Lecture 15 - Mutations 1

Question 1

What are mutations?

Answer 1

Randomly derived changes in the nucleotide sequences of the DNA of an organism, that can be passed on to daughter cells

Question 2

Two types of mutations

Answer 2

1. Somatic mutations

2. Germ line mutations

Question 3

What are somatic mutations?

Answer 3

They are mutations that occur in the somatic (body) cells.

They are passed on by mitosis but not to sexually produced offsprings.

Question 4

What are germ line mutations?

Answer 4

They are mutations that occur in germ line cells (the cells that give rise to gametes).
A gamete passes a mutation on at fertilization

Question 5

Three different phenotypic effects of mutations

Answer 5

1. Silent mutations
2. Gain or loss of function mutations
3. Conditional mutations

Question 6

What are silent mutations?

Answer 6

Mutations that do not significantly alter the phenotype of the organism in which they occur

Question 7

What are gain or loss of function mutations?

Answer 7

Mutations that lead to a protein with new (altered) function or to a non-functional protein

Question 8

What are conditional mutations?

Answer 8

A mutation that has the wild-type phenotype under certain (permissive) environmental conditions and a mutant phenotype under other (restrictive) conditions.

Question 9

Benefits of mutations

Answer 9

-Drive evolution in the form of genetic diversity.
Diversity may benefit the organism immediately - if mutation is in somatic cells or may cause an advantageous change in the offspring

Question 10

Possible cost of mutations

Answer 10

Some germ line and somatic cell mutations are harmful or lethal

Question 11

Two different nucleotide mutations

Answer 11

1. Chromosomal mutations

2. Point mutations

Question 12

What are chromosomal mutations?

Answer 12

They may change position or cause a DNA segment to be duplicated or lost

Question 13

What is a chromosomal deletion?

Answer 13

It is the loss of a chromosome segment

Question 14

What is a chromosomal duplication and deletion?

Answer 14

It results when homologous chromosomes break at different points and swap segments

Question 15

What is a chromosomal inversion?

Answer 15

It results when a broken segment is inserted in reverse order

Question 16

What is a chromosomal reciprocal translocation?

Answer 16

Results when non-homologous chromosomes exchange segments

Question 17

What are point mutations?

Answer 17

They result from the gain, loss, or substitution of a single nucleotide

Question 18

What is a transition mutation?

Answer 18

It happens when a purine is substituted for another purine (GA) or pyrimidine for another pyrimidine (CT)

Question 19

What is a transversion mutation?

Answer 19

It happens when a purine is substituted by a pyrimidine or vice versa

Question 20

What is the open reading frame?

Answer 20

The part of a reading frame that has the potential to be translated

Question 21

Missense mutations

Answer 21

Point mutation in which a single nucleotide change results in a codon that codes for a different amino acid

Question 22

Nonsense mutations

Answer 22

Point mutation in which a single nucleotide change results in a stop codon to form resulting in a shortened protein, which is usually not functional

Question 23

Readthrough mutations

Answer 23

Involve a base substitution that causes a stop codon to be converted into an amino acid codon which results in a lengthened protein

Question 24

AAs with polar but uncharged R groups

Answer 24

Serine, Threonine, Glutamine, Asparagine

Question 25

AAs with positively charged R groups

Answer 25

Lysine, Arginine, Histidine

Question 26

AAs with negatively charged R groups

Answer 26

Glutamic Acid, Aspartic Acid

Question 27

Special AAs

Answer 27

Cysteine, Glycine, Proline

Question 28

AAs with hydrophobic R groups

Answer 28

Isoleucine, Leucine, Methionine, Phenylalanine, Tryptophan, Valine Alanine, Tyrosine

Question 29

Explain frameshift mutations

Answer 29

These mutations interfere with the ORF of a protein-coding gene

Question 30

Phenotypic consequences of frameshift mutations

Answer 30

Non-functional (truncated)proteins are produced. Unless it happens at the extreme 3’ end of the gene

Question 31

Two ways in which mutations can arise

Answer 31

1. Spontaneous mutations

2. Induced mutations

Question 32

What are spontaneous mutations?

Answer 32

Permanent changes in the genetic material that occur without any outside influence. Occur because cellular processes are imperfect

Question 33

What are tautomers?

Answer 33

Each of the four nucleotide bases can exist in two different forms, called tautomers, one of which is common and one is rare

Question 34

Mechanisms by which spontaneous mutations can arise (Lots of examples just name a few)

Answer 34

1. The four nucleotide bases of DNA can have different structure. When a base temporarily forms its rare tautomer, it can pair with the wrong base.
2. Bases in DNA may change because of a chemical reaction. Like the deamination of cytosine.
3. DNA polymerase can make errors in replication.
4. Meiosis is not perfect. Nondisjunction can occur, leading to one too mane or one too few chromosomes.

Question 35

How do induced mutations occur?

Answer 35

They occur when some agent from outside the cell, a mutagen, causes a permanent change in DNA

Question 36

Examples of induced mutations (Lots of examples just name a few)

Answer 36

1. Some chemicals can alter the nucleotide bases. For example, nitrous acid (HNO2) can react with cytosine and convert it to uracil by deamination.
2. Some chemicals add groups to the bases. For example, benzopyrene adds a large chemical group to guanine, making it unavailable for base pairing.
3. Radiation damages the genetic material. First, ionizing radiation (X rays, gamma rats) produces highly reactive chemicals called free radicals. Free radicals an change bases in DNA to forms that are not recognized by DNA polymerase. Second, ultraviolet radiation can damage DNA in another way. It is absorbed by thymine, causing it to form covalent bonds with adjacent bases, also distorting the double helix.