Inheritance

Genetic syndromes can arise from sex chromosome disorders and other chromosomal replication errors.
The focus of discussion will cover various types of chromosomal errors that can lead to genetic disorders.
Key concepts include deletion, duplication, inversion, and translocation errors.

Definition: Deletion occurs when a portion of a chromosome is not copied.
Causes: Errors occurring during mitosis; chromosome structure abnormalities lead to breakage after duplication.
Consequences: Loss of a significant amount of genetic material crucial for cell function, potentially causing abnormalities even in one affected chromosome of a pair.

Definition: Duplication occurs when a segment of a chromosome is duplicated during mitosis, resulting in extra DNA in a chromosomal segment.
Issues in Meiosis: Problems arise during crossing over, leading to chromosomes that mismatch in size and information.
Example: Crossing over may not align with the duplicated segment, leading to chromosomes missing information or having repeated segments.

Definition: Inversion occurs when a portion of a chromosome is flipped 180 degrees.
Effects: Rarely produces problems in the individual because all genetic material is present, just in a different order.
Problems for Offspring: If crossing over occurs, inversions can lead to genetic information being duplicated on one chromosome and missing on the other, resulting in loss of loci (e.g., f or g loci).

Definition: Translocation occurs when genetic information moves from one chromosome to a non-homologous chromosome.
Consequences: Often leads to nonviable individuals, but occasionally viable individuals may have genetic abnormalities.
Real-World Example:
- Williams Syndrome: Caused by a tiny deletion on chromosome seven; leads to physical abnormalities (e.g., upturned nose, wide mouth) and cognitive results (e.g., learning disabilities but above average verbal skills).
- Cri du Chat Syndrome: Caused by a deletion at the end of chromosome five, resulting in smaller head size and facial abnormalities, alongside a distinctive cat-like cry due to laryngeal issues.
- Alagille Syndrome: A translocation between chromosomes two and twenty that can cause heart defects and clubbed fingers.

Each genetic syndrome illustrates how small modifications in genetic material (deletions, duplications) can lead to significant physical and mental health impacts.
Example conditions often emerge with varied symptoms from mild to severe, impacting quality of life and health.

Introduction to Inheritance

Genes: Segments of DNA on a chromosome coding for specific traits or characteristics (e.g., eye color).
Locus: The specific location of a gene on a chromosome.
Alleles: Alternate forms of a gene (e.g., brown, blue, green for eye color).

Dominant Alleles: Require only one copy to be expressed in the phenotype (represented by uppercase letters).
Recessive Alleles: Require two copies to be expressed (represented by lowercase letters).

Genotype: The genetic makeup of an organism (e.g., homozygous dominant (AA), heterozygous (Aa), homozygous recessive (aa)).
Phenotype: The physical expression of a trait (e.g., observable traits such as hair color).

Definition: A genetic cross focusing on a single trait, using a Punnett square to visualize potential offspring.
Example: Cross between two heterozygous individuals (e.g., (Aa \times Aa)).
- Possible genotypes of offspring: 1 homozygous dominant (AA), 2 heterozygous (Aa), and 1 homozygous recessive (aa).
- Common expected ratio: 3 dominant phenotype to 1 recessive phenotype.

Carriers: Individuals who have one recessive allele but do not exhibit the associated disorder.
Common Genetic Disorders:
- Two heterozygote parents can have offspring that expresses the recessive disorder.
- Two parents with a dominant disorder may have non-affected offspring, showcasing how genetic traits are passed.

Inbreeding reduces genetic diversity, increasing the prevalence of genetic disorders over generations.
Example: Historical cases like Charles II of Spain highlight the negative effects of prolonged inbreeding, leading to acute genetic health issues (e.g., Habsburg jaw). Modeled changes in allele frequencies and homozygosity rates show declining heterozygote populations.

Understanding chromosomal errors and inheritance patterns helps elucidate the complex interactions in genetics that lead to diverse phenotypic outcomes and diseases.
Encourages deeper research into genetic disorders and population genetics to understand and address hereditary issues.