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Chapter 2-3

PSYC-223 Chapter Notes - Chapter 2-3: Twin Study, Neural Tube, Infant Mortality


Department
Psychology
Course Code
PSYC-223
Professor
Corrigal
Chapter
2-3

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Chapter 2
-sickle cell disease: red blood cells which carry o2 are misshapen, meaning they cannot pass through the capillaries; they also
lok the paths of ’s so the hae lo iuodefeses agaist ifetio
Biology:
-only one sperm enters the egg
-gametes are sex chromosomes (23 chromosomes) while body cells are autosomes (46 chromosomes)
-sex chromosomes determine gender (two large X= female, one X and one y=male); depends on sperm (all eggs are X)
-in vitro fertilization: sperm and egg are connected in a dish, then the fertilized egg is placed in the uterus (success is about
30%; in addition often results in twins (low birth weights), and is expensive)
-fie parets: a a ould hae fie potetial parets: a door egg, door sper, surrogate other, and two adoptive
parents
-each chromosome has 1molecule of DNA, gene: a group of nucleotide bases that code for specific instructions
-the larger chromosomes (ie #1 and 2 carry more genes than smaller ones ie Y chromosome) (we are 99% alike)
-genotype: the genetic makeup; phenotype: the behaviour, characteristics and traits displayed
-alleles: variants of the same gene form (ie brown, blue, green, grey for eyes), can be homozygous (BB) or heterozygous (Bb),
which is expressed in heterozygotes depends on the dominat vs recessive traits
Ie sickle cell disease is homozygous recessive (aa) so an AA and Aa parent cannot pass on the disease (only the trait)
-incomplete dominance: both the recessive and dominant allele are expressed resulting in an intermediate (Aa has sickle cell
trait and will only experience symptoms in some scenarios lacking oxygen)
-the role of sickle cell: more immune to malaria (tradeoff explains why it is more common in African Canadians than
Europeans); the gene will become less common in Canadian populations with time as it serves no purpose here
-dominant disorders are rarer because the diseased tend not to live to reproductive age-an exception is huntingtons (dominant
protein) because symptoms do not appear until after reproduction (causes progressive degeneration of the nervous system)
-some disorders are sexlinked: the gene causing the disorder is on a sex chromosome (in hemophilia, it is carried on the X and is
recessive, so thus is more common in males)
Females can be carriers of the disorder but never show signs
Abnormal numbers of chromosomes
-triso : Do’s sdroe, has  hroosoe ’s resultig i itelletual disailit ad harateristi features
Limited life expectancy (25-60), usually the egg has an extra 21 with risk increasing with maternal age
-autosome disorders like Down syndrome often result in miscarriage because the autosomes contain so much vital information
-note with the sex disorders (below) no disorder results in solely Y- thus an X chromosome is necessary for life
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Behavioural Genetics
-branch of genetics that deals with inheritance of behavioural and psychological traits
-more difficult because there is no either or (like with alleles); often a dimensional trait such as extroversion
-polygenic inheritance: ie intelligence; phenotypes are distributed, reflecting the activity of many separate genes
Polygenic inheritance results in a bell curve shape (very few would be AABBCCDD or aabbccdd, but many would be a mix such
as AabBccDd)
-monozygotic twins (one egg) are more identical than dizygotic twins (equivalent to being siblings)
-adoption studies: important source of information about heredity vs environment (ie if they resemble their adoptive parents,
environmental role is strong (confounded by placing adopted children into similar homes to original parents)
-twin studies confounded by people treating identical twins more similarly than fraternals
-nearly every psychological phenotype is influenced by genetics (ie depression is more common in identical twins)
includes letter sounds for language, resisting temptation tests, and physically aggressive behaviour (not proven with social
aggressio… greater role of gees % i phsial, ut oshared eiroet is % i soial aggressio
-those found to be physically aggressive were also socially aggressive, but not necessarily vice versa
-traditional view was that heredity was the clay which was molded and shaped by life experience (genotype leading to
phenotype is dependent on the environment)
PKU: homozygous recessive on chromosome 12- lack an enzyme that breaks down phenylalanine, which accumulates and
damages nervous system development). Newborns who are tested for this are placed on a diet limiting phenylalanine so the
disease does not emerge (environmental interference)
Ie women menstruate earlier if they have a stressful childhood
-reaction range: the range of phenotypes that a single genotype can produce based on the environment in which development
takes place
-epigenesis: the interplay between genes and all levels of the environment(from the cellular to the cultural)
-remember that heritability can not be used to calculate an individuals inheritance (ie intelligence is 60% heritable but that
does’t ea % of “uz’s itelligee ame from her parents); likewise the heritability does not apply to all groups (ie those
living in a malnourished environment will not reach their full genetic potential
-heritability coefficient for reading disability is higher for well educated parents (well educated provide an academic
environment so disability is genetic, while non academic parents contribute genetics and environment)
-nature can determine nurture: a child with certain genetics (ie attractive) receives certain environments; children may seek
environments that feed their genetic makeup (ie outgoingsports); deliberate selection of environment that suits genetic
makeup is called niche picking
-nonshared environment makes siblings/twins different and more important to development than shared environment (ie
parent may be more affectionate with one child than the other, teacher may discipline one more, different peers)
Prenatal development Chapter 3
-prenatal development: the changes that transform the fertilized egg into a newborn human (38 weeks)
-zygote period (1-2 weeks): stage end marked by the implantation of the zygote into the uterine wall; in this phase undergoes
cell division (every 12hrs) and travels along the fallopian tube to the uterus
Blastocyst: about 100 cells, occurring at 4 daysa hollow ball (cells do differentiate early)
Germ disc: near the centre of the blastocyst, this part will develop into the infant
Layer of cells closest to the uterus becomes the placenta: exchanges wastes and nutrients between mother&baby
Implantation: the blastocyst burrows into the uterine wall and establishes connections with the mothers blood vessels (triggers
hormonal changes and the stop of menstruation)
-embryonic period: once the blastocyst is completely implanted (3-8th weeks)
Ectoderm: hair,skin, nervous system
Mesoderm: muscle, skeletal system and circulatory system
Endoderm: digestive system and lungs
-most organs are in place in some form, except for sex organs
-amniotic sac forms: surrounds the embryo and is filled with amniotic fluid which protects the embryo and provides
temperature stability
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