During oogenesis in an animal species with a haploid number of 6, one dyad undergoes nondisjunction during meiosis ii. following the second meiotic division, this dyad ends up intact in the ovum. how many chromosomes are present in (a) the mature ovum and (b) the second polar body? (c) following fertilization by
a) 3 cromosomes b)3
The haploid number of a cromosome is the total number ofcromosomes withoutits homologue partner. In this case, if the text indicates that the haploid number of cromosomes is 6, then that is the total number of cromosomes in the result cell.
The ovum contains just half of the information that will be given in order to form the new organisms, in this context, if the result organism has cromosomes, the ovum will only contain 3.
In meiosis II, after both cigotes get together and unite all the 6 cromosomes, it separates again. This means that the second polar body will remain will only 3 cromosomes again.
Nondisjunction is defined as the failure of the chromosomes to seperate during cell division. An animal with a haploid number of 6 (diploid number of 12) undergoes meiosis, and at the meiosis II (cells are already haploid from the meiosis I), nondisjunction occurs. The mature ovum will contain 6+1 chromosomes (n+1) because there is an extra chromosome from the nondisjunction. The second polar body will contain 5 chromosomes (normal would be 6) because the second polar body did not receive that extra chromosome due to nondisjunction. In the event of fertilization of the abnormal ovum with a normal sperm, the zygote will be a diploid (12 chromosomes) normally but since the ovum as an extra chromosome from the nondisjunction then the zygote will have an extra chromosome (13 chromosomes). One pair of chromosomes has an extra single chromosome and this is called a trisomy.