Human Genetics Flashcards
What fossil species is Lucy, and how old is she?
Lucy is an Australopithecus afarensis fossil, approximately 3.2 million years old.
What is the significance of Homo habilis in human evolution?
Homo habilis forms a link between the more ape-like Australopithecus species, such as Lucy, and modern precursors to humans, like Homo erectus.
Over what time period did Homo erectus exist, and how did its appearance change over time?
Homo erectus existed from 1.6 million years ago (MYA) to 0.3 MYA. Over time, later Homo erectus specimens increasingly resembled Homo sapiens.
What are the two competing hypotheses regarding the evolution of modern Homo sapiens?
The two competing hypotheses are the multiregional hypothesis and the out-of-Africa hypothesis. The multiregional hypothesis suggests that Homo sapiens evolved throughout Africa and Asia, while the out-of-Africa hypothesis suggests that Homo sapiens evolved in Africa and later migrated to other regions.
Which hypothesis regarding human evolution is supported by genetic data, and why?
Genetic data strongly support the out-of-Africa hypothesis, as it shows recent common ancestry of all humans, and greater genetic diversity is found in African populations.
How do mitochondrial DNA studies contribute to our understanding of human evolution?
Mitochondrial DNA studies trace maternal ancestry and show that the most recent common ancestor (MRCA) of modern humans, often called “Mitochondrial Eve,” lived around 200,000 years ago in Africa.
What is the significance of the Y chromosome in tracing human ancestry?
The Y chromosome, inherited only from fathers to sons, reveals a more recent MRCA (~50,000 years ago) and shows different Y lineages in various geographic regions, helping trace human migration patterns.
What is the role of recombination in shaping the human genome?
Recombination shuffles genetic material between chromosomes during reproduction, breaking up linkage between adjacent sections of the genome and leading to different gene trees across loci.
What evidence is there for hybridization between Homo sapiens and other hominins like Neanderthals and Denisovans?
Genetic evidence shows hybridization with Neanderthals in Eurasia and traces of Denisovan genes, especially in populations in Oceania, indicating interbreeding with humans who left Africa.
What is FST and how does it relate to population differentiation?
FST is a measure of genetic variation between populations relative to total variation. It quantifies how much allele frequencies differ between populations, indicating levels of genetic divergence.
How does genetic drift affect population differentiation over time?
Genetic drift leads to random changes in allele frequencies, causing isolated populations to diverge over time. With enough time, populations can become genetically distinct, potentially fixing different alleles.
How do humans’ perception of racial differences compare to actual genetic differences?
Human perception of racial differences is often exaggerated. Genetically, humans are 99.9% identical, with most variation (~85%) occurring within populations rather than between them.
What is trans-specific polymorphism, and how does it affect our understanding of evolutionary relationships?
Trans-specific polymorphism occurs when genetic variation persists across species due to balancing selection. It can result in gene trees that conflict with species trees, leading to incomplete lineage sorting.
What is incomplete lineage sorting, and how can it create discordance between gene trees and species trees?
Incomplete lineage sorting happens when genetic variation is not fully sorted before species diverge, causing different gene trees to show different evolutionary relationships than the species tree.
How do skin pigmentation and lactose tolerance genes reflect recent selection in humans?
Skin pigmentation reflects adaptation to UV exposure, while lactose tolerance reflects historical dairy farming practices. Both traits show genetic adaptation based on environmental pressures.
