Chapter 14 – Human Genome
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Transcript Chapter 14 – Human Genome
Chapter 14 – Human
Genome
Human
Chromosomes
Karyotype –
arrangement of
chromosomes in
their homologous
pairs and by
length
Humans – 23 pair
22 pair of
autosomes
1 pair of sex
chromosomes
Pedigree
Graphic representation of genetic
inheritance
Circle = female: square = male
Shaded = have trait; not shaded = do not have
trait
Most recent generation
at bottom
Generations identified by
Roman numerals
Individuals identified by
Arabic numbers (1,2,…)
Simple Recessive Heredity
Most genetic disorders are caused by recessive
alleles
Albinism
Cystic fibrosis (CF)
1 in 20 – carrier;
1 in 2000 – have it
Defective protein in plasma
membrane results in formation and
accumulation of thick mucus in lungs and
digestive tract
Most common disorder among white Americans
Simple Recessive cont.
Tay-Sachs disease
Fatal disorder of central nervous system
Lipid build up on brain
Most common in US among Amish
Phenylketonuria (PKU)
Absence of enzyme that converts certain amino
acids
Damage to CNS, mental retardation
Most common among people with ancestors
from Norway and Sweden
Simple Dominant Heredity
Simple Dominant Traits
Tongue rolling, Hapsburg lip, earlobe
types, hitchhiker’s thumb, almond eyes,
thick lips, hair on middle of fingers
Huntington’s disease
Rare, lethal
Breakdown of brain
Onset between ages of 30-50
Achondroplasia - dwarfism
Codominance in humans
Sickle-cell anemia
Twisted, bent (sickle-shaped) red blood cells
Cells are not able to carry oxygen normally,
blood blow slows, blockage of smaller
vessels, shorter life span for cells
Produces physical weakness and
damage to heart and brain
Most common in African Americans
1 out of 12 are heterozygous –
produce normal and sickle
Multiple Alleles in humans
Blood groups – ABO groups and Rh group
Rh – single gene with 2 alleles – positive
and negative
ABO groups
Determined by presence or absence of certain
molecules on surface of red blood cell
Types : A, B, AB, O
Genes : IA, IB, i
Used to determine parentage
Ex. Child AB, mom A, man w/ O can not be
father
Transfusions – need to know type to
determine compatibility
A – IAIA, IAi
Can get from A or O
Can give to A or AB
B – IBIB, IBi
Can get from B or O
Can give to B or AB
AB – IAIB
Can get from A, B, AB, or O – universal recipient
Can give to AB
O – ii
Can get from O
Can give to A, B, AB, or O – universal donor
Sex-linked traits
Genes are found on the X or Y chromosomes
Colorblindness – most common red-green (found in
1/10 males in US)
Recessive on X chromosome
XBXB, XBXb – normal female
XbXb – colorblind female
XBY – normal male
XbY – colorblind male
Hemophilia – blood does not clot – may bleed to
death from minor cuts
1/10,000 males have
1/1 million females have
Recessive on X chromosome
Calico cats
X chromosome may carry either black
alleles or orange alleles
Females may have spots of both colors – 2
X chromosomes
Males only have one X chromosome so they
will have black spots or orange spots but
not both
Changes in chromosome #
Nondisjunction (homologous pairs do
not split) occurs resulting in unusual
numbers of autosomes – normal is 22
pair
Trisomy – have 3 of a certain
autosome instead of 2 – results in
47 chromosomes
Ex. Down syndrome – trisomy of
chromosome 21 – occurs 1/800
births
Changes in # cont.
Unusual numbers of sex chromosomes
Turner’s syndrome – females
Have only 1 X chromosome
Are sterile, sex organs may not
develop
Klinefelter’s syndrome – males
Have an extra X – XXY
Usually sterile
Applications
Human DNA Analysis
Used to test for genetic disorders
DNA fingerprinting – used to identify individuals
Human Genome Project
Mapped the human DNA strand
Gene therapy – an absent or faulty gene is
replaced by a normal, working gene
Still working on perfecting the practice