In-Depth Notes on Genes and Inheritance

Chapter 7 – Genes and Inheritance

Objectives

  • Understanding Chromosomes and Genes

    • Chromosomes contain genes (made of DNA) that determine characteristics of organisms.

    • Fusion of gametes creates a fertilized egg (zygote) with a new DNA combination.

    • Explain inheritance of sex in humans via XX (female) and XY (male) chromosomes.

    • Adaptations of male (sperm) and female (egg) gametes.

    • Transmission of X and Y chromosomes to offspring and production of male/female children.

    • Relation of variations in species to genetic differences.

    • Introduction to natural selection and its effects on genetic changes over time.

    • Impact of environmental change on species population and potential extinction.

    • Define and measure variation in humans and other organisms using bar charts and frequency diagrams.

    • Natural variation contributes to natural selection and genetic evolution.

Chromosomes and Genes

  • Definition:

    • Chromosomes = DNA strands in the nucleus of Eukaryotic cells.

    • Found in pairs; different species have different chromosome counts.

    • Example chromosomes: Humans (23 pairs; total of 46), Fruit flies (4 pairs).

    • A gene is a fragment of a chromosome that has all the information for a specific trait. Genes are found in pairs on chromosomes as well.

  • Function:

    • Store information for cell growth, development, and traits.

    • Each chromosome consists of hundreds of genes, which convey specific traits.

DNA Structure

  • Nature of DNA:

    • DNA = Deoxyribonucleic acid; resembles a twisted ladder (double helix).

    • Formed from two long molecules of DNA.

    • First discovered in 1950; responsible for determining organism characteristics.

Gametes

  • Definition:

    • Gametes = Sex cells (sperm in males; eggs in females).

    • Plant gametes: Male (pollen grain), Female (egg cell in ovule).

  • Adaptations:

    • Sperm produced in large numbers for fertilization.

    • Eggs larger and contain food reserves, though they are non-motile.

  • Production:

    • Meiosis: Special division resulting in haploid cells (half the number of chromosomes).

    • Human gametes have 23 chromosomes (haploid).

Meiosis Process

  1. Starting Cell:

    • 46 chromosomes (diploid or 2n).

  2. Meiosis I:

    • Diploid cell divides into two haploid cells (23 chromosomes each).

  3. Meiosis II:

    • Each haploid cell divides into two, leading to four haploid gametes (23 chromosomes).

Fertilization

  • Process:

    • Fusion of male and female gamete nuclei creates a zygote.

    • Zygote has 46 chromosomes: a unique DNA combination from both parents.

    • Development into an embryo; eventually grows into a human.

Gender Determination

  • Chromosome Composition:

    • Female = XX, Male = XY (23rd pair of sex chromosomes).

    • Sperm carries 50% X and 50% Y, while eggs carry 100% X.

  • Outcome:

    • Fertilization results in either XX (girl) or XY (boy).

Variation and Its Sources

  • Definition:

    • Variation = Differences in a population of the same species.

  • Types:

    1. Genetic Variation: Inherited differences (e.g., eye color).

    2. Environmental Variation: Non-inherited differences from environmental factors (e.g., scars).

    3. Combined Variation: Resulting from both genetic and environmental factors (e.g., height).

Representation of Variation

  • Data Collection:

    • Surveys for population variation.

  • Types:

    • Continuous Variation: Not in categories (e.g., height).

    • Discontinuous Variation: In categories (e.g., blood type).

  • Graph Construction:

    • Bar graphs used to represent variation data.

    • X-axis for categories; Y-axis for counts.

Natural Selection

  • Definition:

    • Process where organisms with advantageous traits survive and reproduce.

  • Examples:

    • Galapagos finches adapted to specific diets.

    • Impact of mutation and antibiotic resistance in bacteria.

  • Case Study: Peppered Moth

    • Light moths were favored pre-industrial era, dark moths after pollution.

Extinction

  • Definition:

    • Occurs when no living examples of a species remain.

  • Causes:

    • Climate change, habitat loss, overhunting, disease, etc.

  • Prevention:

    • Legislation to protect species, conservation areas, and public education on environmental protection.

Conclusion

  • Understanding Evolution:

    • Genetic changes through natural selection can lead to species evolving or potentially becoming extinct based on environmental changes or failure to adapt.