Specifics for SAC 4 Biology

niche

Explain why the frequency of the CSID allele is significantly higher in the Greenlandic Inuit population (20%) compared to European populations (0.05–0.2%).

• The high frequency is likely due to genetic drift, as the Greenlandic population has historically been small and isolated.

• When a small group of ancestors migrated into Greenland, they likely carried this mutation, causing a founder effect.

• Because the traditional Inuit diet was very high in protein and fat and low in carbohydrates and sugars, there was a lack of negative selection pressure against the allele, allowing it to persist and increase in frequency within the small gene pool.

Describe the specific genetic mutation that causes CSID and its effect on the sucrase-isomaltase enzyme.

• The mutation is a deletion mutation, where two DNA bases, adenine and guanine, are removed at positions 273 and 274 of the SI gene on chromosome 3.

• This results in a loss-of-function, meaning the body cannot produce the functional sucrase-isomaltase enzyme.

• Consequently, the digestive system cannot break down disaccharides into monosaccharides, preventing their absorption

What molecular evidence supports the theory that the North American Arctic was peopled in two distinct waves?

• Scientists determined this through the comparison of nuclear DNA, mitochondrial DNA (mtDNA), and the Y chromosome.

• This molecular homology showed that the Paleo-Eskimos arrived in the first wave about 2500 years ago, while the Neo-Eskimos arrived in a second wave less than 1000 years ago, eventually migrating around the coasts of Greenland

Using the provided SNP data, compare the genetic diversity of the Greenlandic Inuit to populations in the Americas.

• The Greenlandic Inuit carry fewer total variants (SNPs) compared to populations in the Americas. however, the variants that are present in the Inuit population tend to exist at a much higher frequency (greater than 1%).

• This indicates a more homogeneous gene pool with less overall genetic diversity but a high prevalence of specific ancestral alleles

tips for thou sac:

SAC Strategy Tips

• Highlighter Use: Use your highlighters to distinguish between sucrose (fruits) and maltose (grains) to avoid confusion in metabolism questions.

• Recessive Inheritance: Remember that CSID is a recessive disorder, meaning an individual must inherit two copies of the mutated allele to be affected.

• Related Concepts: Be prepared to link this case study to broader concepts like allopatric speciation (isolation of the Inuit) or antigenic drift if the SAC asks for comparisons to other population changes