Biology Chapter 7.2Mendelian Genetics

Pages 140-146

Johann Gregor Mendel

• The first person to accurately describe inheritance.

• Born in 1822 in Austria

• He studied close to 30,000 pea plants over a 10 year period.

Mendelian Genetics Termsgenotype

• The genetic composition of an individual

phenotype

• The physical traits of an individual

heterozygous genotype

• An individual who carries two different alleles for a gene.

• The only heterozygous condition possible for stem length in a garden pea is Tt.

homozygous genotype

• An individual who carries two copies of the same allele.

• The homozygous condition for a tall-stem plant would be TT.

• The homozygous condition for a short-stem plant would be tt.

recessive

• Some alleles are recessive, which means that their effects can be seen only if a copy of a dominant allele is not present. (t)

dominant

• Dominant allele are seen even when a recessive allele is present. (T)

Pea Traits

Peas and Genes

• The resulting seeds will contain information on flower color, seed shape and color, and plant height from both parents.

• Pea plants were an ideal organism for Mendel because their reproduction is easy to control, they complete their life cycle in a matter of weeks, & a single plant can produce thousands of offspring.

A dominant allele

• American albino horses occur when an individual carries an allele that prevents normal coat color development.

• Horses that have only one copy of the allele are albino.

• Humans can have a dominant allele for cheek dimples or 6 fingers and toes.

• Cystic fibrosis is a recessive condition.

• Individuals with CF cannot transport chloride ions into and out of cells lining the lungs, and intestines, and other organs.

• As a result, the cells produce a thick, sticky mucus layer.

• Affected individuals suffer from progressive deterioration of the lungs and have difficulties absorbing nutrients across the lining of the intestine.

• Most children with CF suffer from lung infections and very short life spans.

Cystic Fibrosis (CF)

CF is a Recessive Condition

• The cause of CF is the production of a chloride ion transporter protein (CFTR channel) that cannot embed in a cell membrane.

• Heterozygous individuals or carriers can still produce the functional chloride transporter protein.

• Heterozygous individuals are carriers because they are unaffected but they can pass the trait to the next generation.

• Homozygous recessive individuals cannot make the functional protein because they have two mutant alleles.

Cystic Fibrosis

• The most common genetic disease in Europe.

• 1 in 2500 are affected with the disease.

• 1 in 25 are carriers.

• Percussive therapy is used to loosen mucus inside the lungs.

• The mucus is coughed up, stopping any bacterial infections.

Huntington's Disease(dominant allele)

• Huntington's disease is a fatal genetic condition caused by a dominant allele.

• Patients are restless, irritable, and have difficulty walking, thinking, and remembering.

• The disease starts in middle age.

• There is no cure and the result is death.

• An individual needs only one copy of the allele to be affected by the disease.

Punnett Square (Example: CFTR)

Probability

Punnett Square (Huntington's)

Probability

Practice Problems

Let’s do together...

• In humans, brown eyes are dominant over blue eyes. What type of offspring would you expect if you crossed a heterozygous brown eyed person to a heterozygous brown eyed person?

Let’s do together...

• In humans tongue rolling is dominant to non-tongue rolling. What would be the expected type of offspring if a homozygous tongue roller was crossed to a heterozygous tongue roller?

Let’s do together...

In a certain plant, yellow fruit is dominant to white fruit. A heterozygous plant with yellow fruit is crossed with a plant with white fruit. Determine the probable offspring.

Let’s do together...

Tall plants are dominant to short plants in the garden pea plant. Cross a heterozygous tall plant with a heterozygous tall plant.

Worksheet