PRELIMINARY STAGE 2025
Nglesie Amanfro SHS: 21 points
St Thomas Aquinas: 62 points
Bawku SHS: 40 points
QUESTION
Name the genetic condition caused by an unusual cell division which results in an extra or partial copy of chromosome 21.
ANSWER: Down syndrome
EXPLANATION
Down syndrome (trisomy 21) most commonly results from nondisjunction during meiosis, where chromosome 21 fails to separate properly, leaving a gamete (and resulting embryo) with three copies of chromosome 21 instead of the usual two.
PRACTICE QUESTIONS
1. How many chromosomes does a person with Down syndrome have?
ANSWER: Forty-seven.
2. What is nondisjunction?
ANSWER: The failure of chromosomes to separate properly during cell division.
3. What is a karyotype?
ANSWER: A picture of the chromosomes of a cell arranged in pairs.
4. Which maternal factor increases the risk of Down syndrome?
ANSWER: Older age of the mother.
5. State two features of Down syndrome.
ANSWER: Learning difficulty and a characteristic facial appearance.
6. Which test can detect Down syndrome before birth?
ANSWER: Amniocentesis.
7. What is translocation Down syndrome?
ANSWER: A form in which part of chromosome 21 is attached to another chromosome.
8. Name two other trisomies.
ANSWER: Edwards syndrome (18) and Patau syndrome (13).
9. What is Turner syndrome?
ANSWER: A condition in which a female has only one X chromosome.
10. What is Klinefelter syndrome?
ANSWER: A condition in which a male has XXY chromosomes.
11. What are autosomes?
ANSWER: Chromosomes that are not sex chromosomes.
12. In which division does nondisjunction occur?
ANSWER: In meiosis (or mitosis).