# Predicting Inheritance using Punnett Squares

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Predicting Inheritance using Punnett Squares
Unit 5: Genetics Chapter 11-2

Let’s Review our Vocab! Dominant traits cover up Recessive traits
Dominant Allele = capital letter (B) Recessive Allele = lower case letter (b) P = Parents F1 = first generation offspring F2 = second generation offspring

Dominant or Recessive? B=Black b=white Bb: Dom or Rec? Color?
T=Tall t= short TT: Dom or Rec? Height? P=Purple p=white pp?: Dom or Rec? Color?

Genotype: the actual alleles for a trait
Represented by letters: AA, aa, Aa Homozygous Dominant: 2 dominant alleles (AA) (purebred) Homozygous Recessive: 2 recessive alleles (aa) (purebred) Heterozygous: 1 dominant allele & 1 recessive allele (Aa) (hybrid)

Homozygous or Heterozygous?
BB Kk ff Homozygous dominant Heterozygous Homozygous recessive Purebred or Hybrid? rr Ww NN purebred hybrid purbred

Phenotype: how the trait is seen
Ex: Guinae pig fur color: black or white P = Parents F1 = first generation offspring F2 = second generation offspring

Genotype or Phenotype? Black Bb tt Short KK Pp Tall White Phenotype

Punnett Squares Used to predict the traits of each possible offspring during a cross Five Step Plan 1) Legend 2) Parents 3) Punnett square-set it up 4) Punett square-fill it in 5) Answers in boxes

5-Step Plan for Punnett Squares Flee Map
1) Legend 2) Parents 3) Punnett Square: Set it up 4) Punnett Square: Fill it in 5) Answers Pg 10

Sample Problem You do NOT have to write this slide!
In guinea pigs, Black (B) is dominant to White (b) Black guinea pig (BB) x White guinea pig (bb) What are the chances that the offspring will be black? White? How many offspring will be black? How many will be white?

Five-Step Plan 1) Legend
Always use the first letter of the dominant trait to represent your alleles. (ex: in this case, we use B for black) Set up a table: Genotype Phenotype BB Bb bb Black Black White

2) Parents - Write this as a “cross”
BB x bb

3) Punnett Square - Set it up
Draw a square and divide into four sections Write the genotype (letters) from one parent on top (one letter per box) Write the genotype from the other parent along the left side B B b

b B b B b B b B b 4) Punnett Square - Fill it in
Fill in the boxes with one letter from the top and one letter from the left (2 letters per box) B B b B b B b B b B b

b B b B b B b B b 5) Answers 100% Black offspring 0% White offspring
Each box = a 25% chance of offspring inheriting that genotype Always put a box around your final answer!!! B B 100% Black offspring 0% White offspring Ratio: 4 : 0 OR 1 : 0 (Black : White) b B b B b B b B b

Now you practice on the whiteboard!
Now we have COMPLETELY answered the question and we are done! Always double check! Now you practice on the whiteboard!

Whiteboards Keep your notes & flow map in front of you.
Please do not draw on whiteboard unless instructed. For each problem you will do steps 1 & 2 (legend & parents) first. You will then do steps 3-5 (Punnett square and answers).

Example: Purple Flower (PP) x White Flower (pp)
What % of the offspring will be Purple? White? What is the ratio of purple : white? (Hint: how many of each & reduce) 100 % Purple 0% White 1: 0

Example: Tall (Tt) x short (tt)
What % of the offspring will be Tall? Short? What is the ratio of tall : short? (Hint: how many of each & reduce) 50 % Tall 50% Short 1: 1

Example: Brown eyes (Bb) x Brown eyes (Bb)
What % of the offspring will be Brown eyes? Blue eyes? What is the ratio of brown eyes : blue eyes? (Hint: how many of each) 75 % Brown 25% Blue 3: 1

Example: Dimples (DD) x No Dimples (dd)
What % of the offspring will have dimples? No dimples? What is the ratio of dimples : no dimples? (Hint: how many of each & reduce) 100 % Dimples 0% No dimples 1: 0

Normal thumbs (T) are dominant to hitchiker’s thumbs (t)
Normal thumbs (T) are dominant to hitchiker’s thumbs (t). A man with hitchiker’s thumb marries a women that is heterozygous for a normal thumb. t t T t Tt Tt tt tt % of Normal thumbs? % Hitchiker’s thumbs? Ratio? 50 % Normal 50% Hitchiker’s 1: 1

Free earlobes (F) are dominant to attached earlobes (f)
Free earlobes (F) are dominant to attached earlobes (f). A man with attached earlobes marries a women that is homozygous for free earlobes. f f F Ff Ff Ff Ff % Free Earlobes? % Attached earlobes? Ratio? 100 % Free 0% Attached 1: 0

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