Genetics A study of inheritance

Objectives Understand Phenotype Genotype Dominance Gene Segregation Use a Punnett square to Solve monohybrid crosses Predict genotype ratio Predict phenotype ratio

Gregor Mendel Father of modern genetics

Gregor Mendel Father of modern genetics Researched with pea plants

Gregor Mendel Father of modern genetics Researched with pea plants Developed ideas of dominance and trait segregation

Phenotype Phenotype Physical characteristics

Genotype Phenotype Genotype Physical characteristics Genes we inherit from our parents

Phenotype Notice the similarities: Facial structure

Phenotype Notice the similarities: Facial structure Eyes

Phenotype Notice the similarities: Facial structure Eyes Smile

Phenotype Notice the similarities: Facial structure Eyes Smile Ears

Phenotype Notice the similarities: Facial structure Eyes Smile Ears Nose

Phenotype Notice the similarities: Facial structure Eyes Smile Ears Nose Neck

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH Pod color - yellow or GREEN

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH Pod color - yellow or GREEN Flower position - terminal or AXIAL

Mendelian Genetics We will work with the following three: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH Pod color - yellow or GREEN Flower position - terminal or AXIAL

Predicting Inheritance To determine the chances of inheriting a given trait, scientists use Punnett squares and symbols to represent the genes. UPPERCASE letters are used to represent dominant genes. lowercase letters are used to represent recessive genes.

Predicting Inheritance For example: T = represents the gene for TALL in pea plants t = represents the gene for short in pea plants So: TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant. Remember there are two genes for every trait! One from each parent.

Predicting Inheritance For example: T = represents the gene for TALL in pea plants t = represents the gene for short in pea plants So: TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant. Remember there are two genes for every trait! Mendels’ Principle of Dominance Some genes (alleles) are dominant and others are recessive. The phenotype (trait) of a dominant gene will be seen when it is paired with a recessive gene.

Predicting Inheritance Let’s cross a totally dominant tall plant (TT) with a short plant (tt). Each plant will give only one of its’ two genes to the offspring or F1 generation. TT x tt T T t t

Predicting Inheritance Let’s cross a totally dominant tall plant (TT) with a short plant (tt). Each plant will give only one of its’ two genes to the offspring or F1 generation. TT x tt Mendels’ “Law” of Segregation Each gene (allele) separates from the other so that the offspring get only one gene from each parent for a given trait. T T t t

Punnett Squares Tt The genes from one parent go here. The genes from the other parent go here.

Punnett Squares T t Tt

Punnett Squares T t Tt

Punnett Squares T t Tt

Punnett Squares T t Tt

Punnett Squares T t Tt

Punnett Squares T t Tt F1 generation

Interpreting the Results The genotype for all the offspring is Tt. The genotype ratio is: Tt - 4/4 The phenotype for all the offspring is tall. The phenotype ratio is: tall - 4/4

Punnett Squares T t ?? Your Turn!!

Punnett Squares T t TT Tt tt F2 generation

Punnett Squares T t TT Tt tt Next, give the genotype and phenotype ratios of the offspring (F2 generation). T t TT Tt tt

Punnett Squares Genotype ratio: TT - 1 T t TT Tt tt

Punnett Squares Genotype ratio: TT - 1, Tt - 2 T t TT Tt tt

Punnett Squares Genotype ratio: TT - 1, Tt - 2, tt - 1 T t TT Tt tt

Punnett Squares T t TT Tt tt Genotype ratio: TT - 1, Tt - 2, tt - 1 Phenotype ratio: Tall - 3

Punnett Squares T t TT Tt tt Genotype ratio: TT - 1, Tt - 2, tt - 1 Phenotype ratio: Tall - 3, short - 1

Punnett Squares T t TT Tt tt This is a monohybrid cross. We worked with only one trait. The height of the plant.

Punnett Squares T t TT Tt tt This is a monohybrid cross. We worked with only one trait. The height of the plant. two Later we will work with a dihybrid cross, using the height of the plant and either seed color or seed shape.