Genetic Disordersinheritance patternsbrief review -

• A Karyotype

• It’s a Boy!

Simple Heredity• Simple Dominant Traits

• Cleft Chin

• Widow’s Peak

• Free-Hanging earlobes

• Almond-shaped eyes

• Hitch-hiker’s Thumb

Genetic Disorders caused by Recessive Alleles (4)

1. Cystic Fibrosis• Recessive; defective membrane protein-chloride (protein) ion channels• Mucus builds up in lungs, G I tract

2. Tay-Sach’s Disease* recessive*enzyme (protein) absent that breaks down a lipid stored in the CNS tissues

* fatty acids accumulate in brain preventing nerve transmission. central nervous system;

3. PhenylketonuriaRecessiveInfants tested at birthMissing enzyme (protein) to metabolize phenylalanine ( amino acid) .Excess phenylalanine builds up and is Toxic to the brainControl with dietWARNINGS ON NUTRASWEET

ACTIVITY: Figure 12.3

4. Sickle Cell Disease• Recessive: Hs = sickle cell allele ; H= normal allele • Defective hemoglobin• Sickle-shaped Red Blood Cells

– Blocks blood flow, damages blood vessels, anemia (

• Most common among African Americans and among others living in the tropics where malaria is prevalent.

• Homozygous= sickle Cell Disease (Hs Hs)– sickle=-shaped cells damage & block blood vessels; decreased life span;

anemia, kidney and blood vessel damage.

• Heterozygous= sickle cell trait (H Hs) – Codominance make enough normal red blood cells, so healthy.– Heterozygotes--Advantage against Malaria causing parasite

Sometimes Dominant alleles are responsible for genetic disorders

or abnormalities.• Examples:

• 1. Huntington’s Disease (disease)– Onset between age 30 and 50

• deterioration of nervous system• Irreversible• One in 10,000 in U.S. afflicted

• 2. Polydactyly (genetic abnormality) • 6 fingers/hand• DOMINANT

• Any child born to a parent who has the allele for Huntington’s disease has a 50% chance of inheriting the disease and the disorder.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 14.15

Changes in Chromosome Number

• Down Syndrome– Trisomy 21

Abnormal Numbers of Sex Chromosomes

• Male=has at least 1 Y chromosome

• Female= missing a Y chromosome

• XO, XXX, XXY, XYY

• Mostly sterile, some conditions result in mental retardation to some degree.

Sex-Linked Inheritance

• Traits controlled by genes located on sex chromosomes.

• Mostly the X– more genes than the Y– MORE MALES THAN FEMALES AFFECTED

• 1910 Thomas Hunt Morgan discovered genes linked to sex chromosomes—therefore – Eye color in fruit flies

Sex-linked genetic conditions/disorders

• Color-Blindness• Hemophilia• More common in _______________than

_______________. • Why?

• (Do Problem-Solving Lab 12.3)

Sex-Linkage problems

Which parent determines the sex of the offspring?

What is the chance of having a boy? Girl?-----------------------------------------------------------------------

Suppose a man ( who has hemophilia) and a woman (is a carrier of hemophilia) have a girl. What is the likelihood of this girl having hemophilia?