BIOLOGY 1M03 Lecture Notes - Lecture 6: Specific Language Impairment, Reelin, Y Chromosome
29 Jun 2018
School
Department
Course
Professor
Recent study by Navarette et al. 2011
Study of mammals in general suggests that increased brain size
correlated with reduced fat levels and less so with reduced
digestive system. Idea that our ancestors were buffering
themselves against shortages against food. If you increase your
likelihood of being successful, you don’t have to gaourge upon on
the rare food items that you get, and build up fat. If we have brains
that allow us to find food better then we don’t have to buffer up on
fat in fear of having shortage. You can trim down on fat, less fat =
less energy costly therefore less energy goes into locomotion
Homo may have had a reduction in both fat and digestive system.
oEfficient bipedal
locomotion – helpful as
you can run down animals
oSteady and high quality
food supply (partly due to
cooking)
oCognitive buffering
oLess need for fat
oConcluded it is a combination
of various things for an
increase in brain size.
Locomotion costs decreased
– bipedalism, you can keep
running faster efficiently. 4-
legged can only run fast in
short time.
We propose that during
human evolution improved
die quality, all maternal
subsidies, cognitive buffering, reduced locomotion costs and
reduced allocation to production all operated simultaneously, thus
enabling the extraordinary brain enlargement in our lineage.
A number of hypotheses remain in contention, but it would appear
that several were involved.
People – Homo Sapiens
Big brain
Small face and mouth
Protruding chin
Long limbs
find more resources at oneclass.com
find more resources at oneclass.com
Short trunk
Genetic Features of People Comparisons with our nearest living
relative:
Human and Chimp Genome projects…
1.06% fixed difference in DNA sequence (ignoring repetitive DNA
and indels)
13,454 homologous proteins shared
29% of these proteins have identical amino acid sequences so
exactly same
Many of the other proteins have small changes that may not affect
the protein’s function
Many DNA changes may be neutral and under genetic drift, no
effect on phenotype
Some changes may be favoured by natural selection.
How can we tell?
The Genetic Code is Redundant
Genetic drift acts on synonymous (silent site) or non-synonymous
(replacement) substitutions
3rd position is redundant, no effect on phenotype. Changes in 3rd
position are synonymous. 1st and 2nd position on codon – non-
synonymous. If changes amino acid, it is non-synonymous.
Selection acts only on non-synonymous substitutions. So if that
particular amino acid is important, there will be selection acting on,
even though there is a random change, natural selection will bring
it back. However, genetic drift doesn’t care, it is random process
that doesn’t care about the phenotype.
Directional selection favours base changes that have a positive
effect on protein function.
When comparing species we see genes that are different between
the two, we can ask : they changed by genetic drift (most
differences being synonymous because haven’t change
functionality of protein) but directional selection was responsible
(more non-synonymous)
Comparing between species, the ratio of non-synonymous to
synonymous substitutions in a gene:
A) should be higher in genes that differ (between species)
because of genetic drift
B) should be higher in genes that differ because of directional
selection
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Study of mammals in general suggests that increased brain size correlated with reduced fat levels and less so with reduced digestive system. Idea that our ancestors were buffering themselves against shortages against food. If you increase your likelihood of being successful, you don"t have to gaourge upon on the rare food items that you get, and build up fat. If we have brains that allow us to find food better then we don"t have to buffer up on fat in fear of having shortage. You can trim down on fat, less fat = less energy costly therefore less energy goes into locomotion. Bipedalism, you can keep running faster efficiently. 4- legged can only run fast in short time. We propose that during human evolution improved die quality, all maternal subsidies, cognitive buffering, reduced locomotion costs and reduced allocation to production all operated simultaneously, thus enabling the extraordinary brain enlargement in our lineage.
