Exam Preparation Notes on Genetics, Cell Cycle, and Viruses

Genetics and Inheritance

• Incomplete Dominance: Characteristic where the phenotype of heterozygotes is an intermediate of the phenotypes of both homozygotes.

  • Example: Two pink flowers produce all pink offspring.

• Phenotypic Ratios: When two plants with specific traits are crossed,

  • For incomplete dominance: Crossing two pink flowers might yield a 1 red: 2 pink: 1 white ratio.
  • In a heterozygous blue leafed plant (H'H) and a homozygous white leafed plant (hh), phenotypic ratio is expected to be 1 green: 1 blue.

• Meiosis: Results in four haploid cells that are genetically different due to crossing over and independent assortment.

• Genetic Disorders:

  • Hemophilia: X-linked recessive trait where a heterozygous mother (X^H X^h) and a normal father (X^H Y) have a son; son has a 50% chance of being affected.

Blood Type Genetics

• Blood Type Inheritance:

  • ABO blood types are determined by multiple alleles (IA, IB, i), where IA and IB are codominant, and i is recessive.
  • A mother with blood type A could have genotypes IAIA or IAi, requiring further testing to confirm. Blood type inheritance follows Mendelian genetics principles.

• Antibodies in Blood Serum: Individuals with AB- blood type have no anti-A or anti-B antibodies.

Cell Cycle and Mitosis

• Cell Cycle Phases:

  • G1 phase: Cells grow and prepare for DNA replication; human cells here have 46 chromosomes (23 pairs).
  • S phase: DNA synthesis occurs, doubling the chromosomes.
  • G2 phase: Preparation for mitosis.

• Mitosis: Proceeds through phases: Prophase, Metaphase, Anaphase, Telophase, and results in two diploid cells that are genetically identical.

  • Cytokinesis is the division of cytoplasm following mitosis.

Chromosomal Structures

• Sister chromatids are joined at the Centromere and attach to the kinetochore during cell division.

• In meiosis, homologous chromosomes pair up during Prophase I, allowing for crossing over and genetic variation.

Types of Inheritance

• Polygenic Inheritance: Traits controlled by multiple genes contribute to a phenotype, often resulting in a bell-shaped curve (e.g., human skin color).

• Epistasis: One gene interferes with the expression of another at a different locus.

• Pleiotropy: A single gene influences multiple phenotypic traits.

Cell Signaling and Viruses

• Cell Communication: Can be direct (gap junctions) or through signaling molecules (hormones/neurotransmitters).

  • Types include endocrine (long-distance), paracrine (local), and autocrine signaling.

• Viral Behavior:

  • Viruses can only replicate inside a host cell and their DNA can be integrated via enzymes like integrase.
  • Retroviruses, such as HIV, possess reverse transcriptase allowing them to convert RNA to DNA before integration into the host cell's genome.

Enzymatic Processes

• Kinases and Phosphatases:

  • Kinase: Transfers a phosphate group to another molecule.
  • Phosphatase: Removes phosphate groups, regulating activity of proteins in signaling pathways.

• Gametes and Zygotes:

  • Gametes are haploid cells, while zygotes are formed by the fusion of two gametes (diploid). Humans have 23 pairs of chromosomes (46 total).