Transcript Power Point Slides

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.
Gametes and Zygote
Sperm
Sperm
Ovum
Gametes
(reproductive cells)
Fertilization
Zygote
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.
The Process of Mitosis
Cell nucleus with a pair
of chromosomes
Chromosomes split
and replicate to produce
two identical pairs
The pairs separate,
and the cell divides
Each daughter cell
now has a pair of
chromosomes that is
identical to the
original pair
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
Inheritance of Hemophilia, a Sex-Linked Disorder
Carrier Mother
X
X
X
Normal
Father
Y
XX
Normal
Daughter
(25%)
XX
Carrier
Daughter
(25%)
XY
Normal
Son
(25%)
XY
Hemophilic
Son
(25%)
FREQUENCY OF DOWN SYNDROME (PER 1000)
Relationship Between Maternal Age and
the Incidence of Down Syndrome
100
90
80
70
60
50
40
30
20
10
0
15
20
25
30
35
40
MATERNAL AGE (YEARS)
45
50
Inheritance of a Dominant Gene Disorder
Affected Parent
(Has the Disorder)
Normal
Father
D
r
r
Dr
Affected
(25%)
rr
normal
(25%)
r
Dr
Affected
(25%)
rr
normal
(25%)
(50%)
(50%)
Inheritance of a Recessive Gene Disorder
Carrier Mother
D
D
r
Dr
Affected
(25%)
rr
normal
(25%)
Dr
Affected
(25%)
rr
normal
(25%)
Carrier
Father
r
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
1/800
1/800 men
1/1,200 male births
1/2,000 female births
1/3,00 women
1/300 - 1/100
1/2,300
1/15,000 - 1/5,000
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)
X Linked
Hemophilia
1/2,500 male babies
Multifactorial
Congenital heart disease
Neural tube defect
Cleft lip/cleft palate
1/125
1 - 2/1,000
1/1,000 - 1/5,000
Sources: ACOG (1990); Blatt (1988); Diamond (1989(; Hagerman (1996); Selekman (1993); Stratford (1994).
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
The Concept of Range of Reaction for Intellectual Performance
child A
child B
child C
Reaction Range
Intellectual Performance (IQ)
High
Average
Low
Restricted
Average
Type of Environment
Enriched
Measuring the effects of Nature and Nurture: Twin and Adoption Studies
TYPE OF STUDY
Twin
Adoption
OBJECTIVE
Differences
in genetic
relatedness,
same environment
Same genetic
relatedness,
different
environments
KEY COMPARISONS
Identical twins
together
Fraternal twins
together
Identical twins
together
Identical twins
apart
Correlations of IQ Scores
Correlation of IQ scores
+1.00
+0.90
+0.80
+0.70
+0.60
+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
Major depression
Bipolar disorder
80
70
Risk
60
50
40
30
20
10
Prevalence in
general population
Fraternal twins
Identical twins
Prevalence in
general population
Fraternal twins
Identical twins