2.1 The sequence of amino acids in a protein molecule is coded for by DNA and RNA - NSC Life Sciences - Question 2 - 2017 - Paper 2

The anticodon for glutamic acid, which is coded by the mRNA codon GAG, is CUC.

The last codon on the section of mRNA is ACC. The corresponding DNA base triplet would be TGG.

The first amino acid coded for by this section of mRNA, which starts with the codon GAU, is aspartate.

The mutation that occurred was a substitution mutation where the original base C was replaced by U in the fourth codon. Therefore, the original codon AGC was changed to AUG.

The mutation causes a change in the amino acid sequence of the protein. Specifically, if the fourth codon changes from AGC to AUG, the codon that now codes for methionine (the start codon), which may alter the protein's structure and function significantly.

The process occurring in the nucleus that results in the formation of an mRNA molecule is called transcription. During this process, the DNA double helix unwinds, and one of the strands serves as a template for synthesizing a complementary RNA strand with RNA nucleotides. This is regulated by various enzymes and results in the formation of pre-mRNA, which is then processed to become mature mRNA.

A population is defined as a group of organisms of the same species that interbreed and occupy a specific area at the same time.

Three causes of variation in a population other than mutations are:

1. Crossing over during meiosis
2. Random arrangement of chromosomes during cell division
3. Random mating within the population.

The increased number of squirrels with the mutation on one side of the river can be attributed to natural selection. Squirrels with favorable characteristics caused by the mutation were more likely to survive and reproduce in their environment, leading to a higher prevalence of the mutation in that population.

The process of speciation increases biodiversity because it leads to the formation of new species. As the populations diverge and adapt to their specific environments, the genetic diversity of the ecosystem as a whole increases.

To confirm that species A and B are two different biological species, researchers can conduct DNA tests on both populations to analyze their genetic differences. Alternatively, observing their behavior, breeding patterns, and reproductive isolation can provide evidence of distinct species.

Senzo's phenotype is that of being a colour-blind male.

The genotype of Thuli is Xᶦ Xᵈ, indicating she carries one recessive allele for colour-blindness.

Linda inherited colour-blindness by receiving one recessive allele (Xᵈ) from her father, who is colour-blind (Xᵈ Y), and one normal allele from her mother, resulting in the genotype Xᵈ Xᶦ.

There are generally more males than females with colour-blindness because it is a sex-linked disorder carried on the X chromosome. Males have only one X chromosome (XY), so if they inherit the allele for colour-blindness, they express the trait. Females, however, need two copies of the allele on both X chromosomes (Xᵈ Xᵈ) to be colour-blind, making them less likely to exhibit the condition.

The genetic cross between Molly (X^ᶦ X^ᵈ) and a normal male (X^ᶦ Y) can be represented as follows:

• Gametes from Molly: X^ᵈ, X^ᶦ
• Gametes from the normal male: X^ᶦ, Y

Punnett Square:

Phenotypes:

• Normal females (Xᶦ Xᶦ)
• Normal males (Xᶦ Y)
• Colour-blind males (Xᵈ Y)

This cross illustrates the possible genotypes and phenotypes of their children.