Human GeneticsI. Chromosomes

A. Human genome is comprised of 23 pairs of chromosome

B. Sex chromosomes – the 23rd pair of chromosomes determine gender (male or female)1. Females have X and X2. Males have X and a small Y

The gender of the baby is always determined by?

C. Autosomes – the remaining 22 pairs are non-sex chromosomes

D. Karyotyping - Cell biologists take photographs of cells in mitosis when the chromosomes are easy to see

II. Human TraitsA. Geneticists study how a trait is passed from one

generation to the nextB. Genetics versus Environment

1. Many traits are strongly influenced by environmental factors, such as nutrition and exercise (Ex: average height in 1800s in Europe was 10 cm shorter than today due to poor nutrition)

2. Genes that are denied the proper environment may not reach full expression (Ex: alcoholism is influenced by your genetics, but if you don’t drink you can’t become an alcoholic)

C. Pedigree chart1. Shows the relationships within a family for single

gene traits2. Genetic counselors analyze pedigree charts to

figure out genotypes of family members3. How to read a Pedigree chart:

Circle = Circle = femalefemale

Square = Square = malemale

Horizontal Horizontal line = a line = a couplecouple

Vertical line and a Vertical line and a bracket connect the bracket connect the parents and parents and children.children.

Half-shaded = Half-shaded = person is a person is a carrier carrier

Completely Completely shaded = person shaded = person expresses the expresses the recessive traitrecessive trait

Not shaded Not shaded = person = person does not does not expresses expresses the trait the trait nor is a nor is a carriercarrier

LABEL THIS PEDIGREE CHART

a. Determine which individuals are carriers for albinism (half shade the circles and squares).

b. Is albinism dominant or recessive?

III. Human GenesA. Biologists have identified some genes that control a

single human trait

1. Blood type genes (multiple alleles)Blood Type Blood Type Genotype Surface Protein AntibodiesGenotype Surface Protein Antibodies****

A

B

AB

O

AA or AO

BB or BO

AB

OO

A

B

A & B

--

b

a

--

a & b

**The antibodies are only produced when the recipient is exposed to the wrong surface proteins.

IV. Genetic DisordersA. Recessive Autosomal Disorders - diseases caused by

genes on chromosomes #1-22 where both alleles are recessive for the trait1. Albinism – lack of pigment in hair, skin, and eyes2. Cystic fibrosis – mutation on chromosome 7 that

causes excess mucus in lungs, digestive tract and liver, and increased infection; patients die by drowning on own mucus. More common in people of Northern European descent

Chromosome # 7

CFTR gene

Abnormal CFTR proteins cannot transport Cl- across cell membranes.

Cells in the person’s airways become clogged with a thick mucus.

3. Tay-Sachs disease

a. Deadly lipid storage disorder

b. Caused by defective enzyme that prevents normal formation of the brain causing mental retardation, blindness and early death

c. Affects central and eastern European Jewish populations

4. Sickle cell anemiaa. Abnormal form of hemoglobin causes red blood cells to be

sickle shaped

b. Sickle cells get stuck in capillaries resulting in damage to brain, heart, and spleen

c. Affects 1 in 500 African Americans

Why are most disorders due to recessive alleles?Why are these recessive genetic disorders primarily found in

African and Jewish populations?

B. Dominant Autosomal Disorders1. Achondronplasia – dwarfism

2. Huntington’s disease – mental deterioration and uncontrollable movements; usually occurs in middle age

If everyone with Huntington’s allele dies, how does the disease continue?

If one of your parents has the disease what are the chances of you getting the disease?

H h

hh

Parents Genotypes Hh and hh Hh

Hhhhhh

50% Chance

C. Sex-linked disorders - these genes are found on the X chromosome.

1. Color blindness – 1 in 10 males; 1 in 100 females

2. Hemophilia – lack blood clotting protein; affects 1 in 10,000 males

Why are sex linked disorders more common in males?

D. Chromosomal Disorders1. Most common are non-disjunction, which is the

failure of chromosomes to separate during meiosis, resulting in daughter cells with an abnormal number of chromosomes

3. Turner’s Syndromea. Females missing one of the X chromosomes (0 X)b. Sterile and very short but have normal

intelligence.

4. Klinefelter’s Syndromea. Males with an extra X chromosome (X X Y).b. Sterile and can have several female

characteristics

5. Down Syndrome

a. Have extra twenty first chromosome b. Common in children of mothers over 40c. Dwarfs, mentally retarded and usually have

heart problems.

V. Human Molecular GeneticsA. DNA analysis

1. Testing for allelesa. Parents can get a genetic test for hundreds of

disorders (e.g. Tay-Sachs, CF)b. Scientists look for differences in DNA sequence

on specific genes2. DNA fingerprinting

a. Analyzes sections of DNA that are believed to have little to no function

b. Highly varied from human to humanc. Used to convict criminals and free wrongly

convicted

3. Amniocentesisa. Involves removing some fluid from the woman’s

womb then conducting genetic tests on it.

B. Gene Therapy 1. An absent or faulty gene is replaced by a

normal working gene2. Body is then able to make the correct

protein, eliminating the disorder3. Modified viruses are sometimes used to

insert the corrected gene into human cells

Normal hemoglobin gene

Bone marrow cell

Chromosomes

Genetically engineered virus

Nucleus

Bone marrow

Gene Therapy Movie