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I know it depends on phase. So i am talking of -

1) in human (diploid organism) with cells before prophase (before replication, when 23 pair of homologous chromosomes are present ). I think answer is 2 if we not consider male XY sex chromosome because they are not homologous in which case the answer should be 1. But then i get confuse why genotype is shown like Tt (doesnt this means two alleles per chromosome).

2) in gamete cell. I think the answer should be 1.

Please tell if i'm correct.

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closed as off-topic by David, another 'Homo sapien', Bryan Krause, anongoodnurse, theforestecologist Apr 23 '17 at 2:33

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In short. Yes.

Each diploid cell has 23 pairs of chromosomes (22 of which autosomal)

In relation to the genotype part of the question. The "Tt" refers to each allele on the chromosome and wether it is dominant or recessive. Take for instance, hair colour. On one chromosome, there would be an allele from one parent and on the other an allele from the other parent. This is why two letters are needed, to show the allele given by each parent.

You can think of dominant and recessive in terms of how powerful the copy of the gene(allele) is. An allele that is able to overpower and mask traits is called dominant, one that is not strong and cannot mask traits is called recessive. This is why you need two recessive alleles for recessive disorders, otherwise the dominant allele would cover it up.

As this is a homework question I have tried to explain this in simple terms which you should understand. Hope this helps.

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  • $\begingroup$ Your use of the term sister chromatid is incorrect. I think you mean homologous chromosome. $\endgroup$ – canadianer Apr 18 '17 at 17:19
  • $\begingroup$ Apologies. I deleted half of a paragraph before posting and joined the wrong sentences together. $\endgroup$ – user20453 Apr 18 '17 at 17:23

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