Biology Chapter 5: Chromosomes and Cell Division

Chromosome Structure and Numbering

• Chromosomes are numbered based on length, with chromosome 1 being the longest.
• Chromosomes can be identified by their length, banding pattern, and centromere position.
• Each chromosome has a short (p) arm and a long (q) arm.
• The location of a gene is indicated using a notation like 12p3 (chromosome 12, p arm, band 3).

Mitosis vs. Meiosis

• Mitosis produces genetically identical daughter cells used for body cell division.
• Meiosis produces gametes (sex cells) with half the number of chromosomes as the parent cell.

Diploid and Haploid Cells

• Human somatic cells are diploid (2n = 46).
• Homologous chromosomes are diploid, having the same length, position, and gene sequence, but potentially different alleles.
• One homologous chromosome is inherited from each parent.
• Meiosis produces haploid cells (n = 23), such as sperm and eggs in humans.
• This halving of chromosome number is crucial to maintain the correct chromosome count across generations.

Meiosis Phases

• Meiosis involves two divisions (Meiosis I and Meiosis II), resulting in four haploid cells from one diploid cell.
• Meiosis I separates homologous chromosomes, and Meiosis II separates sister chromatids.
• Meiosis 1: Homologous chromosome pairs separate
• Meiosis 2: Sister chromatids of each chromosome separate, leading to four haploid cell gametes

Crossing Over

• During prophase I, homologous chromosomes pair up to undergo crossing over.
• Crossing over involves swapping segments of DNA between homologous chromosomes.
• The precise location of crossovers is random, leading to genetically diverse gametes.

Fertilization and Zygotes

• Sperm and egg cells, which are haploid, unite in fertilization.
• The combination results in a diploid zygote.

Chromosomal Inheritance and Pedigrees

• Pedigrees are family trees used to trace patterns of inheritance.
• Patterns of inheritance can be analysed by following chromosome movement across generations.

Nondisjunction and Aneuploidy

• Nondisjunction is an error where chromosomes fail to properly separate during meiosis.
• This results in gametes with either an extra chromosome (trisomy) or a missing chromosome (monosomy).
• Aneuploidy refers to any abnormal chromosome number (more or less than normal).

Karyograms

• Karyograms are used to visualize an organism’s chromosomes.
• They can help identify the presence of chromosomal abnormalities, like trisomy or monosomy.

Explore the fundamentals of chromosome structure, numbering, and the differences between mitosis and meiosis. This quiz will test your understanding of diploid and haploid cells and their significance in human genetics. Prepare to dive into the essential concepts that govern cellular reproduction and genetic inheritance.