Topic 4-mutations

Question 1

How do gene mutations occur?

Answer 1

-A change in the DNA base sequence of chromosomes

Question 2

What are the 5 types of errors that can occur?

Answer 2

-Substitution
-Deletion
-Inversion
-Addition
-Duplication

Question 3

How does a mutation affect the order of amino acids and proteins?

Answer 3

-The order of DNA bases in a gene determines the order of amino acids in a particular protein
-If a mutation occurs the sequence of amino and protein can be altered

Question 4

What effect does substitution have?

Answer 4

-The degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA triplet
-Not all substitution mutations will result in a change to the amino acid sequence of the protein

Question 5

What effect do deletions have?

Answer 5

-Changes the number of bases present which will cause a shift in all the base triplets after

Question 6

Are mutations random?

Answer 6

Yes

Question 7

Give an example of when a mutation can occur

Answer 7

When DNA is misread during replication

Question 8

Give some examples of mutagenic agents

Answer 8

-UV radiation
-Ionising radiation (gamma, x-rays)
-Chemicals such as mustard gas, caffeine and colchicine
-Some viruses

Question 9

What do mutagenic agents increase?

Answer 9

The probability of mutations occurring

Question 10

What are chromosome mutations?

Answer 10

-When cells produced contain variations in the numbers of whole chromosomes or parts of chromosomes

Question 11

What are chromosome mutations caused by?

Answer 11

-Errors during meiosis

Question 12

What do chromosome mutations lead to?

Answer 12

-Inherited conditions because the errors are present in the gametes (the heredity cells)

Question 13

What is chromosome disjunction?

Answer 13

Failure of the chromosomes to separate properly

Question 14

What is Down syndrome caused by?

Answer 14

-A person having an extra copy of chromosome 21 or an extra copy of it

Question 15

How does Down syndrome occur?

Answer 15

-Chromosome 21 fails to separate properly during meiosis so one cell gets an extra copy and another does not get a copy
-When the gamete with the extra copy fuses to another gamete at fertilisation, the resulting zygote will have three copies of chromosome 21

Question 16

What are the three sources of variation?

Answer 16

-Crossing over (prophase 1)
-Independent segregation (metaphase 1)
-Random combination (fertilisation)

Question 17

How does crossing over lead to variation?

Answer 17

-In prophase 1 the formation of homologous pairs (bivalents) during synapsis allows for the tangling of chromatids
-The pair of homologous chromosomes have 4 chromatids (2 for each chromosome)
-When the homologous chromosomes lie next to each other the chromatids can intertwine and exchange sections (recombination)
-Chromosomes still contain the same genes but a different combination of allele
-The point at which the chromatids cross over is called chiasma

Question 18

How does independent segregation lead to variation?

Answer 18

-During metaphase 1 it is purely by chance which way round homologous pairs lie when they pair and line up on the equator (synapsis)
-The paternal chromosomes may pass into the same cell or different ones during anaphase 1

Question 19

How many possible combinations of chromosomes are there?

Answer 19

-8,388,608
-As there is 23 pairs of chromosomes in humans

Question 20

How do you calculate the possible combinations?

Answer 20

(n)
2 = n is the number of chromosomes

Question 21

How do you calculate the amount of zygotes?

Answer 21

(2n ) squared

Question 22

How do hereditary mutations occur?

Answer 22

-You can inherit them from your parents
-The mutation is present in gametes, therefore it exists in all cells of the body

Question 23

How do acquired mutations occur?

Answer 23

-Occur in individual cells after fertilisation
-An acquired mutations can be caused my mutagens however for most they have no specific cause

Question 24

What is the main difference between inherited an acquired mutations ?

Answer 24

-An acquired mutation starts in one cell of the body and is found only in the offspring of that cell

Question 25

What is a frameshift?

Answer 25

-The addition/deletion mutation that is likely to result in change to the amino acid sequence but a substitution may not

Question 26

What are changes in the number of chromosomes during anaphase known as?

Answer 26

-Aneuploidy- loss or gain of a chromosome

Question 27

Give 3 examples of conditions developed due to mutations

Answer 27

-Down syndrome
-Kinfelsers syndrome- Males have an extra X chromosome
-Polyploidy-one or both gametes are diploid which fuse to form a polyploidy on fertilisation
-Extremely rare in humans, more common in plants

Question 28

What is non disjunction?

Answer 28

-Failure of a pair of homologous chromosomes to separate in meiosis 1 (anaphase )
-Failure of sister chromatids to separate during meiosis 2 (anaphase 2)
-Failure of sister chromatids to separate during mitosis (anaphase)

Question 29

Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation

Answer 29

-Frequent use of antibiotics creates a selection pressure
-A mutation is formed in a single bacteria to make them resistant to the antibiotic
-The surviving bacteria reproduces asexually through binary fission
-They then pass on advantageous allele/mutated alleles in greater numbers
-This means that the allele frequency increases and eventually it becomes more popular in the population
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