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Beginnings
PART 2
Guideposts for Study
 1. How does conception normally occur, and
how have beliefs about conception changed?
 2. What causes multiple births?
 4. What genetic mechanisms determine sex,
physical appearance, and other
characteristics?
Conception
 ___________ – to make a genetic copy of an
individual
 A single sperm, one of millions from the
biological father, joins an ovum, one of
several hundred thousand produced by the
biological mother's body____________
Uniqueness
 Which sperm meets which
ovum will have tremendous
implications for the new
person
 Changing ideas:
 Did a stork bring you?
 Are you a boy because
you were conceived
under a new moon?
Becoming Parents
 What Causes Multiple Births?
 ________________twins: Twins conceived by the
union of two different ova (or a single ova that has
split) with two different sperm cells; also called
fraternal twins.
 ________________ twins: Twins resulting from the
division of a single zygote after fertilization; also
called identical twins.
 The rise in multiple births is due to a trend toward
delayed childbearing and increased use of fertility
drugs
 _______________________
 Inability to conceive a baby after 12 months of
trying
Mechanisms Of Heredity
 The Genetic Code
 Basis of heredity is a chemical called
deoxyribonucleic acid (
), which
contains all the inherited material passed from
biological parents to children
 Every cell except the sex cells has _____
pairs of chromosomes – _______in all
 Genetic action that triggers growth of body
and brain is often regulated by hormones
The Genetic Code continued…
 Chromosomes: Coils of DNA that carry genes.
 _________: Small segments of DNA located in
definite positions on particular chromosomes.
 Human genome: Complete sequence or mapping of
genes in the human body and their locations.
 _________: Complex process of cell division in which
each gamete (sperm or ovum) ends up with only 23
chromosomes-one from each pair.
 _________: Process by which cells divide in half over
and over again duplicating themselves.
Mechanisms Of Heredity
 What Determines Sex?
 Sex chromosomes are either ___
chromosomes or _____chromosomes
 When an ovum (___) is fertilized by an Xcarrying sperm, the zygote formed is ______,
a female
 When an ovum (X) is fertilized by a _____carrying sperm, the resulting zygote is
______, a male




_____: Paired genes that affect a trait.
Homozygous: two identical alleles for a trait.
Heterozygous: two different alleles for a trait.
________________ inheritance: Pattern of
inheritance in which, when a child recieves
contradictory alleles, only the dominant one is
expressed.
 _________________ inheritance: Pattern of
inheritance in which a child recieves identical
recessive alleles resulting in expression of a
nondominat trait.
 Multifactorial transmission: Combination of genetic
and environmental factors to produce certain
complex traits.
Mechanisms Of Heredity
 Patterns of Genetic Transmission


When an offspring receives alleles for two
contradictory traits, only one of them, the
dominant one, shows itself
The expression of a _______________ trait
occurs only when a person receives the
recessive allele from both parents
Dominant and recessive inheritance
 Can you…



Explain why no two people, other than
monozygotic twins, have the same genetic
heritage?
Explain why it is the sperm that determines a
baby's sex?
Tell how dominant inheritance and recessive
inheritance work, and why most normal traits
are not the products of simple dominant or
recessive transmission?
Genotypes and Phenotypes:
 ___________________: Observable
characteristics of a person
 ___________________: Genetic makeup of
a person, containing both expressed and
unexpressed characteristics.
Nature and Nurture
 Studying the Relative Influences of Heredity and
Environment

If heredity is an important influence on a
particular trait:
__________ should be more alike than
cousins with regard to that trait
 monozygotic twins should be more alike
than _______________ twins
 __________ children should be more
like their biological than their adoptive
parents

Nature and Nurture
 Some Characteristics Influenced by Heredity
and Environment

Monozygotic twins generally look alike; they
are also more concordant than dizygotic twins
in their risk for such medical disorders as
_________________ (high blood pressure),
heart disease, stroke, rheumatoid arthritis,
peptic ulcers, and ___________
Nature and Nurture
 Some Characteristics Influenced by Heredity and
Environment


_________________ children's IQs are
consistently closer to the IQs of their biological
mothers than to those of their adoptive parents and
siblings
Analysis of five major groupings of traits—
____________________, neuroticism,
conscientiousness, agreeableness, and openness
to experience—suggest a heritability of about 40
percent
Some Characteristics Influenced by
Heredity and Environment
 ______________________
 Intelligence and School Achievement
 ______________________
 Psychopathology



Schizophrenia
Autism
Depression
 What practical difference does it make
whether a trait such as obesity, intelligence,
or shyness is influenced more by heredity or
by environment, since heritability can be
measured only for a population, not for an
individual?