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