BIO171 Exam 4

explain why, based on our genomes, humans are similar to each other and diffferent from other members of our biological family

99.6% of our genetic instructions are the same; we differ due to unique genetic mutations & structural genome differences

describe 4 smalll differences in the genome that contribute to genetic variation in humans

insertion of DNA, single nucleotide variant (SNV), deletion of DNA, & tandem repeats (small portions of the genomes are repeated)

describe 1 large difference in the genome that contribute to genetic variation in humans

changes in large portions of chromosomes

roughly how many and what percentage of nucleotides differ between 2 persons?

27 million nucleotides differ; 0.4% of genomes

what is a phylogeny and what information does it convey?

the evolutionary history and relationships of a group of organisms; provides a visual framework for grouping

did humans evolve from chimpanzees or bonobos? use the concept of common ancestor to express the relationship among the 3 species

neither, all 3 evolved from a common ancestor that lived 5-8 million years ago (first humans evolved then later chimps & bonobos evolved)

describe how humans and chimpanzees differ with respect to locomotion

upright walking– chimps: inefficient, use knuckle walking; humans: efficient

tree climbing– chimps: efficient; humans: inefficient

foot– chimps: opposable big toe; humans: non-opposable big toe

foramen magnum– chimps: back of head; humans: underneath the skull

what differences in foot and skull structure between humans and chimpanzees are related to differences between the species in locomotion?

chimps have opposable big toes & could grip surfaces with their feet, while humans lack opposable big toes

chimps’ skull structure caused a forward-leaning posture, while humans’ skull structure caused an upright bipedal posture

jaw shape, tooth size, brain size, & relative length of the thumb and fingers of chimpanzees

larger, U-shaped jaw

larger teeth

1/3 human brain size

relatively shorter thumb w longer fingers (no precision grip)

jaw shape, tooth size, brain size, & relative length of the thumb and fingers of humans

smaller, parabolic jaw

smaller teeth

3x chimps brain size

relatively longer thumb, shorter fingers (precision grip)

what are the four major groups of hominins?

early hominins

australopithecines

robust australopithecines

humans

early hominins

7-4.4 mya

west central and east africa

tree-climbing & bipedalism

small brains

australopithecines

4.2-2.1 mya

east and south africa

bipedalism & tree-climbing

small brains

robust australopithecines

2.7-1.2 mya

east and south africa

bipedalism & tree-climbing

small brains

ate hard foods (roots, nuts, seeds, tubers)

homo habilis (“handy”)

2.4-1.4 mya

east and south africa

bipedalism & some tree-climbing

small/medium brains

stone tools

homo erectus (“upright”)

1.9mya-110,000 years ago

africa and asia

bipedalism

modern body proportions

medium brains

hand axes (more complicated tools)

homo heidelbergensis

700,000-200,000 ya

africa, europe, and possibly asia

large brains

control of fire, wooden spears, and built shelters

homo neanderthalensis

400,000-40,000 ya

europe and asia

large brains (larger than ours)

stout bodies (helped retain heat)

sophisticated tools, clothing, & symbolic objects

homo longi (denisovans)

400,000-30,000 ya

asia

large brains

large molar teeth, robust jaws

homo sapiens

300,000-0 ya

evolved in africa

worldwide

large brains

agriculture 12,000 ya

know the scientific names of the examples of homo species presented

homo habilis

homo erectus

homo heidelbergensis

homo neanderthalensis

homo longi (denisovans)

homo sapiens

how long ago did our lineage diverse from that of neanderthals and denisovans?

600,000 years ago

how long ago did neanderthals and denisovans diverge from each other?

300,000 years ago

what percentage of our genome comes from neanderthals and denisovans & what’re those gene functions

neanderthals = 0.3-4%

denisovans = <1%-5%

shared genes functions: immune system, nerve development; & metabolism

what are the possible combinations of HbA and HbS alleles a person could have, and what severity of sickle cell disease is associated with each?

HbA/HbA — no disease

HbA/HbS — mild disease

HbS/HbS — severe disease

define allele and allele frequency

allele = 1 of 2 or more variants of a gene that determines a particular trait for a characteristic

allele frequency = % of alleles of a particular variant

explain why the frequency of HbS is relatively high in some populations, even though that allele can result in sickle cell disease

bc carrying one copy of the HbS allele provides significant protection for surviving malaria

explain how the HbS allele allowed humans to expand their range in africa beginning 15,000 years ago

the HbS allele allowed humans to overcome malaria which previously made those areas inhabitable

explain why the allele for sickling hemoglobin became prevalent in areas with malaria

it provides 90% protection against severe malaria; the survival advantage offered to carriers (1 HbS allele) by resisiting malaria was so strong that the allele spread rapidly throughout the population

natural selection!

how does natural selection cause changes in traits?

traits that enhance reproduction will increase in frequency

what 3 conditions must be fulfilled for natural selection to occur?

individuals differ in their traits

differences in traits are heritable

differences in traits influence reproduction

be able to determine whether natural selection could be responsible for changes in a trait over time

consider whether the trait influences reproduction & if the 3 conditions are met

explain why the frequency of the allele for sickling hemoglobin is less than 20% in any given population

one copy provides a survival advantage against malaria, while holding 2 copies (HbS/HbS) is usually fatal before reproductive age, which prevents the alllele from becoming too common (balances out)