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

An error during DNA replication can result in the incorporation of incorrect nucleotides into the new DNA strand. If a nitrogen base is added, deleted, or substituted, this alters the sequence of the bases in the DNA. These changes can lead to mutations, potentially resulting in a change in the gene structure, which may disrupt normal gene function and lead to various genetic disorders or phenotypic variations.

The hypothesis described in the passage is known as the 'Out of Africa' hypothesis.

The type of DNA analyzed is mitochondrial DNA (mtDNA).

Mitochondrial DNA is passed down maternally, allowing scientists to trace maternal lineages. By comparing mtDNA sequences among different populations, researchers can identify genetic markers that indicate a common ancestry and migration patterns of early humans, supporting the 'Out of Africa' hypothesis.

Fossil evidence supports the hypothesis by providing physical remains of early human species that have been found primarily in Africa, indicating a common origin.

A new species can form through a process called allopatric speciation, which occurs when a population becomes separated by geographical barriers, such as mountains or rivers. Once isolated, the two populations experience different environmental conditions, leading to divergent evolutionary paths. Over time, natural selection and genetic drift cause changes in the gene pool of each population. As they adapt to their respective environments, they become genetically and phenotypically distinct. Eventually, even if the populations come into contact again, they may no longer be able to interbreed, resulting in the formation of new species.

Part X is the foramen magnum, and the type of teeth at Y are canine teeth.

The foramen magnum's position under the skull indicates that organism C is bipedal, as it allows for an upright posture. This anatomical adaptation facilitates the vertical alignment of the vertebral column, which is essential for efficient walking on two legs.

Skull B belongs to an Australopithecine.

Skull A belongs to a quadrupedal primate.

The change from skull B to C indicates an increase in cranial capacity. A larger cranium allows for a more developed brain, which can facilitate higher cognitive functions and greater intelligence.

Both parents must be heterozygous (Nn) to ensure that there is a possibility for their children to inherit the recessive allele (n). Each parent has one dominant allele and one recessive allele, allowing the chance of producing offspring with the recessive disorder when both pass on the recessive allele.

The possible genotypes of the normal children are NN (homozygous dominant) or Nn (heterozygous).

In the pedigree diagram, both males and females can be affected by the recessive allele, demonstrating that the characteristic is not linked to sex chromosomes. If it were sex-linked, we would expect to see a higher prevalence of the disorder in males compared to females.