Unit 5: Heredity

Overview

• Heredity: How genes and traits are passed from parents to offspring.
• Unit Structure: Divided into two sets of notes - 5.1 and 5.2.

Topic 1: Sexual Reproduction and Heredity

Key Concepts

• Sexual Reproduction:

  • Involves two parents contributing DNA to offspring.
  • Offspring receive DNA from both parents (e.g., from mom and dad).

• Cell Types:

  • Somatic Cells: Body cells (e.g., skin, muscle) that are diploid.
    • Diploid (2n): Cells contain two complete sets of chromosomes, one from each parent.
  • Gametes: Reproductive cells (e.g., sperm, egg) that are haploid.
    • Haploid (n): Cells contain one set of chromosomes.

Chromosomes

• Human Chromosome Count:

  • Diploid Cells: 46 chromosomes (2n = 46), two sets of 23 chromosomes.
  • Haploid Cells: 23 chromosomes (n = 23), one set.

• Chromosome Representation:

  • Diploid (2n): Two sets (one mother, one father).
  • Haploid (n): Single set.

Fertilization

• Process:

  • Fusion of an egg and sperm cell to form a zygote.
  • Zygote has DNA from both parents and contains 46 chromosomes.

• Meiosis:

  • Cell division process creating gametes (haploid cells).
  • Different from mitosis (which creates identical diploid cells).

Genes and Heredity

• Genes:

  • Units of heredity located on chromosomes.
  • Code for traits by producing proteins/functional RNA.

• Gene Locus:

  • Specific location of a gene on a chromosome.

Homologous Chromosomes

• Definition:

  • Chromosomes with the same set of genes from each parent.
  • Not identical; may code for different versions of a trait.

• Sister Chromatids:

  • Identical copies of a chromosome connected by a centromere.

Chromosome Types

• Autosomes: Non-sex chromosomes.
• Sex Chromosomes:
  • Determine sex (XX for female, XY for male).
  • X and Y chromosomes are not true homologous pairs (size and gene differences).

Karyotype

• Definition: Display of all chromosomes.
• 23 pairs for humans: 22 pairs of autosomes, 1 pair of sex chromosomes.
• Example: An X and Y chromosome indicates male.

Conclusion

• Understanding the basics of heredity and chromosome behavior is crucial for deeper topics in genetics.

• Practice questions provided for further exploration.

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These notes cover foundational concepts in heredity, including the difference between diploid and haploid cells, the process of sexual reproduction, and the role of meiosis. It also discusses genes as units of heredity, the structure of homologous chromosomes, and the distinction between autosomes and sex chromosomes.