2.17 Punnett Squares Instructions 12/8 and 12/9 2014

How are traits passed on? Each parent passes down 1 of each of their chromosomes Each chromosome has genes Each parent passes down 1 copy of each of their child’s genes. Each parent passes down 1 of their alleles for a gene. The combination of these alleles is your genotype The way you look because of these alleles is called your phenotype

What is a Geneticist: A scientist who studies genetics There many jobs in science about genetics and heredity. From research about DNAto counseling clients and patients, to medicine and working on genetic diseases geneticists study and work with the passing down of genes. Geneticist can predict the probability, or chances parents pass on their genes.

What is probability Probability is the likely hood, or chance, that something happens In this case, we are looking at the probability, or chance, of offspring getting certain traits from their parents! This is the foundation of genetics

What are Punnett squares: Punnett squares are used to determine the probability of off offspring inheriting a trait. Once you have the genotype combination of the parents, you can determine the probability of getting a certain phenotype

Answering questions Underline key information Put a box around what you are looking for.

Punnett Square Problem 1 In peas, the Purple color color allele is dominant (P) and the white color allele is recessive (p) If a homozygous dominant ___ mom mates with a homozygous recessive ____ dad, what is the probability the offspring are white? The “mom” pea has is homozygous dominant – She has 2 dominant alleles for flower color – Her genotype is PP – Her phenotype is purple flowers, because she has 2 dominant genes The “dad” pea is homozygous recessive – He has 2 recessive alleles for flower color – His genotype is pp – His phenotype is white flowers, because he has 2 recessive genes

Punnett Square Break Down: Step 1 Step 1: Write one parent’s genotype at the top, and the other parent’s genotype on the left side of the square (one allele per square)

Punnett Square Break Down: Step 2 Step 2: Fill in the punnett square: The letters at the top fill in going down, 1 in each box. The side letters fill going from left to right, 1 in each box 1.What are the possible genotypes of the offspring?

Punnett Square Break Down: Step 3 Step 3: Figure out the genotypes and phenotypes for each box. – If there is a dominant allele, then the phenotype will be dominant – If there is no dominant allele, then the phenotype will be recessive What are the possible phenotypes of the offspring?

Punnett Square Break Down: Step 4 Step 4: Figure out the probability of the offspring’s genotype by counting how many of each genotype there is, and dividing by 4 What is the probability for each genotype? Possible Genotypes: Number: Probability: PP: Pp: pp:

Punnett Square Break Down: Step 5 Step 5: Figure out the probability of the offspring’s phenotype by counting how many of each phenotype there is, and dividing by 4 What is the probability for each phenotype? Possible phenotype: Number: Probability : Purple: White:

HW Example A mom that is homozygous dominant for straight thumbs _________ reproduces with a dad that has the homozygous recessive _______ genotype for hitchhiker’s thumb. What is the probability that their child has straight thumbs?

HH h h h H h H