Discovering Behavioral Neuroscience: An Introduction to Biological Psychology
Detailed textbook notes for chapter 5 Genetics and the Development of the Human Brain.
Freberg, L. (2018). Discovering Behavioral Neuroscience: An introduction to Biological Psychology. Cengage Learning.
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W6 CH 5 - Genetics and the Development of the Human Brain
The Genetic Bases of Behavior
From Genome to Trait
- Genotype - The genetic composition of an individual organism.
- Phenotype - The observable appearance of an individual organism.
- Gene - A functional hereditary unit made up of DNA that occupies a fixed location on a
chromosome.
- Gene expression - The translation of the genotype into the phenotype of an organism.
The Process of Gene Expression:
A strand of DNA transcribes itself into a complementary chain of RNA. Each set of three bases (a
codon) instructs a ribosome to make a particular amino acid: in this example, alanine (Ala),
methionine (Met), valine (Val), and lysine (Lys). The amino acids are linked together to form a
protein.
- Allele - Alternative version of a particular gene.
- Homozygous - Having two identical alleles for a given gene.
- Heterozygous - Having two different alleles for a given gene.
- Recessive allele - A gene that will produce its characteristic phenotype only when it
occurs in a homozygous pair.
- Dominant allele - A gene that produces its phenotype regardless of
whether it occurs in a heterozygous or homozygous pair.
Three Alleles Give Rise to Four Types of Blood => The type A and type B
alleles are dominant over type 0, so a person with AO alleles will have type A
blood and a person with BO alleles will have type B blood. Neither type A nor
, type B is dominant over the other, however, leading to the possibility of having type AB blood.
Sources of Genetic Variability
- Meiosis - Cell division that reduces the number of chromosomes in half in the
reproductive cells.
- Linkage - The characteristic of genes located adjacent to one another
to be passed along as a group. However, linked genes are not
automatically inherited together.
- Crossing over - A process occurring during meiosis in which
chromosomes exchange equivalent segments of DNA.
Crossing Over Contributes to Genetic Diversity => The process of crossing
over, in which two chromosomes exchange equivalent segments of genetic
material, adds to diversity by shuffling the parental genes that are inherited
together.
MUTATIONS => A heritable alteration of genes.
- The vast majority of mutations have little effect. There is some overlap in the genetic
encoding of amino acids. If a segment of DNA that normally encodes a particular amino
acid is somehow switched with another segment that produces the same amino acid,
there will be no effect.
- If the mutant allele conveys some advantage to the organism, it is likely to spread within
the population. On the other hand, a mutant allele may have negative, even fatal,
consequences for the organism. In the latter case, it may disappear from the population.
THE SPECIAL CASE OF THE SEX CHROMOSOMES
- Twenty-two pairs of human chromosomes are perfectly matched, but the remaining pair,
the X and Y chromosomes, feature different sets of genes with only a small number of
overlaps.
- The X chromosome (right) resembles most of the other 22 in appearance, but the Y (left)
is quite unusual. Not only is it much smaller, with less than 1 00 active genes compared
with the X's 2,000 or so, but also it has unusually high amounts of "junk" DNA that
doesn't seem to encode anything useful.
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