Punnett Square Practice KEY

Topics: Allele, Albinism, Blood type Pages: 33 (1047 words) Published: January 24, 2015




In rats, black color is dominant
and white color is recessive.
Cross heterozygous black rat with
a white rat

B=black
b=white
Bb x bb

B

b
b

P: 2/4 black,
2/4 white
1:1

b

Bb bb
Bb bb

G: 2/4 Bb
2/4 bb
1:1





Can two white rats have a black
offspring?
Show the Punnett Square to
confirm your answer

B=black
P: 4/4 white
b=white
1:0
bb x bb  2 white rats
G: 4/4 bb
b
b
1:0

b
b

bb bb
bb bb

NO, 2 white rats
cannot have a
black offspring.





In humans the ability to taste a
certain chemical is dominant.
Cross a homozygous taster with a
heterozygous taster.

T=taster
t=non-taster
TT x Tt

T

T
t

G: 2/4 TT
2/4 Tt
1:1

T

TT TT
Tt Tt

P: 4/4 Tasters
1:0




Albinism – lack of pigment – is
caused by a recessive allele.
Cross an albino with a
heterozygous, normally pigmented
person (remember to choose your
letters using the letter of the
dominant allele)

N=normal pigment
n=albino
nn x Nn

n

N
n

n

Nn Nn
nn nn

G: 2/4 Nn,
2/4 nn
1:1
P: 2/4 Normal
2/4 albino
1:1



Cross a homozygous roller
(tongue, of course) with a
heterozygous roller

R=roller
r=non-roller
RR x Rr

R

R
r

G: 2/4 RR
2/4 Rr
1:1

R

RR RR
Rr Rr

P: 4/4 Rollers
1:0





Write the genotype of a
heterozygous curly haired,
homozygous albino, heterozygous
tongue roller, homozygous taster.
Remember, you should have two
alleles for each trait






C=curly, c=straight
N=normal pigment, n=albino
R=roller, r=non-roller
T=taster, t=non-taster

 CcnnRrTT

 Write

the phenotype for the
following person using
these letters for your alleles






C = curly hair, c = straight hair
N = normal pigment, n = albino
R = roller, r = non-roller
T = taster, t = non-taster

ccNnrrTT

ccNnrrTT
straight hair,
normal-pigment, nontongue rolling, taster





A spotted rabbit when crossed with a
solid colored rabbit produced all
spotted offspring. When these F1
rabbits were crossed within
themselves, they produced thirtytwo spotted rabbits and ten solidcolored rabbits. Which characteristic is dependent on the
dominant allele?



32 spotted, 10 solid-colored
  ~ 3:1 ratio of spots:solids
 Therefore, the spotted allele is
dominant





How many of the spotted rabbits
in the F2 generation in the
preceding problem would be
expected to be homozygous?
How many of the solid-colored F2
rabbits would be homozygous?

S=spotted
s=solid
Ss x Ss

S

S
s

G:

s

SS Ss
Ss ss

P:

¼ SS, ¼ ss,
2/4 Ss
1:1:2
¾ spotted
¼ solid
3:1

¼ Homozygous
spotted, ¼
homozygous
solid

In guinea pigs, the coat may be
rough or smooth.




Certain rough coated guinea pigs when
crossed with smooth coated guinea
pigs produce all rough offspring.
Other rough coated guinea pigs when
crossed with smooth coated guinea
pigs produce equal numbers of rough
and smooth coated guinea pigs






Smooth coated guinea pigs
crossed together always produce
smooth coated offspring
Explain these results
Write the genotypes for all
animals involved in the crosses

R=rough
r=smooth

R
r
r

R

Rr Rr
Rr Rr

Rough x smooth  All rough
- RR x rr
Rough x smooth  ½ rough, ½
smooth
- Rr x rr
Smooth x smooth  All smooth
- rr x rr

R

r
r

r

Rr rr
Rr rr

r

r
r

r

rr rr
rr rr







Yellow guinea pigs crossed with white
ones always produce cream colored
offspring.
Two cream colored guinea pigs, when
crossed together, produce yellow, cream
and white offspring in a 1:2:1 ratio.
How are these colors inherited?

G=guinea pig, GY=yellow, GW=white



GYGW = cream-colored
1:2:1 ratio of yellow homozygous,
cream heterozygous, white
homozygous
  Shows incomplete dominance
 There is “blending”

In tomatoes the texture of the skin
may be smooth or...
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