Karyotypes, karyograms and ploidy
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Question
What is a karyotype?
Answer
The **number and appearance** (size and shape) of all the chromosomes in a cell.
Question
What is a karyogram?
Answer
A processed **photograph** of a cell's chromosomes, cut out and arranged in **homologous pairs** by size and centromere position.
Question
What does ploidy mean?
Answer
The number of complete **chromosome sets** in a cell — haploid (n), diploid (2n) or polyploid (3n, 4n…).
Question
What are homologous chromosomes?
Answer
A **matching pair** — same size, same centromere position, carrying the same genes (one from each parent).
Question
How many chromosome sets does a diploid (2n) cell have, and where is it found?
Answer
**Two** sets — found in **body (somatic) cells** (human 2n = 46).
Question
How many chromosome sets does a haploid (n) cell have, and where is it found?
Answer
**One** set — found in **gametes** (egg, sperm) (human n = 23).
Question
What is a polyploid cell?
Answer
A cell with **three or more** chromosome sets (3n, 4n…), common in plants.
Question
Which three criteria are used to classify chromosomes?
Answer
**Size (length)**, **centromere position**, and **banding pattern**.
Question
What does 'acrocentric' mean?
Answer
A chromosome whose **centromere is near one end** rather than in the middle.
Question
How can you tell a gamete from a somatic cell using a chromosome count?
Answer
**Single** chromosomes (one set) = haploid **gamete**; chromosomes in **pairs** (two sets) = diploid **somatic** cell.
Question
What is non-disjunction?
Answer
When a chromosome pair (or sister chromatids) **fails to separate** during meiosis, giving a gamete an **extra or missing** chromosome.
Question
What is trisomy, and give an example?
Answer
Having **three copies** of one chromosome instead of a pair — e.g. **trisomy 21 (Down syndrome)** or **trisomy 18 (Edward's syndrome)**.
Question
List the steps to build a karyogram.
Answer
**Stain** the chromosomes, **photograph** them, **cut out** each one, **pair up the homologues**, and **arrange** the pairs largest to smallest.
Question
Why are chromosomes studied during cell division for a karyogram?
Answer
Because then they are **condensed (short and thick)** and clearly **visible** under a microscope.
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Topic 4.4 hub
Cell and nuclear division
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