What is Genetics?Genetics is the scientific study of heredity

What is a Trait?A trait is a specific characteristic

that varies from one individual to another.Examples: Brown hair, blue eyes, tall,

curly

What is an Allele?Alleles are the

different possibilities for a given trait.Every trait has at least

two alleles (one from the mother and one from the father)

Example: Eye color – Brown, blue, green, hazel

Examples of Alleles:A = Brown Eyesa = Blue EyesB = Green Eyesb = Hazel Eyes

What are Genes?Genes are the sequence of DNA that codes for a protein and thus determines a trait.

Gregor MendelFather of Genetics1st important studies of

heredityIdentified specific traits in the

garden pea and studied them from one generation to another

Dominant vs. RecessiveDominant - Masks the other trait; the trait

that shows if presentRepresented by a capital letter

Recessive – An organism with a recessive allele for a particular trait will only exhibit that trait when the dominant allele is not present; Will only show if both alleles are presentRepresented by a lower case letter

R

r

Dominant & Recessive Practice

TT - Represent offspring with straight hair

Tt - Represent offspring with straight hair

tt - Represents offspring with curly hair

T – straight hairt - curly hair

Genotype vs. PhenotypeGenotype – The genetic makeup of an

organism; The gene (or allele) combination an organism has. Example: Tt, ss, GG, Ww

Phenotype – The physical characteristics of an organism; The way an organism looksExample: Curly hair,

straight hair, blue eyes, tall, green

Homozygous vs. HeterozygousHomozygous – Term used

to refer to an organism that has two identical alleles for a particular trait (TT or tt)

Heterozygous - Term used to refer to an organism that has two different alleles for the same trait (Tt)

RR

Rr

rr

Punnett SquaresPunnett Square – Diagram

showing the gene combinations that might result from a genetic cross

Used to calculate the probability of inheriting a particular traitProbability – The chance

that a given event will occur

Punnett SquareParent

Parent Offspring

How to Complete a Punnett Square

You Try It Now!Give the genotype and phenotype for the

following cross: TT x tt (T = Tall and t = Short)

TT x ttStep One: Set Up Punnett Square (put one parent

on the top and the other along the side)

T T t t

TT x ttStep Two: Complete the Punnett Square

T T t t

Tt Tt

Tt Tt

TT x ttStep Three: Write the genotype and phenotype

T T t t

Tt Tt

Tt Tt

Genotype: 4 - Tt

Phenotype:100% Tall

Remember: Each box is 25%

You Try It Now!Give the genotype and phenotype for the

following cross: Tt x tt

Tt x ttStep One: Set Up Punnett Square (put one parent

on the top and the other along the side)

T t t t

Tt x ttStep Two: Complete the Punnett Square

T t t t

Tt tt

Tt tt

Tt x ttStep Two: Complete the Punnett Square

T t t t

Tt tt

Tt tt

Genotype: Tt - 2 (50%)tt - 2 (50%)

Phenotype:50% Tall50% Short

Remember: Each box is 25%