Lecture 2: Mutation, Variation and genome organisation

Question 1

What are mutation?

Answer 1

• the failure to store genetic information faithfully.
• affect whole chromosome or single genes
• spontaneous or induced
• harmful, neutral or beneficial
• the source of ALL genetic variation
• necessary for natural selection and evolution

Question 2

Causes of mutation.:

Answer 2

induced mutations- radiation, UV, X-rays. Anything that increases chemical reactivity in the cells - MUTAGEN
e.g. Chernobyl 1986
Fukushima 2011

Question 3

Karyotype..

Answer 3

is simply a picture of a person’s chromosomes

Question 4

Humans chromosomes are present in..

Answer 4

pairs they’re diploid.

23 pairs, 2n = 46

Question 5

Gametic cells are

Answer 5

(egg and sperm)

haploid!

Question 6

Chromosomal variation:

Answer 6

• Polyploidy
• Aneuploidy
• Translocations
• Deletions
• Inversions

Question 7

Polyploidy:

Answer 7

cells and organisms are those containing more than two paired (homologous) sets of chromosomes.

Question 8

Bacteria are usually…Diploid, monoploid or dispermy?

Answer 8

MONOPLOID

Question 9

If greater than 2 sets of chromosomes i.e. dispermy

Answer 9

results in 3 complete sets of chromosomes; 3n = 69.

Happens in 1-3% of conceptions - ALWAYS LETHAL .

Question 10

Dispermy-

Answer 10

fertilisation of one egg by two sperm

Question 11

Polyploidy in higher plants is

Answer 11

common. Related species often vary in ploidy.

Question 12

Aneuploidy is when

Answer 12

one set of chromosomes is incomplete. e.g. a chromosome is missing, an extra chromosome is present

Question 13

Autosome..

Answer 13

any chromosome that is not a sex chromosome

Question 14

Nullisomy:

Answer 14

Autosomes when both members of a pair are missing - lethal

Question 15

Monosomy:

Answer 15

Autosomes when one member of a pair is missing - lethal

Question 16

Trisomy:

Answer 16

Autosomes when one extra chromosome; usually lethal

Question 17

Trisomy 21 -

Answer 17

Down syndrome.

Longevity = 40+ not considered lethal

Question 18

Aneuploidy in sex chromomses..

Answer 18

Lacking a chromosome:
45X - Turner’s syndrome
45Y - Inviable
Extra chromosomes: 47XYY, 47XXY, 47XXX Minor effects

Question 19

Translocations:

Answer 19

Exchange of parts between NON-HOMOLOGOUS chromosomes

Question 20

Homologous chromosomes..

Answer 20

=chromosomes that contain alleles for the same gene

Question 21

Translocation;

carriers and offspring

Answer 21

carriers are normal

Offspring can have the wrong number of copies of each chromosome - usually lethal

Question 22

Deletions:and example

Answer 22

• Part of a chromosome is missing
• Patient only has one copy of each gene in that region
• severity depends on size of missing region
• chromosome 5, Cri-du-chat syndrome

Question 23

Inversions:

Answer 23

Breakpoints in chromosome appear. Middle section is inverted.
say: ABCDEFGHI
ABC|DEF|GHI
ABCFEDGHI
Often no effect on phenotype- a balanced rearrangement.
Possible problem in meiosis

Question 24

Meiosis…

Answer 24

type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells

Question 25

Structure of DNA:

Answer 25

-sugar phosphate backbone
-polymer made up of units called nucleotides
-bases held together by H-bonds
-Adenine
-Thymine
-Guanine
-Cytosine
-AT & CG
(in RNA T swaps to U)

Question 26

DNA is a

Answer 26

Double helix

Question 27

Size of the human genome…

Answer 27

3X10^9 (3 billion) base pairs long

Question 28

Cricks second great discovery :

Answer 28

The genetic code.
Where 3 nucleotides are called a codon
Every codon specifies one amino acid
An amino acid can be encoded by more than one codon - the code is DEGENERATE

Question 29

Organisation of the human genome:

Answer 29

• 20-300 genes
• only 1.5% encodes for proteins
• ~3% regulates protein expression
• ~ 45% caused by transposons
• ~6.6% not transcribed
• ~44% Contains many useful variations

Question 30

DNA mutations: coding region mutations..

Answer 30

• substitutions

- insertions and deletions

Question 31

DNA mutations: Non-coding region mutations..

Answer 31

• repeat length variation

- Useful genetic markers

Question 32

Substitution Mutation…

Answer 32

CAT<> CAC

Can be silent (synonymous mutation) or replacement mutation (non-synonymous) depending on where the substitution occurs

Question 33

Insertion/ deletion (indels) mutation…

Answer 33

Result is different protein encoded due to a shift in the open reading frame

Question 34

Non- coding region mutation:
% of genome not involved in protein coding/expressio?..
Variation in these parts is..

Answer 34

95%
Very useful!
Single Nucleotide Polymorphisms (SNPs)

Question 35

How many SNPs are found in man?

Answer 35

12,000,000 - 0.3% of genome

Question 36

What is an SNP?

Answer 36

a variation in a single nucleotide that occurs at a specific position in the genome, where each variation is present to some appreciable degree within a population

Question 37

Satellite DNA..

Answer 37

Micro satellites (or simple tandem repeats). Nearly always harmless. Widely used in finding diseases, conservation genetics, evolutionary genetics, agricultural improvement

Question 38

Gametic mutations:
Heritable?
Effect?
Affect all cells?

Answer 38

Heritable? YES
Effect? Can be severe
Affects all cells? YES

Question 39

Somatic mutations:
Heritable?
Effect?
Affect all cells?

Answer 39

Heritable? NO
Effect? Usually mild
Affects all cells? NO

Question 40

Genetic variation is caused by…

Answer 40

MUTATION

Question 41

there would be no evolution without

Answer 41

MUTATIONS

Question 42

Mutations can affect

Answer 42

Chromosomes or nucleotides

Question 43

Chromosomal mutations are often..

Answer 43

Lethal

Question 44

The genetic code is…

Answer 44

Degenerate

Question 45

Nucleotide mutation scan occur in ..

Answer 45

Coding or non-coding regions

Question 46

Gametic mutations are,,

Answer 46

inherited