Mendel Biology Chapter 10.1 p. 258-268

10.1 Mendel’s Laws of Heredity p. 259-268

Gregor Mendel Austrian monk Considered the “father of genetics” The first person to succeed in predicting how traits would be transferred from one generation to another using the garden pea plant

Genetics The branch of biology that studies heredity Heredity Traits The passing on of characteristics from parents to offspring Traits Characteristics that are inherited i.e. eye color, height, etc.

Why Mendel chose the garden pea? Easily cultivated Short generation time Reproduces sexually and can be cross-pollinated Gametes (sex cells) Male = sperm; female = egg Pollination Transfer of the male pollen grains to the pistil of a flower Fertilization When the male gamete unites with the female gamete

Parts of a Flower

Types of Pollination Cross-pollination self-pollination

How Mendel studied the garden pea plant? Controlled his experiments Studied only one trait at a time He analyzed his data mathematically He chose true breeding garden pea plants Offspring are identical to parents He studied 7 traits of the garden pea

Pea traits that Mendel studied

Mendel’s Monohybrid Cross The offspring of parents that have different forms of a trait, such as tall and short Monohybrid cross (mono = one) The two parent plants differed by a single trait – height P1 – parent generation F1 –first generation F2 – second generation P = parent F = “filial” son or daughter

Mendel’s Monohybrid Cross The First Generation Crossed 2 true breeding plants 1 tall and 1 short All offspring of the 2 parent plants were tall P1 X F1

Mendel’s Monohybrid Cross The Second Generation Self-pollinated the plants from the first generation ¾ the offspring were as tall as the tall plants in the parent and first generation ¼ the offspring were as short as the short plant in the parent generation 3:1 ratio tall to short

Second Generation X

Mendel’s Monohybrid Cross The rule of unit factors Each organism has 2 factors that control each of its traits These factors are genes Genes exist in alternative forms called alleles Ex. Plant height – one alleles is for tall and another is for short One comes from the mother and one from the father

Mendel’s Monohybrid Cross The rule of dominance Each trait has an allele that will be observed more than the other Dominant (gene) The observed trait Tall plant Recessive (gene) The trait that disappeared Short plant Only shows when both alleles are recessive

Dominate and Recessive

Mendel’s Monohybrid Cross Recording the results for crosses Dominate allele is always written first Uppercase letter is used for dominate T – tall Lowercase letter is used for recessive t – short

Mendel’s Monohybrid Cross Law of segregation During fertilization, male and female gametes randomly pair to produce 3 combinations of alleles. Concluded that each plant in the F1 generation carried one dominate allele and one recessive allele and the F2 generation either received 2 dominate; 2 recessive; or one of each

Phenotypes and Genotypes Two organisms can look alike but have different underlying gene combinations Phenotype The way an organism looks or behaves What you see Genotype The gene combination an organism contains The genetic makeup

Phenotypes and Genotypes Homozygous The two alleles for the trait are the same TT or tt Heterozygous The two alleles for the trait are different Tt

Can you determine the phenotype? White and purple garden pea flowering plants Purple is dominate (P) White is recessive (p)

Homozygous Dominate Cross Cross = Purple X Purple P

Homozygous Recessive Cross Cross = White X White p

Heterozygous Cross Cross = Purple X Purple P p

Mendel’s Dihybrid Crosses Cross where the peas differ in 2 traits Ex. Seed color and Seed shape A cross involving two traits

Mendel’s Dihybrid Crosses The First Generation Two true breeding plants (P1) RRYY = round yellow seed (homozygous dominate) rryy = wrinkled green seed (homozygous recessive) When they were crossed all the plants had round yellow seeds (F1)

Mendel’s Dihybrid Crosses Dihybrid Cross = round yellow X wrinkled green RY ry RrYy RyYy

Mendel’s Dihybrid Crosses The Second Generation (F2) Self-pollinated plants from the first generation Resulted in 9 round yellow, 3 round green, 3 wrinkled yellow, 1 wrinkled green A ratio of 9:3:3:1

Mendel’s Dihybrid Crosses The law of independent assortment Genes from different traits are inherited independently of each other Ex. A pea plant that is RrYy, the alleles will separate and the traits will separate

Mendel’s Dihybrid Crosses Heterozygous Cross = round yellow X round yellow RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy

Punnett Squares Devised by an English biologist Reginald Punnett in 1905 Short hand way of finding the expected ratio of genotypes The phenotype can also be determined by the Punnett Squares

Punnett Squares Monohybrid crosses Cross between two plants but only looking at one trait Alleles of each parent are represented in the cross One parent is on the top the other is on the side

Heterozygous tall parent = Tt Monohybrid Cross Heterozygous tall parent = Tt Cross = Tt X Tt T t T t TT Tt tt 

Punnett Squares Dihybrid crosses Cross between two plants, and you are looking at two traits Both traits will be represented in the cross RrYy X RrYy (both are heterozygous)

Heterozygous round yellow seed parents = RrYy Dihybrid Cross Heterozygous round yellow seed parents = RrYy Cross = RrYy X RrYy RY Ry rY ry RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy 

PRACTICE PUNNETT SQUARES Probability Genetic is like flipping a coin it can go either way The Punnett Square is only able to show us the chance/probability that the offspring will be a certain way All the offspring could be the same PRACTICE PUNNETT SQUARES

Monohybrid Punnett Square

Dihybrid Punnett Square

Dihybrid Punnett Square