Human Inheritance Chapter 12

Pedigree Signs = Affected = Female = Male = Carrier

A Pedigree I II III

Uses of Pedigrees Can follow blood lines of pedigreed animals Useful for breeding show quality animals Can look for genetic diseases within a family Can see how diseases are inherited

Human Pedigree Symbols

Autosomal Recessive Pedigree

A Carrier A person who is heterozygous for a recessive trait is called a carrier. A carrier does not have the trait but can pass it to their offspring. If two carriers have a child, they have a 25% chance of having a child with the recessive trait.

Simple Recessively Inherited Diseases Cystic fibrosis Tay-Sachs Disease Phenyketonuria

Cystic fibrosis (CF) 1 in 20 Americans carry the allele 1 in 2000 white American children are born with CF Due to the a defective protein in the plasma membrane, thick mucus collects in the digestive tract and lungs Special diet and therapy help with survival Death used to occur in the 20’s now

Symptoms of Cystic Fibrosis People with CF can have a variety of symptoms, including: * very salty-tasting skin; * persistent coughing, at times with phlegm; * frequent lung infections; * wheezing or shortness of breath; * poor growth/weight gain in spite of a good appetite; and * frequent greasy, bulky stools or difficulty in bowel movements.

Statistics for Cystic Fibrosis About 1,000 new cases of cystic fibrosis are diagnosed each year. More than 70% of patients are diagnosed by age two. More than 45% of the CF patient population is age 18 or older. The predicted median age of survival for a person with CF is more than 37 years.

Tay-Sachs Disease Disorder attacks central nervous system Absence of an enzyme that breaks down a lipid that forms and is stored in the CNS (central nervous system) cells Found mostly in descendents of Ashkenazic Jews from eastern Europe Babies start exhibiting lack of development at about 6 months of age. Usually Tay-Sachs is fatal between 2 & 5 yrs. old

Phenylketonuria (PKU) Allele common in people with Swedish & Norwegian ancestors Individuals lack enzyme that breaks down phenylalanine to tyrosine Phenylalanine builds up and causes damage to the CNS All babies are tested at 2-3 days old If the test is positive, baby is put on a special diet that prevents this disease Diet sodas with Nutrasweet contain phenylalanine and have a warning on the label

Dominantly Inherited Genetic Disease Huntington’s Disease Caused by a rare dominantly inherited gene Areas of the brain deteriorate as the disease progresses Onset is between 30 and 50 years of age People often have had kids by the time onset happens There is a DNA test today to determine if the allele has been inherited Most people are recessive for this trait

Sex-linked Traits Traits carried on the X chromosome that are recessive. Females can carry the trait but not have the trait as heterozygous individuals A female passes the trait to male offspring as the X of the XY sex chromosomes is from the mom.

Sex-Linked Traits Hemophilia Colorblindness

Hemophilia People with hemophilia lack Factor 8 and 9 that cause clotting of blood. A small cut can result in a huge amount of blood loss. A bruise can cause severe internal bleeding that can result in death.

Hemophilia Due to intermarriages in the European Royal Families, hemophilia became a problem. The most famous family with hemophilia was the Russian Royal Family whose son was a hemophiliac.

Queen Victoria’s Hemophilia Pedigree

Colorblindness Colorblindness is a sex-linked trait. Red-green colorblindness is the most common type of colorblindnes. Green and red appear as shades of gray.