Distinguish 23 pairs 46 chromosomes and the human gamete total
Usual human model: 23 pairs = 46 individual chromosomes in a diploid nucleus; each gamete has 23 individuals in one set. XX/XY labels one sex-chromosome pair within the full set.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Recall the nucleus, DNA base pairing, gametes, fertilisation, enzymes, membrane carriers and chemical synapses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which is the usual human diploid nuclear count?
What you will learn
- Use the human diploid and haploid model counts
- Keep pairs and individual objects clearly labelled
Original teaching model. Counts and records are stipulated; drawings are schematic.
| Feature | Meaning |
|---|---|
| Diploid pairs | 23 |
| Diploid individuals | 46 |
| Gamete individuals | 23 in one set |
| Composition | 22 autosome pairs + one sex-chromosome pair |
Use the human diploid and haploid model counts
In the usual human diploid cell model, the nucleus contains 23 pairs of chromosomes. Each pair contains two individual chromosomes, giving 23 × 2 = 46 chromosomes in two sets. The number 23 labels pairs here, while 46 labels individual objects. Saying a usual human diploid nucleus has 46 pairs would double the required total incorrectly.
Human gametes in the usual syllabus model have one set of 23 individual chromosomes. An egg with 23 and a sperm with 23 combine at fertilisation to give 46 in the resulting diploid nucleus. The gamete number is not 23 pairs, and the fertilisation calculation joins two chromosome contributions rather than counting one contribution twice.
Keep pairs and individual objects clearly labelled
The diploid model contains 22 autosome pairs and one sex-chromosome pair. An XX or XY label therefore refers to the sex-chromosome part, not every chromosome in the cell. In the specified XY model, the X and Y can differ in size and information; the word pair does not mean those two chromosomes are identical copies.
These counts describe the usual human model required by the syllabus, not a clinical chromosome result for every possible cell or individual. A mature mammalian red blood cell lacks a nucleus, and biological chromosome variations exist. Use the stated cell context and distinguish a general teaching count from a personal genetic conclusion.
Sources for this lesson
Pause and explain
What is the usual model gamete chromosome total?
Worked example
How many individual chromosomes are represented by 23 pairs?
Show the worked solution
- Use two individuals per pair.
- Multiply 23 by 2.
Answer 23 pairs represent 46 individual chromosomes in the usual human diploid model.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Calculate the individual total for 23 human model chromosome pairs.
Give me a hint
Multiply each pair by two.
Compare my reasoning
- Use 23 pairs.
- Multiply 23 by 2 and label individuals.
23 × 2 = 46 individual chromosomes in the usual human diploid model.
Look for these in your work
- Give 46
- Label individuals and diploid context
Combine the usual model egg total 23 with the sperm total 23. State the resulting total and set number.
Give me a hint
Add contributions and keep ploidy distinct.
Compare my reasoning
- Calculate 23 + 23.
- Identify two sets in the combined nucleus.
The resulting nucleus has 46 individual chromosomes in two sets, or 23 pairs in the usual human model.
Look for these in your work
- Give the sum
- Give set or pair arrangement
A diagram shows only XX but claims those are the only two chromosomes in a usual human body-cell nucleus. Correct the scope.
Give me a hint
The label tracks only the sex-chromosome pair.
Compare my reasoning
- Retain XX as that pair in the stipulated model.
- Include 22 other autosome pairs in the usual total.
XX labels the sex-chromosome pair; the usual diploid model also has 22 autosome pairs, giving 23 pairs and 46 individual chromosomes altogether.
Look for these in your work
- State the labelled subset
- Give the full model count
Common mistakes
- 23 pairs and 23 individual chromosomes are different counts.
- XX/XY is the sex-chromosome part, not the whole human set.
What can you explain now?
What is the usual model gamete chromosome total?
Compare with the explanation
23 individual chromosomes in one set
The gamete is haploid in this model.
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Make it stick
Explain use the human diploid and haploid model counts and keep pairs and individual objects clearly labelled. Use the stated cell, chromosome sets and information pathway before opening the solutions.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.