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Powerpoint Lecture Outline
Human Genetics
Concepts and Applications
Eighth Edition
Ricki Lewis
Prepared by
Dubear Kroening
University of
Wisconsin-Fox Valley
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Chapter 3
Development
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Stages of the Human Life Cycle
• Genes orchestrate our physiology after
conception through adulthood
• Development is the process of forming an
adult from a single-celled embryo
• In humans, new individuals form from the
union of sex cells or gametes
– Sperm from the male and oocyte from the
female form a zygote
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Gametes
• Form from cell division of germline cells
• Meiosis is cell division to produce
gametes
• Meiosis has two divisions of the nucleus
(Meiosis I and Meiosis II) and produces
cells with half the number of
chromosomes (haploid)
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Meiosis
• Reduces the genetic material by half
• Why is this necessary?
from mother
from father
child
too
much!
meiosis reduces genetic content
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Homologous Chromosomes
• Carry the same genes
• Pair during Meiosis I
• Separate in the
formation of gametes
• One copy of each pair
is from the mother
and one is from the
father.
Figure 1.2
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Sexual Reproduction
• Meiosis and sexual reproduction
increases genetic diversity in a
population
• Variation is important in a changing
environment
• Evolution is the genetic change in a
population over time
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Comparison of Mitosis and Meiosis
Table 3.1
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Meiosis: Cell Division in Two Parts
Meiosis I
(reduction
division)
Meiosis II
(equational
division)
Diploid
Haploid
Haploid
Figure 3.3
Result: one copy of each chromosome in a gamete.
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Meiosis
Interphase precedes meiosis I
Meiosis I
Meiosis II
Prophase I
Prophase II
Metaphase I
Metaphase II
Anaphase I
Anaphase II
Telophase I
Telophase II Figure 2.13
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Meiosis I : the reduction division
Spindle
fibers
Nucleus
Nuclear
envelope
Prophase I
(early)
(diploid)
Prophase I
(late)
(diploid)
Metaphase I
(diploid)
Anaphase I
(diploid)
Telophase I
(diploid)
Figure 3.4
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Prophase I
Late prophase
Early prophase
• Chromosomes condense
• Homologs pair
• Spindle forms
• Crossing over occurs • Nuclear envelope
fragments
Figure 3.4
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Metaphase I
• Homolog pairs align
along the equator of
the cell
Figure 3.4
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Anaphase I
• Homologs separate
and move to opposite
poles
• Sister chromatids
remain attached at their
centromeres
Figure 3.4
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Telophase I
• Nuclear membrane
reforms
• Spindle disappears
• Cytokinesis divides cell
Figure 3.4
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Meiosis II : the equational division
Prophase II
(haploid)
Figure 3.4
Metaphase II
(haploid)
Anaphase II
(haploid)
Telophase II
(haploid)
Four
nonidentical
haploid
daughter cells
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Prophase II
• Nuclear envelope
fragments
• Spindle forms
Figure 3.4
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Metaphase II
• Chromosomes align
along equator of cell
Figure 3.4
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Anaphase II
• Centromeres divide
• Sister chromatids
separate
Figure 3.4
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Telophase II
• Nuclear envelopes reform
• Chromosomes decondense
• Spindle disappears
• Cytokinesis divides cells
Figure 3.4
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Results of Meiosis
Gametes
• Four haploid cells
• Contain one copy of
each chromosome and
one allele of each gene
• Each cell is unique
Figure 3.4
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Table 3.1
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Recombination (crossing over)
• Occurs in prophase of
meiosis I
A
A
B
B
C
• Homologous
chromosomes exchange
genes
• Generates diversity
b
C
D D
E
F
E
F
a
a
e
f
c
b
c
d
d
e
f
Figure 3.5
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Recombination (crossing over)
A
a
B
• Exchange between
homologs
• Occurs in prophase I
C
C
c
D D
E
F
d
E
F
e
f
b
c
d
e
f
Figure 3.5
Letters denote genes and case denotes alleles
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Recombination (crossing over)
a
A
B
b
C
•Creates chromosomes
with new combinations of
alleles for genes A to F
D
E
F
A
a
B
c
b
c
d
d
C
D
E
F
e
f
e
f
Figure 3.5
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Chiasmata
In prophase I, crossing over or
recombination events create
chiasmata.
Figure 3.5
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Independent Assortment
The homolog of one chromosome can be inherited
with either homolog of a second chromosome.
Figure 3.6
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Spermatogenesis: sperm
formation
Figure 3.7
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Spermatogenesis
• Stem cells in testes divide
mitotically to produce
spermatocytes
•. Spermatocytes divide by
meiosis to produce four
equal sized haploid
spermatids that mature into
four sperm
Figure 3.9
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Oogenesis
Figure 3.11
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Oogenesis: Ovum Formation
•
•
•
•
Cells of the ovary divide to form oocytes
Oocytes divide by meiosis
Unequal cytoplasmic division
A discontinuous process
– At birth, oocytes are arrested in prophase I
– At ovulation, an oocyte continues to
metaphase II
• The four meiotic products produce a
functional ovum and three polar bodies.
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Fertilization
The ovum
completes
meiosis II after
fertilization
Figure 3.13
• Fertilization is the union of sperm and
ovum
• After fertilization, chemical reactions occur
preventing additional sperm from entering
the ovum
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Stages of Development
Table 3.2
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Early Development:
Ovulation to Implantation
Figure 3.14
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Cleavage
• Mitotic cell division; a morula
• Cells are called blastomeres
• The developing embryo becomes a
blastocyst, a hollow ball of cells
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Blastocyst
• The inner cell mass
(ICM) develops into the
embryo
• Other cells become the
extraembryonic
membranes important
for implantation and
support of embryonic
growth
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Gastrulation
• Primary germ layers form
• Cells differentiate
• Supporting structures form
– Chorionic villi
– Yolk sac
– Allantois
– By 10 weeks the placenta is fully formed
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Germ Layers:
Endoderm, Mesoderm, and
Ectoderm
Figure 3.15
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Germ Layers
Ectoderm:
the outermost germ layer develops
skin
nervous system
eye lens
Mesoderm:
the middle germ layer develops
muscle
connective tissue
blood vessels
kidneys
Endoderm: the innermost germ layer develops
lining of GI tract
liver
pancreas
thymus
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Multiple Births
Dizygotic twins
• Form from two differ zygotes
• Two ova are fertilized
• Same genetic relationship as any
siblings
Monozygotic twins
• One ova is fertilized
• Developing embryo splits during early
development
• Genetically identical
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Figure 3.16
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Embryo Develops
Figure 3.18
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Critical Periods of Development
• Organs develop at different times: a critical
period
• During its critical period, an organ is
vulnerable to toxins, viruses, and genetic
abnormalities
• Altering the normal development may cause
birth defects
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Critical Periods of Development
Figure 3.20
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Teratogens
• Cause birth defects during development
• Examples
– Thalidomide
– Cocaine
– Cigarettes
– Alcohol
– Some nutrients
– Some viruses
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• Fetal
• Alcohol
Syndrome
Figure 3.21
• Fetal Alcohol Syndrome
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Maturation and Aging
• Genes may impact health throughout life
• Single gene disorders are expressed early in life
and tend to be recessive
• Adult onset single gene traits are often dominant
• Interaction between genes and environmental
factors
Example: malnutrition before birth
coronary artery disease , stroke, hypertension ,
type 2 diabetes
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Table 3.3
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Aging
• Segmental progeroid syndromesaccelerated aging
• Increases the rate of aging associated
changes
• Inheritance of longevity –chromosome 4
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Table 3.4
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