Name: Date EXERCISE 5 ABO BLOOD GROUP Work with a small group or as your underst

Question

Name: Date EXERCISE 5 ABO BLOOD GROUP Work with a small group or as your understanding of the forc alone to complete this exercise. Review Figures 8.6, 8.7, and 88. Use this information, as well this exercis es of evolution, to help you answer the following questions 1. Many populations thro about the distribution. ughout central Eurasia share high frequencies of the B allele. What does this pattern suggest evolutio nary history of these populations? Describe the evolutionary force that likely caused this trait Percentage of population that has the B allele ?0-5 ·10-15 ·20-25 5-10 15-20 25-30 From Mourant ot al 1976 The Distribution of the Human Blood Groups and Othe Polymorph ams, 2nd edition. Map 2. Copyrigh t O Oxford University Press, Inc By permission of COxford University Prets FIGURE 8.7 Distribution of the B Allele Relative distributions of the B allele vary geographically, with the B allel being more common in Central Asia 2. The O allele is unusually frequent in the Americas. What does this pattern suggest about the evolutionary history of these populations? Describe the evolutionary force that likely caused this trait distribution. EXERCISE 6 LACTOSE TOLERANCE Work with a small group or alone to complete this exercise 1. Describe a population where you would expect to find a low frequency of adult lactose tolerance. Percentage of population that has the O allele 50-60 70-80 90-100 60-7080-90 FIGURE 8.8 Distribution of the O Allele Relative distributions of the O allele vary geographically. Notice the O allele is more common in the Americas and parts of Australia O 2. Why is adult lactose tolerance infrequent in that population? Q alele vary gsogra hcally otie 3. Describe a population where you would expect to find a high frequency of adult lactose tolerance

Explanation / Answer

1. Human blood groups are interesting from both medical and evolutionary perspectives. Different blood groups confer resistance or susceptibility to a wide range of infectious diseaseand, likely as a result of this, have been under long-term balancing selection across primates. They also vary dramatically in frequency across human populations and, probably, across time as well.

the genetic makeup of an individual. Genotype can refer to an organism's entire genetic makeup or the alleles at a particular locus.

The ABO determining variants are on the 1240k capture array that has been used to genotype many samples, so I was able to look them up in a sample of around ~500 ancient individuals (the same individuals used here). I looked up present-day allele frequencies in gnomAD. It’s harder to genotype the RHD deletion from capture data so I used a smaller dataset of around ~200 individuals with published shotgun data to genotype this deletion. I couldn’t find it in gnomAD so I used allele frequencies from 1000 Genomes.

it tuns out that the O allele is at high frequency in hunter-gatherers, but relatively rare on the Steppe. The B allele seems to be absent in both hunter-gatherers and early farmers, and seems to be introduced from the steppe in the Bronze Age. The Rh- allele seems to be relatively common in hunter-gatherers and, particularly, in steppe populations, and relatively rare in early farmers, partly confirming Haldane and Cavalli-Sforza’s hypotheses. Allele frequency estimates are in the figures below (bars show 95% binomial confidence intervals). due tothese evolutionary aspects most of the central europeans possess B allele.

2.

All major ABO blood alleles are found in most populations worldwide, whereas the majority of Native Americans are nearly exclusively in the O group. O allele molecular characterization could aid in elucidating the possible causes of group O predominance in Native American populations. In this work, we studied exon 6 and 7 sequence diversity in 180 O blood group individuals from four different Mesoamerican populations. Additionally, a comparative analysis of genetic diversity and population structure including South American populations was performed. Results revealed no significant differences among Mesoamerican and South American groups, but showed significant differences within population groups attributable to previously detected differences in genetic drift and founder effects throughout the American continent. Interestingly, in all American populations, the same set of haplotypes O(1), O(1v), and O(1v(G542A)) was present, suggesting the following: (1) that they constitute the main genetic pool of the founding population of the Americas and (2) that they derive from the same ancestral source, partially supporting the single founding population hypothesis. In addition, the consistent and restricted presence of the G542A mutation in Native Americans compared to worldwide populations allows it to be employed as an Ancestry informative marker (AIM). Present knowledge of the peopling of the Americas allows the prediction of the way in which the G542A mutation could have emerged in Beringia, probably during the differentiation process of Asian lineages that gave rise to the founding population of the continent.

3,4. Approximately 65 percent of the human population has a reduced ability to digest lactose after infancy. Lactose intolerance in adulthood is most prevalent in people of East Asian descent, affecting more than 90 percent of adults in some of these communities.

Lactose intolerance in infants (congenital lactase deficiency) is caused by mutations in the LCTgene. The LCT gene provides instructions for making the lactase enzyme. Mutations that cause congenital lactase deficiency are believed to interfere with the function of lactase, causing affected infants to have a severely impaired ability to digest lactose in breast milk or formula.

Lactose intolerance in adulthood is caused by gradually decreasing activity (expression) of the LCTgene after infancy, which occurs in most humans. LCT gene expression is controlled by a DNA sequence called a regulatory element, which is located within a nearby gene called MCM6. Some individuals have inherited changes in this element that lead to sustained lactase production in the small intestine and the ability to digest lactose throughout life. People without these changes have a reduced ability to digest lactose as they get older, resulting in the signs and symptoms of lactose intolerance.

5. high lactose tolerance is observed in north europeans.

Lactose tolerance is exceptionally widespread in Northern European countries such as Sweden and Finland, with tolerance levels of 74% and 82%, respectively. Theoretically, this may result either from a strong local selection pressure for lactose tolerance, or from immigration of lactose tolerant people to Northern Europe. We provide several lines of archaeological and historical evidence suggesting that the high lactose tolerance in North Europeans cannot be explained by selection from in situ milk consumption. First, fresh cow milk has not belonged to the traditional diet of Swedes or Finns until recent times. Second, not enough milk has been available for adult consumption. Cattle herding has been neither widespread nor productive enough in Northern Europe to have provided constant access to fresh milk. We suggest that the high prevalence of lactose tolerance in Finland in particular may be explained by immigration of people representing so-called Corded Ware Culture, an early culture representing agricultural development in Europe.

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