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Chromosomes usually exist in pairs in a somatic cell. One of the pair came from the mother and the other from the father. Homologous pair refers to those pair of chromosomes that have the same gene sequence; however the genes do not have to be identical. For example in this figure the genes are represented by the letters G, T, and R. If the gene for length of stems in plants (tall or short) is represented by the letter "T" , the upper case (T) represents tall and lower case (t) represents short. (same for G and R) in this figure. Chromosomes A and B are homologous because they have the same gene sequence G's and T's on the same chromosome, however one of the chromosomes have a T and the other t.
18. How many homologous pair of chromosomes are in this figure?
a) 1 b) 3 c) 6 d) 12
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19. Which chromosomes are homologous?
a) A and D : B and C : E and F
c) A and B : C and D : E and F
b) A and C : B and D : E and F
d) none of these
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Examine the figure showing a prophase nucleus. In your
notes draw this figure showing the three pairs of chromosomes and add to
the long red and blue homologous pair the genes "A" and "B".
Indicate one of the homologous pair "A" genes with an upper case
A and it's homologue with a lower case a. Indicate one of
the homologous pair "B" genes with an upper case B and it's homologue
with a lower case b. Place lower case b and upper
case A on the long red chromosome and the upper case B and lower
case a on the long blue chromosome (see below).
|b
|B
|
and
|
|
|
| A
| a
long red
long blue
Compare your answer to the figure on the next page. click
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Created by the Center for Learning Technologies, Academic Technology Services.
Last modified October 22, 1997.