Test Cross

To discover whether an animal showing the dominant trait is homozygous or heterozygous, it must be crossed with an animal that is:

• homozygous dominant

• homozygous recessive

• heterozygous

• choices B & C

Which scenario best supports the conclusion that a black guinea pig's genotype is homozygous dominant?

• after mating with a white guinea pig, 2 black & 2 white guinea pigs were produced

• after mating with a white guinea pig, 10 black & 8 white guinea pigs were produced

• after mating with a white guinea pig, 12 black guinea pigs were produced

• after mating with a black guinea pig, 4 black guinea pigs were produced

Tags

NGSS.HS-LS3-1

NGSS.HS-LS3-2

In a test cross to determine whether a fruit fly is homozygous (WW) or heterozygous (Ww) for long wings, 7 long-winged flies & 1 short winged-fly are produced. Which is a valid conclusion?

• the unknown fruit fly is WW

• the unknown fruit fly is Ww

• the unknown fruit fly is ww

• more offspring are needed

Tags

NGSS.HS-LS3-1

NGSS.HS-LS3-2

NGSS.HS-LS3-3

In hamsters, long tails (L) are dominant to short tails (l). A student wishes to perform a test cross to determine whether a female long-tailed hamster is homozygous or heterozygous for tail length. She mates the hamster with a male long-tailed hamster & studies the offspring, which are 100% long-tailed. She concludes that the female hamster's genotype is "LL". What mistake(s) did the student make?

• she should have mated the female hamster with a male that was known to be hybrid

• she should have mated the female hamster with a short-tailed male hamster

• she should have mated the female hamster with another long-tailed female

• she has to mate members of the litter before she can make a conclusion

Tags

NGSS.HS-LS3-1

NGSS.HS-LS3-2

Crossing an individual that is homozygous recessive with an organism with an unknown genotype that exhibits a dominant phenotype is known as a what?

• Hybrid cross

• heterozygous cross

• test cross

• homozygous cross

How is a test cross performed in a laboratory setting?

• By crossing two individuals with the same recessive phenotype

• By crossing an individual with a dominant phenotype with an individual that is homozygous dominant for the trait

• By crossing an individual with a dominant phenotype but unknown genotype with an individual that is homozygous recessive for the trait in question.

• By crossing two individuals with the same dominant phenotype

Cross (Dad)Bb X (Mom)BB. List the possible genotypes from this cross.

• BB, Bb, bb

• BB

• BB, Bb

• bb,Bb

Tags

NGSS.HS-LS3-1

NGSS.HS-LS3-2

In a test cross, what is the purpose of using a homozygous recessive individual?

• To determine the genotype of the unknown parent

• To increase genetic diversity

• To produce only dominant phenotypes

• To ensure all offspring are recessive

Which of the following is a correct example of a test cross?

• Crossing a homozygous dominant with a homozygous recessive

• Crossing two heterozygous individuals

• Crossing a heterozygous individual with a homozygous recessive

• Crossing two homozygous recessive individuals

What is the expected phenotypic ratio in the offspring of a test cross if the unknown genotype is heterozygous?

• 1:1

• 3:1

• 1:2:1

• All dominant