Question

Consider a diploid cell where 2n = 6. During metaphase I of meiosis, as the pairs of homologous chromosomes line up on the metaphase plate, each pair may orient with its maternal or paternal homolog closer to a given pole. There are four equally probable arrangements of the homologous pairs at metaphase I. (Note that this problem assumes that no crossing over has occurred.)

The cells below show the eight possible combinations of chromosomes that the daughter cells of meiosis II can receive.

Sort each daughter cell into the appropriate bin depending on which arrangement at metaphase I would create it.

Answer 1

One aspect of meiosis that generates genetic variation is the random orientation of homologous pairs of chromosomes at metaphase I. Each pair can orient with either its maternal or paternal homolog closer to a given pole; as a result, each pair sorts into daughter cells independently of every other pair. Due to independent assortment alone, a diploid cell with \(2 n\) chromosomes can produce \(2^{n}\) possible combinations of maternal and paternal chromosomes in its daughter cells. For the cell in this problem \((n=3)\), there are \(2^{3}\), or 8, possible combinations; for humans \((n=23)\), there are \(2^{23}\), or \(8.4\) million, possible combinations. Note that when crossing over occurs, the number of possible combinations is even greater.

Answer 2

1 daughter	Arrangement 2
2	Arrangement 3
3	Arrangement 1
4	Arrangement 4
5	Arrangement 5
6	Arrangement 4
7	Arrangement 4
8	Arrangement 1

Answer 3

Arrangement 1: 3 and 8 will be in one combination
Arrangement 2: 2 and 7 will be in one combination
Arrangement 3: 1 and 4 will be in one combination
Arrangement 4: 5 and 6 will be in one combination