Pedigree

Simulation Activity

Pedigree

1.1 Section Title

Simulation Activity

After you've tried the simulation at least once, click the button below to answer questions showing that you've understood the concepts covered here.

Simulation Assessment

You must try the simulation before answering the questions.

This simulation draws pedigrees, based on the ratios you learned in Chapters 16 and 17. Select a mode of inheritance and other settings, then click "Generate Pedigree" to see one possibility for the inheritance of a single trait, based on the settings you choose. Click "Show Carriers" to see which individuals are unaffected, but have one allele for the trait. Clicking "Generate Random Pedigree" draws a family tree and hides the mode of inheritance and parental genotypes. Can you determine the mode of inheritance for the randomly drawn trees, based on who is and is not affected?

After you've tried the simulation at least once, click the button below to answer questions showing that you've understood the concepts covered here.

Simulation Assessment

Question 1 of 8

Questions

Question

Using the following settings, press "Generate Pedigree" (NOT "Generate Random Pedigree") three to six times, and notice the frequency of affected sons and daughters in the F₁ to F₄ progeny.

Settings:
Mode of inheritance - X-linked recessive
Parental generation -
Male - Nonmutant
Female - Heterozygous
Matings between relatives - disallow
Progeny in first generation - 4
Show carriers - turn on

Why aren't there any affected females in the F₁ generation under these conditions?

There is only one affected allele segregating in the pedigree.

Only males can be affected because the trait is X-linked recessive.

The recessive allele is less likely to be inherited than the mutant allele.

X-linked traits are only seen in males.

Correct.

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Incorrect.

Question

Using the following settings, press “Generate Pedigree” three to six times, and notice the frequency of affected sons and daughters in the F₁ to F₄ progeny.

Settings:
Mode of inheritance – Y-linked
Parental generation –
Male – Mutant
Female – Homozygous nonmutant
Matings between relatives – disallow
Progeny in first generation – 4
Show carriers – turn on

Why aren’t there any affected females in the F₁ to F₄ generations under these conditions?

There could be affected females, but the simulation would have to be run many more times.

Only males can be affected because the trait is linked to the Y chromosome.

Females cannot be affected because the allele is on the inherited paternal X chromosome.

Only males can be affected because they only receive one X chromosome from their mother.

Correct.

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Incorrect.

Question

Using the following settings, press “Generate Pedigree” three to six times, and notice the frequency of affected sons and daughters in the F₁ to F₄ progeny.

Settings:
Mode of inheritance – Dominant
Parental generation –
Male – Heterozygous
Female - Heterozygous
Matings between relatives – disallow
Progeny in first generation – 4
Show carriers – run simulation three times with “show carriers” on, and three times with “show carriers” off

A carrier is an individual who has an allele associated with a trait but does not display the trait. They are, however, able to pass on the allele to their offspring. When setting the simulation’s conditions as described above, why does it make no difference whether or not you turn on “show carriers”?

Only individuals with two mutant alleles are affected and so there cannot be any carriers for this trait.

Only individuals with two mutant alleles are affected. All individuals with the disease are also carriers.

Individuals with one mutant allele express the disease phenotype and so cannot be carriers.

Individuals with one mutant allele do not express the disease phenotype and so can only be carriers.

Correct.

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Incorrect.

Question

Using the following settings, press “Generate Pedigree” three to six times, and notice the frequency of affected sons and daughters in the F₁ to F₄ progeny.

Settings:
Mode of inheritance – Recessive
Parental generation –
Male – Homozygous mutant
Female – Homozygous nonmutant
Matings between relatives – disallow
Progeny in first generation – 4
Show carriers – turn off

Why aren’t there any affected individuals in the F₁ generation?

Two recessive alleles are required to express the phenotype, and F₁ individuals always receive one nonmutant allele from the unaffected parent.

Two recessive alleles are required to express the phenotype, and F₁ individuals always marry individuals that are not affected.

One recessive allele is required to express the phenotype, and F₁ individuals only have a 50% chance of inheriting the mutant allele.

One recessive allele is required to express the phenotype, and F₁ individuals that are the same sex as the affected parent have a 50% chance of inheriting the mutant allele.

Correct.

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Incorrect.

Question

Using the following settings, press “Generate Pedigree” three to six times, and notice the frequency of affected sons and daughters in the F₁ to F₄ progeny.

Settings:
Mode of inheritance – Recessive
Parental generation –
Male – Heterozygous
Female – Heterozygous
Matings between relatives – disallow
Progeny in first generation – 4
Show carriers – turn on

Why is there a higher number of carriers than affected individuals?

Offspring inherit alleles from their parents. Since both parents are carriers, the offspring are more likely to be carriers.

Offspring have a 50% chance of being a carrier, but only a 25% chance of being affected.

Offspring have a 25% chance of being a carrier, and a 50% chance of being affected.

Offspring that are homozygous for a recessive trait usually die. Carriers will live, so more of them are present in the pedigree.

Correct.

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Incorrect.

Question

Using the following settings, press “Generate Pedigree” three to six times, and notice the frequency of affected sons and daughters in the F₁ to F₄ progeny.

Settings:
Mode of inheritance – X-linked dominant
Parental generation –
Male – Mutant
Female – Heterozygous
Matings between relatives – disallow
Progeny in first generation – 4
Show carriers – turn off

Why are all daughters, but only some sons, affected in the F₁ generation?

Females pass one of their X chromosomes to their daughters, so all daughters in the F₁ will have the disease.

Females pass one of their X chromosomes to their sons, so at least half of all the sons in the F₁ will have the disease.

Fathers pass on their X chromosome to their daughters, so all daughters in the F₁ will have the disease.

Fathers pass on their X chromosome to their sons, so all of the sons in the F₁ will have the disease.

Correct.

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Incorrect.

Question

Using the following settings, press “Generate Pedigree” three to six times, and notice the frequency of affected sons and daughters in the F₁ to F₄ progeny.

Settings:
Mode of inheritance – Recessive
Parental generation –
Male – Heterozygous
Female – Homozygous mutant
Matings between relatives – disallow
Progeny in first generation – 4
Show carriers – turn on

Why is there a higher number of carriers than affected individuals?

Since both parents have disease alleles, all the offspring will inherit at least one mutant allele.

Offspring have a 75% chance of inheriting at least one mutant allele, but only a 50% chance of having the disease.

Offspring have a 75% chance of inheriting at least one mutant allele, but only a 25% chance of having the disease.

Offspring that are homozygous for a recessive trait usually die. Carriers will live, so more of them are present in the pedigree.

Correct.

You have one more chance to answer the question correctly. Try again.

Incorrect.

Question

Using the following settings, press “Generate Pedigree” three to six times, and notice the frequency of affected sons and daughters in the F₁ to F₄ progeny.

Settings:
Mode of inheritance – Recessive
Parental generation –
Male – Homozygous mutant
Female – Homozygous mutant
Matings between relatives – disallow
Progeny in first generation – 4
Show carriers – turn off

Why are all the offspring in the F₁ generation affected?

Because offspring reflect a mix of the parental phenotypes, all offspring of affected parents are affected.

All offspring in the F₁ generation will not always be affected; the simulation just hasn’t been run enough times to show an alternate outcome.

All gametes produced that combine to make up the F₁ generation have the mutant allele. It is impossible to have a carrier in the F₁ generation.

All gametes produced that combine to make up the F₁ generation have the mutant allele. Some of the offspring should be carriers of the mutant allele.

Correct.

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Incorrect.

Chapter 1. Pedigree

1.1 Section Title

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