Question

) Why do we not see any evidence (at birth or in spontaneous abortions) of chromosome 1 monosomies or trisomies?

B) Do you think they occur? Explain.

Answer 1

ANSWER A and B :-

1. A monosomic condition is a type of chromosomal anomaly in which a a cell has only one copy of the original chromosome which were present in pair, whereas on the other hand. a trisomic condition is characterized by presence of three copies of chromosome in a cell instead of two copies. This indicates that in the first case. there will be loss of genetic material whereas the second case is associated with gain of genetic material.
2. These conditions are called as chromosomal anomalies and usually occur at the time of crossing over of the homologous chromosomes during Meiosis. At the time of crossing over, the two homologous chromosomes align together exchanging their segments although fail to separate from the complex resulting in failure of the chromosomes to segregate thereby resulting in imbalance in the number of chromosomes in the resulting cells.
3. Although, with respect to chromosome number 1, minor genetic changes have been seen and said to have associated, but this doesn't change the fact that random meiotic errors can affect any chromosome whether it is X-chromosome (Turner's syndrome) or Down's syndrome as in case of the autosomal chromosomes.
4. There are chances that errors during the process of crossing over may be related to any autosomal or sex chromosome taking into consideration every chromosome carries the same probability of undergoing non-disjunction during meiosis. The main reason for this phenomena is the failure of the checkpoints which are associated with this process that keeps a check on the involvement, duplication of genetic material and its segregation in the form of chromosomes. If at any point error happens, the chromosome will be affected randomly and not in a selected manner which may involved the participation of a wide variety of factors as can be seen in conditions like cancer affected many chromosomes.