IMAT - International Medical Admissions Molecular Genetics and Inheritance Questions and Answers

Question 1

A scientist analyzing a sample of DNA finds that it contains 28% adenine. Based on Chargaff's rules, what percentage of guanine should be present in this sample?

Accepted Answer

22%

Answer

According to Chargaff's rules, the amount of adenine (A) is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). If adenine is 28%, then thymine is also 28%, making the total for A+T = 56%. The remaining percentage for G+C is 100% - 56% = 44%. Since G equals C, the percentage of guanine is 44% / 2 = 22%.

Question 2

In a dihybrid cross between two heterozygous individuals (AaBb), what is the expected phenotypic ratio of the offspring if the genes assort independently?

Accepted Answer

9:3:3:1

Answer

This is a classic Mendelian dihybrid cross. When two individuals heterozygous for two independently assorting traits are crossed, the offspring exhibit a phenotypic ratio of 9:3:3:1. This ratio represents the four possible combinations of the two traits: 9/16 will show both dominant phenotypes, 3/16 will show the first dominant and second recessive phenotype, 3/16 will show the first recessive and second dominant phenotype, and 1/16 will show both recessive phenotypes.

Question 3

A frameshift mutation is caused by which of the following events?

Accepted Answer

The insertion or deletion of one or more nucleotides.

Answer

Frameshift mutations occur when nucleotides are inserted or deleted from the DNA sequence in a number that is not a multiple of three. This alters the reading frame of the codons during translation, leading to a completely different and usually non-functional protein from the point of the mutation onwards.

Question 4

In the lac operon of E. coli, what is the role of allolactose?

Accepted Answer

It functions as an inducer, inactivating the repressor protein.

Answer

The lac operon is an inducible operon. In the presence of lactose, some of it is converted to allolactose. Allolactose acts as an inducer by binding to the repressor protein, causing a conformational change that prevents the repressor from binding to the operator. This allows RNA polymerase to transcribe the structural genes needed for lactose metabolism.

Question 5

A man with type A blood and a woman with type B blood have a child with type O blood. What is the probability that their next child will have type AB blood?

Accepted Answer

25%

Answer

For a child to have type O blood (genotype ii), they must inherit a recessive 'i' allele from each parent. This means the man with type A blood must have the genotype I^A i, and the woman with type B blood must have the genotype I^B i. A Punnett square of this cross (I^A i x I^B i) shows the possible offspring genotypes are I^A I^B (Type AB), I^A i (Type A), I^B i (Type B), and ii (Type O), each with a 25% probability.

IMAT - International Medical Admissions Test Practice Test

IMAT - International Medical Admissions Test Practice Test

IMAT - International Medical Admissions Molecular Genetics and Inheritance Questions and Answers