Predicting Inheritance using Punnett Squares Unit 5: Genetics Chapter 11-2.
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Transcript of Predicting Inheritance using Punnett Squares Unit 5: Genetics Chapter 11-2.
• Dominant traits cover up Recessive traits– Dominant Allele = capital letter (B)– Recessive Allele = lower case letter (b)
Let’s Review our Vocab!
P = Parents
F1 = first generation offspring
F2 = second generation offspring
• 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?
Dominant or Recessive?
• 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
Purebred or Hybrid?• rr• Ww• NN
• Homozygous dominant• Heterozygous• Homozygous recessive
• 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• Genotype• Genotype• Phenotype• Genotype• Genotype• Phenotype• 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
5-Step Plan
Sample ProblemYou 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
• 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
Bb
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)
BB
b
b
B
B
B
B
b
b
b
b
• 5) Answers– Each box = a 25% chance of offspring inheriting
that genotype– Always put a box around your final answer!!!
BB
b
b
B
B
B
B
b
b
b
b
100% Black offspring0% White offspringRatio: 4 : 0 OR 1 : 0 (Black : White)
• 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)
P P
p
p
What % of the offspring will be Purple? White?
What is the ratio of purple : white?
(Hint: how many of each & reduce)
Pp Pp
PpPp
100 % Purple0% White
1: 0
Example:Tall (Tt) x short (tt)
t t
T
t
What % of the offspring will be Tall? Short?
What is the ratio of tall : short?
(Hint: how many of each & reduce)
Tt Tt
tttt
50 % Tall50% Short
1: 1
Example:Brown eyes (Bb) x Brown eyes (Bb)
B b
B
b
What % of the offspring will be Brown eyes? Blue eyes?
What is the ratio of brown eyes : blue eyes?
(Hint: how many of each)
BB Bb
bbBb
75 % Brown25% Blue
3: 1
Example:Dimples (DD) x No Dimples (dd)
D D
d
d
What % of the offspring will have dimples? No dimples?
What is the ratio of dimples : no dimples?
(Hint: how many of each & reduce)
Dd Dd
DdDd
100 % Dimples0% No dimples
1: 0
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
% of Normal thumbs? % Hitchiker’s thumbs?
Ratio?
Tt Tt
tttt
50 % Normal50% Hitchiker’s
1: 1