Gentetic variation (meiosis)

Question 1

Species usually have different numbers of chromosome. Why are animals that are bred from two different species normally infertile?

Answer 1

1. (usually) an uneven number of chromosomes;
2. Chromosomes cannot pair
3. chromosomes are not homologous
4. meiosis cannot occur

Question 2

Explain the role of independent segregation in meiosis.

Answer 2

1. To provide genetic variation;
2. Allows different combinations of
   maternal and paternal chromosomes/
   alleles;
3. To produce haploid cells (half the
   chromosome number);
4. Allows homologous pairs to arrange randomly
   at equator of cell

Question 3

What is the importance of meiosis?

Answer 3

Halves chromosome number and restores diploid number at fertilisation

Question 4

Describe and explain how selection will have affected the genetic diversity of sugar
beet.

Answer 4

1. Diversity reduced

2. As alleles have been chosen

Question 5

Explain the appearance of a chromosomes

Answer 5

Two chromatids;
Due to DNA replication;
Joined by a centromere;

Question 6

Explain how the gametes with the combinations of alleles Ef and eF have been produced.

Answer 6

Crossing over;

Exchange of alleles between chromatids

Question 7

Describe and

explain how the production of gametes by meiosis contributes to this variation

Answer 7

Independent assortment/random alignment of (homologous) chromosomes;
Different combinations of maternal and paternal chromosomes;
OR
Crossing over;
Different combination of alleles/exchange of genetic material

Question 8

Describe how crossing over occurs during meiosis I.

Answer 8

chromosomes in each homologous pair twist around each other;

chromatids break and rejoin to chromatid on sister chromosome

Question 9

What is the biological importance of reducing the chromosome number when the cell
divides by meiosis?

Answer 9

Restoring diploid number

Later fertilisation

Question 10

Describe 5 differences between meiosis and mitosis

Answer 10

Meiosis:
1. Reduces the chromosome number
2. Homologous chromosomes associate in pairs
3. Crossing-over
4. Two divisions → 4 offspring cells
5. Genetically different product
    Mitosis:
1. Maintains the same chromosome
number as in the parent nucleus
2. Homologues do not pair
3. No crossing-over;
4. One division → 2 offspring cells;
5. Genetically identical product;

Question 11

Explain why the chances of inheriting a genetic disorder increase with a smaller community who only reproduce with people in that comunity

Answer 11

1. Less genetic diversity
2. As individuals only breed within group
3. Therefore Higher chance of inheriting allele

Question 12

Suggest how a mutation can lead to the production of a protein that has one amino
acid missing.

Answer 12

loss of 3 bases

3 bases code a for 1 amino acid

Question 13

Suggest how the production of a protein with one amino acid missing may lead to a
genetic disorder

Answer 13

1.Change in sequence of bases
2. Therefore change in bonds formed in 1^0
3 . Therefore change in tertiary structure
4. Leading to a non-functional protein

Question 14

Suggest four reasons why populations might show very low levels of genetic diversity.

Answer 14

1. genetic bottleneck
2. inbreeding
3. Population might have started with small
   number of individuals
4. founder effect

Question 15

How do changes to whole sets of chromosomes occur?

Answer 15

When organisms have more than the usual 2 sets of chromosomes. This is called polyploidy

Question 16

Describe what non-disjunction is and what it results in

Answer 16

1. When individual homologous pairs of chromosomes fail to separate
2. during meiosis
3. resulting in gametes having 1 less or 1 more chromosomes