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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?