DNA mutations

Question 1

What are mutations considered to be the source of?

Answer 1

genetic variation

Question 2

What are causes of mutations?

Answer 2

Environmental factors, spontaneous mutations, and errors during DNA replication

Question 3

What happens if DNA replication errors are not corrected?

Answer 3

Incorrect nucleotide bases are used as templates in future replication, propagating the mutation.

Question 4

What are spontaneous mutations?

Answer 4

Mutations that arise randomly and by chance without any known cause; most common type.

Question 5

How common are mutations at a single nucleotide?

Answer 5

very rare

Question 6

How do mutation rates vary across organisms?

Answer 6

Multicellular organisms have low mutation rates; viruses have higher rates, especially RNA viruses.

Question 7

Why do RNA viruses have higher mutation rates?

Answer 7

RNA backbone is delicate and lacks proofreading capability.

Question 8

What types of cells can acquire mutations?

Answer 8

Somatic cells and germline cells.

Question 9

What happens when a somatic cell mutates?

Answer 9

It produces a population of identical daughter cells with that mutation.

Question 10

How does timing of somatic mutation affect spread?

Answer 10

Earlier mutations affect larger regions of the body.

Question 11

Are somatic mutations passed to offspring?

Answer 11

no

Question 12

What mutations are passed to progeny?

Answer 12

germline mutations

Question 13

What happens when a germline mutation occurs?

Answer 13

Every cell in the embryo carries the mutation

Question 14

What did Joshua and Esther Lederberg test?

Answer 14

Whether mutations occur in response to environment or randomly.

Question 15

Joshua and Esther Lederberg: what method did they use

Answer 15

replica plating

Question 16

what is a non-selective plate

Answer 16

agar plate where all bacteria can grow

Question 17

what is a selective plate

Answer 17

agar plate containing penicillin where only resistant bacteria grow

Question 18

Joshua and Esther Lederberg: what happened after transferring colonies to a penicillin plate

Answer 18

only a few colonies survived

Question 19

Joshua and Esther Lederberg: what did surviving colonies indicate

Answer 19

they carried mutations for antibiotic resistance

Question 20

Joshua and Esther Lederberg: did resistance arise due to exposure to penicillin

Answer 20

no

Question 21

Joshua and Esther Lederberg: what was concluded from this experiment

Answer 21

Mutations occur randomly before exposure; environment selects beneficial mutations.

Question 22

Why are DNA repair mechanisms important?

Answer 22

Prevent cell death, cancer, aging, and disease.

Question 23

What are mutagens?

Answer 23

Agents like radiation or chemicals that increase mutation rates.

Question 24

What enzyme repairs DNA backbone breaks?

Answer 24

DNA ligase.

Question 25

What corrects mismatched nucleotides during replication?

Answer 25

DNA polymerase proofreading.

Question 26

How are mismatches detected?

Answer 26

they create a kink in DNA recognized by proteins.

Question 27

What happens during mismatch repair?

Answer 27

Nuclease cuts DNA, removes section, DNA polymerase and ligase repair it.

Question 28

what signals base excision repair?

Answer 28

Presence of uracil in DNA.

Question 29

Which enzyme removes uracil?

Answer 29

DNA uracil glycosylase.

Question 30

What happens after uracil removal?

Answer 30

AP endonuclease cuts backbone → gap formed → repaired by DNA polymerase and ligase.

Question 31

What does nucleotide excision repair fix?

Answer 31

Multiple damaged nucleotides.

Question 32

How does nucleotide excision repair work?

Answer 32

Removes damaged section → DNA synthesis fills gap.

Question 33

What are point mutations?

Answer 33

Single nucleotide pair changes.

Question 34

What are SNPs?

Answer 34

Single nucleotide polymorphisms (base substitutions).

Question 35

What is the most common point mutation?

Answer 35

Single nucleotide substitution.

Question 36

What is a missense mutation?

Answer 36

Changes amino acid (e.g., sickle-cell anemia).

Question 37

What happens in sickle-cell anemia?

Answer 37

Valine replaces glutamate in beta-globin → reduced oxygen binding.

Question 38

What is a silent mutation?

Answer 38

Codon change does not alter amino acid.

Question 39

What is a nonsense mutation?

Answer 39

Converts codon into stop codon → shorter protein.

Question 40

What is an insertion mutation?

Answer 40

Addition of nucleotides.

Question 41

What is a deletion mutation?

Answer 41

Removal of nucleotides.

Question 42

What happens if 3 nucleotides are deleted?

Answer 42

one amino acid is missing.

Question 43

What disease is caused by 3-nucleotide deletion?

Answer 43

Cystic fibrosis (CFTR transporter).

Question 44

Why is CFTR defective?

Answer 44

Protein unstable and degraded before reaching membrane.

Question 45

When do frameshift mutations occur?

Answer 45

Insertions/deletions not in multiples of 3.

Question 46

What is the effect of frameshift mutations

Answer 46

Alters codon grouping → often nonfunctional protein.

Question 47

What are chromosomal mutations?

Answer 47

Large-scale DNA changes visible under microscope.

Question 48

what are the four types of chromosomal mutations

Answer 48

Deletions, duplications, inversions, translocations.

Question 49

What is deletion?

Answer 49

Loss of chromosomal fragment.

Question 50

deletion: What if centromere is lost?

Answer 50

Chromosome lost in future divisions.

Question 51

deletion: effect in embryos

Answer 51

fatal

Question 52

What is duplication?

Answer 52

Extra copy of chromosomal region.

Question 53

possible effect of duplication

Answer 53

Can create new genes (duplication and divergence).

Question 54

what is inversion

Answer 54

Chromosome segment reversed.

Question 55

what are the consequences of inversion

Answer 55

Usually minimal but can affect gamete formation.

Question 56

What is translocation?

Answer 56

Exchange between non-homologous chromosomes.

Question 57

What is reciprocal translocation?

Answer 57

Two chromosomes exchange segments.

Question 58

potential issue of translocation?

Answer 58

Improper chromosome pairing → missing genes in offspring.

Question 59

How do gene families arise?

Answer 59

Gene duplication and mutation.

Question 60

Example gene family?

Answer 60

Beta-globin gene family.

Question 61

Function of beta-globin genes?

Answer 61

Oxygen transport in red blood cells.

Question 62

When did beta-globin evolution begin?

Answer 62

~200 million years ago

Question 63

Why are beta-globin genes similar?

Answer 63

Result of duplication and divergence.

Question 64

what is genomics

Answer 64

scientific field that sequences, interprets, and compares whole genomes

Question 65

how are complete genomes sequenced

Answer 65

- use a whole genome shotgun sequencing approach - genome is broken up into sets of overlapping fragments that are sequenced - sequences are then put in order

Question 66

what are the two main insights from the human genome project

Answer 66

1. genes for microRNAs are more common than previously thought 2. many sequences are Transcripts of Unknown Function (TUFs) because their role in the cell is unknown

Question 67

what was the expected number of human genes vs actual

Answer 67

100,000 vs 21,000

Question 68

what was found during the comparison of chimpanzee and human genes

Answer 68

- most protein-coding sequences are similar but theres differences in the regulatory sequences ~ causes phenotypic differences

Question 69

what has the human genome project revealed

Answer 69

common sets of genes that are mutated in cancerous cells; > 120 distinct mutations may be involved

Question 70

what did Dr. Talluah Andrews study

Answer 70

research focused on the analysis of single cell RNASeq data

Question 71

what did the complete genome sequences of cancerous and non-cancerous cells identify

Answer 71

over 600 mutations in the cancerous cells