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