Exam Preparation Notes on Genetics, Cell Cycle, and Viruses

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 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 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.

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.

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 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.

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).