#50 Using a Punnett #50 Using a Punnett SquareSquare

Homozygous: Genotype with Identical alleles, same

letters (RR = dominant, rr = recessive)

HeterozygousGenotype with different alleles, but

dominant one shows up (Bb always has the dominant phenotype).

Vocabulary

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

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

Using a PUNNETT SQUARETo 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:

Using a PUNNETT SQUARENow 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

Using a PUNNETT SQUAREPlace one of the parents on top, and

one on the left. You should get a something similar to this:

Using a PUNNETT SQUAREFinally, 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:

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%)

1. Cross a homozygous dominant tall plant with a homozygous recessive short plant

What letters would you use to represent this cross?

Dominant trait = tall Dominant trait = tall

Recessive trait = shortRecessive trait = short

T = tall T = tall

t = short t = short

What is the genotype of a homozygous What is the genotype of a homozygous dominant tall plant?dominant tall plant?

GenotypeGenotype% %

TTTT% %

TtTt% tt% tt

TT TT

TT x ttTT x tt

What is the genotype of a homozygous What is the genotype of a homozygous recessive short plant?recessive short plant? tt tt

t t

T

T

PhenotypePhenotype% tall% tall% %

shortshort

Tt Tt

Tt Tt

0100

0

0100

#2. Cross a heterozygous brown haired #2. Cross a heterozygous brown haired rabbit with a homozygous recessive white rabbit with a homozygous recessive white haired rabbit.haired rabbit.

o What letters would you use to represent this cross?

Dominant trait = Dominant trait = brown hairbrown hair

Recessive trait = white hairRecessive trait = white hair

B = brownB = brown

b = whiteb = white

What is the genotype of a heterozygous What is the genotype of a heterozygous brown haired rabbit?brown haired rabbit?

GenotypeGenotype% %

BBBB% %

BbBb% %

bbbb

Bb Bb

Bb x bbBb x bb

What is the genotype of a homozygous What is the genotype of a homozygous recessive white haired rabbit?recessive white haired rabbit? bb bb

b b

B

b

PhenotypePhenotype% %

brownbrown% %

whitewhite

bb bb

Bb Bb

0 50

50

50 50

3. Cross a homozygous dominant long 3. Cross a homozygous dominant long haired guinea pig with a haired guinea pig with a heterozygous long haired guinea pig.heterozygous long haired guinea pig.

o What letters would you use to represent this cross?

Dominant trait = Dominant trait = long hairlong hair

Recessive trait = Recessive trait = short hairshort hair

L = longL = long l = short l = short

What is the genotype of a homozygous What is the genotype of a homozygous dominant long haired guinea pig?dominant long haired guinea pig?

GenotypeGenotype% %

LLLL% %

LlLl% ll% ll

LLLL

LL x LlLL x Ll

What is the genotype of a heterozygous What is the genotype of a heterozygous long haired guinea pig?long haired guinea pig? Ll Ll

L l

L

L

PhenotypePhenotype% long% long% %

shortshort

LL Ll

LL Ll

50 50

0

0100

4. Cross a heterozygous wrinkly 4. Cross a heterozygous wrinkly elephant with another heterozygous elephant with another heterozygous wrinkly elephant.wrinkly elephant.

What letters would you use to represent this cross?

Dominant trait = Dominant trait = wrinkly skinwrinkly skin

Recessive trait = smooth skinRecessive trait = smooth skin

W = wrinklyW = wrinkly

w = smooth w = smooth

What is the genotype of a heterozygous What is the genotype of a heterozygous wrinkly-skinned elephant?wrinkly-skinned elephant?

GenotypeGenotype% %

WWWW% %

WwWw% %

wwww

WwWw

Ww x WwWw x Ww

What is the genotype of a heterozygous What is the genotype of a heterozygous wrinkly-skinned elephant?wrinkly-skinned elephant? WwWw

W w

W

w

PhenotypePhenotype% %

wrinklywrinkly% %

smoothsmooth

Ww ww

WW Ww

25 50

25

25 75

PhenotypePhenotype% round% round% %

wrinkledwrinkled

5. 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?

RR x RrRR x Rr

R r

R

R

RR Rr

RR Rr

R = round

GenotypeGenotype% %

RRRR% Rr% Rr% rr% rr

r = wrinkled

50 50

0

0 100