Biology Chapter 8: Chromosomes and Human Genetics

Chromosomes and Human Genetics Overview

• Human Karyotype: Used to identify sex chromosomes and abnormalities in chromosome number.

  • Sex Chromosomes: XX (female) or XY (male).

  • Autosomal Chromosomes: 22 pairs of homologous chromosomes that are identical in length, shape, and genes.

• Objectives of Study:

  • Identify sex chromosomes and abnormalities through karyotype analysis.

  • Diagram chromosomes, denoting genes, alleles, and loci.

  • Define genetic carriers and differentiate between genotype and phenotype.

  • Explain genetic determination of sex and its relationship to sex-linked trait inheritance.

  • Compare inheritance patterns of recessive, dominant, and sex-linked disorders.

  • Calculate genetic disorder inheritance probabilities using Punnett squares.

  • Analyze human pedigrees to determine genetic inheritance patterns.

Genetic Disorders

• Definition: A genetic disorder is caused by defective genes or abnormal chromosome structures/numbers, inherited from parents or occurring spontaneously.

  • Examples of Genetic Disorders:

  • Spinal muscular atrophy (SMA), Sickle Cell Disease, Tay-Sachs disease, Cystic Fibrosis.

  • Genetic disorders can be categorized as recessive or dominant based on inheritance.

Gene Therapy

• Definition: Gene therapy corrects abnormal genes causing diseases by introducing healthy genes into patient cells.

  • First approved in 2012.

  • Has successfully treated various genetic disorders.

• Process of Gene Therapy:

  1. Remove stem cells from the patient.

  2. Introduce a viral vector carrying the healthy gene to the cells.

  3. After testing, inject modified cells back into the patient.

Chromosomal Abnormalities

• Types of Chromosomal Abnormalities

  • Numerical Abnormalities: Trisomy (extra chromosome) and Monosomy (missing chromosome).

  • Example: Down syndrome (Trisomy 21).

  • Structural Abnormalities: Changes in structure, such as deletions, inversions, duplications, and translocations.

  • These abnormalities lead to various genetic disorders.

Alleles and Genotypes

• Locus: The specific physical location of a gene on a chromosome.

  • Homozygous: Two identical alleles (AA or aa).

  • Heterozygous: Two different alleles (Aa).

• Genetic Carriers: Individuals who carry one allele for a recessive disorder but do not exhibit symptoms themselves.

Patterns of Inheritance

• Recessive Disorders: Occur if an individual inherits two copies of the recessive allele (aa). Parents can be carriers (Aa).

• Dominant Disorders: Require only one copy of the dominant allele (AA or Aa) to express the disorder; not possible to be a carrier.

• Sex-Linked Disorders: Inherited mutations located on sex chromosomes (X or Y). More prevalent in males, as they have one X and one Y chromosome.

Pedigrees and Analysis

• Pedigree Charts: Visual representation of family relationships used to track inheritance patterns across generations.

  • Symbols: Circles (females), Squares (males), filled symbols signify affected individuals.

• Used to analyze whether a condition is dominant, recessive, or sex-linked based on family history.

Future of Genetic Therapies

• Progress in Genetic Studies: Rapid growth in gene and cell therapy clinical trials.

  • Notable therapies are incredibly costly, with some treatments exceeding millions.

  • CRISPR Technology: A revolutionary gene-editing tool that edits specific DNA sequences with precision, providing a potential future pathway for correcting genetic disorders.