Fundamentals of Genetics and Biological Reproduction

Understanding Biological Reproduction

Reproduction is the fundamental process by which living descendants arise, similar to themselves. This process guarantees the survival of the species by transmitting genetic information.

Asexual Reproduction

Asexual reproduction involves a single parent and creates identical copies of itself. Gametes are not needed. Descendants arise from the division of the organism or one of its cells.

Key Types of Asexual Reproduction

• Bipartition: Cell division into two identical cells (e.g., bacteria and protozoa).
• Sporulation: Successive divisions of the nucleus. Each new nucleus and cytoplasm is enveloped by a membrane, forming a spore that gives rise to a new individual (e.g., fungi, algae, mosses, ferns).
• Gemmation (Budding): Formation of a bud, built by a mass of cells, which then divides and develops into a new organism.
• Splitting or Fragmentation: Division of the parent into one or more fragments, where each fragment generates a complete individual (e.g., algae, worms, and coelenterates).

Sexual Reproduction and Gametes

Sexual reproduction requires the participation of two parents, who contribute specialized cells called gametes. Descendants inherit characteristics from both parents.

Gamete Characteristics

Gametes are haploid cells formed by the meiosis of diploid cells. The genetic information carried by each gamete is unique and differs from the other parent's contribution.

• Female Gametes: Oosphere (in plants) or egg (in animals).
• Male Gametes: Antherozoid (in plants) or sperm (in animals).

Gamete Formation and Specialized Organs

Gametes are formed in specialized organs: Gonads in animals and Gametangia in plants. The male gonads are the testes, and the female gonads are the ovaries.

Individuals can be classified based on their gonads:

• Unisexual: Individuals possess only one type of gonad (either male or female). When males and females have features that make them visibly different, this is called sexual dimorphism.
• Hermaphrodite: Individuals possess both types of gonads (testes and ovaries).

Fertilization and Zygote Formation

Fertilization originates from the union of gametes, forming the zygote, which multiplies and develops into a new individual.

In some species, an individual can arise from an unfertilized egg; this process is called parthenogenesis.

Mendel's Laws of Inheritance

These principles describe how traits are passed from parents to offspring.

First Law: Uniformity of Hybrids (F1)

When two pure lines that differ in a single character are crossed, the first filial generation (F1) is uniform.

Example:

• Homozygous dominant (AA) = Yellow
• Homozygous recessive (aa) = Green
• The resulting F1 generation (Aa) is uniformly Yellow.

Second Law: Segregation of Alleles (F2)

In the hybrid cross of the first generation (F1), the alleles separate and distribute into gametes independently. Individuals obtained in the F1 generation (Aa) carry both the dominant allele (A) and the recessive allele (a).

The resulting F2 generation shows a phenotypic ratio of 3 dominant to 1 recessive.

Third Law: Independent Assortment

The alleles responsible for different characters are inherited independently from each other and combine randomly in the offspring.