POINT > Review some genetics vocabulary POINT > Define genotype and phenotype POINT > Define homozygous and heterozygous POINT > Use a Punnett Square to predict genotypes of offspring POINT > Describe codominance

POINT > Review some genetics vocabulary Genetics is the scientific study of heredity

POINT > Review some genetics vocabulary A trait is a physical characteristic that is different from one individual to another. Ex. Brown hair, blue eyes, purple flowers, large leaves

POINT > Review some genetics vocabulary Genes are the sequence of DNA that determines a trait.

POINT > Review some genetics vocabulary Alleles are the different gene possibilities for a trait. ex. The gene for flower color has one allele for purple flowers, one allele for white flowers Every trait in an individual has two alleles (one from the mother and one from the father) A parent passes one of its alleles to each offspring

POINT > Review some genetics vocabulary Mendel: The Father of Genetics 1 st important studies of heredity Mendel identified traits in pea plants and studied them from one generation to another

POINT > Review some genetics vocabulary Dominant alleles – Covers up the other trait; the dominant trait is always expressed Represented by a capital letter Recessive alleles - The recessive trait is only expressed when the dominant allele is not present Represented by a lower case letter R r

POINT > Review some genetics vocabulary TT - Two dominant alleles Tt - One dominant and one recessive allele tt - Two recessive alleles T - tall plant (dominant) t - short plant (recessive)

POINT > Review some genetics vocabulary P – Original parents F 1 – First generation F 2 – Second generation P X P = F 1 F 1 X F 1 = F 2

POINT > Define genotype and phenotype Genotype – The genetic makeup of an organism ex. Tt, ss, GG, Ww Phenotype – The physical characteristics of an organism The way an organism looks ex.: curly hair, straight hair, blue eyes, tall, green seeds, etc

POINT > Define genotype and phenotype The genotype determines the phenotype!

POINT > Define homozygous and heterozygous Homozygous –two identical alleles for a particular trait (TT or tt) Heterozygous - two different alleles for the same trait (Tt) RR Rr rr

CHECK: What is a phenotype? What is heterozygous? What is homozygous? What is a genotype?

POINT > Define homozygous and heterozygous Example: R allele is for red eyes (dominant) r allele is for white eyes (recessive) Homozygous dominant -Two dominant alleles (ex. genotype = RR) This individual (RR) will show the dominant phenotype, and have red eyes

POINT > Define homozygous and heterozygous R allele is for red eyes (dominant) r allele is for white eyes (recessive) Homozygous recessive - Two recessive alleles (ex. genotype = rr) This individual (rr) will show the recessive phenotype, and have white eyes

POINT > Define homozygous and heterozygous R allele is for red eyes (dominant) r allele is for white eyes (recessive) Heterozygous - One dominant allele (R) and one recessive allele (r) (ex. genotype = Rr) This individual (Rr) will show the dominant phenotype, and have red eyes

POINT > Use a Punnett Square to predict genotypes of offspring Punnett Square – Diagram showing the allele combinations that might result from a genetic cross We use it to calculate the probability of inheriting a particular trait Probability – The chance that a given event will occur

CHECK: What is a Punnett square? What is probability?

POINT > Use a Punnett Square to predict genotypes of offspring Purple Parent White Parent F 1 Offspring Remember Mendel’s first cross: Purebred purple flowers X purebred white flowers Purebred purple flowers = PP (homozygous dominant) Purebred white flowers = pp (homozygous recessive) PP x pp PP p p Pp

POINT > Use a Punnett Square to predict genotypes of offspring Purple Parent F 2 Offspring F 1 offspring = Pp (heterozygous) = 100% purple flowers Remember Mendel’s second cross: F 1 x F 1 Pp x Pp Pp P p PP Pp pp

POINT > Use a Punnett Square to predict genotypes of offspring Purple Parent F 2 Offspring F 2 offspring = 25% PP (homozygous dominant) = 50% Pp (heterozygous) = 25% pp (homozygous recessive) = 75 % purple flower plants 25% white flower plants Pp P p PP Pp pp

TT x tt Step One: Set Up Punnett Square (put one parent on the top and the other along the side) T T t t POINT > Use a Punnett Square to predict genotypes of offspring

TT x tt Step Two: Complete the Punnett Square T T t t Tt POINT > Use a Punnett Square to predict genotypes of offspring

TT x tt Step Three: Write the genotype and phenotype T T t t Tt Genotype: 100% Tt Phenotype: 100% Tall Remember: Each box is 25% POINT > Use a Punnett Square to predict genotypes of offspring

Test ex. The allele for black berries in a plant is dominant (B) and the allele for red berries is recessive (b). What is the genotype of a heterozygous plant? What is the phenotype of a heterozygous plant? If a heterozygous plant is crossed with a plant with red berries, what percentage of offspring will have black berries? What percentage will have red berries? Bb Black 50%

POINT > Describe codominance All of the traits Mendel studied were dominant or recessive Codominance - Situation in which both alleles contribute to the phenotype of the organism. Ex. A white cow is crossed with a brown cow and the offspring are spotted brown and white x

CHECK: What is codominance?

Homework: Read pages S.A. #1-3 GRAS pages 58-60