Q: Which formula would you use to calculate the genetic distance in centimorgans (cM) between two loci based on the number of recombinant and total meiotic events?

$cM = \frac{\text{Number of recombinants}}{\text{Total informative meiotic events}} \times 100$

Question 1

In a twin study, 61% of monozygotic twins raised together are concordant for type II diabetes, while only 23% of dizygotic twins are concordant. What does this suggest about the heritability of type II diabetes?

Accepted Answer

Genetics has a greater influence than environment.

Question 2

Which of the following best describes the difference between monozygotic and dizygotic twins?

Accepted Answer

Monozygotic twins result from the division of a single fertilized egg, while dizygotic twins result from two separate fertilization events.

Question 3

If a trait shows similar concordance rates in both monozygotic and dizygotic twins, what is the most likely interpretation?

Accepted Answer

Environmental factors play a larger role than genetic factors in determining the trait.

Question 4

Which of the following is a major pitfall of twin studies when estimating heritability?

Accepted Answer

Monozygotic twins may not always share exactly the same environment or genetics due to de novo mutations and epigenetic differences.

Question 5

A de novo mutation is best defined as:

Accepted Answer

A genetic change that occurs spontaneously during gametogenesis or embryonic development, not inherited from either parent.

Question 6

In a pedigree analysis, which type of mutation is most likely to be detected using generational data and sequencing?

Accepted Answer

Monogenic mutations with large effect size.

Question 7

If a de novo mutation occurs during early embryonic development, what is the most likely outcome in terms of the distribution of the mutation in the individual's cells?

Accepted Answer

The individual may be a mosaic, with some cells carrying the mutation and others not.

Question 8

Which formula would you use to calculate the genetic distance in centimorgans (cM) between two loci based on the number of recombinant and total meiotic events?

Accepted Answer

$cM = \frac{	ext{Number of recombinants}}{	ext{Total informative meiotic events}} 	imes 100$

Question 9

A researcher compares the genome of a child with severe hypercholesterolemia to those of both parents and finds a mutation present only in the child. What type of mutation is this?

Accepted Answer

De novo mutation

Question 10

Why might two twin studies on height conducted in different populations yield different concordance rates for monozygotic and dizygotic twins?

Accepted Answer

Environmental and genetic factors can vary between populations, affecting heritability estimates.

Question 11

Which of the following best explains why twin studies do not always identify the specific genes involved in a trait?

Accepted Answer

Twin studies estimate heritability but do not pinpoint which genes are responsible.

Question 12

A mutation rate during DNA replication is approximately $1 	imes 10^{-10}$ nucleotides per division. If an individual has $10^{13}$ cell divisions during development, how many mutations would you expect per genome?

Accepted Answer

$10^{3}$ mutations

Question 13

Which of the following is NOT a variable that twin studies attempt to control for when estimating heritability?

Accepted Answer

The specific gene responsible for the trait

Question 14

In the context of de novo mutations, what is 'loss of heterozygosity' (LOH)?

Accepted Answer

A phenomenon where a cell loses the normal (wild-type) allele, leaving only the mutant allele, which can unmask a recessive mutation.

Question 15

Which of the following best describes a mosaic de novo mutation?

Accepted Answer

A mutation that occurs after fertilization, resulting in some cells carrying the mutation and others not.

Question 16

Why is it important to compare the genome sequence of a child with both parents when searching for de novo mutations?

Accepted Answer

To identify mutations present in the child but absent in both parents, confirming they are de novo.

Question 17

Which of the following statements about concordance in twin studies is correct?

Accepted Answer

Concordance measures how similar a trait is between two individuals, such as twins.

Question 18

A pedigree shows a mutation that appears in a child but not in either parent. What is the most likely explanation?

Accepted Answer

A de novo mutation occurred during gametogenesis or early embryonic development.

Question 19

Which of the following is a limitation of using pedigrees to study genetic diseases?

Accepted Answer

Pedigrees are less effective for detecting polygenic or de novo mutations with small effect sizes.

Human Genetics Sep 26

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