Chap 4- Principles of Genetic Variation, DNA damage and repair

Question 1

Genetic locus

Answer 1

address for variations in DNA

Question 2

homozygotes

Answer 2

identical alleles from mother and father

Question 3

heterozygotes

Answer 3

different alleles from mother and father

Question 4

p arm

Answer 4

short arm of chromosome

Question 5

q arm

Answer 5

long arm of chromosome

Question 6

how to read chromosome location

Answer 6

Chromosome number, which arm, region, band, sub-band

Question 7

outcome of mutations

Answer 7

• normal phenotype
• disease phenotype
• no effect
• beneficial effect

Question 8

SNP

Answer 8

• single nucleotide polymorphism
• one nucleotide replaced by another
• quantity of DNA remains same
• do not usually cause a problem, most common type of mutation

Question 9

trisomy

Answer 9

having an extra chromosome

Question 10

deletion

Answer 10

loss of genetic material

Question 11

point mutation

Answer 11

small scale mutation only effecting a few nucleotides, usually don’t cause problem

Question 12

polymorphism

Answer 12

genetic mutation that occurs in greater than 1% of population

Question 13

rare mutations

Answer 13

occur in less than 1% of population

Question 14

hygiene hypothesis

Answer 14

being “dirty” helps to make immune system strong because you are exposed to many more pathogens, able to undergo change

Question 15

purifying (negative) selection

Answer 15

• when genetic variation is so bad lower survival rate or reproductive capacity
• harmful mutations will slowly be eliminated over time

Question 16

positive darwinian selection

Answer 16

• give advantage to people who have good/required mutations

- have higher survival rates and reproductive rates

Question 17

origins of DNA sequence variation

Answer 17

• DNA replication errors
• chromosome segregation and recombination errors
• endogenous chemical damage (most common!)
• exogenous chemical damage

Question 18

how frequent are DNA replication errors?

Answer 18

1 incorrect base for every 1 million nucleotides

Question 19

replication slippage

Answer 19

• certain parts of DNA that have tandem repeat nucleotides do not get replicated
• reach large area of repeated sequence, skips this area and forms a loop in the DNA, loop in additional replications leads to expansion

Question 20

misaligned cross over

Answer 20

• occurs during meiosis prophase I
• exchanges unequal amount of genetic material
• leads to deletions or mutations

Question 21

nondisjuction

Answer 21

chromosomes do not separate properly, causes unequal distribution of genetic material

Question 22

is extra genetic info more tolerated in sex chromosomes or somatic chromosomes?

Answer 22

sex chromosomes

Question 23

base modification

Answer 23

add chemical component to a base i.e. methylation

Question 24

crosslinking

Answer 24

• unwanted connections in DNA

- can sometimes be caused by base modifications

Question 25

hydrolytic DNA damage

Answer 25

- loss of water molecule - disrupts bond between base and sugar, leaves abasic site - common result is loss of purine or pyrimidine

Question 26

glycolytic bonds

Answer 26

connect sugar with base

Question 27

phosphodiester bonds

Answer 27

connect sugar with phosphate

Question 28

aberrent DNA methylation

Answer 28

- cytosine commonly gets methylated - SAM acts as methyl donor - abnormal methylation -> transcription factors cant bind to DNA, DNA replication effected - converts euchromatin to heterochromatin

Question 29

oxidative damage

Answer 29

damage due to ROS

Question 30

ionizing radiation

Answer 30

- x-rays or gamma rays | - generate ROS and causes double stranded DNA breaks

Question 31

non-ionizing radiation

Answer 31

- can cause cross linking - linking between adjacent pyrimidines - creates thymine dimers

Question 32

mutagenic chemicals

Answer 32

- cause DNA adducts which are bulky additions to DNA | - distort stability of DNA

Question 33

types of single strand DNA repair

Answer 33

- base excision repair - nucleotide excision repair - mismatch repair

Question 34

types of double strand DNA repair

Answer 34

- non-homologous end joining | - homologous recombination

Question 35

base excision repair

Answer 35

- occurs when something happens to a single base | - base is cut out and repaired

Question 36

DNA mismatch repair

Answer 36

- repairs errors that occur during replication and recombination - identify the area that has mismatch, DNA makes a loop with faulty region that is is then removed and replaced with new nucleotides - loop is made with help of mut proteins

Question 37

nucleotide excision repair

Answer 37

- repairs DNA damage caused by UV rays - UV rays causes dimers and cross linking - uses Uvr proteins to scan for damage, cut out damage, replace nucleotides

Question 38

homologous recombination

Answer 38

- help of homologous DNA as template to repair DNA - can lead to loss of particular area in DNA - available for cells during G2

Question 39

non-homologous end joining

Answer 39

- usually during G1 phase - no template strand needed - part of DNA resected, joined together - can result in loss of part of DNA

Question 40

C-T mutations

Answer 40

- very common hotspot for mutation - cytosine is easily methylated - deamination and methylation can cause switch to thymine - since thymine normally in DNA can go undetected while checking for errors

Question 41

C-U muations

Answer 41

- c can be deaminated - deamination can result in change to Uracil - uracil DNA glycolase recognizes U, cuts it out - because U isnt normally found in DNA it is commonly fixed