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Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
Chapter 20, Problem D.11

In Island Melanesia and Polynesia, most mtDNA haplotypes are of Asian ancestry, whereas Y chromosome haplotypes are predominantly New Guinean. Provide a hypothesis for this sex-biased distribution.

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1
Understand the biological basis of mtDNA and Y chromosome inheritance: mtDNA is maternally inherited, meaning it is passed down from mothers to their offspring, while the Y chromosome is paternally inherited, passed from fathers to sons.
Recognize that the observed pattern—Asian ancestry in mtDNA and New Guinean ancestry in Y chromosomes—suggests different migration or mating patterns for males and females in these populations.
Formulate a hypothesis that could explain this sex-biased distribution, such as a scenario where Asian women migrated and integrated into New Guinean male populations, leading to Asian mtDNA lineages and New Guinean Y chromosome lineages.
Consider historical or anthropological factors that might support this hypothesis, such as patrilocality (where women move to the husband's community), male-biased local residence, or differential migration routes for men and women.
Summarize the hypothesis by linking the genetic evidence to social or demographic behaviors that result in the observed pattern of Asian mtDNA and New Guinean Y chromosome haplotypes.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mitochondrial DNA (mtDNA) Inheritance

mtDNA is inherited exclusively from the mother, making it a useful marker for tracing maternal ancestry. Because it does not recombine, mtDNA haplotypes reflect maternal lineage and migration patterns over generations.
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Y Chromosome Inheritance

The Y chromosome is passed from father to son, serving as a marker for paternal ancestry. Its haplotypes reveal male lineage and can show different migration or admixture patterns compared to maternal markers.
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Sex-Biased Gene Flow and Migration

Sex-biased gene flow occurs when males and females contribute differently to the gene pool due to cultural practices like patrilocality or matrilocality, or historical migration events. This can lead to contrasting patterns in mtDNA and Y chromosome distributions.
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Related Practice
Textbook Question

Describe how selection at a locus can result in a loss of polymorphism surrounding the locus.

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How can ancient DNA provide insight into past migrations that analyses of extant human genomes fail to uncover?

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Textbook Question

Denisovans are known from bones found in Denisova Cave in the Altai Mountains in Siberia, but traces of their DNA are found in Australians and Melanesians, whose ancestors likely migrated across Asia much farther to the south. How can these geographic differences be reconciled?

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Textbook Question

When the human genome is examined, the chromosomes appear to have undergone only minimal rearrangement in the 100 million years since the last common ancestor of eutherian mammals. However, when individual humans are examined or when the human genome is compared with that of chimpanzees, a large number of small indels and SNPs can be detected. How are these observations reconciled?

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Textbook Question

The mtDNA sequence of Neanderthals is more similar to that of modern humans than to that of Denisovans. However, analyses of nuclear DNA clearly indicate that Neandertals and Denisovans share a more recent common ancestor than either of these hominins shares with modern humans. Propose a hypothesis to resolve the discrepancy between the mtDNA and the nuclear genome.

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Textbook Question

A 9-bp deletion in the mitochondrial genome between the gene for cytochrome oxidase subunit II and the gene for tRNAᴸʸˢ is a common polymorphism among Polynesians and also in a population of Taiwanese natives. The frequency of the polymorphism varies between populations: The highest frequency is seen in the Maoris of New Zealand (98%), lower levels are seen in eastern Polynesia (80%) and western Polynesia (89%), and the lowest level is seen in the Taiwanese population. What do these frequencies tell us about the settlement of the Pacific by the ancestors of the present-day Polynesians?

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