3.4.3 Genetic Diversity - mutations and meiosis

Question 1

Give 2 possible causes of variation that result from meiosis during gamete formation

Answer 1

1. Random segregation of chromosomes

2. Crossing over and recombination of chromosomes

Question 2

Explain what happens to chromosomes in meiosis

Answer 2

1. Chromosomes condense
2. Chromosomes undergo independent segregation and arrange themselves in homologous pairs
3. Crossing over and recombination of sections of chromosomes (this is rare)
4. Chromosomes join to spindles at the middle of the cell joined by the centromere
5. Homologous chromosomes are pulled apart to opposite poles (meiosis 1)
6. the pairs of chromosomes are then separated at the centromere in meiosis 2 producing 4 genetically unique gametes

Question 3

Describe how meiosis causes variation and explain the advantage of variation to the species

Answer 3

Crossing over
Independent assortment / segregation (Random assortment)

Some members of the species will be better adapted so may survive if the environment changes. So will be able to reproduce and pass on the advantageous alleles

Question 4

State ways in which meiosis and mitosis is different

Answer 4

1. Meiosis reduces the chromosome number where as mitosis maintains the chromosome number
2. In meiosis, chromosomes associate in pairs where as in mitosis, chromosomes do not pair
3. In meiosis there are 2 nuclear divisions that produce 4 gametes where as in mitosis there is 1 nuclear division producing 2 body cells
4. Meiosis results in genetically unique daughter cells where as in mitosis, the daughter cells are all genetically identical

Question 5

Stages of meiosis 1

Answer 5

1. Homologous chromosomes pair up randomly (independent segregation /assortment)
2. Chromatids from each pair wrap around each other then crossing over and recombination of portions of chromatids occurs
3. One of each pair of chromosomes is randomly separated into 2 daughter cells

Question 6

Stages of meiosis 2

Answer 6

1. Sister chromatids are pulled apart at the centromere by spindle fibres and separated into 4 haploid daughter cells
2. Resulting gametes have varying combinations of alleles

Question 7

Describe the role of the centromere in mitosis

Answer 7

It holds the chromatids together
It attached the chromatids to the spindle and then splits the chromatids apart by pulling them to separate poles of the cell

Question 8

Homologous chromosomes carry the same genes but are not genetically identical. Why?

Answer 8

Homologous chromosomes have different alleles

Question 9

Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. How?

Answer 9

Homologous chromosomes pair up
Crossing over produces new combinations of alleles
Chromosomes separate at random
This produces varying combinations of chromosomes
Chromatids then separate at meiosis 2

Question 10

Explain the role of independent segregation in meiosis

Answer 10

To provide genetic variation
Allows different combinations of maternal and paternal chromosomes
Produces Haploid cells

Question 11

Identify the 2 ways that meiosis produces variation

Answer 11

Crossing over

Independent segregation

Question 12

Name an event that occurs during division 1 of meiosis that does not occur in division 2

Answer 12

Pairing up of homologous pairs, crossing over followed by their separation to either pole

Question 13

How is mitosis similar to the second division of meiosis

Answer 13

Separation of sister chromosomes

Question 14

Define mutation

Answer 14

Any chance to the quantity of bases or the base sequence of DNA in an organism

Question 15

Identify the 3 types of mutation that can occur

Answer 15

1. Base substitution
2. Bae deletions
3. Chromosome mutations

Question 16

Describe how DNA nucleotide substitutions can lead to a non-functional protein

Answer 16

1. A DNA nucleotide of a gene is replaced by a different nucleotide with aa different base
2. This change alters the DNA triplet and its resulting mRNA codon
3. The altered codon translates into a different amino acid
4. This results in a different primary structure
5. Different hydrogen, ionic, disulphide bonds will form a new tertiary structure
6. Protein with different shape results with different function / non-functional.

Question 17

Describe how DNA nucleotide deletions can lead to a non-functional protein

Answer 17

1. A DNA nucleotide is lost from a normal DNA sequence.
2. This causes a “frame shift” - each triplet after the deletion is shifted to the left by one base.
3. This alters the resulting mRNA codons
4. The altered codons translate into different amino acids
5. This results in a different primary structure
6. Different hydrogen, ionic, disulphide bonds will form a new tertiary structure
7. Protein with different shape results with different function/ non-functional

Question 18

What is a chromosome mutation?

Answer 18

Changes in the structure or number of whole chromosomes

Question 19

What is “non-disjunction”?

Answer 19

1. Where homologous chromosomes fail to separate during meiosis 1
2. This results in a gamete having too many or too few chromosomes e.g. down’s syndrome sufferers have an extra chromosome

Question 20

What is the equation for calculating the possible chromosome combinations as a result of independent segregation during meiosis

Answer 20

No. chromosome combinations = 2^n

where n = the number of PAIRS of chromosomes

Question 21

What is the equation for calculating the possible chromosome combinations as a result of independent segregation during meiosis AND random fertilizations of games

Answer 21

No of chromosome combinations - (2^n)^2

where n = the number of PAIRS of chromosomes

Question 22

Explain the difference in a cell that has undergone meiosis 1 and meiosis 2

Answer 22

Meiosis 1 - only 2 nuclei / cells, only homologous chromosomes separated

Meiosis 2 - 4 nuclei / cells, separation of sister chromosomes (haploid cells)

Question 23

How is chromosomes number halves in meiosis

Answer 23

Separation of homologous pairs

One of each pair ends up in the daughter cells

Question 24

In down syndrome, people have an extra chromosome (trisomy) - how does this happen?

Answer 24

In meiosis

Homologous chromosomes / sister chromatids fail to separate

Question 25

Define proteome

Answer 25

Full range of proteins that a cell can produce / that the genome can code for