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Chapter 5

PSYB64H3 Chapter Notes - Chapter 5: Neural Tube Defect, Single-Nucleotide Polymorphism, Spina Bifida

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Janelle Leboutillier

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Introduction to Physiological Psychology
Week 4 – June 2 nd
, 2015
Chapter 5:
Genome: a complete set of chromosomes.
oIdentifies the characteristics that define a species.
oThere are between 20’000 and 25’000 genes in the human genome.
oProteome: the set of proteins encoded by the genome.
The next step in genetic research, identification of the set of proteins encoded by the
genome of a species.
Genotype: the genetic composition of an organism.
oIdentifies the genetic basis for individual characteristics.
oConsists of 23 matched pairs of chromosomes.
oChromosome: a strand of DNA found within the nucleus of a cell.
Deoxyribonucleic acid (DNA): molecules that compose chromosomes.
oVast majority of DNA is found in the nucleus, but some is located in mitochondria.
omDNA: mitochondrial DNA that originates from the mother.
Mutate at a fairly regular rate.
Phenotype: the observable appearance of an organism.
oIdentifies the end result of the interactions between genes and environment.
Gene: a functional hereditary unit made up of DNA that occupies a fixed location on a chromosome.
oResponsible for the production of particular proteins.
Gene expression: the translation of a genotype into the phenotype of an organism.
oThe process of gene expression:
Transcription: DNA partially unwinds and a strand of complementary RNA is made.
Translation: RNA instructs ribosomes to produce amino acids.
Completed protein.
Allele: alternative version of a particular gene.
oAn individual can have, at most, two versions of an allele.
oHomozygous: having two identical alleles for a given gene [e.g., the gene types for two Type A
blood (AA)].
oHeterozygous: having two different alleles for a given gene [e.g., the gene for Type A blood and
a gene for Type O blood (AO)].
oRecessive allele: a gene that will produce its characteristic phenotype only when it occurs in a
homozygous pair.
oDominant allele: a gene that produces its characteristic phenotype regardless of whether its
paired allele is heterozygous or homozygous.
oImprinted gene: a gene of which only the mother’s or father’s copy (allele) is expressed, but not
both in the normal Mendelian sense.
Genes that don’t follow the rules of dominance.
Approximately 1% of mammal’s genes are imprinted.
Implicated in genetic disorders, behavioral disorders (i.e., autism and bipolar disorder),
and vulnerability to cancer.
Ribonucleic acid (RNA): a molecule that is similar to DNA that participates in the translation of genetic
sequences into proteins.
Codon: a sequence of three bases on the DNA molecule that encode one of 20 amino acids.
Meiosis: cell division in sexually reproducing organisms that reduces the number of chromosomes in half
of the reproductive cells, such as sperm, eggs, and spores.
oAnalogous to shuffling a deck of cards.
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Creates a huge number of possible genetic combinations.
oLinkage: the characteristic of genes located adjacent to one another to be passed along as a
oCrossing over: a process during meiosis in which chromosomes exchange equivalent segments
of DNA material.
Mutation: a heritable alteration of genes.
oCan be advantageous, neutral, or disadvantageous.
oInheriting a dominant mutant allele or two copies of recessive mutant allele will affect an
organism’s phenotype.
Sex-linked characteristics: phenotypical characteristics that result from expression of genes on the X
chromosome that aren’t duplicated on the Y chromosome.
oMales are more likely to experience sex-linked disorders than females.
oX chromosome inactivation: the process by which one X chromosome in each female cell is
silenced to equalize the amount of proteins produced by males and females.
Occurs in random patterns from cell to cell.
E.g., calico cats
Single nucleotide polymorphism (SNP): variation that occurs in a gene when a single base is changed
from one version to the next.
oCan be a major source of variation between individuals of a species.
oE.g., Alzheimer’s disease (AD): a degenerative, ultimately fatal condition marked initially by
memory loss.
A person with two E4 genes has a 91% chance of developing AD.
Average age of onset is 68 years.
Anencephaly: a neural tube defect in which the rostral neural tube doesn’t develop normally, resulting in
incomplete formation of the brain and skull.
oMajority of fetuses with anencephaly either die in utero or don’t survive more than a few hours
after birth.
Spina bifida: a neural tube defect in which the caudal part of the neural tube doesn’t close properly.
oSurgery is usually used within the first 24 hours of life to correct the condition.
oMost children will experience paralysis of the lower limbs.
oProduces a number of physical and psychological challenges.
oPeople with spina bifida live well into adulthood with modern treatment.
oDeficiencies in folic acid might be responsible for a large number of cases of neural tube
Down syndrome: an abnormal genetic condition resulting from a genotype with three copies of
chromosome 21, responsible for moderate mental retardation and a characteristic physical appearance.
oAlso referred to as Trisomy 21.
oMajor cause is abnormal division, or disjunction, of the mother’s twenty-first chromosome during
oIQs range between 35 and 50
oPhysical features include a small skull, large tongue, almond-shaped eyes, a flat nasal bridge,
and abnormalities of the hands and fingers.
oSubject to heart deformities, which contribute to shorter life expectancy.
oCorrelated with a high risk of AD.
Fragile – X syndrome: a heritable genetic disorder that produces cognitive and physical abnormalities.
oHaving more than 200 codon repeats on the X chromosome leads to this disorder.
oIntellectual consequences vary from typical intelligence to moderate retardation.
oPhysical characteristics include low set ears, and a large forehead and jaw.
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