Imagine you have a line of corn with cytologically distinct forms of chromosome

Question

Imagine you have a line of corn with cytologically distinct forms of chromosome 15. The tip of the chromosome can have a knob (15K), a broken portion (15B), or the wild-type form (15). You fertilize a 15K/15B plant with pollen from a 15/15 plant, and find that most of the offspring are 15K/15 or 15B/15, as expected. However, you occasionally find rare types. For each of the rare types, explain the stage of meiosis at which it originated, and in which parent it originated. (3 pts)

15K/15K/15

15K/15B/15

15K

Explanation / Answer

Here, the progeny 1 (15K/15K/15) and progeny 2 (15K/15B/15) have three chromosomes. This condition is called trisomy (2n + 1) and the principle behind the formation of these offspring is called aneuploidy. These types of offspring are produced due to the occurrence of non-disjunction (a translocation mutation) in the meiosis.    

During meiosis, the homologous chromosomes align during the prophase. These chromosomes crossover at some point and rejoin to form recombinant chromatids, and move towards the opposite poles during anaphase. Sometimes, error occurs in meiosis during the meiosis –I, i.e. during the separation of homologous chromosomes. These errors result in excess or less chromosomes in the daughter cell, and this is called “nondisjunctioning.”

The 15K/15K/15, is originated in 15K plant and the15K/15B/15 is originated in 15B plant.The 15K is a monopoly condition, which is formed due to non-disjunction at meiosis –II (second meiotic division) in the plant 15.

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.