Human Heredity

Chapter 14

Vocabulary 1. genome

2. karyotype

3. sex chromosome

4. autosome

5. pedigree chart

6. sex-linked gene

7. nondisjunction

8. DNA fingerprinting

9. Human Genome Project

10.gene therapy

I. Human Heredity A. Human Chromosomes

1. Karyotype = set of photographs of chromosomes grouped in order in homologous pairs

2. Sex chromosomes = 23rd pair of chromosomes determines sex (females XX, males XY)

3. Autosomes = remaining 44 chromosomes that are not sex chromosomes

B. Human Traits

1. Pedigree chart = shows the relationships within

a family for single gene traits

2. Genetic counselors analyze pedigree charts to

figure out genotypes of family members

3. Genetics vs. Environment

a. Many traits are strongly influenced by

environmental factors, such as nutrition

and exercise

b. Genes that are denied the proper

environment may not reach full

expression

1) Ex: average height in 1800s in Europe was 10

cm shorter than today due to poor nutrition

2) Ex: susceptibility to alcoholism is influenced

by your genetics

Circle = female Square = male

Horizontal line =

a couple

Vertical line and

a bracket

connect the

parents and

children.

Half-shaded =

person is a carrier

Completely shaded

circle or square =

person expresses

the trait

Not shaded =

person

neither

expresses

the trait nor

is a carrier

4. How to read a pedigree chart

DRAW

5. Ex: Albinism

pedigree chart

DRAW &

Complete

Determine which individuals are carriers for

albinism (half shade the circles and squares).

Figure out the genotypes for each individual on the

chart.

D. Autosomal disorders

1. Recessive allele disorders a. Tay-Sachs - nervous system breakdown and death

in 1st few years of life

b. Albinism – lack of pigment in skin, hair, eyes

c. Cystic fibrosis – excess mucus causing increased

susceptibility to infection Chromosome # 7

CFTR gene

Missing 3 DNA

bases,

phenylalanine is

missing from the

CFTR protein.

Abnormal CFTR

proteins cannot

transport Cl- across cell

membranes.

Cells in the person’s

airways become clogged

with a thick mucus.

2. Dominant allele

disorders

a. Dwarfism – disorder

of bone growth; 1 in

40,000 births

b. Huntington’s

disease – loss of

muscle control and

mental functioning

until death,

symptoms appear

over 30 years old

3. Codominance disorders

a. Sickle cell anemia

1) common among those of

African descent

2) twisted red blood cell or

“sickle” gets stuck in

capillaries resulting in

damage to brain and

heart

3) Why does this disease

persist? -- those

heterozygous for sickle

cell anemia are more

resistant to malaria

Malaria

Sickle cell

II. Human Chromosomes A. Genes make up only about 2-5% of

chromosomes (the rest doesn’t seem to

code for anything that we know of right

now)

B. Sex-linked genes = genes located on the

X or Y chromosome

1. >100 sex-linked disorders are located on the

X (X is much larger than Y)

2. X-linked alleles are always expressed in

males since they have only one X

chromosome

3. Colorblindness

a. Red-green colorblindness is found in 1

out of 10 males in the U.S.

4. Hemophilia a. Recessive allele causes no protein for

blood clotting, bleed to death from minor cuts

b. 1 in 10,000 males affected

5. Muscular Dystrophy a. Weakening and loss of skeletal muscle

b. 1 in 3,000 males affected

Color Blindness Test

C. X-chromosome inactivation 1. If one X chromosome is enough for a male,

how does the cell adjust to the extra X in females?

2. In females, one X is randomly switched off.

3. Ex: In female cats, one X chromosome is switched off in different areas of the body resulting in two different colored spots (calico).

Tortoiseshell cat Calico cat

D. Chromosomal Disorders 1. Nondisjunction = most common error in meiosis

occurs when homologous chromosomes fail to

separate

2. Nondisjunction results in an abnormal # of

chromosomes ending up in a sex cell

3. Down syndrome

a. 3 copies of chromosome 21

b. Results in mild to severe mental retardation

c. 1 in 800 babies born in the U.S. have Down

syndrome

Homologous

chromosomes fail to

separate

Meiosis I:

Nondisjunction Meiosis II

E. Sex chromosome disorders 1. Turner syndrome – XO, female inherits

only one X

a. 1 in 2,500 females

b. Sterile, sex organs do not develop at puberty

2. Klinefelter syndrome – XXY, an extra X

a. 1 in 500 to 1,000 males

b. Usually sterile, often male sex organs and breasts develop

c. No instances of YO, so X chromosome contains info. necessary for survival of embryo

III. Human Molecular Genetics A. Human DNA Analysis

1. Testing for Alleles a. If 2 prospective parents suspect that they might

carry a recessive allele for a genetic disorder, they can ask for a genetic test

b. Genetic tests are available for 100s of disorders

2. DNA fingerprinting a. Analyzes sections of genes that vary widely

between individuals

b. Get from samples of blood, hair, semen, and skin

c. High reliability - DNA fingerprinting is used in the justice system

B. The Human Genome Project 1. Began in 1990 and finished in 2000

2. an ongoing effort to analyze the human genome sequence

3. Worldwide we are searching for genes that may provide useful info. for understanding traits and to develop new drugs and treatments

4. Discoveries on the human genome is public info. and new info. can be found online

C. Gene Therapy

1. An absent or faulty gene is replaced by a normal,

working gene

2. Viruses are used to insert the corrected DNA into a

cell’s DNA (virus is modified to not cause disease)

3. Gene therapy treatments are high risk and not

always successful; procedure is still considered

experimental

Normal hemoglobin

gene

Bone marrow cell

Chromosomes

Genetically engineered virus

Nucleus

Bone

marrow