OxfordAQA International A Level Biology
OxfordAQA International A Level Biology 3.1.9 Genetic Diversity may Arise by Meiosis Exam Questions
Free OxfordAQA International A Level Biology revision for 3.1.9 Genetic Diversity may Arise by Meiosis: what you need to know, common mistakes and exam-style questions with answers. Covers the two divisions of meiosis, haploid gametes, independent segregation, crossing over and random fertilisation.
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About OxfordAQA International A Level Biology 3.1.9 Genetic Diversity may Arise by Meiosis
This Unit 1 topic explains how meiosis produces genetically different haploid gametes. You need to describe the two nuclear divisions, explain how independent segregation of homologous chromosomes and crossing over create variation, and explain how random fertilisation adds further variation. You should be able to recognise chromosome behaviour in diagrams or photographs. Meiosis links to DNA and chromosomes, genetic diversity and species diversity in Unit 1, and to inheritance, allele frequencies and evolution in Unit 3. Exam questions often ask you to calculate the number of possible chromosome combinations and to compare meiosis with mitosis from Unit 2.
What you need to know
- Meiosis overview Meiosis involves two nuclear divisions and produces four haploid daughter cells from one diploid cell. Haploid cells have one set of chromosomes; diploid cells have two.
- Homologous chromosomes Homologous pairs carry the same genes at the same loci but may carry different alleles. In meiosis I the homologous chromosomes separate; in meiosis II the sister chromatids separate.
- Independent segregation Homologous pairs line up randomly in meiosis I, so each gamete gets a different combination of maternal and paternal chromosomes. The number of combinations is 2^n, where n is the number of homologous pairs.
- Crossing over Chromatids of homologous chromosomes wrap around each other and exchange equivalent sections at chiasmata, producing new combinations of alleles on each chromatid.
- Random fertilisation Any male gamete can fuse with any female gamete, which produces even more genetic variation in offspring.
Common mistakes in 3.1.9 Genetic Diversity may Arise by Meiosis
- Saying crossing over happens between sister chromatids. It occurs between non-sister chromatids of homologous chromosomes.
- Mixing up meiosis I and meiosis II. Homologous chromosomes separate in meiosis I; chromatids separate in meiosis II.
- Saying meiosis produces two cells. It produces four genetically different haploid cells.
- Using 2n for the number of combinations. Use 2 to the power of n, where n is the number of homologous pairs.
Try three 3.1.9 Genetic Diversity may Arise by Meiosis exam-style questions
1. A species has a diploid number of 8. Calculate the number of genetically different gametes that can be produced by independent segregation alone. (2 marks)
Show the mark scheme answer
n = 4 homologous pairs; 2^4 = 16 combinations.
2. Explain how crossing over leads to genetic variation. (3 marks)
Show the mark scheme answer
Homologous chromosomes pair up; non-sister chromatids exchange equivalent sections of DNA at chiasmata; produces new combinations of alleles on chromatids.
3. Give two differences between meiosis and mitosis. (2 marks)
Show the mark scheme answer
Meiosis has two divisions, mitosis one; meiosis produces four cells, mitosis two; meiosis produces haploid cells, mitosis diploid / same number of chromosomes; meiosis produces genetically different cells, mitosis genetically identical cells. (Any 2)
3.1.9 Genetic Diversity may Arise by Meiosis FAQs
What does OxfordAQA International A Level Biology 3.1.9 Genetic Diversity may Arise by Meiosis cover?
It covers the two divisions of meiosis, haploid gametes, independent segregation, crossing over and random fertilisation.
Which unit is 3.1.9 Genetic Diversity may Arise by Meiosis examined in?
It is part of Unit 1, The diversity of living organisms, which is examined at International AS. The Unit 5 synoptic paper at A2 can also draw on this content.
How do I recognise meiosis in a diagram?
Look for homologous chromosomes paired up or separating (meiosis I), or for four haploid cells forming. If cells have half the original chromosome number, the division is meiosis.
