Unit 5 (Mendelian Genetics)

True breeding

Organisms that produce offspring of the same variety over many generations of self pollination

• Ex. true breeding purple pea plant will only produce purple offspring with self pollination

Generations

• P generation: true breeding parental generation

• F₁ generation (first filial): hybrid offspring of P generation

• F₂ generation (second filial): offspring of the F₁ generation

Punnett Squares

Diagrams used to predict the allele combinations of offspring from a cross with known genetic compositions

Homozygous

An organism that has a pair of identical alleles for a character

Heterozygous

An organism that has two different alleles for a gene

Genotype

The genetic makeup (alleles) of an organism

Phenotype

An organisms appearance, which is determined by the genotype

Testcross

Determines if the dominant trait is homozygous or heterozygous

F₂ generation

Always a 3:1 ratio

• Pp x Pp

• F₁ is always heterozygous

Law of Segregation

The two alleles for the same trait separate during gamete formation and end up indifferent gametes

Monohybrid

F₁ hybrids

• Monohybrid crosses: Bb x Bb

Law of Independent Assortment

Genes for one trait are not inherited with genes of another trait

• Only applies to genes that are located on different chromosomes (not homologous) or genes that are very far apart on the same chromosome.

Dihybrid

• YYRR x yyrr (p) → YyRr (F₁)

• Dihybrid cross: a cross between F₁ dihybrids (YyRr x YyRr)

• Produces a 9:3:3:1 phenotypic ratio

Law of Probability

• The probability that two or more independent events will occur together in some specific combination

Multiplication rule

The probability that two or more independent events will occur together in some specific combination

• Ex. coin flip → ½ x ½ = ¼

Addition rule

The probability that two or more mutually exclusive events will occur

• Ex. rolling a dice → 1/6 + 1/6 = 1/3

Pedigree

Family tree that gives a visual of inheritance patterns of particular traits

• If a trait is dominant, one parent must have the trait

• Dominant traits do not skip a generation

X-linked traits

Males are more commonly affected than females because they only have one X chromosome