1. #50 Using a Punnett Square

2. Vocabulary Heredity- The passing on of traits from parent to offspring
Genetics- The study of heredity
Gene- Units of heredity; segments of DNA on chromosomes
Dominant- A trait that is shown when at least 1 dominant allele is present , represented by a capital letter (ex. B)“stronger trait”
Recessive- A trait that is only shown if 2 recessive alleles are inherited , represented by a lower case letter (ex. b) “weaker trait”
Allele- different forms of the same gene; represented by a letter (“B” or “b”)
Genotype- Gene makeup of an organism (RR, Rr, or rr)
Phenotype- Physical appearance (brown hair, green eyes)
Homozygous- genotypes with the same alleles; either 2 dominant or 2 recessive
Heterozygous- genotypes with different alleles; one dominant and one recessive
Punnett Square- a tool to predict the probability of inheriting traits

3. What is a PUNNETT SQUARE?
A tool to predict the probability of certain traits in offspring that shows the different ways the alleles of each genotype can combine
A way to show possible phenotypes & genotypes

4. What is a PUNNETT SQUARE?
Letters stand for dominant and recessive alleles
An uppercase letter stands for a dominant allele
Lowercase letters stand for recessive alleles

5. Using a PUNNETT SQUARE
To set up a Punnett square, draw a large square, and then divide it into 4 equal sections (also squares). It should look something like this:

6. Using a PUNNETT SQUARE
Now you need two parents to mate, ones with a known genotype
For example, a red flower (genotype Rr) and a white flower (genotype rr). Rr x rr

7. Using a PUNNETT SQUARE
Place one of the parents on top, and one on the left. You should get a something similar to this:

8. Using a PUNNETT SQUARE
Finally, take each letter in each column and combine it with each letter from each row in the corresponding square. You should now have a picture close to this:

9. Using a PUNNETT SQUARE
The two-letter combinations are the possible genotypes of offspring
They are: Rr, Rr, rr, and rr genotypes
From this it is possible to determine the probability (chance) that a flower will have a red phenotype (2/4 or 50%) or a white phenotype (2/4 or 50%)

10. 1. Cross a homozygous dominant tall plant with a homozygous recessive short plant
Recessive trait = short
What letters would you use to represent this cross?
Dominant trait = tall
T = tall
t = short

11. What is the genotype of a homozygous dominant tall plant? TT
What is the genotype of a homozygous recessive short plant? tt
TT x tt
Genotype
% TT
% Tt
% tt
t t
100 Tt Tt
T T
Phenotype
% tall
% short
100 Tt Tt

12. #2. Cross a heterozygous brown haired rabbit with a homozygous recessive white haired rabbit.
Dominant trait = brown hair
Recessive trait = white hair
What letters would you use to represent this cross?
B = brown
b = white

13. What is the genotype of a heterozygous brown haired rabbit? Bb
What is the genotype of a homozygous recessive white haired rabbit? bb
Bb x bb
Genotype
% BB
% Bb
% bb
b b 50 Bb Bb B b 50
Phenotype
% brown
% white 50 bb bb 50

14. 3. Cross a homozygous dominant long haired guinea pig with a heterozygous long haired guinea pig.
Dominant trait = long hair
Recessive trait = short hair
What letters would you use to represent this cross?
L = long
l = short

15. What is the genotype of a homozygous dominant long haired guinea pig? LL
What is the genotype of a heterozygous long haired guinea pig? Ll
LL x Ll
Genotype
% LL
% Ll
% ll 50
L l 50 LL Ll L
Phenotype
% long
% short
100 LL Ll

16. 4. Cross a heterozygous wrinkly elephant with another heterozygous wrinkly elephant.
Dominant trait = wrinkly skin
Recessive trait = smooth skin
What letters would you use to represent this cross?
W = wrinkly
w = smooth

17. What is the genotype of a heterozygous wrinkly-skinned elephant? Ww
Ww x Ww
Genotype
% WW
% Ww
% ww 25
W w 50 W w WW Ww 25
Phenotype
% wrinkly
% smooth 75 Ww ww 25

18. A plant that is homozygous dominant for round seeds is crossed with a heterozygous plant. What is the probability that the offspring will have wrinkled seeds?
R = round
r = wrinkled
RR x Rr
Genotype
% RR
% Rr
% rr 50
R r 50 R RR Rr
Phenotype
% round
% wrinkled
100 RR Rr