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Dihybridcrossesworksheet

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Name: Period:

Dihybrid crosses practice problems

1.

Dobby the House Elf falls head over heels for Elf-ette named Dabbin’. The marry and decide to raise a family of little house elves. Dobby’s pointed ears are dominant, and knows that he is heterozygous for ear shape. Dabbin’s ears are round. Dobby’s long nose is a recessive trait, and Dabbin’ is homozygous dominant for her stubby nose.

Using a Punnett square, determine the probability that they will have an elf child with a stubby nose and pointed ears. Fill in the Punnett square below to support your answer.

Dobby genotype: Dabbin genotype:

2.

Hagrid has been breeding his creatures again. This time he is breeding Cerberus, his 3 headed dog. Having three heads is dominant over having 2 heads. He has also discovered that having chocolate brown fur is dominant to yellow fur. Hagrid crosses Cerberus (who is heterozygous for both traits) to a female that is also heterozygous for both traits. Hagrid’s customers want the super rare 2-headed, yellow furred dogs. What is the expected frequency of these dogs in the cross he conducts? Use the Punnett square below to support your answer.

Name: Period:

3.

Gru needs a minion army – his regular minions are too incompetent, and he wants to hybridize them with the evil purple minions. He knows that purple color is a recessive trait, and that 2 eyes is dominant to one eye. Gru wants an army of two eyed, purple minions. Gru breeds

2 minions that are heterozygous for both traits and produces 144 minion babies. How many of these minions should be purple and have 2 eyes?

Use the Punnett square below to support your answer, and be sure to show all of your work.

4.

Gru knows that his purple army can be supported by a steady diet of bananas, and that this is the source of their strength. Unfortunately, there is a rare, recessive mutation that causes minions to be allergic to bananas (tolerance to bananas, B , is a dominant trait). Another rare mutation, t , cases minions to be toothless. Without teeth, they can’t even gum the bananas. Gru wants to breed 2 heterozygous minions, and he is wondering what proportion of the offspring will be toothless and/or allergic to bananas.

Name: Period:

5.

Mr. and Mrs. Incredible are expecting another baby! This time, they have done some research into some of their incredible, super power genes, and they think they have an idea of what traits their new, incredible baby will posses. Mr. Incredible’s strength is is a dominant trait, and he knows that he is heterozygous ( Rr ) for his ridiculous strength. In contrast, Mrs. Incredible is homozygous dominant ( EE ) for her elastic body. Mrs. Incredible lacks ridiculous super strength, and Mr. Incredible does not have elastic body. What are the possible phenotypes of their baby?

6.

You have decided to breed your little ponies, and you want to produce rarity – an albino unicorn (both recessive traits to the dominant traits, yellow coat and lack of horn). You breed a pony that is a unicorn and is heterozygous for coat color with a pony that is heterozygous for lacking a horn and is white. What is the expected frequency of rarities in this cross?

Name: Period:

Dihybrid crosses practice problems

1.

Dobby the House Elf falls head over heels for Elf-ette named Dabbin’. The marry and decide to raise a family of little house elves. Dobby’s pointed ears are dominant, and knows that he is heterozygous for ear shape. Dabbin’s ears are round. Dobby’s long nose is a recessive trait, and Dabbin’ is homozygous dominant for her stubby nose.

Using a Punnett square, determine the probability that they will have an elf child with a stubby nose and pointed ears. Fill in the Punnett square below to support your answer.

Dobby genotype: Eenn Dabbin genotype: eeNN

E = pointy e= round

N = stubby nose n = long nose eN

En

EeNn en eeNn

50% chance (E-N-)

2.

Hagrid has been breeding his creatures again. This time he is breeding Cerberus, his 3 headed dog. Having three heads is dominant over having 2 heads. He has also discovered that having chocolate brown fur is dominant to yellow fur. Hagrid crosses Cerberus (who is heterozygous for both traits) to a female that is also heterozygous for both traits. Hagrid’s customers want the super rare 2-headed, yellow furred dogs. What is the expected frequency of these dogs in the cross he conducts? Use the Punnett square below to support your answer.

H = 3 heads h = 2 heads

B = chocolate b = yellow

1/16 = 2-headed, yellow

HB

Hb hB hb

HB

HHBB

HHBb

HhBB

HhBb

Hb

HHBb

HHbb

HhBb

Hhbb hB

HhBB

HhBb hhBB hhBb hb

HhBb

Hhbb hhBb hhbb

Name: Period:

3.

Gru needs a minion army – his regular minions are too incompetent, and he wants to hybridize them with the evil purple minions. He knows that purple color is a recessive trait, and that 2 eyes is dominant to one eye. Gru wants an army of two eyed, purple minions. Gru breeds

2 minions that are heterozygous for both traits and produces 144 minion babies. How many of these minions should be purple and have 2 eyes?

Use the Punnett square below to support your answer, and be sure to show all of your work.

HB Hb hB

H = yellow h = purple

B = 2 eyes b = 1 eye

3/16 x 144 = 27 minions should be hhB-

HB

Hb hB

HHBB

HHBb

HhBB

HHBb

HHbb

HhBb

HhBB

HhBb hhBB hb

HhBb

Hhbb hhBb hb HhBb Hhbb hhBb hhbb

4.

Gru knows that his purple army can be supported by a steady diet of bananas, and that this is the source of their strength. Unfortunately, there is a rare, recessive mutation that causes minions to be allergic to bananas (tolerance to bananas, B , is a dominant trait). Another rare mutation, t , cases minions to be toothless. Without teeth, they can’t even gum the bananas. Gru wants to breed 2 heterozygous minions, and he is wondering what proportion of the offspring will be toothless and/or allergic to bananas.

BT Bt bT bt

B = tolerance b = allergic to bananas

T = normal teeth t = toothless

7/16 should either lack teeth, be allergic to bananas, or both

BT

Bt bT bt

BBTT

BBTt

BbTT

BbTt

BBTt

BBtt

BbTt

Bbtt

BbTT

BbTt bbTT bbTt

BbTt

Bbtt bbTt bbtt

Name: Period:

5.

Mr. and Mrs. Incredible are expecting another baby! This time, they have done some research into some of their incredible, super power genes, and they think they have an idea of what traits their new, incredible baby will posses. Mr. Incredible’s strength is is a dominant trait, and he knows that he is heterozygous ( Rr ) for his ridiculous strength. In contrast, Mrs. Incredible is homozygous dominant ( EE ) for her elastic body. Mrs. Incredible lacks ridiculous super strength, and Mr. Incredible does not have elastic body. What are the possible phenotypes of their baby?

Re re

E = elastic e = normal

R = Strength r = no super strength

rE RrEe rrEe

(Rree x rrEE)

50% elastic, super strength

50% elastic, no super strength

6.

You have decided to breed your little ponies, and you want to produce rarity – an albino unicorn (both recessive traits to the dominant traits, yellow coat and lack of horn). You breed a pony that is a unicorn and is heterozygous for coat color with a pony that is heterozygous for lacking a horn and is white. What is the expected frequency of rarities in this cross?

A = yellow a = albino

H = hornless h = unicorn

(Aahh x aaHh)

25% should be rarities (aahh) aH ah

Ah

AaHh

Aahh ah aaHh aahh

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