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Chromosomes

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How would a pair of sister chromosomes differ from homologous chromosomes?

If the reproductive cell only has 23 chromosomes, then how come all of our body cells (somatic cells) have 46 chromosomes?

Briefly describe the constituent molecules found within a chromosome. You may use a diagram to illustrate your answer. Reference your sources.

What is a gene? What is a genome? What does a gene do?

How many genes (approximately) does the human genome contain?

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I am not sure what you mean by sister chromosomes. But I have this explanation which I hope might help answer your question.

Homologous chromosomes are similar in all aspects. However, sister chromatids are identical to each other. In the S phase of the cell cycle, the DNA is replicated and an identical copy of the chromatid is made. These two chromatids are then called sister chromatids. Nonsister chromatids are not identical to each other as they represent different but homologous chromosomes. The nonsister chromatid will carry the same type ...

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Human chromosomes and formulas; abnormal chromosome number

I am having trouble writing the formulas. I know what each X and Y chromosome each possess but I don't know who to write a formula with that.

1. Write a formula for:
(a) a male with Down syndrome (due to the presence of an extra chromosome 21)
(b) a female with Turner syndrome (only one X chromosome)
(c) a female with cri du chat syndrome (deletion of a portion of p arm of chromosome 5)
(d) a male with Klinefelter syndrome (two X chromosomes and one Y chromosome)
(e) a female with a Philadelphia chromosome (tanslocation between chromosomes 9 and 22). People suffering from a form of leukemia (chronic myeloid leukemia) frequently harbor cells containing the Philadelphia chromosome.

2. Abnormalities in chromosome number are detrimental and usually lethal. Speculate as to why the impact of abnormal numbers in chromosome 21 and in sex chromosomes are relatively mild.

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