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A child with trisomy 18 has the genotype AAA for one of the genes on chromosome 18. The parents' genotypes are AA (mom) and Aa (dad). Consider the following statement: "Nondisjuction must have occurred in mom." Is this statement correct or incorrect? Support your answer with an explanation.

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Deanna Hettinger
Deanna HettingerLv2
28 Sep 2019

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Related questions

Nondisjuction is a cell division error in which either homologous chromosomes or sister chromatids fail to separate and thus do not migrate to opposite poles. It is responsible for conditions such as monosomy (one member of a chromosome pair is missing) and trisomy (three copies of a chromosome is present rather than two).

Nondisjunction can occur during the first or second meiotic division.

Part A- Jill is heterozygous for gene A and is going to have a child with Jack, who is homozygous recessive for gene A.

Which of the following offspring genotypes could result from fertilization of a normal haploid sperm with an egg that had undergone nondisjunction in meiosis I?
Check all that apply.

1)AAa

2)Aaa

3)aaa

4)Aa

5)aa

6)a

I put AAa, Aaa, Aa, but it was not correct

Part B-

Which of the following offspring genotypes could result from fertilization of a normal haploid sperm with an oocyte that had undergone nondisjunction in meiosis II?

Check all that apply.

1)AAa

2)Aaa

3)aaa

4)Aa

5)aa

6)a

Part E-

If Jack and Jill have a child with an aaa genotype, during which meiotic division, and in which parent, could nondisjunction have occurred?

Check all that apply.

1) Meiosis I in the mother

2 Meiosis II in the mother

3) Meiosis I in the father

4) Meiosis II in the father

The answer is not Meisis I in the mother

1) Enter a numerical decimal fraction.Last week you were wondering what Jessica and Tom's babies might look like with respect to their eyebrows and earlobes (both Tom and Jessica have thick eyebrows, controlled by gene E, with thick eyebrows dominant to thin eyebrows, and both of them have free earlobes, controlled by gene F, with free earlobes dominant to attached earlobes). You know that Tom's mom has attached earlobes. Additionally, Tom's mom has thin eyebrows, and so does Jessica's dad. No one in Jessica's pedigree going back to her great grandparents are known to have had attached earlobes, so you assume that she must be homozygous for this trait. If your inferences based on their known pedigrees are correct, what is the probability that Jessica's and Tom's first baby will have free earlobes and thin eyebrows?

2)

Years pass, and Jessica and Tom just had a kid, and they send you a picture of the three of them. You are surprised to see that the baby has thin eyebrows and attached earlobes.

What does this tell you?

Select all the answers that apply:

Select one or more:

a. At least some of Jessica's direct ancestors must be carriers for the recessive allele of gene E, including at least one of her parents.

b. Jessica's dad must be 'true-breeding' for both gene E and gene F.

c. Jessica's mom must be a carrier for gene E.

d. Jessica's genotype must be Ee Ff.

e. Given what you know now about Jessica and Tom's genotypes after seeing their first baby, you realize that prior to inception, the chances of their child showing the thin eyebrow, attached earlobe phenotype was only 1/16.

f. Tom's genotype must be Ee ff.

9. Identify each of the following statements as TRUE or FALSE (remember to provide

reasoning to justify your answer).

i. If a pair of loci exhibits significant linkage disequilibrium, those loci must be

physically linked on the same chromosome.

ii. Each of us received half of our mitochondrial DNA from our mom and half

from our dad, but the paternally inherited alleles are always recessive, so the

maternal contribution determines the phenotype.

iii. For populations in which individuals preferentially mate with their close

relatives, there will tend to be an excess of homozygous individuals relative to

the expectations of Hardy-Weinberg equilibrium.

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