Genetics Ms. Tetrev

Do all dogs look alike? What types of features indicate a particular breed? Can you tell individuals within a particular breed apart? What does this tell you about the inheritance of these features?

Genetics The science of heredity, began with Mendel, who is regarded as the father of genetics. Mendel performed cross-pollination in pea plants. Mendel followed various traits in the pea plants he bred.

The passing of traits from generation to the next generation is called INHERITANCE or Heredity. True-breeding means it consistently produces offspring with only one form of a trait. Why is it important that Mendel’s Experiments used a true-breeding plant?

Mendel performed cross-pollination by transferring male gametes from the flower of a true-breeding green-seed plant to the female organ of a flower from a true-breeding yellow-seed plant. The parent generation is also known as the P generation

The offspring of this P cross are called the first filial (F1) generation. The second filial (F2) generation is the offspring from the F1 cross. Why are the seeds in the F1 generation all yellow?

Mendel studied seven different traits. Mendelian Genetics 4/24/2017 Mendel studied seven different traits. Seed shape --- Round (R) or Wrinkled (r) Seed Color ---- Yellow (Y) or  Green (y) Pod Shape --- Smooth (S) or wrinkled (s) Pod Color ---  Green (G) or Yellow (g) Seed Coat Color ---Gray (G) or White (g) Flower position---Axial (A) or Terminal (a) Plant Height --- Tall (T) or Short (t) Flower color --- Purple (P) or white (p)

An Allele is an alternative form of a single gene passed from generation to generation. Example: The gene for seed shape in pea plants exists in two forms, one form or allele for round seed shape (R) and the other for wrinkled seed shape (r).

Dominant -The stronger allele, represented by a capital letter (R) Recessive- the weaker allele that is masked, represented by a lowercase letter (r)

An organism with two of the same alleles for a particular trait is homozygous. Gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure  An organism with two different alleles for a particular trait is heterozygous. Gene combination of one dominant & one recessive allele   (e.g. Rr); also called hybrid

An organism’s allele pairs are called its genotype An organism’s allele pairs are called its genotype. The gene combination for a trait What genes, letters, the organism has (TT, Tt, tt) The observable characteristic or outward expression of an allele pair is called the phenotype. The physical feature resulting from a genotype What it looks like!

Following the Generations Mendelian Genetics 4/24/2017 Following the Generations Cross 2 Pure Plants TT x tt Results in all Hybrids Tt Cross 2 Hybrids get 3 Tall & 1 Short TT, Tt, tt

Mendel’s Law of Segregation Two alleles for each trait separate during meiosis. During fertilization, two alleles for that trait unite. Heterozygous organisms are called hybrids.

Punnett Squares Predict the possible offspring of a cross between two known genotypes

Mendelian Genetics 4/24/2017 Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

Applying the Law of Segregation Mendelian Genetics 4/24/2017 Applying the Law of Segregation copyright cmassengale

Monohybrid A cross that involves hybrids for a single trait is called a monohybrid cross.

P1 Monohybrid Cross r r Rr Rr R R Rr Rr Trait: Seed Shape Mendelian Genetics 4/24/2017 P1 Monohybrid Cross Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Wrinkled seeds RR x rr Genotype: Rr Phenotype: Round Genotypic Ratio: All alike Phenotypic Ratio: All alike r r Rr Rr R R Rr Rr

P1 Monohybrid Cross Review Mendelian Genetics 4/24/2017 P1 Monohybrid Cross Review Homozygous dominant x Homozygous recessive Offspring all Heterozygous (hybrids) Offspring called F1 generation Genotypic & Phenotypic ratio is ALL ALIKE

F1 Monohybrid Cross R r RR Rr R r Rr rr Trait: Seed Shape Mendelian Genetics 4/24/2017 F1 Monohybrid Cross Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Round seeds Rr x Rr Genotype: RR, Rr, rr Phenotype: Round & wrinkled G.Ratio: 1:2:1 P.Ratio: 3:1 R r RR Rr R r Rr rr

F1 Monohybrid Cross Review Mendelian Genetics 4/24/2017 F1 Monohybrid Cross Review Heterozygous x heterozygous Offspring: 25% Homozygous dominant RR 50% Heterozygous Rr 25% Homozygous Recessive rr Offspring called F2 generation Genotypic ratio is 1:2:1 Phenotypic Ratio is 3:1

Law of Independent assortment Random distribution of alleles occurs during gamete formation Genes on separate chromosomes sort independently during meiosis. Each allele combination is equally likely to occur

Dihybrid Cross The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross. Dihybrids are heterozygous for both traits.

Mendelian Genetics 4/24/2017 Dihybrid Cross A breeding experiment that tracks the inheritance of two traits. Mendel’s “Law of Independent Assortment” a. Each pair of alleles segregates independently during gamete formation b. Formula: 2n (n = # of heterozygotes)

Dihybrid Cross RrYy x RrYy Traits: Seed shape & Seed color Mendelian Genetics 4/24/2017 Dihybrid Cross Traits: Seed shape & Seed color Alleles: R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations

Mendelian Genetics 4/24/2017 Dihybrid Cross RY Ry rY ry RY Ry rY ry

Dihybrid Cross RY Ry rY ry Round/Yellow: 9 Round/green: 3 Mendelian Genetics 4/24/2017 Dihybrid Cross RY Ry rY ry Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy

Mendelian Genetics 4/24/2017 Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1