Download 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