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Chapter 3

PSY100H1 Chapter Notes - Chapter 3: Estrous Cycle, Extracellular Fluid, Rna Interference

Course Code
Michael Inzlicht

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Genetic and Biological Foundations
What is the Genetic Basis of Psychological Science?
-Major event in the biological revolution was the Human Genome Project
oMapped the entire structure of human genetic material
-Within nearly every cell, there is a genome
oGenome provides instructions for everything, from how to grow a nose to
where to place it on the body
What part of the body the cell becomes is determined by which
genes are turned on and off within the cell and this is determined
from the cues from outside the cell
Genome – option, environment determines which option is taken
Turning on and off of genes provides insight how physical bodies
develop and how the brain works
Genetics – typically used to describe how characteristics are passed
down by inheritance, but also refers to the process of turning on
and off of genes
-Within each cell there are chromosomes, which are structured made up of genes
oTypical human: 23 pairs, half of each from different parent
Genes are components of DNA
Gene – unit of heredity that determines a particular
characteristic in an organism
Segment of DNA that is involved in producing proteins that
carry out specific tasks
oGene expression – process by which genes produce
the RNA and the proteins they then produce or
switching a gene on
Gene: how to produce proteins, when to
produce proteins, environment determines
The environment during development is
likely to cause genes to switch on or off

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Genes – option, environment determined
which action is taken
Gene expression plays a role in specializing
cells for specific functions
Gene expression – physical body
Gene expression – involved in al
psychological activity allows us to learn,
see, fall in love
DNA is a double helix of sugar, phosphate and nitrogen molecules
The sequence of molecules along the DNA strand specifies
and exact instruction, through the production of RNA, to
manufacture distinct proteins
Thousands different types
Basic chemicals that make up the structure
of the cell and direct it activities
-The relatively small number of gens in the human DNA (30 000) suggests that the
complexity of humans is not simply due to our processing a large number of gens,
but more likely due to subtleties in the way that genes are expressed and regulated
- Important to understand how genes interact
oHow to alter gene function
1. Heredity involves passing along genes through reproduction
-Selective breeding was used by Mendel to discover that there a mechanisms
responsible for heredity
-From his experiment Mendel deduced that there are units of heredity (now
referred to as genes) that exist in two versions
oAlleles are the versions of genes
Dominant alleles (genes) are expressed whenever they are present
Recessive alleles (genes) are expressed only when they are matched
with similar gene (another recessive gene)
a.Genotype and phenotype

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-The existence of dominant and recessive gens means that not all genes are
outwardly expressed
-Genotype – the genetic constitution determined at the moment of conception, the
actual genetic make up
-Phenotype – observable physical characteristics that result from both genetic and
environmental influences
oExample: for Mendel, even thought he had two purple flowers and the had
the same phenotype, they could have had different genotypes (one being
PP and the other being Pp)
-Environmental factors that could affect the phenotype: good nutrition – bigger
size, sun tan – change in complexion
b. Polygenic effect
-When there is a certain variability for a trait (such as height) within a population
indicates that the characteristic is polygenic or that it is influenced by many genes,
as well as the environment
oMost human traits and diseases are polygenic
2. Genotype variation is created by sexual reproduction
-Although siblings have same parents, they differ in many way
oThis occurs because the combination of genes in different due to random
cell division which occurs prior to reproduction
From calculating all the possible outcomes that can arise from the
combination of 23 chromosomes, the result is one of 8 million
possible outcomes and the parent themselves is one out 8 possible
So there are 64 trillion possible combinations
oThe net outcome is a unique genotype is created at
the moment of conception, and this accounts for the
genetic variation in human species
-The zygote grows via cell division
oSometimes there are mutations and most of the time they are benign
Occasionally a mutation might produce an advantage or
disadvantage in terms of survival and reproduction
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