In general, why do changes in chromosome structure or numbertend to affect an individual’s phenotype? Explain why somechanges in chromosome structure, such as reciprocal translocations,do not.
Oogenesis
The formation of the ovum (mature female gamete) from undifferentiated germ cells is called oogenesis. This process takes place in the ovaries (female gonads). Oogenesis consists of three stages known as the multiplication phase, growth phase, and maturation phase.
Cell Division
Cell division involves the formation of new daughter cells from the parent cells. It is a part of the cell cycle that takes place in both prokaryotic and eukaryotic organisms. Cell division is required for three main reasons:
In general, why do changes in chromosome structure or number
tend to affect an individual’s
changes in chromosome structure, such as reciprocal translocations,
do not.
Chromosome is a compact structure of a DNA molecule wrapped around some proteins. It is generally seen in dividing cell whereas in metabolically active cells, somewhat loose state known as chromatin is present. DNA or deoxyribonucleic acid is a polymer of deoxyribonucleotides connected together via phosphodiester bond. It holds information of structure and functions of a cell.
A gene is a stretch of nucleotides present on a chromosome. It is the region that encodes the information for the synthesis of any RNA or protein molecule.
Whenever there is any kind of change in the structure of a chromosome, it may be due to some kind of rearrangements, duplications, or deletions. Deletion leads to the loss of some genes present on the deleted segment. Duplication leads to the addition of an extra set of genes present on the duplicated segment and rearrangements lead to reshuffling of genes present on a chromosomal segment within the chromosome or with some other chromosome.
Change in the number of a chromosome may result due to the addition of a whole chromosome, deletion of a chromosome from the whole genome set. Loss of a chromosome or a chromosomal set leads to loss of genes present on the chromosome causing haploinsufficiency or complete loss of those genes from the genome of the affected individual. The addition of a chromosome or a set of chromosomes leads to the presence of an extra pair of genes in the genome.
The loss or addition of genes in the genome affects the product of the genes and the functions performed by the gene product. The loss of gene product result in lack of the function performed by the product and thus the phenotype of the individual is affected. In case of presence of an additional set of genes result in formation of more than normal amount of gene product. This may overexpress a pathway or over inhibit a pathway and thus the balanced state of the functionality of the body is affected. Thus the phenotype of the individual is affected.
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