EasyBiologyHigh School (11–12)Heredity and Evolution › Principles of Inheritance and VariationNumericalAPA-LevelIB
A normal human body cell has 46 chromosomes…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A normal human body cell has chromosomes.
- How many chromosomes are in a body cell of a person with Down syndrome?
- How many chromosomes are in a body cell of a person with Turner syndrome?
- A person with Klinefelter syndrome has the karyotype 47, XXY. How many sex chromosomes does this person have?
Need a reminder? The key ideaShow
Non-disjunction gives gametes with or chromosomes. Meiosis I gives four abnormal gametes. Meiosis II gives two abnormal and two normal gametes. Chi-square is , and for one degree of freedom the critical value at the 5 per cent level is 3.84.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Normal number: .
Plan. Add or take away one chromosome as each syndrome says.
Step 1. (a) Three copies of chromosome 21 give chromosomes.
Step 2. (b) One X only gives chromosomes.
Step 3. (c) The karyotype XXY has three sex chromosomes, two X and one Y.
Answer: ; ; .
Check. Klinefelter syndrome also has chromosomes, with an extra X and not an extra chromosome 21.
Watch out. Turner syndrome is a female with chromosomes and not an XXY person.
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