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Lecture 2

PSYCH 9A Lecture 2: Psych 11A - Lecture 2 - Psychology Fundamentals


Department
Psychology
Course Code
PSYCH 9A
Professor
Bruce Berg
Lecture
2

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PSYCH 11A - LECTURE 2
CHAPTER 2 - GENETICS & EVOLUTIONARY ROOTS OF BEHAVIOR
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There are many different kinds of cells in our bodies:
-Red blood cells: contain large amounts of a protein called hemoglobin. Hemoglobin picks up oxygen when red
blood cells pass through the lungs and then drops off the oxygen when these cells pass through the body’s other
tissues.
-Intestinal goblet cells: found in the lining of small intestine, manufacture granules of a protein called mucigen.
When a goblet cell releases mucigen granules into the intestine, they combine with water to make mucin, a
component of the mucus that lubricates the intestine.
-Retinal photoreceptors: rod cells, which serve as light detectors in the eye, contain a protein called rhodopsin
that absorbs light.
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GENETICS AND DNA
-Biological influences on behavior are governed by genes.
-Genes - sections of DNA molecules, stored within chromosomes in every cell, that describe the structure and
expression of specific proteins.
-The variables that can lather the biochemistry within the cells is the environment outside of the cell, timing,
temperature, and sheer stimulation.
-The nucleus of each biological cell contains chromosomes, which each contain a single molecule of DNA.
-Within this molecule, genes govern the cell’s functioning by providing detailed instructions for making
proteins.
-The cell’s control center - Cells contain nuclei, which contain chromosomes, which contain DNA.
-A DNA molecule - the production of proteins is governed by the sequence of subunits on the DNA molecule.
The sequence determines the structure of the protein that will be produced as well as when, where, and in what
amount the protein will be made.
-The double strands of a DNA molecule are arranged in helical form - the double helix. This discovery in 1953
won Watson & Crick the Nobel prize. The molecule unzips to allow access to the genetic code provided by the
sequence of ATGC bases.
GENOME
-Humans have 23 pairs of chromosomes and roughly 25,000 protein-coding genes.
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-One pair of chromosomes - sex chromosomes, is either XX or XY; this pair determines whether the person is
genetically female or male. The other 22 pairs are called autosomes.
-These are collectively called a person’s genome.
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GENE EXPRESSION
-In each cell, some genes are expressed at any point in time and others are not.
-Gene expression is controlled by the biochemical environment inside the cell, which is influenced by the
organism’s:
-Overall environment.
-Experience.
-Behavior.
-An organism’s genome therefore specifies only its genotype.
-The overt traits and behaviors of the organism define its phenotype - the
product of the genotype and experience (physical and social
environment), which are in continual interaction.
-Parents’ chromosome pairs combine to create a child’s:
-Cells in the human body generally contain 46 chromosomes, that is,
23 pairs. When females produce an egg, however, the egg contains
just 23 chromosomes - one from each of the mothers pairs. The
same is true when male produce sperm cells - they contain just one
chromosome from each of the fathers pairs. When egg and spam
combine, the baby ends up with the appropriate number of
chromosomes.
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INTERACTIONS AMONG GENES
-Most characteristics are influenced by the action of many genes.
-Some depend on a single pair of genes.
- Common human traits that depend on a single gene pair: red-green color blindness, dangling earlobes,
baldness, dimples, susceptibility to poison ivy.
-Chromosomes come in pairs, and since genes are located on chromosomes, genes also come in pairs.
-Each gene occupies a specific position within its chromosome - called the gene’s locus.
-Each gene is paired with another gene: the pairs are located at corresponding positions on pairs of
chromosomes.
-Not all heritable traits have functions (e.g. dimple), thus serve as a reminder that some phenotypic differences
are merely the results of random variation in the human genome.
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DOMINANT VS. RECESSIVE
-Allele - one of two or more alternative forms of a gene that arise by mutation and are found at the same place
on a chromosome.
-The paired genes may or may not be the same allele.
-If they are different:
-One gene may be dominant and the other recessive.
-Or the genes may be codominant (both are expressed - e.g. blood type).
-Or one may be incompletely dominant (phenotype intermediate to the two coded by the genes).
-Genes are inherited from an organism’s parents, and the laws of Mendelian inheritance control how traits
shaped by single genes are passed along; for example, a person who inherits a gene for dimples (a dominant
trait) from a single parent will have dimples, while a person needs two copies of the gene for PKU (a recessive
trait) to have the disorder.
-Most genetic variation, though, is not so simple.
-Even single-gene variations can be incompletely Mendelian (as in the serotonin transporter).
-More importantly, the vast majority of an organism’s traits, from physical variations like height to specific
disorders like schizophrenia, are influenced by many genes. These traits are still influenced by biology, but in
much more complicated ways.
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POLYGENIC INHERITANCE
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