1. The human
body contains
100 trillion
cells.
There is a
nucleus inside
each human
cell (except red
blood cells).
Each nucleus
contains 46
chromosomes,
arranged in
23 pairs.
One
chromosome
of every pair is
from each
parent.
The
chromosomes
are filled with
tightly coiled
strands of
DNA.
Genes are segments
of DNA that contain
instructions to make
proteins— the
building blocks
of life.

2. Gametes and Zygote Sperm Sperm Ovum Gametes (reproductive cells)
Fertilization
Zygote

3. The Process of Meiosis for Sperm Cells
Cell with 46 chromosomes (only one pair of homologous
chromosomes is shown here). Each member of the pair has begun to replicate similar to
mitotic cell division.
First meiotic cell division
begins, but does not proceed
as in mitosis. Instead of the
replicated chromosome splitting
apart, one member of each
homologous pair becomes a
part of the first-generation
daughter cell.
The second meiotic division
proceeds after the first is completed;
now the replicated chromosome
acquired in the first-generation
daughter cell splits apart.
Each of the four gametes
produced by the two-step process
now has acquired one member
of the pair of homologous
chromosomes.

4. The Process of Mitosis
Each daughter cell now has a pair of chromosomes that is identical to the original pair
Cell nucleus with a pair of chromosomes
Chromosomes split
and replicate to produce
two identical pairs
The pairs separate, and the cell divides

5. GENOTYPE AND PHENOTYPE
GENOTYPE: Set of genetic traits a person inherits; a person’s inborn capacity or potential
PHENOTYPE: Set of traits a person actually displays, resulting from a combination of the person’s genotype (potential) and life experiences that modify that potential

6. Inheritance of Hemophilia, a Sex-Linked Disorder
Carrier Mother X X XX XX
Normal
Carrier X
Daughter
Daughter
(25%)
(25%)
Normal
Father XY XY
Normal
Hemophilic Y
Son
Son
(25%)
(25%)

7. FREQUENCY OF DOWN SYNDROME (PER 1000)
Relationship Between Maternal Age and the Incidence of Down Syndrome
100 90 80 70 60
FREQUENCY OF DOWN SYNDROME (PER 1000) 50 40 30 20 10 15 20 25 30 35 40 45 50
MATERNAL AGE (YEARS)

8. Inheritance of a Dominant Gene Disorder
Affected Parent
(Has the Disorder) D r rr
normal
(25%) Dr
Affected
(25%) r
Normal
Father Dr
Affected
(25%) rr
normal
(25%) r
(50%)
(50%)

9. Inheritance of a Recessive Gene Disorder
Carrier Mother D r Dr
Affected
(25%) rr
normal
(25%) D
Carrier
Father Dr
Affected
(25%) rr
normal
(25%) r

10. Risk of Selected Genetic Disorders
Chromosomal
Down Syndrome
Klinefelter syndrome (XXY)
Fragile X syndrome
Turner syndrome (XO)
Dominant Gene
Polydactyly
Achondroplasia
Huntington disease
Recessive Gene
Cystic fibrosis
Sickle-cell disease
Tay-Sachs disease
X Linked
Hemophilia
Multifactorial
Congenital heart disease
Neural tube defect
Cleft lip/cleft palate
1/800
1/800 men
1/1,200 male births
1/2,000 female births
1/3,00 women
1/ /100
1/2,300
1/15, /5,000
1/2,500 white persons (risk of being a carrier is 1/25)
1/625 African Americans (risk of being a carrier is 1/10)
1/3,600 Eastern European Jews(risk of being a carrier is 1/30 - 1/300)
1/2,500 male babies
1/125
1 - 2/1,000
1/1, /5,000
Sources: ACOG (1990); Blatt (1988); Diamond (1989(; Hagerman (1996); Selekman (1993); Stratford (1994).

11. Who Should Seek Prenatal Counseling?
1. Couples who already have a child with some serious defect such as Down syndrome, spina bifida, congenital heart disease, limb malformation, or mental retardation
2. Couples with a family history of a genetic disease or mental retardation
3. Couples who are blood relatives (first or second cousins)
4. African Americans, Ashkenzzi Jews, Italians, Greeks, and other high-risk ethnic groups
5. Women who have had a serious infection early in pregnancy (rubella or toxoplasmosis) or who have been infected with HIV
6. Women who have taken potentially harmful medications early in pregnancy or habitually use drugs or alcohol
7. Women who have had X rays taken early in pregnancy
8. Women who have experienced two or more of the following: stillbirth, death of a newborn baby, miscarriage
9. Any woman thirty-five years or older
Source: Adapted from Fienbloom & Forman (1987) p. 129

12. Intellectual Performance (IQ)
The Concept of Range of Reaction for Intellectual Performance
child A
child B
child C
High
Intellectual Performance (IQ)
Reaction Range
Average
Low
Restricted
Average
Enriched
Type of Environment

13. Measuring the effects of Nature and Nurture: Twin and Adoption Studies

14. Correlations of IQ Scores
+1.00
+0.90
+0.80
+0.70
+0.60
Correlation of IQ scores
+0.50
+0.40
+0.30
+0.20
+0.10
Identical twins reared together
Siblings reared apart
Identical twins reared apart
Unrelated children reared together
Non-identical twins reared together
Unrelated children reared apart
Siblings reared together