Transcript Human Genetics Presentations

I. Introduction
A. 46 chromosomes in each cell
(23 pairs)
B. Autosomes: all
chromosomes except sex
chromosomes (22 pairs)
C. Sex chromosomes:
determine gender (1 pair)
1.Sex determination
a)XX = female
b)XY = male
2.During meiosis, each egg from
the female gets an X; 1/2 male
sperm get X, 1/2 get Y
3.Males determine gender of
offspring!
a)Except in birds and reptiles
where female is XY and male
is XX
II. Studying human genetics
A. Difficult because
1. Long generations (25 yrs)
2. Single births
3. Ethical concerns
B.Methods for studying humans
1.Pedigrees: record that shows
how a trait is inherited within a
family
2.Population sampling
1.Selecting a small # of people to
represent an entire population
2.Must be a random sample
3.Ex: through random sampling,
researchers discovered that
65% of people in US taste PTC,
35% cannot
3.Identical twin studies
a)Identical genetic codes
b)Separated at birth: study which
traits are genetic(Nature) & which
are environmental (Nurture)
III. Inheritance of human traits
A. Dominant traits
1. Polydactyly - extra fingers &
toes
2. Dwarfism - small size
3. Curly hair
4. Huntington disease - nervous
disorder
5. Piebaldness - white patches of
hair
Piebaldness=Genetic
Vitiligo=AutoImmune
B.Recessive traits
1.Straight hair
2.Freckles
3.Albino
4.Cystic fibrosis - lung disorder
5.Deafness
6.PKU - nervous disorder
C.Codominance
1.Sickle cell anemia - irregularly
shaped red blood cells
• O allele = healthy(HH)
• 1 allele = mild case(HS),
resistant to malaria
• 2 alleles =
severe case(SS)
D.Multiple alleles
1.3 or more alleles which
code for a single trait
2.Human blood type
a) 3 possible alleles: IA, IB,
iO
b)IA & IB are codominant,
iO is recessive
c)41% of US is Type O -- o
allele is most common
5.Possible blood types
Blood
Type
A
B
Genotypes
IA IA
I A iO
I BI B
I BiO
Antigens
A
B
AB
IA IB
A&B
O
iO iO
None
Universal
acceptor
Universal
donor
Example punnet squares for type
A dad and type B mom
E.Polygenic traits
1.Controlled by 2 or more genes
2.Skin color - the more genes, the
more melanin  darker skin
color
3.Height - more dominant alleles 
taller
4. Eye Color
F.Sex-linked traits
1.Genes located on X
chromosome
2.Males only have one X, so only
have one allele controlling
these genes
3.Males more likely to have
disorders that are sex-linked
because they only need 1
recessive allele
4.Carrier: someone who has
one allele for a disorder -does not have the disease but
can pass it on to children
5.Only women can be carriers
for sex-linked traits
6.Examples: hemophilia,
muscular dystrophy,
colorblindness
7.Color vision
a)XC=Color Vision, Xc=colorblind
b)Males - 8% colorblind (XcY)
c)Females - 1% colorblind (XcXc)
Red-Green
Total
Normal
What are the chances for a healthy
dad and a mom who is a carrier for
colorblindness to have a child that
is colorblind?
Hemophilia in the
Royal Families of Europe
IV.Genetic disorders
A. Nondisjunction: failure of
chromosomes to separate
during meiosis
1. Normal = 23 chromosomes
2. Abnormal = 22 or 24
3.Monosomy: too few
chromosomes, one
chromosome left unpaired
a)Turner syndrome: female with
only 1 X chromosome
b)Short stature, sterile
4.Trisomy: too many
chromosomes, extra copy of one
a)Down’s syndrome: trisomy 21
b)1 in 1400 when mother under
age 25, 1 in 100 by age 40
B.Detecting genetic disorders
1.Physical characteristics features, disabilities
2.Ultrasound - pictures of baby in
utero using sound waves
3.Amniocentesis - sample of fluid
from around baby, can examine
baby’s cells
http://www.biology.iupui.edu/biocourses/n100/2k4csomaldisordersnotes.html
http://www.katie.com/babyblog/archives/000538.html
4.Karyotype: picture of a person’s
cromosomes
• taken from any cells -- blood
in adults, amnio for baby
Normal
Trisomy 21
V. Biotechnology
A. Genetic engineering:
manipulating the DNA of an
organism
1. Select useful traits, such as
resistance to diseases
2. Transgenic organisms:
contain a gene from another
organism
B. DNA fingerprinting
1. Analysis of DNA sequences
to determine identity
C.Gene therapy
1. Once we know which genes
code for specific proteins and
cause disorders
2. Insert a normal gene into a
chromosome to replace a
dysfunctional gene
3. On hold until more research
can be completed