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

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Presentation on theme: "Predicting Inheritance using Punnett Squares Unit 5: Genetics Chapter 11-2."— Presentation transcript:

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

3 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

4 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?

5 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)

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

7 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

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

9 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

10 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

11 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?

12 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

13 2) Parents - Write this as a cross – BB x bb

14 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

15 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

16 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)

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

18 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).

19 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

20 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

21 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

22 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

23 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

24 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


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