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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 - PowerPoint PPT Presentation
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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
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