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17.3Inheritance

Meiosis Core — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

10 min read 22 parts Lesson 4 of 9 1 quiz

📚 Cambridge IGCSE Biology 0610 Hub / Topical Revision
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Lesson summary

17.3 Meiosis — IGCSE BIOLOGY notes: Describe meiosis as a reduction division producing genetically different haploid gametes and compare it with mitosis.Meiosis = a type of nuclear division that gives rise to genetically different cells.It is a reduction division in which the chr…

  • Why halving is needed
  • Random fertilisation
  • Constant chromosome number
  • Flowering plants
  • Independent assortment
  • Role — meiosis is involved in the production of gametes (sex cells)

Part 1 of 6What meiosis is

Meiosis
Meiosis a type of nuclear division that gives rise to genetically different cells.
  • It is a reduction division in which the chromosome number is halved from diploid to haploid.
Role
  • Role meiosis is involved in the production of gametes (sex cells).
Why halving is needed
  • Why halving is needed otherwise the chromosome number would double at fertilisation in the zygote.

Part 2 of 6Process of meiosis

1
Each chromosome copies itself, forming X-shaped chromosomes, which line up in the centre of the cell.
2
First division: chromosomes pair up, recombination occurs, and fibres pull the pairs apart.
3
Second division: chromosomes line up and fibres pull them apart, as in mitosis.
4
Four haploid daughter cells are produced.
5
These cells form the gametes.

Part 3 of 6Why meiosis is important

1Gametes
  • Gametes it produces sperm cells and egg cells in animals, and pollen grains and ovum in plants.
2Variation
  • Variation it forms new combinations of maternal and paternal chromosomes every time a gamete is made.
3Random fertilisation
  • Random fertilisation gametes fuse at random, so each offspring differs from the others.
4Constant chromosome number
  • Constant chromosome number fertilisation restores the diploid number.

Part 4 of 6Mitosis and meiosis compared

FeatureMitosisMeiosis
DivisionsOneTwo
Cells producedTwoFour
Chromosome numberDiploid (46 in humans)Haploid (23 in humans)
Genetic make-upIdentical to parent and each otherDifferent from parent and each other

Part 5 of 6Gamete formation sites

1Animals
  • Animals testes and ovaries, the gonads.
2Flowering plants
  • Flowering plants anthers and ovules.

Part 6 of 6More from the specification

1
Independent assortment of maternal genes
  • Independent assortment of maternal genes random orientation of homologous pairs during metaphase I redistributes parental genes to generate extensive gametic variation.
2
Protein synthesis
  • Making proteins from amino acids using the DNA code.
3
Monohybrid inheritance
  • Inheritance of one gene.
4
Reductive Division in Meiosis
  • Meiosis involves two successive nuclear divisions following a single round of DNA replication,
    • reducing chromosome number from diploid (2n) to haploid (n) in specialized gametes.
5
Generation of Novel Allelic Combinations
  • Independent assortment of maternal and paternal homologous chromosomes and crossing over between non-sister chromatids produce unique allele combinations in every gamete.
6
Maintenance of Diploidy Across Generations
  • Fusion of male and female haploid gametic nuclei during fertilisation restores the complete diploid chromosome complement in the resulting zygote.
7
Homozygous
  • Having two identical alleles.
8
Sequence
  • The order of bases in DNA or amino acids in a protein.
9
Phenotype
  • The observable characteristic.
10
Specific
  • Able to act on only one type of substrate.
11
Heterozygous
  • Having two different alleles.
12
Probability
  • The chance that an offspring has a given genotype or phenotype.
13
Punnett square
  • A grid predicting offspring genotypes.
14
Blood group
  • A phenotype set by alleles I-A, I-B and I-O.
15
Allele
  • A version of a gene.
16
Inheritance
  • Transmission of genetic information from generation to generation.
17
Recessive
  • Expressed only when no dominant allele is present.
18
Dominant
  • Expressed when present in the genotype.
19
Protein
  • A long chain of amino acids containing carbon, hydrogen, oxygen and nitrogen.
20
Genotype
  • The alleles an organism has.

Key terms

TermMeaning
MeiosisReduction division giving four genetically different haploid cells.
HaploidHaving one set of chromosomes.
Reduction divisionDivision that halves the chromosome number.
GameteA sex cell with a haploid nucleus.
GonadAn organ in which meiosis occurs: testis or ovary.
Independent assortmentRandom sorting of chromosome pairs into gametes.

Avoid these mistakes

1
Saying meiosis produces two cells — it produces four.
2
Saying meiosis cells are diploid — they are haploid.
3
Saying meiosis makes identical cells — they are genetically different.
4
Confusing meiosis with mitosis — meiosis makes gametes and mitosis makes body cells.

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