#50 Using a Punnett Square

Homozygous: Genotype with Identical alleles, same letters (RR = dominant, rr = recessive) Heterozygous Genotype with different alleles, but dominant one shows up (Bb always has the dominant phenotype). Vocabulary

What is a PUNNETT SQUARE? A tool to predict the probability of certain traits in offspring that shows the different ways the alleles of each genotype can combine A way to show possible phenotypes & genotypes

What is a PUNNETT SQUARE? Letters stand for dominant and recessive alleles –An uppercase letter stands for a dominant allele –Lowercase letters stand for recessive alleles

Using a PUNNETT SQUARE To set up a Punnett square, draw a large square, and then divide it into 4 equal sections (also squares). It should look something like this:

Using a PUNNETT SQUARE Now you need two parents to mate, ones with a known genotype For example, a red flower (genotype Rr) and a white flower (genotype rr). Rr x rr

Using a PUNNETT SQUARE Place one of the parents on top, and one on the left. You should get a something similar to this:

Using a PUNNETT SQUARE Finally, take each letter in each column and combine it with each letter from each row in the corresponding square. You should now have a picture close to this:

Using a PUNNETT SQUARE The two-letter combinations are the possible genotypes of offspring They are: Rr, Rr, rr, and rr genotypes From this it is possible to determine the probability (chance) that a flower will have a red phenotype (2/4 or 50%) or a white phenotype (2/4 or 50%)

1. Cross a homozygous dominant tall plant with a homozygous recessive short plant What letters would you use to represent this cross? Dominant trait = tall Dominant trait = tall Recessive trait = short Recessive trait = short T = tall T = tall t = short t = short

What is the genotype of a homozygous dominant tall plant? What is the genotype of a homozygous dominant tall plant? Genotype Genotype % TT % Tt % tt  TT TT x tt TT x tt What is the genotype of a homozygous recessive short plant? What is the genotype of a homozygous recessive short plant?  tt t t T TT T Phenotype Phenotype % tall % short Tt

#2. Cross a heterozygous brown haired rabbit with a homozygous recessive white haired rabbit. o What letters would you use to represent this cross? Dominant trait = brown hair Dominant trait = brown hair Recessive trait = white hair Recessive trait = white hair B = brown B = brown b = white b = white

What is the genotype of a heterozygous brown haired rabbit? What is the genotype of a heterozygous brown haired rabbit? Genotype Genotype % BB % Bb % bb  Bb Bb x bb Bb x bb What is the genotype of a homozygous recessive white haired rabbit? What is the genotype of a homozygous recessive white haired rabbit?  bb b b BbBb Phenotype Phenotype % brown % white bb Bb 0 50

3. Cross a homozygous dominant long haired guinea pig with a heterozygous long haired guinea pig. o What letters would you use to represent this cross? Dominant trait = long hair Dominant trait = long hair Recessive trait = short hair Recessive trait = short hair L = long L = long l = short l = short

What is the genotype of a homozygous dominant long haired guinea pig? What is the genotype of a homozygous dominant long haired guinea pig? Genotype Genotype % LL % Ll % ll  LL LL x Ll LL x Ll What is the genotype of a heterozygous long haired guinea pig? What is the genotype of a heterozygous long haired guinea pig?  Ll L l LL LL Phenotype Phenotype % long % short LLLl LLLl

4. Cross a heterozygous wrinkly elephant with another heterozygous wrinkly elephant.  What letters would you use to represent this cross? Dominant trait = wrinkly skin Dominant trait = wrinkly skin Recessive trait = smooth skin Recessive trait = smooth skin W = wrinkly W = wrinkly w = smooth w = smooth

What is the genotype of a heterozygous wrinkly-skinned elephant? What is the genotype of a heterozygous wrinkly-skinned elephant? Genotype Genotype % WW % Ww % ww  Ww Ww x Ww Ww x Ww What is the genotype of a heterozygous wrinkly-skinned elephant? What is the genotype of a heterozygous wrinkly-skinned elephant?  Ww W w WwWw Phenotype Phenotype % wrinkly % smooth Wwww WWWw

Phenotype Phenotype % round % wrinkled 5.A plant that is homozygous dominant for round seeds is crossed with a heterozygous plant. What is the probability that the offspring will have wrinkled seeds? RR x Rr RR x Rr R r RRRR RRRr RRRr R = round Genotype Genotype % RR % Rr % rr r = wrinkled