IGCSE Biology Study Notes: Inheritance (Chapter 17, Part 1)

Introduction

• Inheritance: Process by which genetic information is passed from parents to offspring.
• Genetic Information: Carried in the form of DNA located in chromosomes within the cell's nucleus.

Genetic Material

• DNA: Contains genetic information in the form of genes.
• Gene: Length of DNA that codes for a protein; instructions for specific traits or characteristics.
• Alleles: Different versions of a gene leading to variations in traits (e.g., blood type).

Chromosomes and Sex Determination

• Diploid Cells: Normal human cells with 23 pairs (46 total) chromosomes.
• Sex Chromosomes: Determine the sex of an individual (XX for females, XY for males).
  • Sperm and Egg: Female eggs always X; male sperm can be X or Y, determining the baby's sex.
• Punnett Square: Tool to demonstrate sex inheritance using X and Y chromosomes.

Protein Synthesis

• DNA Role: Provides instructions for making proteins, which perform various cell functions.
• Transcription and Translation:
  • Transcription: DNA sequence is copied into mRNA in the nucleus.
  • Translation: mRNA moves to ribosomes to assemble amino acids into proteins.

Gene Expression

• Cell Function: Not all genes expressed in every cell; only necessary proteins are produced.
• Gene Regulation: Genes can be turned "on" (expressed) or "off" (not expressed) based on protein needs.

Haploid vs. Diploid

• Haploid Nucleus: Contains a single set of chromosomes (23 total).
• Diploid Nucleus: Contains two sets of chromosomes (23 pairs, 46 total).

Cell Division: Mitosis vs. Meiosis

Mitosis

• Purpose: Growth, repair, replacement, and asexual reproduction.
• Process:
  • Produces genetically identical cells (diploid).
  • Involves one cell division.

Meiosis

• Purpose: Production of gametes (sex cells) with genetic diversity.
• Process:
  • Produces genetically different cells (haploid).
  • Involves two cell divisions.
  • Chromosome number halved from diploid to haploid.

Conclusions

• Difference between mitosis and meiosis in terms of cell type, number of daughter cells, and genetic diversity.

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