Punnett Squares Note Frame 11

Key Term Punnett Square Crossing Complete dominance

Punnett Squares Punnett Square is a way to predict all possible combinations of alleles from crossing parents Used to predict the genotype and phenotype of offspring Need to know genotypes of parents

Complete Dominance is when the dominant allele will mask the expression of the recessive allele

Example: In pea plants, the colour of the flower purple (P) is dominant over white (p). Use a Punnett square to find the possible outcomes of crossing a male heterozygous plant with a female homozygous recessive plant.

Get info from the question How to Make a Punnett Square Write symbols and what they stand for. Get info from the question “purple (P) is dominant over white (p)” Purple = P White = p

Get info from the question 2. Write the genotypes of each parent Get info from the question Pp Male heterozygous plant pp Female homozygous recessive plant Male = Pp Female = pp

3. Draw a Punnett Square ♂ Pp Male= ♀ Female= pp

♂ P Pp p ♀ p p Male= Female= pp 4. Write parent genotypes on top and side – one allele in each box ♂ P Pp p Male= ♀ p p Female= pp

♂ Pp p p p P P P ♀ p p p p p p Male= Female= pp 5. Cross the male and female alleles to find the genotype of the offspring ♂ Male= Pp p p p P P P ♀ Female= pp p p p **Always write capital letter first! p p p

♂ Pp p P ♀ p p P p p Purple White p p P p p Purple White Male= Female= 6. Write the phenotype for each possible offspring ♂ Pp Male= p P ♀ Female= pp p p P p p Purple White Purple = P White = p p p P p p Purple White

♂ Pp p P ♀ p p P p p Purple White p p P p p Purple White Male= Female= 7. Write the answer as a ratio or percent (whatever you find easier!) ♂ Pp Male= p P ♀ Female= pp p p P p p Purple to white 2:2  1:1 Purple White p p P p 50% purple 50% white p Purple White

Practice 1 In humans, dimples (D) is dominant over no-dimples (d). Use a Punnett square to find the possible outcomes of crossing a male and female who are both heterozygous for dimples.

♂ d D ♀ DD Dd D Dd dd d Dimples = D Male = Dd No dimples = d Female = Dd ♂ d D ♀ DD Dd D Dimples to non-dimple 3:1 Dimples Dimples Dd dd 75% dimple 25% non-dimple d Dimples No Dimples

Practice 2 In humans, being able to roll your tongue (R) is dominant over not being able to roll your tongue (r). Use a Punnett square to find the possible outcomes of crossing a male who is homozygous recessive and female who is heterozygous for tongue rolling.

♂ r r ♀ Rr Rr R rr rr r Roll = R Male = rr No roll = r Female = Rr Roll to no-roll 1:1 Roll Roll rr rr 50% Roll 50% no-roll r No roll No roll

Practice 3 In humans, long eyelashes (L) is dominant over short eyelashes (l). Use a Punnett square to find the possible outcomes of crossing a male who has short eyelashes with a female who is homozygous with long eyelashes.

♂ l l ♀ Ll Ll L Ll Ll L Long lashes = L Male = ll Short lashes = l Female = LL ♂ l l ♀ Ll Ll L Long lashes : short 1:0 Long Long Ll Ll 100% Long L Long Long