Question

1. Explain the structural unit of the eukaryotic nucleosome, including DNA and protein components. In addition, describe how the nucleosome is assembled. Be specific regarding the number and type of the subunits and how these subunits are put together to make the entire nucleosome.
2. Explain what chromosomal mutations are, give and explain four examples, and tell me how these errors contribute to genetic variation.

Answer 1

The basic structural unit of DNA packaging in eukaryotes is a nucleosome. The structure of a nucleosome consists of a segment of DNA wound around eight histone proteins and resembles like a thread wrapped around a spool. Each histone octamer is composed of two copies each of the histone proteins H2A, H2B, H3 and H4.

The nucleosome assembly has two main steps - First of all histone H3 and H4 are deposited onto DNA as an H3/H4 tetramer in the first step ,to form a nucleosome precursor

In secondl step, the nucleosome is completed by the association of two H2A/H2B dimers with this precursor.

Chromosome mutation is a mutation which changes the structure of an individual chromosome, leading to imbalance involving only a part of chromosome, such as duplication , deletion and translocation .

Examples of chromosomal mutations are-

a. Down's syndrome or trisomy 21.- It is caused by random error in cell division that results in the presence of an extra copy of chromosome 21.

b.Edward's syndrome or trisomy 18 is caused by the presence of third copy of all part of chromosome 18. Thus , many parts of the bodies are affected.

c.Patau syndrome - It is a serious rare genetic disorder caused by having an additional copy of chromosome 13 in some or all of the body's cell.

d.Jacobsen syndrome - It is caused by a loss of genetic material from chromosome 11. Beacuse the deletion occurs at the end of the long q arm of chromosome 11. Hence, this jacobsen syndrome is also known as 11q terminal deletion disorder .

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