Genetics & Genetic Diseases

Genetics & Genetic Diseases

Chapter Overview

  • Title: Genetics & Genetic Diseases

  • Key Terms: genome, DNA, proteins, chromosomes, genes, cell.

    • Genome: The complete set of genes or genetic material present in a cell or organism.

    • DNA: Deoxyribonucleic acid; the molecule that carries the genetic instructions for life.

    • Proteins: Vital molecules that perform a variety of functions in the body, acting alone or in complexes.

    • Chromosomes: Structures within cells that contain genes.

    • Genes: Segments of DNA that contain instructions for making proteins.

    • Cell: The basic unit of life.

Learning Objectives

  • Explain how genes can cause disease.

  • Distinguish between dominant and recessive genetic traits.

  • Describe sex-linked inheritance and how genetic mutations may occur.

  • Understand mechanisms of genetic disease and list important inherited diseases.

  • Explain how nondisjunction can result in trisomy or monosomy and list disorders resulting from it.

  • Identify tools used in genetic counseling and their relevance.

  • Discuss how genetic disorders can be treated.

Introduction to Genetics

  • Genetics: The branch of biology that deals with heredity and variation in organisms.

    • Inherited traits can produce diseases, highlighting the importance of genetics in human health.

Chromosomes and Genes

Mechanisms of Gene Function

  • Genes dictate the structure and function of a cell.

  • Gene Production: Involves the synthesis of enzymes and other molecules which impact cell activity. Genes can be either active or inactive.

The Human Genome

  • The human genome contains approximately 30,000 genes plus large amounts of noncoding DNA, referred to as pseudogenes.

Genomics and Proteomics

  • Genomics: The study of genomes.

  • Proteomics: The study of the proteome, which is the entire set of proteins expressed by a genome.

  • Proteome: Refers to the protein composition of a cell or organism at a given time.

Expression of Genomic Information

  • Genomic information is expressed in numerous ways, often depicted with ideograms.

  • DNA sequences are represented by nucleotide bases: A (adenine), C (cytosine), G (guanine), and T (thymine).

Chromosome Structure

Human Genome Composition

  • Human Cells: Exhibit a distinctive karyotype during metaphase, showing distinct chromosomes.

  • Chromatin: The material of which chromosomes are composed, consisting of DNA and protein.

    • Each human somatic cell contains 46 chromosomes arranged in 23 pairs.

Genetic Transmission to Offspring

Meiosis Process

  • Meiosis: A type of cell division that reduces the chromosome number by half, resulting in the formation of gametes (sperm and ova).

  • Diploid Parent Cell: Contains paired chromosomes.

  • Results in haploid gametes, each containing 23 chromosomes.

  • Meiotic Processes:

    • Meiosis I and II: Critical stages where genetic recombination (crossing over) occurs, providing genetic diversity.

Basics of Hereditary Traits

  • Genes can exhibit dominance or recessiveness:

    • Dominant Genes (Alleles): Represented by uppercase letters (e.g., A); manifest regardless of the second allele.

    • Recessive Genes (Alleles): Represented by lowercase letters (e.g., a); require two copies for expression.

    • Codominant Genes: Both alleles in a heterozygote are fully expressed.

Case Study: Inheritance of Albinism

  • Example Parental Genotype:

    • Mother (Carrier): Aa

    • Father (Carrier): Aa

  • Offspring outcomes include:

    • AA: Normal pigmentation

    • Aa: Normal pigmentation (carrier)

    • aa: Albinism

Sex-Linked Traits

  • Sex chromosomes determine gender:

    • XX: Female

    • XY: Male

  • The large X chromosome carries many more genes than the smaller Y chromosome.

  • Conditions such as color blindness demonstrate sex-linked inheritance patterns.

Example: Sex-Linked Inheritance in Offspring

  • Mother: Carrier for color blindness (XX).

  • Father: Normal vision (XY).

  • Offspring possibilities include normal females and color-blind males.

Genetic Mutations

  • Definition: Changes in the DNA sequence that can disrupt normal gene function, possibly leading to diseases.

  • Mutagens: Agents that cause changes in the DNA (e.g., certain chemicals or radiation).

  • Categories of genetic diseases:

    • Single-Gene Diseases: Caused by mutations in a single gene.

    • Multiple-Gene Diseases: Caused by mutations in multiple genes interacting with environmental factors.

    • Epigenetic Factors: Modifications affecting gene expression without altering the DNA sequence.

Examples of Genetic Disorders

  • Conditions include:

    • Phenylketonuria (PKU)

    • Huntington disease

    • Cystic fibrosis

    • Sickle cell disease

    • Various types of cancers (e.g., breast cancer, retinoblastoma)

Effects of Nondisjunction

  • Nondisjunction: The failure of chromosome pairs to separate properly during cell division, leading to abnormal chromosome numbers in gametes.

    • Trisomy: Condition where an individual has three copies of a chromosome (e.g., Down syndrome).

    • Monosomy: Condition where an individual has only one copy of a chromosome.

Chromosomal Disorders

  1. Down Syndrome: Caused by an extra copy of chromosome 21 (Trisomy 21).

  2. Klinefelter Syndrome: Presence of an extra X chromosome in males (XXY).

  3. Turner Syndrome: Affects females with a single X chromosome (X0).

Prevention and Treatment of Genetic Diseases

Genetic Counseling

  • Involves professional consultations to assess risk and support families dealing with genetic disorders.

    • Tools: Pedigrees and Punnett squares are often used to predict inheritance patterns.

Karyotype Analysis

  • Genetic testing methods:

    • Amniocentesis: Testing amniotic fluid for chromosomal abnormalities.

    • Chorionic Villus Sampling (CVS): Sampling of placental tissue to assess genetic disorders.

Gene Therapy for Genetic Diseases

  • Focuses on treating genetic conditions by targeting the underlying genetic cause.

    • Often aims to relieve or avoid symptoms rather than provide a permanent cure.

Types of Gene Therapy

  1. Gene Replacement: Involves replacing a faulty gene with a functioning one.

  2. Gene Augmentation: Involves adding copies of a gene to improve gene function.

  3. RNA Interference: Targeting and silencing specific gene expressions.

Clinical Applications

  • Leber Congenital Amaurosis: Treatment strategies using viral vectors to deliver therapeutic genes.

  • Cystic Fibrosis: Approaches include delivering genes via mist inhalation devices.

DNA Analysis Techniques

  • Electrophoresis: Technique used to separate DNA fragments based on size.

  • DNA Fingerprinting: Method of identifying individuals by their unique DNA profiles.

Questions and Further Discussion

  • Prepared for Q&A to clarify any doubts regarding genetic principles and their implications.