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Questions and Answers

What is a common effect of aneuploidy in humans?

Resistance to cancer

Increased fertility

Spontaneous miscarriages (correct)

Enhanced cognitive abilities

Which of the following is NOT a way in which mutations can result?

DNA copying mistakes during cell division

Normal cell differentiation (correct)

Exposure to non-ionizing radiation

Infection by viruses

What is the frequency of genomic mutations that involve changes in chromosomal structure?

1/1000 cell divisions

1/1700 cell divisions (correct)

1/500 cell divisions

1/25-50 cell divisions

Which type of mutation is associated with Down syndrome?

Genomic mutation: aneuploidy Signup and view all the answers

What is the effect of genomic mutations on fertility?

Makes reproduction incompatible with life Signup and view all the answers

What is the primary mechanism of mutations resulting from exposure to ionizing radiation?

Chromosomal breaks and rearrangements Signup and view all the answers

What is the definition of polymorphism?

A variation in the DNA sequence present at a frequency greater than 1 to 3% Signup and view all the answers

What is the general effect of aneuploidy on cancer cells?

It is more common in cancer cells Signup and view all the answers

What is a common location where genetic mutations are found?

In cancer cells Signup and view all the answers

What is a consequence of a nonsense mutation?

A premature stop in translation Signup and view all the answers

What type of mutation can be caused by both insertions and deletions?

Frameshift mutation Signup and view all the answers

What is a characteristic of synonymous mutations?

They do not change the amino acid sequence Signup and view all the answers

What is a result of a mutation in a germline cell?

The offspring will definitely receive the mutation Signup and view all the answers

What is a difference between transitions and transversions?

Transition is a change from one purine to another, while transversion is a change from one purine to one pyrimidine Signup and view all the answers

What type of mutation occurs when there is a change in a base that does not alter the amino acid sequence?

Synonymous mutation Signup and view all the answers

What is a consequence of a missense mutation?

A change in the amino acid sequence Signup and view all the answers

What is the primary difference between a mutation and a polymorphism in terms of disease causality?

A mutation always causes a disease, while a polymorphism does not Signup and view all the answers

What type of genetic variation is characterized by variations in the number of copies of long genome segments?

Polymorphism of the number of copies Signup and view all the answers

What is a characteristic of genetic diseases related to trinucleotide repeats?

They are inherited in a Mendelian pattern Signup and view all the answers

What is true about the affected regions in polymorphisms of the number of copies?

They are too small to be seen cytogenetically Signup and view all the answers

What is the main difference between the inheritance pattern of a mutation and a polymorphism?

Mutations have a clear inheritance pattern, while polymorphisms do not Signup and view all the answers

What is the primary reason why genetic diseases related to trinucleotide repeats are difficult to diagnose?

The affected regions are too small to be seen cytogenetically and too long to be sequenced Signup and view all the answers

Study Notes

Mutations and Polymorphisms

Mutations are rare in population and recent in evolution, while polymorphisms are common in population and old in evolutionary terms.
Mutations have a strong effect, while polymorphisms have a weak effect or no effect.

Origin of Mutations

Mutations can result from:
- DNA copying mistakes during cell division
- Exposure to ionizing radiation
- Exposure to chemicals called mutagens
- Infection by viruses

Classification of Mutations

Genomic mutations:
- Alterations in the number of intact chromosomes (aneuploidy)
- Alterations of the structure of individual chromosomes
Genetic/Molecular mutations:
- Alterations in individual genes
- Substitutions, deletions, and insertions on a small scale

Genomic Mutations

Changes in the number of chromosomes (aneuploidy):
- Most common mutation in humans (1/25-50 cell divisions)
- Causes spontaneous miscarriages
- Common in cancer cells
Changes in chromosomal structure:
- Alteration in the structure of individual chromosomes
- Involves only part of a chromosome
- Frequency: 1/1700 cell divisions
- Generally incompatible with life or normal reproduction
- Common in cancer cells

Genetic Mutations

Alter individual genes
Two basic mechanisms:
- Errors in DNA replication
- Mutations in the DNA mismatch repair system

Classification of Genetic Mutations

Substitutions:
- Can be transitions (change of one purine for another purine) or transversions (change of one purine by one pyrimidine or the opposite)
- Can be:
  - Missense (change in amino acid sequence)
  - Nonsense (inserts an artificial STOP codon, finishing translation prematurely)
  - Synonymous (change in base but no change in amino acid encoded due to the degeneration of the genetic code)
  - Silent (occurs in a non-coding region)
Insertions and deletions:
- Can cause frameshift mutations
- Can alter the amino acid sequence

Inheritance and Consequences

Not all mutations have clinical consequences:
- Silent mutations
- Synonymous mutations
If the mutation occurs in a germline cell, the change will be inheritable
If the mutation occurs in a somatic cell, the offspring will not receive it

Variations in the number of copies of long genome segments
Affected regions are too small to be seen cytogenetically and too long to be sequenced

Polymorphisms of the Number of Copies

Variations in the number of copies of long genome segments
Affected regions are too small to be seen cytogenetically and too long to be sequenced

Comparison of Mutations and Polymorphisms

Mutation:
- Usually causes a disease
- Follows a Mendelian inheritance pattern
- Not frequent in population
Polymorphism:
- Causes increased risk, but not direct disease
- No clear pattern of inheritance
- Common in population

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