1. Misheel
Topic 4.1; Chromosomes, Genes, Alleles and Mutations
Chromosomes are made of DNA and protein; they contain genes (heritable factors that
control characteristics). Alleles are different forms of a specific gene. The gene locus is a
specific position of a gene on a chromosome. The same species carry the same genes at the same
loci on the same chromosome (also known as homologous); they also have the same number os
chromosomes. A genome is the entire genetic information of an organism.
A mutation is a permanent change in the base sequence of DNA. Organisms eventually
evolve from their ancestors due to natural selection and the numerous cumulative mutations, few
cause diseases. Mutation is possible because there is the possibility of mistakes occurring, even
though the DNA replication is protected by base-pairing. This is likely after contact to mutagens,
like radiation and some chemicals. This mutation may cause a genetic disease. A known
mutation is base-substitution, in which one base is replaced for another. This can change a single
amino acid, but if it doesn’t, it’s known as the silent mutation. If the change has caused one
different amino acid to be produced, it’s labeled as missense mutation (sickle cell). For a
nonsense mutation, the change in base sequence results in a STOP codon – shortening the
polypeptide (cystic fibrosis).
Sickle cell disease, a missense mutation, produces valine instead of glutamine, which
leads to production of abnormal red blood cells. Those with one copy of the faulty gene can
cope; however it is challenging and dangerous for those with two copies. This disease is a prime
example of natural selection; which there is a variation within a species due to a mutation, and
then passes passed on to the off springs. However, this can be treated with utilization of stem
cells, or so proven in mice. Retroviruses inserted into the corrected gene began to produce
healthy red blood cells, after the faulty genes were repaired and replaced. This opens endless
opportunities for treatment of mutation diseases.