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) Lets 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 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 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 Phenotype Genotype 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) Legend2) Parents3) Punnett Square: Set it up 4) Punnett Square: Fill it in 5) Answers Pg 10 5-Step Plan
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: GenotypePhenotype BB Bb bb 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 BB bbbb
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 bbbb 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 bbbb B B B B b b b b 100% Black offspring 0% White offspring Ratio: 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 pppp What % of the offspring will be Purple? White? What is the ratio of purple : white? (Hint: how many of each & reduce) PpPp PpPp PpPpPpPp 100 % Purple 0% White 1: 0
Example: Tall (Tt) x short (tt) t t TtTt What % of the offspring will be Tall? Short? What is the ratio of tall : short? (Hint: how many of each & reduce) Tt tt 50 % Tall 50% Short 1: 1
Example: Brown eyes (Bb) x Brown eyes (Bb) B b BbBb 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 % Brown 25% Blue 3: 1
Example: Dimples (DD) x No Dimples (dd) D D dddd What % of the offspring will have dimples? No dimples? What is the ratio of dimples : no dimples? (Hint: how many of each & reduce) Dd 100 % Dimples 0% No dimples 1: 0
Normal thumbs (T) are dominant to hitchikers thumbs (t). A man with hitchikers thumb marries a women that is heterozygous for a normal thumb. t t TtTt % of Normal thumbs? % Hitchikers thumbs? Ratio? Tt tt 50 % Normal 50% Hitchikers 1: 1
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 FFFF % Free Earlobes? % Attached earlobes? Ratio? Ff 100 % Free 0% Attached 1: 0