Complex Inheritance and Human Heredity

Chapter 11: Complex Inheritance and Human Heredity

• Human inheritance differs from Mendel's laws.
• Lesson 1 focuses on basic patterns.
• Lesson 2 deals with complex inheritance patterns.
• Lesson 3 explores chromosomes and human heredity.

Lesson Overview

• The inheritance of traits through generations can be illustrated using a pedigree.
• Objectives include understanding inheritance patterns, identifying genetic disorders, and analyzing human pedigrees.

Essential Questions

• How to analyze genetic patterns to determine dominant or recessive inheritance.
• What are examples of dominant and recessive disorders?
• How to construct human pedigrees from genetic information.

Vocabulary

• Review: genes
• New: carrier, pedigree

Recessive Genetic Disorders

• Recessive traits manifest when an individual is homozygous recessive.
• Dominant alleles mask recessive disorders.
• Heterozygous individuals can be carriers.

Understanding Carriers

• Carriers are heterozygous for a disorder, carrying one copy of the recessive allele.
• They can pass the allele to offspring, potentially causing the disorder if the other parent contributes a recessive allele as well.

Cystic Fibrosis (CF)

• CF stands as a common recessive genetic disorder, especially among Caucasians.
• CF affects mucus-producing glands, digestive enzymes, and sweat glands.
• Faulty chloride ion absorption leads to thick mucus, causing lung and pancreatic issues, resulting in infections.
• Treatments include physical therapy, medication, special diets, and digestive enzymes.
• Genetic tests are available to identify CF carriers.

Albinism

• Albinism stems from mutations causing a lack of melanin in hair, skin, and eyes.
• White hair, pale skin, and pink pupils are characteristic.
• The absence of pigment in the eyes can cause vision problems and sensitivity to UV radiation.
• Individuals benefit from protecting their skin from the sun.

Galactosemia

• Inability to digest galactose, a sugar in milk, characterizes galactosemia.
• Lactose from milk is normally broken down into galactose and glucose; galactose requires conversion to glucose by the GALT enzyme.
• Those with galactosemia lack the GALT enzyme or have a defective version, necessitating dairy avoidance.
• Liver damage, kidney dysfunction, cataracts, developmental delays, and increased infection risk are all possible symptoms.

Tay-Sachs Disease (TSD)

• TSD is a recessive genetic disorder found on chromosome 15.
• It predominantly affects Jews of Eastern European descent and features a cherry-red spot on the back of the eye.
• Absence of enzymes needed to break down fatty acids (gangliosides) causes brain accumulation.
• This accumulation causes brain nerve cell swelling, leading to mental and physical deterioration.

Recessive Genetic Disorders in Humans

Dominant Genetic Disorders

• Mutations in a single gene copy lead to dominant genetic disorders.
• Only one mutated allele from one parent is required for the disorder's expression.
• Individuals without the disorder are homozygous recessive with two normal, non-mutated genes.

Huntington's Disease

• Huntington's disease is a dominant genetic disorder affecting the nervous system at a rate of 1 in 10,000 in the U.S.
• Symptoms start between ages 30 and 50, possibly including brain function loss, uncontrollable movements, and emotional symptoms.
• Genetic tests can identify the responsible mutated gene.
• There is currently no preventive treatment or cure.

Achondroplasia

• Achondroplasia is the most common form of dwarfism, defined by a small body size and short limbs.
• Individuals typically reach an adult height of about 4 feet with a normal life expectancy.
• For 75% of affected individuals, it arises from a new mutation despite average-sized parents.
• Achondroplasia does not usually stop individuals from being able to lead normal lives.

Understanding Inheritance Check

• Dominant Disorder:
  • 50% chance if the affected parent is heterozygous.
  • 100% chance if the affected parent is homozygous dominant.
• Recessive Disorder:
  • 50% chance if the unaffected parent is a carrier (heterozygous).
  • 0% chance if the unaffected parent is homozygous dominant, but you will be a carrier.

Pedigrees

• Pedigrees are diagrams displaying phenotypes of genetically related families across generations.
• They provide clues about genotypes.

Analyzing Pedigrees

• Pedigrees are useful in examining both recessive and dominant genetic disorders.
• Individual genotypes inferred from phenotype of self, parents, and offspring.

Dominant or Recessive Challenge

• When a disorder is present in every generation, and affected individuals have at least one affected parent it is likely Dominant.

Recessive Challenge

• If affected individuals can have unaffected parents who are likely carriers, and parents produce both affected and unaffected offspring then it is likely recessive

Predicting Disorders

• Family records lead to accurate disorder predictions.
• Human genetic studies face challenges because of time, ethics, and generations.
• Good record-keeping, along with pedigree analysis determines phenotypes and infers genotypes.

Key Concept #1

• Genetic patterns can be analyzed using pedigrees.
• Pedigrees can track the inheritance of traits across generations.
• By examining which family members have traits we can infer a dominant or recessive inheritance pattern.

Key Concept #2

• Huntington's disease and achondroplasia are examples of dominant disorders.
• Examples of recessive disorders consist of cystic fibrosis, albinism, galactosemia, Tay-Sachs disease.

Key Concept #3

• Human pedigrees can be made by gathering family conditions through generations.
• This helps show inheritance patterns and figuring out genotypes based on phenotypes.