Independent orientation of chromosomes at metaphase I results in an increase in the number of
A) gametes.
B) possible combinations of characteristics.
C) homologous chromosomes.
D) sex chromosomes.
The correct answer and explanation is :
Correct Answer: B) possible combinations of characteristics.
Explanation (Approx. 300 words):
During meiosis, the process that produces gametes (sperm and eggs), one of the key events that contributes to genetic variation is the independent orientation of chromosomes at metaphase I.
In metaphase I of meiosis, homologous chromosomes (one from the mother and one from the father) line up along the metaphase plate in pairs. Each pair aligns independently of the other pairs. This means the maternal and paternal chromosomes can be distributed randomly to the two daughter cells. This phenomenon is known as independent assortment or independent orientation.
The number of possible combinations of chromosomes due to independent assortment is 2ⁿ, where n is the number of chromosome pairs (in humans, n = 23). So, the number of possible chromosome combinations just from independent assortment is 2²³, which equals over 8 million possible combinations per gamete.
This greatly increases the genetic diversity of gametes, and ultimately, offspring. When fertilization occurs, the combination of two gametes—each with over 8 million possible chromosome combinations—results in over 70 trillion possible genetic outcomes for each zygote, not including variation introduced by crossing over, another mechanism during meiosis.
Let’s look at the incorrect options:
- A) Gametes: The number of gametes is determined by the reproductive process, not by chromosome orientation.
- C) Homologous chromosomes: The number of homologous chromosomes remains the same; it’s their arrangement that varies.
- D) Sex chromosomes: Independent orientation affects all chromosome pairs equally, not just the sex chromosomes.
Thus, the correct answer is B) possible combinations of characteristics, as independent orientation significantly increases the genetic variability among gametes and resulting offspring.