PSYC 2450 Chapter Notes - Chapter 3: Genetic Disorder, Quantitative Trait Locus, Congenital Disorder
CH3 Hereditary Influences on Development
-challenges in presenting information in a clear way evident when trying to explain it to 4-year-old.
-chapter approaches human development from hereditary perspective, seeking to determine how one's
genotype (genes one inherits) expressed as phenotype ( observable or measurable characteristics).
-review evidence for hereditary contributions to psychological attributes ex intelligence,
personality, mental health, and patterns of behaviour.
-implies: many noteworthy phenotypic characteristics influenced by genes passed to us by our
Principles of Hereditary Transmission
-must start conception: moment when an ovum released by woman's ovary and on way to uterus via fallopian tube
fertilized by a man's sperm.
-establish what is inherited at conception, can examine mechanisms by which genes influence
characteristics we display.
The Genetic Material
-sperm cell penetrates lining of ovum, biochemical reaction repels other sperm, preventing them from repeating
-sperm cell begins to disintegrate, releasing genetic material; ovum releases its genetic material, and new
cell nucleus forms around hereditary information
-zygote single cell formed at conception from union of a sperm and an ovum.
-only 1 / 20th the size of a pin
-What hereditary material is present in human zygote?
- new cell nucleus contains46 elongated, threadlike bodies ; chromosomes, each consists of thousands of
chemical segments, genes-the basic units of heredity
-chromosomes come in matching pairs. Each member of pair corresponds to other in size, shape, and
hereditary functions it serves
-each parent contributes 23 chromosomes to each of their children.
-Genes actually stretches of deoxyribonucleic acid, DNA, complex "double-helix" molecule resembles twisted
ladder , provides chemical basis for development
-unique feature of DNA : it can duplicate itself
- makes it possible for a one-celled zygote to develop into human being.
Growth of the Zygote and Production of Body Cells
-zygote moves through fallopian tube toward prenatal home in uterus, begins to reproduce itself through mitosis
-divide into two cells, two become four, four become eight, eight become sixteen etc .
-before each division, cell duplicates 46 chromosomes, duplicate sets move in opposite directions.
- division of cell proceeds, resulting in two new cells, each has identical 23 pairs of chromosomes
( 46 in all) thus same genetic material as original cell
-Mitosis continues throughout life, generating new cells that enable growth and replacing old ones that are
The Germ (or Sex) Cells
-germ cells: serve one special hereditary function- to produce gametes (sperm in males ; ova in females).
-different type of cell reproduction than process of mitosis.
-shares some characteristics of mitosis, but differs in ways that make resulting cells able to join w/ gametes
to create unique cell that will become unique individual
Production of Gametes through Meiosis
-germ cells produce sex cells through meiosis
-first duplicates 46 chromosomes.
-event called crossing-over often takes place: Adjacent duplicated chromosomes cross and break at one or
more points along their length, exchanging segments of genetic material
-transfer of genes during crossing-over creates new , unique hereditary combinations.
- next , pairs of duplicated chromosomes (some altered by crossing-over) segregate into two new
cells that each contains 46 chromosomes.
-Finally, new cells divide so each of resulting gametes contains 23 single, or unpaired,
-conception= sperm w/ 23 chromosomes unites w/ ovum w/ 23 chromosomes,
producing a zygote w/ full complement of 46 chromosomes.
-Why is it, offspring of same parents sometimes barely resemble each other? meiosis makes us genetically unique
-independent assortment principle stating : each pair of chromosomes segregates independently of all other
chromosome pairs during meiosis.
-When pair of chromosomes segregates during meiosis, matter of chance which of two chromosomes will end up in
particular parent cell.
- because each chromosome pair segregates independently of all other pairs according to principle of
independent assortment, many different combinations of chromosomes could result from meiosis of single
-laws of probability : each parent can produce 223- more than 8 million- different genetic combinations in
sperm or ova.
-father produce 8 million combinations of 23 chromosomes ; mother produce 8 million, any
couple could theoretically have 64 trillion babies w/o producing two children inheriting same
set of genes
-odds of exact genetic replication in two siblings smaller than 1 in 64 trillion. Why?
-crossing-over process alters genetic composition of chromosomes increasing the number of
possible variations in individual's gametes
-Each brother or sister inherits half of each parent's genes,
-although two siblings never inherit same half, owing to random process which parental
chromosomes (and genes) segregate into sperm and ovum , combine to produce each child
-monozygotic (or identical) twins twins who develop from single zygote that later divides form two genetically
-Occasionally, zygote split into separate but identical cells, which become two individuals.
- monozygotic (or identical) twins ; developed from single zygote , have identical genes.
-occur in about 1 of every 250 births around world
-should show very similar developmental progress if genes have much effect on human development.
-occurring approx 1 of 125 births, : dizygotic (or fraternal) twins- pairs result when mother releases two ova at same
, each fertilized by different sperm
-albeit fraternal twin born together, have no more genes in common than any other pair of siblings
-fraternal twins often differ considerably in appearance, need not be same sex.
-Canada and other developed countries, incidence of multiple births involving three or more infants increased
- births in Canada involving three or more infants nearly tripled b/w 1979 and 1999, while total number of
births decreased 7.7 percent
-increase attributed to use of assisted reproductive technologies; fertility drugs, artificial
insemination, in vitro fertilization,
-Most of these multiple births involve siblings fraternal, not identical
Male or Female?
-chromosomal portraits, / karyotypes, reveal 22 of 23 pairs of human chromosomes (autosomes) similar in males
-Sex determined by 23rd pair (sex chromosomes).
-In males, 23rd pair consists of X chromosome and Y chromosome.
-females, both of sex chromosomes are Xs
-Throughout history, mothers often been belittled, tortured, divorced, beheaded failing to bear husbands a
-both social and biological injustice that fathers determine sex of their children.
-When sex chromosomes of genetic (XY) male segregate into gametes during meiosis, half of
produced contain X chromosome , half Y chromosome
-ova produced y genetic (XX) female all carry X chromosome.
-Thus child's sex determined by whether X-bearing or Y-bearing sperm fertilizes ovum.
What Do Genes Do?
-How do genes promote development?
-they call for production of amino acids, which form enzymes + proteins necessary for formation &
functioning of new cells
-regulate production of pigment , melanin in the iris
- brown eyes have genes , call for much of this pigment, whereas lighter (blue or green) eyes call
for less pigmentation
-Genes guide cell differentiation, specialize for certain parts
- Genes influence and influenced by biochemical environment surrounding them during development.
-particular cell might become part of eyeball or elbow depending on what cells surround it during
early embryonic development
-some responsible for regulating pace and timing of development
-specific genes are "turned on" or "turned off" by other regulatory genes at different points in life
-Regulatory genes, might "turn on" genes responsible for growth spurt in adolescents,
shut growth genes down in adulthood.
-Environmental factors clearly influence how genes function
- ex child who inherits genes for tall stature may / may not be tall as adult
-maybe experience very poor nutrition for prolonged period early in life, could end up being only average /
below average in height, despite genetic potential
-Environment affects actions of genes at several different levels
-nucleus contains chromosomes and genes
-environment w/in nucleus may affect expression of genetic material.
-internal environment that surrounds cell may affect gene's expression.
-external environment affects expression of genetic material
-some effects of external environment experienced by all , some experienced by a some people
-former : "experience-expectant interactions," ; latter : "experience-dependent interactions"
-important : realization genes do not simply "code" for human characteristics, but interact w/ environment
at many levels to produce proteins eventually influence human characteristics.
*-approach how genes influence development : consider major patterns of genetic inheritance: ways in which
expressed in their children's phenotypes.
How Are Genes Expressed?
-four main patterns of genetic expression: simple dominant-recessive inheritance, co dominance, sex-linked
inheritance, , polygenic (or multiple gene) inheritance.
Single-Gene Inheritance Patterns
-Genes influence human characteristics in different ways.
-Sometimes characteristics determined by actions of a single gene , sometimes by many genes working
together: polygenic inheritance.
-Understanding single-gene inheritance patterns can help build understanding of actions of genes and
interactions w/ environment.
-turn to understanding mechanisms at work when many genes interact to influence characteristics.
Simple Dominant-Recessive Inheritance.
-Many human characteristics influenced by only one pair of genes (called alleles):
-Gregor Mendel contributed to our knowledge of single gene-pair inheritance by cross-breeding different