Human Inheritance

ABO Blood Groups and Genetic Disorders

Important Vocabulary

1. Carrier: someone who is heterozygous for a trait

2. Multiple alleles: traits that have more than 2 possible alleles; still only inherit 2 alleles

3. Co-dominance: when two different alleles are present and BOTH alleles are expressed.

4. Mutation: a change in an organism’s DNA; changes how a gene functions

a. leads to 2 or more alleles for a given trait

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Variations in Alleles

1. Variations in traits arise from mutations

2. Many mutations produce genes that don’t functiona. most of these mutations produce non-functioning proteins

b. non functioning proteins can cause lethal genetic defects

c. sometimes mutations produce proteins that have different functions

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ABO Blood Groups

1. Multiple alleles

a. 3 different alleles; IA, IB, & i b. 6 genotypes / 4 phenotypes

IA IA or IA i = Type A

IB IB or IB i = Type B IA IB = Type AB

i i = Type O 2. IA and IB are co-dominant;

both are expressed if bothare present

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Guide to who can give and who can receive in donating blood

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Genetic Disorders are caused by defective genes.

Defective genes arise from mutations in DNA.

Cystic Fibrosis1.Mode of inheritance

a. recessive allele on chromosome # 7

2. Symptoms:

a. thick mucus forms in lungs & digestive tract

b. Affected people have trouble breathing; contract lung infections easily

c. Affected people live to be about 30 years old

1 in 25 Caucasians in US are carriers

1 in 2500 are affected

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Sickle-Cell Anemia1. Mode of inheritance a. recessive allele on

chromosome # 112. Symptoms a. blood cells become

sickle shaped; don’t carry oxygen

b. sickle shaped cells clog blood vessels & cause pain & swelling

c. Affected persons live to be about 50

3. Carriers are resistant to malaria

Normal blood cells live 120 days

Sickle-shaped blood cells live 10-20 days

8 to 10% African Americans are carriers

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Tay Sachs1. Mode of Inheritance a. recessive allele on

chromosome # 152. Symptoms a. Fatty substance builds up

in nerve cells in brain b. Gradual paralysis & loss of

nerve function c. Affected children die by

age 4 or 53. Carriers resistant to

tuberculosis

11% of Jewish population are carriers

Also common in French-Canadians &

Cajuns

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PKU1. Mode of Inheritance

a. recessive allele on chromosome # 12

2. Symptoms

a. body does not break down phenylalanine

b. high level of phenylalanine interferes with nervous system development; leads to mental retardation

c. Easily treated by following strict diet

d. all newborns tested for PKU

Foods farthest away from the target must be avoided.

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Huntington’s Disorder

1. Mode of inheritance

a. dominant allele on chromosome # 4

2. Symptoms

a. brain cells slowly break down; causes jerking muscles, slurred speech, difficulty swallowing, loss of balance, reasoning & memory loss, & eventually death

b. Symptoms usually begin at 35- 45 years of age

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Sex-linked traits: Genes located on the sex chromosomes.

Important Vocabulary

1. Autosome: a regular body chromosome (# 1 - 22)

2.Sex chromosome: chromosome that determines the sex of an individual; X & Y

a. XX = female

b. XY = male

c. The sex chromosomes are # 23

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Sex Linked Traits1. Sex-linked trait: A trait that is determined by a

gene found on one of the sex chromosomes.2. Occur more often in males because males only

receive one X chromosome (one copy of the gene).

3. Fathers pass the X chromosome on to daughters only.

4. Mothers pass an X chromosome on to sons and daughters.

5.Females must receive 2 copies of the defective gene to show the trait.

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Hemophilia

1.Mode of inheritance

a. recessive allele on X

chromosome

2. Main Symptom

a. blood fails to clot properly

b. may bleed internally – especially at the knees and elbows

Hemophilia can be traced through a pedigree of the royal family.

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Color-blindness

1. Mode of Inheritance

a. recessive allele on X chromosome

2.Symptoms

a. inability to distinguish red and green colors

b. Normal life span

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