Genetics Fundamentals: Inheritance Patterns & Reproduction

Sexual Reproduction & Meiosis

Sexual Reproduction: Takes place when two sex cells, or gametes, from two parents of different sexes join together.

Meiosis: A cell division process through which haploid cells are formed.

Fundamental Genetic Concepts

• Traits: Each of the characteristics present in an organism that can be inherited by its offspring.
• Gene: A section of DNA that contains information about a certain trait and controls that trait.
• Alleles: Different forms of a gene.
• Homozygous: When two alleles for a specific trait are identical (e.g., AA, aa).
• Heterozygous: When two alleles for a specific trait are different (e.g., Aa).
• Genotype: An organism's complete set of genes.
• Phenotype: The observable way in which a genotype is expressed under specific environmental conditions.

Non-Mendelian Inheritance Patterns

• Intermediate Inheritance: The F1 heterozygous phenotype exhibits an intermediate trait between the two homozygous parents, as neither allele is dominant over the other.
• Co-dominance: Occurs when two alleles manifest themselves simultaneously, meaning the F1 filial generation is heterozygous and exhibits traits from both parents.

Exceptions to Mendel's Law of Independent Assortment

Gene Linkage

Linkage occurs between two genes when they are found on the same chromosome. These linked genes tend to be transferred together to the offspring, resulting in an exception to Mendel's Third Law (Independent Assortment).

Genetic Recombination

Genetic recombination allows gametes with new genetic combinations to appear as a result of crossover between homologous chromosomes during meiosis. This process introduces the possibility of creating gene combinations that alter the expected results for both the crossing of independent genes and the crossing of totally linked genes.

Sex Determination Mechanisms

• Chromosomal Determination: In humans, the sex of an individual depends on the presence of a pair of sex chromosomes (XX for females, XY for males).
• Environmental Determination: Sex is determined by environmental conditions (e.g., temperature in some reptiles).
• Gene Determination: Sex inheritance is determined by a specific gene that may have several alleles.
• Karyotype Determination: In some insects, sex is determined by the number of chromosomes.

Sex-Linked Inheritance

Human Sex Chromosomes

Human sex chromosomes (X and Y) have two main segments:

• Homologous Segment: Contains genes found on both X and Y chromosomes.
• Differential Segment: Contains genes found exclusively on either the X or Y chromosome.

Examples of Sex-Linked Traits

Examples of sex-linked inheritance include:

• Color Blindness: An inability to distinguish between certain colors, typically red and green.
• Hemophilia: A disorder characterized by the failure of blood to clot properly.