Unit 3 Notes-BIOL 1103

Unit 3 Notes: Introduction to Genetic Testing

Pre-Class Quiz

1. Definitions of Genetic Terms

   • Chromatid: Identical copies of a chromosome present after replication.

   • Ploidy: The number of sets of chromosomes in a cell.

   • Haploid number: Half the number of chromosomes of a diploid cell.

   • Homologous chromosome: Matched pairs of chromosomes containing genes for the same traits in identical locations along their length.

2. Matching Terms with Definitions

   • Phenotype: Observable trait of an individual.

   • Homozygous Genotype: Alleles on the maternal and paternal chromosomes are the same.

   • Heterozygous Genotype: Alleles on the maternal and paternal chromosomes are different.

3. Dominant Alleles:

   • An allele is dominant if it always determines the phenotype. If two alleles for the same gene are present, the dominant allele determines the phenotype.

4. Relevance of Genetic Tests for Bladder Cancer:

   • Pre-symptomatic testing is most relevant for individuals like Sasha who have a family member with a genetic disorder but do not currently show symptoms.

5. Types of Genetic Testing and Example Diseases:

   • Diagnostic Genetic Testing: ILDR gene used as a marker for cancer progression.

   • Carrier Genetic Testing: Sickle Cell Anemia (inherited in autosomal recessive pattern).

   • Predictive Genetic Testing: Age-related Macular Degeneration.

Pre-Class Reading: Genetic Variation

• Significance of Genetic Variation: Vital for survival amid changing environmental conditions; allows species to adapt over time.

• Asexual vs Sexual Reproduction:

  • In asexual reproduction, variation arises mainly from mutations.

  • In sexual reproduction, variation comes from mutations and recombination during meiosis.

• Patterns of Inheritance:

  • Traits influenced by multiple genes and environment, resulting in complex inheritance patterns.

  • Some traits may be influenced by a single gene, typically follow predictable inheritance patterns.

Sex Chromosomes

• In mammals, the X and Y chromosomes determine gender:

  • Females have two X chromosomes; males have one X and one Y.

• Other organisms can have different sex chromosomes (e.g., birds and reptiles).

• Sex determination can occur through non-genetic methods (e.g., temperature for certain reptiles).

Genetic Testing Overview

• Genetic Test: Analysis of DNA for variations associated with diseases.

• Hypertrophic Cardiomyopathy (HCM): Thickens heart walls; affects 0.1-0.2% of population; can lead to sudden death.

• Genetic Discrimination: Unfair treatment based on genetic differences; laws protect against discrimination by insurers and employers.

U.S. Criminal DNA Databases

• Types:

  • Forensic Database: DNA from crime scenes.

  • Offender Database: DNA from arrested or convicted individuals.

• CODIS: The FBI's Combined DNA Index System linking profiles across local, state, and federal levels.

Genetic Testing Benefits and Concerns

1. Concerns:

   • Cost, emotional impact of test results, possibility of incomplete variant detection.

2. Benefits:

   • Reduces uncertainty regarding health outcomes and aids in preventative measures for asymptomatic patients.

Reasons for Genetic Testing

• Assist in family planning and life decisions.

• Help alleviate anxiety due to uncertainty about genetic conditions.

Genetic Testing in Sports Medicine

• Evaluate risk for specific injuries based on genetic factors.

Genetic Information Non-Discrimination Act (2008)

• Protection: Prevents health insurance denial based on genetic variations.

• Exclusions: Does not cover life insurance, disability, or long-term care insurance.

SNPs and Genetic Variations

1. SNPs (Single Nucleotide Polymorphisms):

   • Definition: A variation of a single DNA base that can differ between individuals.

   • Majority of nucleotides in the genome are identical; human DNA is over 99.5% similar among individuals.

2. Types of DNA Variations:

   • Insertions: Addition of DNA nucleotides.

   • Deletions: Removal of DNA nucleotides.

Anatomy of a Chromosome

• Chromosomes consist of both coding and non-coding DNA.

• Major Types of Genetic Variations:

  1. SNPs: Single nucleotide differences.

  2. Insertions: Extra nucleotides added.

  3. Deletions: Loss of nucleotides.

Genetic Variations Effects

• Variations can alter protein structure or gene expression, leading to phenotypic differences.

• Example of Genetic Impact on Proteins:

  • Enzymes, regulators, and structural proteins perform various cellular functions.

Patterns of Inheritance Determination

• Defined by the number of altered variants needed for a trait to be expressed:

  • Examples include autosomal recessive, autosomal dominant, sex-linked recessive traits.

Autosomal Recessive Traits

• Cystic Fibrosis: Recessive trait requiring both gene copies to express.

• Genetic Carriers: Individuals who carry one copy of a recessive allele but do not express the trait.

Genetic Nomenclature**

• Recessive alleles: lower case letters; dominant alleles: upper case letters.

• Autosomal Recessive: Carriers are Aa; affected are aa; unaffected are AA.

• Autosomal Dominant: One copy of dominant allele is sufficient for expression; AA or Aa exhibit traits.

Genetic Testing Techniques

1. Polymerase Chain Reaction (PCR): Used to amplify specific DNA sequences.

2. Sanger Sequencing: Identifies exact sequences over approximately 1000 base pairs.

3. Hybridization Techniques: Base pairing between complementary strands.

Pedigree Analysis for Inheritance Pattern

• Mapping inheritance traits to determine modes of inheritance (autosomal dominant, recessive; X-linked).

• Characteristics of various inheritance patterns:

  • Autosomal Recessive: Offspring can exhibit traits without parents showing, generational skipping.

  • Autosomal Dominant: All affected individuals typically have affected parents.

  • X-Linked Recessive: More common in males, with females often being carriers.

Application of Genetic Testing in Disease Diagnosis

• Identifies single specific genetic variations, panels of genes, or whole genomic sequencing to reveal genetic disorders.