3.4.3 Mutations And Meiosis

Question 1

What is a gene mutation?

Answer 1

When there is a spontaneous change in the base sequence of the DNA in chromosomes, that occurs during DNA replication.

Question 2

When are mutations passed onto offspring and why?

Answer 2

Only mutations that occur in gametes are passed onto the offspring, not those that occur in body cells, as genetic information is passed onto from gametes.

Question 3

What is a substitution mutation?

Answer 3

When a base is swapped (take one out and replaced with another), that does not cause a frame-shift, so no other codons are changed or affected.

Question 4

What are the three consequences of a substitution mutation?

Answer 4

Nonsense code, mis-sense mutation or silent mutation

Question 5

What is a nonsense code?

Answer 5

Results in a stop codon, so the polypeptide production stops prematurely.

Question 6

What is a mis-sense mutation?

Answer 6

It causes a different amino acid to be coded for. The effect of this depends on the function of the amino acid eg. Haemoglobin can’t bind to oxygen.

Question 7

What is a silent mutation?

Answer 7

The substituted base still codes for the same amino acid so there is no effect, due to the degenerate code eg. If UAU becomes UAC it still codes for tyrosine

Question 8

What is a deletion mutation?

Answer 8

When a base is lost
Causes a frame-shift so changes the triplet code of all of the subsequent codons.

Question 9

What is an addition mutations?

Answer 9

When a base is added.
Causes a frame-shift so changes the triplet code of all of the subsequent codons.

Question 10

What are mutagens?

Answer 10

They speed up the mutation rate (carcinogens)
Eg. UV light, tar in tobacco smoke, diet etc.
The environment cannot cause a mutation to occur but it can increase the likelihood that a mutation will occur.

Question 11

What is a polyploidy chromosome mutation?

Answer 11

Changes in whole sets of chromosomes, when organisms have three or more sets of chromosomes eg. Wheat plants with more seeds per head.

Question 12

What is a non-disjunction chromosome mutation?

Answer 12

Changes in number of individual chromosomes, when individual homologous pairs fail to separate during meiosis. A gamete will have one extra or one fewer chromosome. Eg. Down syndrome

Question 13

What is the general chain of effects of a mutation?

Answer 13

A mutation is a change in the base sequence of DNA in a chromosome.
This changes the amino acid sequence in the polypeptide chain.
This changes the bonding in the tertiary structure (hydrogen, ionic or disulphide).
Changes the shape of the protein so it cannot carry out its function correctly.

Question 14

What is meiosis?

Answer 14

A type of cell division which produces 4 haploid daughter cells from one diploid parent cell, involving 2 divisions.

Question 15

What is meiosis used for in humans?

Answer 15

Production of gametes (sperm and egg cells) that are haploid, as they fuse together to form a diploid cell.

Question 16

What is a diploid cell?

Answer 16

Normal number of chromosomes so two copies of each - 46 in humans

Question 17

What is a haploid cell?

Answer 17

Half normal number of chromosomes so one copy of each - 23 in humans

Question 18

What happens before meiosis can take place?

Answer 18

DNA replication
Number of organelles increase
Mass of DNA doubles

Question 19

What happens in meiosis 1?

Answer 19

Homologous Pairs of chromosomes separate

Question 20

What happens in meiosis 2?

Answer 20

Individual chromatids separate

Question 21

What is independent segregation?

Answer 21

When homologous pairs of chromosomes are separated in meiosis 1, this causes variation.
This is because the two chromosomes have the same genes but may not have the same alleles.
It is random which chromosome goes to each daughter cell

Question 22

What is a homologous pair of chromosomes?

Answer 22

Have the same gene at the same locus (but may have different alleles)

Question 23

What are the 3 ways meiosis causes variation?

Answer 23

Independent segregation
Crossing over
Random assortment of chromatids

Question 24

What is random assortment of chromatids?

Answer 24

In meiosis 2 when chromatids separate, each daughter cells gets a random combination of chromatids from the parent cell.

Question 25

What is crossing over?

Answer 25

When homologous chromosomes line up on the equator in meiosis 1 (prophase-metaphase) Non-sister chromatids can cross over and become tangled so that a section of the chromatid is exchanged Now have a recombined chromatid on each chromosome New combination of alleles in each of the gametes so increased variation

Question 26

what is non disjunction?

Answer 26

when chromosomes fail to separate during meiosis 1 or 2 which results in changes to the number of chromosomes in the daughter cells

Question 27

what are the rules for life cycles?

Answer 27

meiosis: 2n-n mitosis: n-n or 2n-2n fertilisation: n+n-2n

Question 28

What is polyploidy?

Answer 28

Changes in whole sets of chromosomes when organisms have three or more sets rather than the usual 2.

Question 29

What is aneuploidy?

Answer 29

Change in one singular chromosome due to one individual chromosome failing to separate.

Question 30

What is genetic diversity?

Answer 30

The number of different alleles of genes in a population, allowing natural selection to occur.

Question 31

What is natural selection?

Answer 31

The process that leads to evolution in a population, in which a change in the environment causes those in a population who possess an advantages allele to survive and reproduce. Over many generations, all of the organisms in the population will possess the advantages allele so the population will have evolved.

Question 32

What is evolution?

Question 33

What is evolution?

Answer 33

The change in allele frequency over many generations in a population, resulting in a species becoming better adapted for its environment (physically, anatomically or behaviourally)

Question 35

What is survival of the fittest?

Answer 35

The organisms that are best adapted to their surroundings will survive and reproduce.

Question 36

What are the VEMEESRAF stages of natural selection?

Answer 36

There is variation in the population (State what the variation is in the example eg. Neck length of giraffes) That is caused by random mutations Environmental changes create selection pressures so organisms must compete in order to survive. (State what the environmental changes is in the example eg. Drought causes less food) Some organisms are better adapted to survive the competition if they possess the advantages allele And reproduce To pass on the beneficial allele to offspring Over many generations, the advantageous alleles become more frequent in the gene pool than the non-advantageous alleles (so eventually the population has evolved)

Question 37

What is directional selection?

Answer 37

Changes characteristics of a population One of the extremes has a selective advantage A change in the environemt occurs The normal distribution curve is shifted to the left or right Over many generations due to natural selection This means that the advantageous alleles become occurs more frequently in the population.

Question 38

What is antibiotic resistance an example of?

Answer 38

Directional selection

Question 39

What is stabilising selection?

Answer 39

Preserves characteristics of a population. The modal trait has the selective advantage There is no change in the environment The modal trait remains the same, as selection against both extremes occurs. Maintains the favourable characteristic so the advantages allele occurs more frequently in the population.

Question 40

What is a species?

Answer 40

A group of organisms with similar characteristics that can reproduce to make fertile offspring.