Incomplete dominance

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Intermediate in phenotype

Blood type co-dominance

Genetics – Dominant Traits,

Recessive

Hitchhiker’s Thumb

• Dominant allele – hiker’s thumb

• Recessive – straight thumb

Tongue Rolling

• Ability to Roll is dominant

• Inability to roll is recessive

Mid-Digital Hair

• Presence of hair results from dominant allele

• Absence results from recessive allele

Widows Peak – a dominant trait (straight hairlines are recessive

Pedigree analysis

Genetic Disorders

(Trisomy 21) = Down’s syndrome results from 3 copies of chromosome pair

Sickle Cell Anemia• Occurs most often in people of

African descent

• Is recessive on chromosome #11

• Abnormal blood protein changes shape of blood cell

• Misshaped and carries less oxygen

• Cells get less oxygen and suffocate with this disorder

• Misshaped cells cause blocked capillaries and arteries - often strokes

There is a interesting thing about sickle cell anemia. People who carry the tendency to have sickle cell anemia are less likely to die from malaria. Sometimes what is bad in one situation helps out in another.

Malaria is a disease caused by a parasite that likes to set up

housekeeping in the red cells.This parasite is carried by the

Anopheles mosquito.

Anopheles

Albinism

• Lack of pigmentation

• Often sickly, tired and/or weak

• Eyes lack pigment and appear red due to blood vessels

Phenylketonuria (PKU)• Enzyme missing to break down the

amino acid phenylalanine

• Child usually does not survive long

Tay Sachs Disease

• Harmful fatty acids produced in brain of a developing child

• Enzymes not produced to reduce levels

• Nerve cells are injured by the fatty acids

• Characteristic cherry red spot in the eye develops

• No cure• Death occurs by age 5 on

average

ColorblindnessIf Mom has it, all her sons will

and girls have a 50:50 chance of getting it

PunnettSquare

X Xc X Xc X

Y XcY XcY

All daughters are carriers, but with one working X, they do not show colorblineness

All sons colorblind – boo hoo, sniff, sniff

Colorblind Mom: Xc XcOkay Dad: XY

Take the Test

Colorblindness Gene is located on the X-Chromosome. Use of a Pedigree to Track

Transmission

Testing for Genetic Disorders

Karyotyping – picturing human chromosomes

Fetal Diagnosis for Genetic Problems – Amniocentesis & the

Needle of Doom

Overall lessons:

1. Your overall phenotype is controlled thousands of separated genes.

2. Some alleles are co-dominant so there can be more than two phenotypes per gene.

3. Genetics is never simple! – it becomes complicated when more than one gene is involved in producing a phenotype (Green eyes for ex.)

4. Pedigree analysis can help one determine human genotypes.

5. Harmful recessive genetic traits can persist in the population through carriers

6. Genetic testing will become more widespread.

7. Not all genetically-caused disorders are inherited. Some are caused by mutation of your genes by chemicals or radiation.

Overall Lessons about Genetics

Incomplete dominance

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