Biological
psychology
this summary is based on lecture slides, the book Psychobiology by Chris Chandler, explanations received
during class and other resources that help explain and remember certain concepts better
1 - Laura C./ Tilburg University/ 23-24/ Biological Psychology
, Evolution & genetics
- Darwin proposed that all organisms are related and share a common
ancestor; he attempted to explain how modern organisms are successful
adaptions of previous generations- these modifications occurring in the
process of natural selection (=those organisms that possess beneficial
characteristics are more likely to survive and reproduce)
via reproduction, these characteristics are passed on to the next generation;
organisms that are not ideally equipped to interact with their environment
stand a smaller chance of adapting to that environment, limiting their
opportunity to survive and reproduce (survival of the fittest)
- with natural selection, there is no specific plan, the environment is the influence, and
evolution is a relatively slow process; genetic modification is an even quicker form of
selection, in which genes are added or deleted for the benefit of the organism or at
least mankind
- evidence for the theory of evolution:
biogeography
fossil record
(looking at the different geological layers reveals changing fossils and these
changes permit the palaeontologist to chart the evolution of species)
structural similarity
(across species there are comparative similarities. In evolutionary terms, these
have developed from a common ancestor)
embryology
(by comparing the development of embryos, it was revealed that there are
similar stages in utero across species)
molecular biology
- mammals evolved from reptiles about 10 million years ago; they were able to feed
their offspring using mammary glands (breastfeeding); they further evolved and
developed the ability to produce and internal environment suitable for the protection
and development of their offspring – pregnancy; the development in utero (in the
uterus) of new living organism permits greater safety and protection from harsh
environments; however, there are still many challenges to the foetus (for example
alcohol)
- in the categories of mammals, humans are arguably the most advanced form of life
compared to the orders of primates; included in the primates are the apes, including
the gibbons, orangutans, gorillas, and chimpanzees; we don’t come from
chimpanzees, though
- humans are members of the family Hominines; within this family, there are two
genera: Australopithecus and Homo; we come from the Homo group – humans are
Homo sapiens
- humans have a relative, Homo erectus, that is now extinct; the Homo species emerged
about 2 million years ago and might come from one species of Australopithecus.
- it is suggested that the Homo sapiens can all be traced back to Africa; about 200,000
years ago Homo sapiens appeared and about 50,000 years ago modern humans began
2 - Laura C./ Tilburg University/ 23-24/ Biological Psychology
, to migrate out of Africa- this is the ‘’Out of Africa’’ hypothesis- people moved from
the African plains in search of resources; the environmental pressures have therefore
shaped modern humans but while we look different and come from different
environments, we are all the same species; the increase in brain volume happened
before the Homo genus arrived, possibly driven by the increased use of tools
- human genes are not that different from those of our close relatives-the chimpanzee
and the bonobo; the differences are argued to be due to changes in transcription and
translation of the genetic codes; we both have opposable thumbs, but ours are more
helpful in manipulating objects; the biggest and most important difference is the
brain; the human brain has evolved over tens of millions of years to be the most
powerful organ in the natural world and now we can look at its genetic basis: there are
important changes in the protein sequences in the human genome, together with
duplication and deletion of genes, and further changes in non-coding regions of the
genome that are involved in gene expression; humans have, for example, lost some
genes for olfactory receptors (other animals have big brains too, but they are nowhere
near as complex as the human brain)
- the brain itself is an evolutionary development of the vertebrate’s spine; the big
difference in brains comes when we look at more recent adaptions of the brain, most
notably the cerebrum, which is the most developed part of the human brain, and more
developed compared to other species; the human brain has more convolutions (sulci),
hence conferring a greater volume to the cortex; in terms of being human, the cortex
is the main brain difference; neurons and communication is the same, but architecture
and function of cortex are uniquely human
y-chromosomal Adam- the most recent common ancestor from whom all currently living
people are descended on the father’s side
mitochondrial Eve- the most recent woman from whom all living humans are descended
matrilineally through transmission of mitochondrial DNA
- traits become more common based on a few key
steps:
variation
heritability
struggle for existence
survival and reproductive rates
- we can see evolution in real-time in experiments
made with antibiotics and how bacteria learns to
adapt to environments with high concentration of
antibiotic
From evolution to genetics
chromosome: a threadlike structure of nucleic acids and protein found in the nucleus of most
living cells, carrying genetic information in the form of genes
gene: a distinct sequence of nucleotides forming part of a chromosome
nucleotides: they form the basic structural unit of nucleic acids such as DNA
3 - Laura C./ Tilburg University/ 23-24/ Biological Psychology
, - in behavioural genetics, there are two subtypes of heritable characteristics or traits:
qualitative
quantitative
qualitative traits are often influenced by a single gene and follow a simple pattern of
inheritance
- phenotypes are qualitatively different
- qualitative traits are typically unaffected by environmental factors; there are several
factors that may alter the pattern of inheritance of the characteristic or disorder.
- genetic heterogeneity describes an eventuality where clinically similar disorders are
caused by mutations in the same gene, result in diverse conditions
- sometimes individuals who have inherited disease-associated alleles do not always
express the disease completely or partially= penetrance – an allele that does not
always lead to the disorder is said to have low penetrance
- mosaicism is when not all the cells in the body are genetically identical; this may
come about via atypical cellular divisions during early development- such as in
Turner’s syndrome (where there is a deletion of the X chromosome from the normal
XX genotype in some but not all the cells)
- environmental factors, especially those in utero, can give rise to disorders that are
similar to those of the genetic origin = phenocopies (example: the rubella virus that
can cause deafness as can several genetic defects)
multiple genes, some of only modest contribution, influence a quantitative trait; they do not
follow simple patterns of inheritance- they are more variable and less predictable than their
qualitative counterparts
- the phenotype with a quantitative trait is expressed along a continuum (for example,
ADHS); phenotypic expression of a quantitative trait, unlike the qualitative traits, is
subject to alteration and migration by environmental factors
- many disorders are polygenetic; the term quantitative trait loci (QTL) describes how
many multiple genes at different locations on the chromosome contribute to the
quantitative trait
- using linkage analysis, geneticists can investigate QTLs, looking for common
occurrences in individuals with a
particular characteristic or disorder
Mendelian genetics
- Mendelian inheritance refers to certain
patterns of how traits are passed from
parents to offspring; these general patterns
were established by the Austrian monk
Gregor Mendel, who performed thousands
of experiments with pea plants in the 19th
century
- Mendel noted that only one trait appeared
in the first-generation cross – this is
referred to as the dominant trait (yellow
4 - Laura C./ Tilburg University/ 23-24/ Biological Psychology
, seeds, in this case either Y1 or Y2); the recessive trait (green seeds, as with g1 and
g2) was not expressed because it was overridden by the yellow seed trait (in a Y1:g1
seed, the Y1 factor is expressed and the g1 factor is suppressed); in the second
generation, green-seeded pea plants were produced (g1:g2) despite not being observed
in the first-generation plants; the recessive trait was passed on to the second
generation (as with our Y1:g1 plant); the first-generation plants were carriers of the
recessive trait (g1), but because it was combined with a dominant trait (Y1) it was not
observable => there is a difference between observed traits and genetic traits (what is
observed is called the phenotype and what is transmitted genetically is the genotype)
Human karyotype
- karyotype= an organised set of
chromosomes
- the karyotype of a human contains 46
chromosomes: 22 identical pairs from
mother and father and 1 set of ‘sex’
chromosomes (x and x chromosome for
females and x and y chromosome for
males)
- before birth, the X chromosome of the
mother and father ‘battle’ for a place in
the DNA; parents bring to the table three
X chromosomes, and therefore some have to be deactivated
DNA in the cell
genome= the whole genetic information of an organism
chromosome= a long strand of DNA wound around histones (= protein used to fold the
DNA so it doesn’t tangle); it contains many genes
gene= part of DNA with an instruction to make proteins
telomere= region at the end of the chromosome (protects the DNA during cell division; the
more a cell divides, the smaller the telomere gets; people who reach 90 or 100 y.o have
longer telomeres)
allele= the two alternative forms of a gene found at
the same place on a chromosome; they exist only in
pairs to produce a phenotypic effect (an observable
trait)
gene loci= a specific/ fixed position on a chromosome
where a particular gene/ genetic market is located
5 - Laura C./ Tilburg University/ 23-24/ Biological Psychology
,autosomal dominant trait= patter of inheritance characteristic of some genetic disorders;
autosomal means that the gene in question is located on one of the non-sex chromosomes
(=autosomes); dominant means that a single
copy of the mutated gene (from one parent) is
enough to cause the disorder=> a child of a
person affected by an autosomal dominant
condition has a 50% chance of being affected
by that condition via inheritance of a dominant
allele (e.g. Huntington’s disease)
autosomal recessive disorder, on the other
hand, requires two copies of the mutated gene
(one from each parent) to cause the disorder
x-linked recessive inheritance= a mode of inheritance in which a mutation is a gene on the
X chromosome that causes the phenotype to be always expressed in males and in females
who are homozygous for the gene mutation
6 - Laura C./ Tilburg University/ 23-24/ Biological Psychology
,genotype vs phenotype:
genotype= is the genetic makeup of a cell in an organism
phenotype= traits that can be observed in the organism, based on genes and environment
selection can occur for specific phenotypes; a phenotype doesn’t always have to be visible- it
can also be sensitivity to certain things, becoming depressed, tendency to be persistent,
chance to develop a specific disease, etc.
DNA (Deoxyribonucleic Acid)
- the DNA is the recipe book for making proteins
- its physical structure is described using the term double helix: a molecule of DNA is
made from two linked strands that wind around each other and look like a twisted
ladder; each strand has a sugar-phosphate backbone; one sugar-phosphate and a base
created a nucleotide (the building block of RNA and DNA)
- the DNA is a long chain of nucleotides that form base pairs:
nucleotide A opposite T (A-T)
nucleotide C opposite G (C-G)
7 - Laura C./ Tilburg University/ 23-24/ Biological Psychology
,8 - Laura C./ Tilburg University/ 23-24/ Biological Psychology
,Transcription and translation
- in the nucleus a piece of DNA, a gene, is copied (=transcription) into messenger
RNA (mRNA)
- in the cytoplasm, the mRNA of the gene is translated into a protein at the ribosome
(the ‘protein factory’)
the genetic code- a gene contains information for making a protein
- proteins are made of amino acids ( a protein can consist of one or more chains of
amino acids = polypeptides)
- there are approx. 20 different amino acids are used to make proteins
- 3 nucleotides together (= triplet code/ codon) are the key to which amino acid will be
produced in the protein
step 1: transcription: from DNA to RNA
- a gene from the DNA template is transcribed to a primary RNA
- the difference between RNA and DNA:
RNA has U instead of T nucleotide
RNA is shorter than DNA
RNA can leave the cell nucleus
- only one copy of a recipe is allowed to leave the library!
9 - Laura C./ Tilburg University/ 23-24/ Biological Psychology
, step 2: splicing RNA into mRNA
- exons and introns form a gene; however, only exons code for proteins; the primary
transcript RNA reads the DNA, including the introns; however, the mRNA splices the
exons together, removing the introns; the mRNA is then transported out of the nucleus
into the cytoplasm where translation is going to occur
step 3: translation of mRNA into a chain of amino acids
- mRNA connects with a ribosome, and each mRNA condon merges/ sticks with
transfer RNA (tRNA) anticodon
- each tRNA molecule has an amino acid on one end and an anticodon on the other;
appropriate condon combinations meet at the ribosome, determining the order of
amino acids in the growing protein chain
- each new amino acid
combines with the previous
one and starts to form a chain:
the protein
- when the mRNA is
finished, the primary protein is
completed; the mRNA may
combine again with a
ribosome to repeat the process
(peptides vs amino acids- peptides
are short chains of amino acids
that have been linked by amide- or
peptide-bonds)
10 - Laura C./ Tilburg University/ 23-24/ Biological Psychology
