Passage of information
Cambridge A-Level Biology (9700) · Unit 16: Inheritance · 9 flashcards
Passage of information is topic 16.1 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 16 — Inheritance , alongside The roles of genes in determining phenotype and Gene control. In one line: Haploid refers to a cell or organism having a single set of unpaired chromosomes. In humans, gametes (sperm and egg cells) are haploid, containing 23 chromosomes each. This is represented as 'n'.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 9 flashcards — 3 definitions and 6 key concepts — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
The term 'haploid' (n)
Haploid refers to a cell or organism having a single set of unpaired chromosomes. In humans, gametes (sperm and egg cells) are haploid, containing 23 chromosomes each. This is represented as 'n'.
What the Cambridge 9700 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- explain the meanings of the terms haploid (n) and diploid (2n)
- explain what is meant by homologous pairs of chromosomes
- explain the need for a reduction division during meiosis in the production of gametes
- describe the behaviour of chromosomes in plant and animal cells during meiosis and the associated behaviour of the nuclear envelope, the cell surface membrane and the spindle (names of the main stages of meiosis, but not the sub-divisions of prophase I, are expected: prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II and telophase II)
- interpret photomicrographs and diagrams of cells in different stages of meiosis and identify the main stages of meiosis
- explain that crossing over and random orientation (independent assortment) of pairs of homologous chromosomes and sister chromatids during meiosis produces genetically different gametes
- explain that the random fusion of gametes at fertilisation produces genetically different individuals
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Passage of information
- › Use 'independent assortment' when discussing the random alignment of homologous pairs at the equator; use 'crossing over' for the exchange of alleles between non-sister chromatids.
- › Define haploid (n) as one set of chromosomes and diploid (2n) as two sets of chromosomes, applicable to all organisms.
- › In Hardy-Weinberg problems, always find q first by using the frequency of the homozygous recessive (q squared).
- › Recognize that a 9:3:3:1 ratio from a dihybrid cross confirms that genes are on separate autosomes and assort independently.
- › Use comparative language or a table where each row addresses one specific feature for both subjects being compared.
Define the term 'haploid' (n).
Haploid refers to a cell or organism having a single set of unpaired chromosomes. In humans, gametes (sperm and egg cells) are haploid, containing 23 chromosomes each. This is represented as 'n'.
Define the term 'diploid' (2n).
Diploid refers to a cell or organism containing two complete sets of chromosomes, one from each parent. Somatic cells (body cells) in humans are diploid, containing 46 chromosomes (23 pairs). This is represented as '2n'.
What are homologous pairs of chromosomes?
Homologous chromosomes are pairs of chromosomes, one inherited from each parent, that have the same genes at the same loci. They are similar in size, shape, and banding pattern. They pair up during meiosis I.
Explain the necessity of reduction division during meiosis in gamete production.
Reduction division (meiosis) is necessary to halve the chromosome number in gametes. Without it, fertilization would result in offspring with double the normal chromosome number, leading to genetic abnormalities. Meiosis ensures that the diploid number is maintained across generations.
Outline the main events that occur during Anaphase I of meiosis.
During Anaphase I, homologous chromosomes are separated and pulled to opposite poles of the cell. Sister chromatids remain attached at the centromere. This segregation reduces the chromosome number from diploid to haploid.
Outline the main events that occur during Metaphase II of meiosis.
During Metaphase II, the sister chromatids, now considered individual chromosomes, line up randomly along the metaphase plate in each of the two daughter cells. The spindle fibers are attached to the centromeres of each chromosome.
Explain how crossing over during Prophase I of meiosis increases genetic variation.
Crossing over involves the exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I. This creates new combinations of alleles on each chromosome, increasing genetic variation in the resulting gametes.
Explain how independent assortment (random orientation) increases genetic variation.
Independent assortment refers to the random orientation of homologous chromosome pairs at the metaphase plate during Metaphase I of meiosis. Each pair aligns independently of the others, resulting in different combinations of maternal and paternal chromosomes in the daughter cells, which increases genetic variation.
Explain how the random fusion of gametes at fertilization produces genetically different individuals.
The fusion of any one sperm cell with any one egg cell during fertilization is a random process. Since gametes are genetically unique due to crossing over and independent assortment, and fertilization is random, an enormous number of genetically different zygotes are possible.
More topics in Unit 16 — Inheritance
Passage of information sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Passage of information deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
How to study this Passage of information deck
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