Variation and inheritance | Year 9 Biology (Cambridge) PDF Download

Variation within a Species

• Definition: Variation refers to the differences in traits among individuals of the same species, influenced by both genetic inheritance and environmental factors.
• Causes of Variation:
  • Genetic Factors: Differences in genes inherited from parents.
  • Environmental Factors: External influences such as climate, diet, and habitat.
• Examples:
  • Human height variations due to genetic diversity inherited from parents.
  • Plant leaf color variations influenced by exposure to sunlight and soil nutrients.

Chromosomes, Genes, and DNA

• Chromosomes: Structures within cells that contain genetic information.
  • Types of Chromosomes: Humans have 23 pairs, including sex chromosomes (XX for females, XY for males).
• Genes: Segments of DNA that determine specific traits.
  • Alleles: Different forms of a gene (e.g., blue eyes allele vs. brown eyes allele).
• DNA (Deoxyribonucleic Acid): Double-helix molecule carrying genetic instructions.
  • Function: Provides the genetic blueprint for all living organisms.
• Example: Inheritance of blood type (A, B, AB, O) determined by specific genes on chromosomes.

Fertilisation and Inheritance

• Fertilisation: Fusion of male gamete (sperm) with female gamete (egg) to form a zygote.
  • Genetic Diversity: Each zygote inherits a unique combination of genes from both parents.
• Inheritance Patterns:
  • Dominant and Recessive Traits: Dominant traits mask recessive traits in heterozygous individuals.
  • Sex-Linked Traits: Traits determined by genes on sex chromosomes (e.g., color blindness on the X chromosome).

Fetal Growth and Development

• Stages of Development:
  • Embryonic Stage: Formation of organs and major body systems.
  • Fetal Stage: Growth and refinement of organs until birth.
• Factors Affecting Development:
  • Genetic Influences: Inherited genetic predispositions and mutations.
  • Environmental Influences: Maternal nutrition, exposure to toxins, and prenatal care.
• Example: Development of fetal brain structures influenced by both genetic predispositions and maternal health during pregnancy.

Natural Selection

• Definition: Process where organisms with advantageous traits survive and reproduce, leading to evolutionary change.
• Mechanisms:
  • Adaptation: Traits that increase survival and reproductive success in specific environments.
  • Selective Pressures: Environmental factors that favor certain traits over others.
• Examples:
  • Darwin's finches evolving different beak shapes to exploit different food sources on the Galápagos Islands.
  • Industrial melanism in peppered moths as a response to pollution-induced changes in habitat.

Summary

Understanding variation and inheritance involves exploring the interplay between genetic information, environmental factors, and evolutionary mechanisms. From the molecular level of DNA and chromosomes to the observable traits shaped by natural selection, these concepts provide insights into the diversity and adaptation of life on Earth.