Autosomal Dominant Disorders Inheritance Quiz

Genetic Assessment and Counselling

• Genetic assessment and counselling are essential for patients at risk of inherited disorders to provide access to advice, resources, and support.

Nature of Inheritance

• Genes are the basic units of heredity that determine physical and cognitive characteristics of individuals.
• Genes are composed of DNA (Deoxyribonucleic acid).
• Genetics is the study of how and why chromosomal disorders occur.
• Cytogenetics is the study of chromosomes by light microscopy and the method by which chromosomal aberrations are identified.

Chromosomal Structure

• Humans have 46 chromosomes (22 pairs of autosomes and 1 pair of sex chromosomes) in each cell.
• Spermatozoa and ova each carry only half of the 23 chromosomes.
• Each chromosome in the sperm cell has a similar size and shape function (autosome, or homologous chromosome) in the ovum.

Genotype, Phenotype, and Genome

• A person's genotype is their actual gene composition.
• A person's phenotype is their outward appearance or expression of the genes.
• A person's genome is the complete set of genes present (approximately 50,000-100,000 genes).

Genetic Disorders

• Genetic disorders are defects in the structure or number of genes or chromosomes.
• Inherited or genetic disorders can be passed from one generation to the next.
• Genetic disorders occur when an ovum and sperm fuse in meiotic division or due to other genetic abnormalities.

Mendelian Inheritance: Dominant and Recessive Patterns

• Homozygous: a person has two healthy genes (one from each parent).
• Heterozygous: a person with different genes (a healthy gene from one parent and an unhealthy gene from the other parent).
• Autosomal Dominant Disorders:
  • Either has two unhealthy genes (homozygous dominant) or heterozygous with a gene causing the disease.
  • 50% chance of a child having the disorder or being a carrier, and 25% chance of a child being disease and carrier-free.
• Autosomal Recessive Inheritance:
  • Diseases do not occur unless two genes for the disease are present.
  • 25% chance a child will be disease and carrier-free, 50% chance a child will be like the parents (free of disease but carrying the gene), and 25% chance a child will have the disease.

Imprinting

• Imprinting refers to the differential expression of genetic material, allowing researchers to identify chromosomal material from the male or female parent.

Chromosomal Abnormalities (Cytogenic Disorders)

• Nondisjunction Abnormalities:
  • Result from uneven division of chromosomes, leading to one new sperm cell or ovum with 24 chromosomes and the other with 22 chromosomes.
  • If a spermatozoa or ovum with 24 or 22 chromosomes fuses with a normal spermatozoa or ovum, the zygote will have either 47 or 45 chromosomes.
• 45 chromosomes are not compatible with life, and the embryo or fetus will likely be aborted.

Genetic Disorders Assessment

• Physical Assessment:
  • Assess family members with disorders, siblings, and couples seeking counseling.
  • Pay attention to specific body areas (space between the eyes, height, contour, shape of ears, number of fingers and toes, presence of webbing).
• Diagnostic Testing:
  • Karyotyping: a sample of peripheral venous blood or a scraping of cells from the buccal membrane.
  • Cells are stained, placed under a microscope, photographed, and chromosomes are identified by size, shape, and stain, cut from the photograph, and arranged.