Biology Meiosis and Fertilization Concepts

Random Segregation

• During Anaphase II, sister chromatids separate randomly to opposite poles of the haploid cell.
• This random separation creates four gametes, each with a unique combination of chromosomes.
• It is impossible to predict which chromatid will end up in each gamete.
• Segregation increases the genetic variation of gametes and offspring.

Telophase II

• The coiled chromatids begin to uncoil.
• Cytokinesis II occurs, resulting in four haploid gametes.
• Each gamete inherits one allele of every gene.
• A new nuclear membrane forms around the two chromatids in each gamete.
• The microtubules break down.
• One centrosome goes to each daughter cell.
• Depending on the organism's gender, the gametes are either sperm or egg cells.

Internal Fertilization

• Internal fertilization has a higher fertilization success rate per gamete compared to external fertilization.
• Internal fertilization provides a direct route for sperm to reach the egg inside the female's body.
• This reduces the impact of external environmental factors on sperm cells.
• Disadvantages of internal fertilization:
  • Less mating partner options, leading to lower genetic variation.
  • More energy is required to find a mating partner and perform mating.
  • Fewer gametes are produced, leading to a lower overall amount of offspring.

Asexual Reproduction

• Asexual reproduction occurs when one parent produces offspring through cell division.
• The offspring are genetically identical clones of the parent.
• No fusion of gametes occurs during asexual reproduction.
• Asexual reproduction in plants is called vegetative propagation.

Vegetative Propagation

• Vegetative propagation occurs when a parent plant produces a genetically identical offspring.
• Examples include tubers, stolons, rhizomes, suckers, fragmentation, and runners.
• Tubers are swollen underground stems that store food and can produce new plants.
• Stolons are long stems that grow along the surface and produce new roots and leaves.
• Rhizomes are underground stems that give rise to new shoots and roots.
• Suckers are new shoots that arise from roots or underground stems.
• Fragmentation occurs when a part of the parent organism separates and develops into a new individual.
• Runners are stems that extend from a plant and produce new roots at nodes, forming new genetically identical plants.
• Bulbs are underground buds that can develop into new plants.

Sexual Reproduction

• Sexual reproduction involves the fusion of gametes from two parents.
• The offspring inherits genetic material from both parents and is not genetically identical to either.
• Gametes are sex cells such as sperm and egg cells in humans.
• The process of producing gametes is called meiosis.

Self-Pollination

• Self-pollination occurs when a plant produces both pollen and ovules, which then combine to produce offspring.
• Self-pollination can result in either genetically identical or different offspring, depending on whether the plant is homozygous or heterozygous for the genes.
• Self-pollination is considered a type of sexual reproduction because it involves the fusion of gametes.

Continuity of Species

• During reproduction, genetic information (DNA) is copied and passed on to offspring.
• The offspring's genetic material is stored in their cells' nuclei.

Protein Structure

• Proteins play a crucial role in supporting the survival of organisms.
• Protein shape and function are closely related.
• There are four levels of protein structure: primary, secondary, tertiary, and quaternary.
• Primary structure: The sequence of amino acids in a polypeptide chain.
• Secondary structure: The way a polypeptide chain coils into helixes due to hydrogen bonds.
• Tertiary structure: The further coiling of polypeptide chains into a three-dimensional shape, involving additional types of bonds like ionic bonds.
• Quaternary structure: The interaction of multiple polypeptide chains to form a functional protein.

Crossing Over

• Crossing over is a process that occurs during meiosis I.
• It involves the exchange of genetic material between non-sister chromatids of homologous chromosomes.
• Crossing over creates new combinations of alleles, contributing to genetic variation.
• Crossing over does not occur in mitosis because homologous chromosomes do not align side-by-side during the process.

Sister Chromatids

• Sister chromatids are two identical copies of a single chromosome.
• They carry the same alleles for all genes.
• Crossing over can occur between sister chromatids, but it does not lead to new allele combinations.
• The longer the distance between genes along a chromosome, the greater the chance of crossing over.

Alleles

• Alleles are alternate forms of a gene.
• Alleles are located at specific positions on chromosomes called loci.
• By convention, a capital letter represents a dominant allele, and a lowercase letter represents a recessive allele.
• Homologous chromosomes carry alleles for the same genes at corresponding loci.