expressed in heterozygotes.

Recessive

Allele that is expressed only when homozygous.

Genotype

Genetic makeup

Phenotype

Physical appearance

Punnett Square

Diagram used to predict offspring genotypes

Principle of Segregation

Traits of diploid organisms determined by combination of genes inherited from parents

Principle of Independent Assortment

Genes for different traits assort independently if they are on different chromosomes.

Linked genes

Genes located on same chromosome

Unlinked genes

Genes on different chromosomes that assort independently.

Sex (X) linkage

Genes located on the X chromosome

Incomplete dominance

1 allele is not completely dominant to the other, shows intermediate phenotype.

Polygenic inheritance

Phenotype determined by multiple genes

Environmental effects

Phenotype influenced by both genotype & the environment

Multiplication rule

Probability of independent events both occurring = multiply probabilities.

Addition rule

Probability of either of two events occurring = add probabilities (if mutually exclusive).