Chapter 6

Mendelian Genetics

Genetics – the scientific study of heredity

Gregor Mendel is said to be the father of genetics.

Mendel used pea plants to study the inheritance of traits.

True-breeding – plants that produce offspring identical to themselves.

Parents that have different traits will produce hybrids.

Hybrids are offspring of parents with different traits.

Mendel’s Pea Traits

Traits – Traits are specific characteristics (like blue eyes or 5 fingers)

Genes are factors that are passed from one generation to the next. (From parents to offspring)

Alleles are different forms of a gene (like purple or white flowers).

Law of Dominance

This principle states that some alleles are dominant and others are recessive.

The dominant allele is represented by an uppercase letter.

P – purple flowerThe recessive allele is represented by a

lowercase letter.p – white flower

Dominant – Trait that will hide or mask the recessive trait

Recessive – Trait that will show only when found with another recessive allele

Genotype – what the alleles are

Phenotype – observable characteristics

P Generation is the first parental generation.

F1 is called the first filial generation or the first offspring when the P generation is crossed.

F2 is called the second filial generation or the offspring from crossing the F1 generation.

Mendel’s Law of Segregation

• Mendel wanted to know what happened to the recessive alleles.

• He allowed for F1 plants to self pollinate and this resulted in some F2 plants showing the recessive trait.

• The two alleles separate when organisms produce gametes, or sex cells. Each gamete carries a single copy of each gene.

• Homozygous - Organisms that have two identical alleles for a particular trait

Ex. TT or tt• Heterozygous - Organisms that have two

different alleles for a particular trait (Hybrids) Ex. Tt

Punnett squares show:• Possible genotypes• The alleles in the gametes of parents• All possible results of a genetic cross

Probability

• Probability is the likelihood that a specific event will occur.

• Flip a coin 100 times; record the number of times it is heads _____ and tails_____

• Principles of probability can be used to predict the traits of offspring produced by genetic crosses

Mendel’s Law of Independent Assortment

Genes for different traits can segregate (on separate chromosomes) independently during the formation of gametes.

Example: Seed shape doesn’t determine seed color.