Transcript Human Genetics - Chapter 16

Human Genetics
Concepts and Applications
Tenth Edition
RICKI LEWIS
16
Human
Ancestry
PowerPoint® Lecture Outlines
Prepared by Johnny El-Rady, University of South Florida
Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Human Evolution
The fossil record is incomplete but provides
evidence to the events in human evolution
DNA analysis provides additional information
Species with common DNA sequences are
more likely to have arisen from a common
ancestor
2
Homo sapiens
“The wise human”
Probably first
appeared about
200,000 years ago
60 million years ago
an ancestral
rodentlike insect
eater flourished
Chapter opener
3
Aegyptopithecus
30-40 million years ago (MYA)
Monkeylike animal, size of a cat
Found in tropical forests of Africa, tree dweller
Social
Possible ancestors of gibbons, apes, and
humans
4
Dryopithecus
22-32 MYA
Oak ape
Found in SW and central
Europe
One of first hominoids
Ancestor to apes and
humans
Figure 16.1
Lived in trees but could walk
Size of a 7 year old, small
brains, and pointed snout
5
Hominin
Ancestor to humans
Fossils from 4-19 MYA scarce
6 MYA hominin line broke off from apes
At least three candidates for first hominin
Ardipithecus kadabba (from Ethiopia)
Sahelanthropus tchadensis (from Chad)
Orrorin tugenensis (from Kenya)
6
Figure 16.2
7
Australopithecus
2-4 MYA
Bipedal, not a tree dweller
Several species
Flat skull bases
Stood 4 to 5 feet tall
Humanlike teeth
Brain size of a gorilla’s
Hunter-gatherer lifestyle
8
Australopithecus
4.1 MYA A. anamensis
3.6 MYA A. afarensis (Lucy)
- Larger brain, more humanlike skull
- Less prominent face
2.5 MYA A. garhi
- Hunted and butchered meat
- 4.5 feet tall, long arms like ape
- Small cranium, large teeth, apelike face
- Fossils from Afar region
9
A. afarensis “Lucy”
Figure 16.3
10
Homo habilis
2.3 MYA
Humanlike cave-dweller
Cared intensely for young
First to use tools extensively (habilis
means handy)
Coexisted with and was followed by
Homo erectus
11
Table 16.1
12
Homo erectus
1 MYA
Shallow forehead, massive
brow ridges, brain about 1/3
the size of modern humans
Angled skull-base, possible
speech
Social, cooperative, used fire
Male-female pairs
Found in China, Java, Africa,
Europe, and SE Asia
Pockets may have persisted
until about 35,000 years ago
Figure 16.4
13
Homo sapiens idaltu
Lived about 156,000
years ago
Physically similar to
modern humans
Probably resembled
an Australian
aborigine
Figure 16.5
14
Homo neanderthalensis
Split from the human lineage about
516,000 years ago
Lived all over Europe
Reconstructions of skeletons indicates
major differences from us
- Larger brains; prominent brow arches
- Muscular jaws; distinct spacing of teeth
- Large, barrel-shaped chest
15
Homo neanderthalensis
Neanderthals coexisted with the lighterweight, finer-boned Cro-Magnons from
30,000-40,000 years ago
Cro-Magnons had signs of cultures, including:
- Communal graves, jewelry, and intricate
cave art
For reasons unknown, by 28,000 years ago
Neanderthals disappeared
16
Modern Humans
Cave art from about 14,000 years ago
indicates that by that time our ancestors
had achieved milestones in cultural
evolution
- Fine hand coordination; use of symbols
A preserved man, frozen in ice from about
5,200 years ago, is genetically like us
- Ötzi, the Ice Man
17
Molecular Evolution
The study of evolution through comparison of:
- DNA and protein sequences
- Chromosome banding
- Genome structure
Mutations occur in DNA over time
Comparing two DNA sequences
- Fewer changes indicate closer relation
and more recent divergence
- More changes, more ancient divergence
18
Comparing Chimps and Humans
We have more in common with chimpanzees
than any other animal
DNA hybridization and protein comparisons
reveal that chimps and humans share
98.7% of their gene-encoding proteins
Comparison of insertions and deletions
(indels) suggests that our similarity is only
about 96.6%!
19
What Makes Us Human
Traits defining “humanness” may be rare
Keratin gene
- Affects hair coverage
- Expressed in chimps and gorillas
- Nonsense mutation in humans
Speech – FOXP2 gene
Hemoglobin genes
- Humans switch from embryonic to fetal versions
of hemoglobin
- Longer fetal period, increased brain growth
20
What Makes Us Different
Underlying difference that makes us humans
may be in gene expression not the genome
sequence
Our genome is like that of the pufferfish,
minus many of the DNA repeats and introns
Overall, the human genome has a more
complex organization of the same basic
parts than simpler animals
- Contains many more duplicated genes
21
Ancient DNA
DNA has been isolated from a few well
preserved fossils
- 17 million-year-old magnolia leaf in amber
- 4-5 million-year-old insects in amber
Researchers at Penn State University have
sequenced nearly all of the mammoth
genome from specimens that were flashfrozen at high altitudes
22
Comparing Chromosomes
Karyotypes among great apes differ mostly
by inversions
Karyotypes between apes and more
primitive primates differ predominantly by
translocations
All mammals share identical Xchromosome banding
Synteny is the correspondence of gene
order preserved between two species
23
Table 16.2
24
More Genetic Markers
Mitochondrial DNA (mtDNA)
- Used to trace maternal lineage
- Lack of DNA repair in mitochondria
leads to a faster mutation rate
Y chromosome
- Sons inherit it from their fathers
- Used to trace male lineage
25
Mitochondrial “Eve”
mtDNA sequences of indigenous peoples
worldwide were compared to determine
the common ancestral mtDNA sequence
Hypothesized ancestral woman lived
approximately 170,000-200,000 years
ago in Africa
This is remarkably close to the date of the
Homo sapiens idaltu fossils
26
Populating the New World
People spread across Eurasia and
elsewhere by 40,000 years ago, and
lastly through Siberia
During the last Ice Age (23,000 to 18,000
years ago), people entered the Americas
by crossing the Bering Strait from Siberia
Today, Native Americans carry a very
distinctive genetic nametag: Five mtDNA
and two Y chromosome haplogroups
27
Populating the New World
By 14,000 years ago, Native Americans had
arrived inland
- Genetic evidence also suggests that
some populations died out
The earliest Eskimos came from a different
migration than the one that was ancestral
to Native Americans and modern Eskimos
- The left no present-day descendants
28
Figure 16.18
29