Genetics Answers

3) Chemical elements of tobacco smoke can change the nucleotide sequence in a DNA molecule by

replacing adenine with thymine or guanine with cytosine. Which kind of mutation is this one? Draw and

explain the mechanisms and consequences of such a change.

1) A.I., a 6-year-old boy, is undergoing examination due to a slight developmental delay. He has

difficulty climbing stairs, running, has reduced physical strength and low endurance during intense physical

exercise. Muscle biopsy results showed a pronounced change in muscle fiber size.

Based on these results, the child has a preliminary diagnosis of having Duchene muscular dystrophy

(DMD). Duchene muscular dystrophy is a serious recessive disease linked to the X chromosome, which is

characterized by the rapid progression of muscular dystrophy, which ultimately leads to a complete loss of

the patient’s ability to move and consequent death.

To confirm diagnosis and determine the mutation in the dystrophic gene in A.I, DNA diagnostics

were performed. Aberrations were found in the coding part of the gene

Questions for discussion:

1. What type of mutation causes Duchene muscular dystrophy?

2. Describe the mechanism of mutation occurrence. What are the consequences of this mutation?

3. Determine the genotypes of parents and the patient.

4. Determine the risks for the next child to have the same illness.

1) A large number of DNA disorders occur in human cells. Up to 10,000 DNA damage can be recorded

daily in our body. However, the action of genetic homeostasis mechanisms allows maintaining the relative

constancy of the cell genotype.

1. What do you know about the main ways to maintain genetic cell homeostasis? What are they

characterized by?

2. In what phases of the mitotic cycle can DNA damage be corrected?

3. What environmental factors can lead to genetic disorders?

4. What are the consequences of genotype violations in somatic cells if they are not corrected?

4) When so much damage occurs in DNA that during excision reparation the cell does not have time to

completely eliminate them. As a result, after replication of this DNA the daughter chain has “gaps” that are

formed at the site of damage of the mother DNA chain,.

1. What type of reparation corrects such damage?

2. What are the molecular mechanisms the cause of this disorder?

3. Feature of postreplication reparation.

4. What other types of postreplication reparation do you know, describe.

3) A 3-year-old boy, was sent to a dermatology clinic due to a pronounced sensitivity to sunlight and the

appearance of multiple skin spots. Clinical examination revealed photophobia, conjunctivitis and significant

lentiginous hyperpigmentation of unprotected from the sun skin surface; otherwise, its development and

inspection data were normal. Child-patient is from an unrelated marriage.

The dermatologist said that the child has a classic manifestation of pigment xerodermia. To confirm the

diagnosis, a skin biopsy was performed to evaluate DNA reparation. The results of this test confirmed the

diagnosis of pigment xerodermia. Despite appropriate preventive measures, at the age of 15 the child got

metastatic melanoma and died after 2 years. His parents have two other children; no one of them is sick

with pigment xerodermia.

Issues for discussion:

1. What type of reparation is knocked out by pigment xerodermia?

2. What are the molecular mechanisms of reparation of this disorder?

3. Determine the genotypes of parents, all children.

4. Calculate the risk of having sick children in this family.

5. Make a comparative characteristic with photoreactivation.

1. A DNA fragment encoding a polypeptide has a following order of nitrogenous bases:

AAAACCAAAATACTTATACAA. During replication, the third adenine on the left was cut from the

chain. Determine the structure of the polypeptide chain encoded by this DNA region according to normal

and mutated condition. Identify the type of gene mutation.

What is a frequency distribution? Explain how the graph is made for a quantitative trait that is continuous.

Explain the difference between a continuous trait and a discontinuous trait. Give two examples of each. Are quantitative traits likely to be continuous or discontinuous? Explain why

transcribe the following dna code from the nucleus to the mrna molecule

TAC - GGA - CAG - GCG - CCG - CAA - CGC -TAT - ACT

 What evolutionary factors can cause allele frequencies to change and possibly lead to a genetic polymorphism? Discuss the relative importance of each type of process.