║⊕QUESTION⊕║ "DNA is software, proteins are hardware, cells are factories." ↓ CLASS 12 EVOLUTION ↑ Explain with a graph how natural selection operates in a population with reference to a) sickle cell anemia b) beak size of finches c) insecticide resistance
Answers
Answer:
A. in sickle cell anemia not affected only carreir are selected from malaria .due to sickle shape of rbc malaria pathogen not able to complete its life cycle
B. diff size of beaks of finches are good example of adaptive radiation ...all are adopted from a common ancestor for acts on diff food substrate .....so alll s
are selected without competiton
C.. is an example of evolution by anthropogenic action
Answer:
Explanation:
Causes of Microevolution: Mutation and Gene Flow
As discussed previously, mutations – random, accidental changes in the sequence of nucleotides in DNA – are the original sources of genetic variation.
Only mutations can create new alleles – new raw material for natural selection.
UV or ionizing radiation, chemicals, and viruses constantly generate mutations in a gene pool, destabilizing genetic equilibrium and creating the potential for adaptation to changing environments.
However, both rates of mutation and their effects on the fitness of the organism vary.
In multicellular organisms, most mutations occur in body cells and do not affect eggs and sperm; these are lost when the individual dies and usually do not affect evolution.
Only mutations in gamete-producing cells can become part of the gene pool.
The rate at which mutations enter the gene pool is low, due to DNA “proofreading” and repair enzymes - and the extensive amount of DNA which does not code for protein.
Mutations which do change nucleotide sequences in functional genes may also have no effect (because the Genetic Code is redundant - multiple codons code for the same amino acid), or very little effect, if the amino acid is not located in a critical part of the protein.
Occasionally, however, a single nucleotide substitution can have a major effect on a protein – as we previously saw with sickle-cell anemia. Usually, the effect of a mutation on a protein is harmful; rarely is it helpful. In the case of sickle-cell anemia, it is both – depending on the environment.
Sickled cells carry oxygen much less efficiently, but prevent malaria infections. Overall, the chance that a single mutation will increase the fitness of a multicellular organism is extremely low.
If the environment changes, however, the adaptive value of a new allele may change as well.
Over time, mutations accumulate, providing the variation needed for natural selection.
For the small genomes of viruses and bacteria, mutations affect genes directly and generation times are short, so rates of mutation are much higher.
For an HIV population in one AIDS patient, rates of viral mutation and replication are so high that in a single day, every site in the HIV genome may have experienced mutation (Figure below).
This rapid generation of new alleles challenges our best efforts at drug treatment and explains the evolution of antibiotic resistance.
Because of the abundance of random, spontaneous mutations, HIV generates a large amount of raw material for natural selection and readily evolves resistance to new “environments” created by single drugs .
Drug “cocktails,” which contain multiple anti-viral chemicals, are our effort to change the “environment” and keep up with mutation in the human-HIV evolutionary race.
For microorganisms, mutation is a strong force for evolution.
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