3.1 Errors that occur during DNA replication may sometimes lead to mutations - NSC Life Sciences - Question 3 - 2016 - Paper 2

Errors during DNA replication may occur when incorrect nitrogen bases attach to the original strand. If a nitrogen base is added or deleted, the sequence or order of the bases changes in the new DNA molecule, which can result in a change in the gene structure. Such mutations may affect the protein produced or alter its function.

The hypothesis described is the 'Out of Africa' hypothesis, which suggests that all modern humans originated from a single group that migrated from Africa.

The type of DNA analysed is mitochondrial DNA (mtDNA), which is inherited only from the mother.

Mitochondrial DNA can be traced along the maternal line, allowing researchers to establish maternal ancestry and migration patterns, thus supporting the hypothesis of a common origin for modern humans from Africa.

Fossil evidence can also support the hypothesis, as it provides physical remains that can be dated and analyzed to show the lineage of modern humans.

A new species is formed when a population becomes separated by a geographical barrier, leading to two distinct populations. This separation hinders gene flow, resulting in each population being exposed to different environmental conditions. Over time, natural selection acts independently on both populations, leading to genetic differences, and eventually, they may become so different that they can no longer interbreed.

Part X is labeled as the foramen magnum, and the type of teeth at Y is canines.

The foramen magnum’s location below the skull indicates that organism C is bipedal. This positioning allows the vertebral column and spine to extend vertically, facilitating upright walking and balance.

(a) Skull B belongs to an Australopithecine.

(b) Skull A belongs to a quadrupedal primate.

There is an increase in the cranium size from organism B to organism C, which allows for a larger brain or cerebrum. This increase in size is associated with greater intelligence.

Both parents must be heterozygous because they each possess one dominant allele (N) and one recessive allele (n). This genetic makeup allows for the possibility of having affected children if the recessive allele from each parent combines.

The possible genotypes of the normal children are NN or Nn.

In the pedigree diagram, both males and females exhibit the recessive trait, suggesting that the inheritance pattern is not confined to one sex, hence indicating that this characteristic is not sex-linked.