Human Genetics

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A short introduction to
Human Genetics
Chromosomes!
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First you need FERTILIZATION
(Remember Family Life??)
Female egg cell with half of mom DNA
Male sperm cell ..with half of dad DNA

They become one fertilized cell with a
complete Set of DNA
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Using early microphotography techniques,
scientists capture conception as it occurred.
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FERTILIZATION, Continued
The cell then begins to divide
Your first two months!
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Chromosomes!!! ..at this point all
present and accounted for
Humans should have 46 chromosomes
The fertilized egg cell is now a
ZYGOTE
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• tiny threadlike structures in nucleus of cell
• (with the exception being mature red blood cells
  which have no nucleus)

Bummer for us!
contain sections of DNA GENES
humans---gt 22 pairs of chromosomes two sex
chromosomes 50-100,000 genes
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Chromosomes A view inside...
Each pair of chromosomes contain a section of our
DNA.
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In the 1950's, scientists were able to view the
set of human chromosomes.
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scientists identify and number chromos from 1-22
This arrangement is called a Karyotype
The 23rd pair are the sex chromosomes.
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Chromosomes are sorted arranged into a 23
PAIR Karyotype for study..
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What makes us a BOY or a GIRL?
The recipe is in the last set of chromos..
Two X Chromos GIRL
X Y BOY
The sex chromosome X is inherited from the
mother. The father gives either an X (female) or
a Y (male). This is this chromosome
which determines the sex of the baby.
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The difference between BOYS and GIRLS...
..are found in sexual characteristics.
(Remember Phenotypes?..)
Secondary
Primary
genitals
body shape hips/pelvis/shoulders
muscle/fat distribution
testes/ovaries
sperm/egg formation
body size hands/stature
facial/body hair
voice characteristics
breast development females -gt 3 stages
males -gt 1 stage
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Why did Mother Nature put this silly looking
feather bouquet on my butt ?
In other animals, Secondary Sex Characteristics
may include
color/markings
antlers
I get it now!
decorative tail/appendages
scent glands
Miss Q.T. Peacock says Im attracted to men
with pretty feathers on their butt
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a chromosomal anomaly- presence of an extra
chromosome in the cell
A trisomy - 47 chromosomes instead of the usual
46.
A Partial Trisomy occurs when PART of an extra
chromosome, attaches itself to one of the other
chromosomes. A Trisomy Mosaic is where SOME
cells contains the extra chromosomal material.  
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In the vast majority of cases a trisomy
"happens" before conception.
sperm or egg containes 24 chromosomes instead of
23.
cell or zygote has 47 chromosomes instead of the
normal 46.
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It usually goes like this...
with the usual 23 chromosomes in both the sperm
and ovum.
This would result in a baby without a trisomy.
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However, sometimes...
.. the ovum contains 24 chromosomes instead of
the usual 23.
This would result in a baby with a trisomy.
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When it comes to chromosomes, more genetic
material is NOT necessarily better.
extra genetic material effects every stage of
development and growth. Not always for the
better.
A trisomy can occur on any set of chromosomes.
The following are the most common..
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Trisomy 13 also known as Patau's
Syndrome
An individual with full trisomy 13 at age 7 years
(survival beyond the first year is uncommon). 
He is deaf and legally blind
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Trisomy 18 (Edward's Syndrome) 1/8000
live births
Possible Malformations Back part of head may
be prominent Short eyelids Small mouth and
unusually small jaw A small head Fold of the
eyelid in the lateral corner of the eye Low set
malformed ears
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Trisomy 21 (Down Syndrome)
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Down Syndrome
first described by physician named John Langdon
Down in 1866
while working in a mental institution, he
described (in an essay) a set of children with
common features who were different from other
children with mental retardation
Hannah
Carrie
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Trisomy 21 (Down Syndrome)
Decreased muscle tone at birth Separated sutures
(joints between the bones of the
skull) Asymmetrical or odd-shaped skull Round
head with flat area at the back of the head Small
skull Upward slanting eyes Small mouth with
protruding tongue (see tongue problems) Broad
short hands Single crease on the palm (see
below) Retarded growth and development Delayed
mental and social skills (mental retardation)
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People with Downs CAN do..
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Focusing on Abilities Dollywood worker has Down
Syndrome By Marfi Davis-News-staff writer
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SPECIAL OLYMPICS!
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End of Part 1