Download Chapter 13 Chromosomes

Chapter 16 Human Origins and Evolution
Answers to Review Questions
1.
c, e, b, g, f, a, d, h overlaps: a + f, d + h, f + g
2.
Hominoids are ancestral to apes and humans, whereas hominins are ancestral to humans
only. Thus, hominoids are more ancient.
3.
Physically, chimpanzees are not as similar to us as were the australopithecines, yet the
australopithecines are in a different genus from us.
4.
A single gene can control the rates of development of specific structures, causing
enormous differences in the relative sizes of organs in two species.
5.
The hunting behavior of A. garhi and the time and place where it lived suggests that it
could have been a bridge between Australopithecus and Homo.
6.
Fossil evidence and mtDNA evidence support an "out of Africa" emergence of modern
humans. Anthropological evidence indicates three waves of migration of native Americans from
Siberia; molecular evidence suggests one migration.
7.
Y chromosome and mitochondrial DNA sequences enable researchers to trace the genetic
contributions of fathers and mothers, respectively.
8.
Bipedalism, larger brain, improved fine coordination
9.
If it is that highly conserved it must be vital, and variants would be selected out of
modern human populations.
10.
Small insertions and deletions might alter the regulation of the same protein in chimps
and humans, but not introduce a new structure or function or drastically alter an existing one.
11.
Estimating passage of time requires a steady interval, such as a minute. Mutation rates
vary.
12.
a.
Differences in genes that control rates of development of particular structures
b.
Variants of single genes with obvious effects, such as body hair
In general, differences in gene expression can account for phenotypic distinctions
between humans and chimps despite similarity in genome sequence.
13.
Gene sequences are more specific because different codons can encode the same amino
acids.
14.
Mutation rates are not the same across genomes. Genes mutate at different rates.
15.
One gene encodes one polypeptide, and so comparing the evolution of a gene tracks a
tiny part of the biology of the organism. DNA hybridization assesses relationships among many
genes, and thus means more. Also, much of the genome does not encode protein.
16.
A chromosome band may contain many genes, and so comparing them is not specific.
17.
Knowledge of a DNA, RNA, or polypeptide sequence and the mutation rate is necessary
to construct an evolutionary tree diagram. An assumption is that mutation rate is constant. A
limitation is that only one biochemical is considered, and not large scale characteristics such as
behavior and anatomy.
18.
SNP – variation in sequence at a single site indel = patterns of insertions and deletions
(CNVs) linkage patterns = groups of neighboring SNPs
19.
Human and chimp genomes differ by copy numbers.
20.
Keratin gene mutation accounts for minimal body hair on humans. Other possibly single
gene traits of humanity are a larger brain, longer fetal development, and language.
21.
Sterilizing people with mental retardation. Encouraging poor people to limit family size.
Avoiding marriage to a person who carries a disease-causing allele.
22.
Positive and negative natural selection do not have intent to alter a population in a
particular way. Positive selection increases the prevalence of an adaptive trait and negative
selection acts against a harmful trait. Positive eugenics encourages reproduction and negative
eugenics discourages it.
Answers to Applied Questions
1.
Neanderthals may have died out via natural selection because they could not adopt fast
enough to a changing climate
2.
A group of australopithecines who were especially good hunters may have broken off
from a larger group and found a new place to live and breed.
3.
The australopithecines were geographically dispersed, so different groups could have
evolved in different ways to a greater extent than did the more widespread Homo.
4.
a.
A small duplication occurred in human chromosome 11 to give rise to the
Betazoid karyotype. The Klingon and Romulan karyotypes could have arisen from fusion
of human chromosomes 15 and 17.
b.
The Betazoids are our closest relatives because of greater similarity in
chromosome bands and chromosome arrangement. Cytochrome c sequences and intron
pattern in the collagen gene are identical between humans and Betazoids.
c.
They are not distinct species because they can interbreed.
d.
(3)
5.
Many animals have much more acute senses of taste and smell than we do.
6.
Natural selection must have acted against traits that chimps have that we do not,
suggesting that we no longer required these traits to reproduce.
7.
People in developing nations might be alarmed by white-coated strangers wielding
hypodermic needles seeking blood samples. A compromise would be to collect hair instead of
blood, and use PCR to amplify the genes. Another compromise is to offer vaccines in exchange
for tissue samples.
8.
The action was eugenic because it indirectly selected against nonwhite students. It was
not eugenic in that, superficially, all applicants were evaluated using the same criteria.
9.
The child would be a modern human.
10.
Spinal muscular atrophy is on human chromosome 5 and might be on horse chromosome
21
11.
The BAZ1B gene encodes a bromodomain next to a zinc finger domain. It is deleted in
Williams-Beuren syndrome, which is a developmental disorder, OMIM 605681. Chimp and
baboon have similar sequences.
12.
Correct genetic conditions: woolly hair, dwarfism, albinism Incorrect: feeblemindedness
13.
Assumes Y chromosome represents surnames. This isn't true for Jewish immigrants to the
US early in the 20th century, for example. Sometimes names are changed. Y leaves out females,
mtDNA leaves out males, sometimes data don't agree. These techniques do not account for
mixing of populations, especially in recent time. Ethnicity and race are not biological
distinctions.
14.
Opinion. The guidelines are eugenic if the goal is to decrease the incidence of the
conditions, to improve society.
15.
a.
Interpretation depends upon which data are considered. One conclusion is that
Homo brains are larger than the other three, supporting correlation of brain size to
intelligence. However, inclusion of Homo floresiensis, if she really is Homo, contradicts
this hypothesis.
b.
16.
A lot of evidence is missing.
a. Homo sapiens
b. nearby evidence of other species, clues to the climate or environment
17.
Not eugenics because the goal was personal, not societal.
18.
a.
6 mya = most recent common ancestor of human and chimp 1.8 mya = Homo
appearing 0.5 mya = Neanderthal split from modern human lineage
19.
b.
Lice live on us.
c.
Lice spread as Homo spread geographically. Need to analyze more genes.
d.
Need fossil evidence too.
a.
Forced sterilization
b.
If a trait in one family is deemed inherited, it might be assumed to be inherited in
another family, when that might not be the case.
c.
Wealthy people seeking partners among other wealthy people
d.
How common the negative traits were in the general population. Whether the
family members were really related biologically. Environmental influences on the traits
considered. Evidence of family members without the negative traits who have beneficial
ones.
20.
Males with the E-M81 subhaplotype left Africa from Morocco to go to Spain and
Portugal.
A SECOND LOOK
1.
Australopithecus garhi may have overlapped with Homo habilis, who overlapped with H.
erectus.
2.
mtDNA sequences would indicate where the founding females came from, and Y
chromosome sequences would track the males.
3.
Either hypothesis could apply, depending upon who the Hobbits really were and when
their ancestors left Africa. Their DNA must be compared to that of modern peoples to distinguish
between the hypotheses.