Untitled

Autosomes

• Total of 44 autosomes in a human karyotype (22 pairs).
• Male karyotype: X and Y chromosomes present.
• Total sister chromatids: 92 (each chromosome has 2 chromatids).

Chromosome Pairs

• Homologous pairs: 22 (23 in females).
• X and Y are non-homologous; X and X are homologous.

Cell Types

• Karyotype obtained from somatic cell (e.g., skin cell) vs. gametic cell (sperm or egg).
• Egg cell always has X; sperm can have X or Y.

Genetic Disorders

• Trisomy indicates an extra chromosome (e.g., Down syndrome).
• Total chromosomes in trisomy: 47 (not 46).

Cell Cycle

• Interphase phases: G1, S, G2; cells do not divide in G0 but are functional.
• Chromatin in interphase is long and thin for gene access.

Mitosis

• Phases of mitosis: Prophase, Metaphase, Anaphase, Telophase; Cytokinesis is separate.
• Cells should not be in mitosis simultaneously; must be in interphase for functionality.
• Cell size is largest at G2, where preparation for division occurs.
• Checkpoints: G1, G2, and M checkpoint ensure cell conditions are optimal before division.

Chromosome Terminology

• Chromosomes during mitosis are condensed; chromatids exist post-S phase.
• Chromatin is the uncondensed state of DNA throughout interphase.
• Homologous chromosomes are present but may not be visible until condensed.

Meiosis

• First division in meiosis is reductional, results in haploid cells (23 chromosomes).
• Homologous chromosomes line up and separate in Metaphase I leading to genetic variation.
• Crossing over increases genetic diversity.

Key Points on Genetic Contributions

• Each parent contributes half the chromosome count; offspring represent a mix of ancestry.
• Child inherits genetic traits from both sets of grandparents, creating diverse genetic combinations.