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Biology

17.1 Using Keys

  • Objective: Use and construct keys to identify species.

  • Scenario: Victor encounters a snake and wants to know its species and danger level.

  • Fact: There are 2700 snake species, each with unique features.

  • Utilizing a Key:

    • Instead of checking images, he employs a key for efficient identification.

    • Asks practical questions:

      1. Do hollow fangs drop down when it opens its mouth? (YES/NO)

      2. Is its head heart-shaped? (YES/NO)

  • Key Example:

    • If YES to hollow fangs and heart-shaped head, queries further about stripes.

    • Result: Snake identified as Bitis arietans (puff adder), a venomous species.

Designing Keys

  • Constructing a Key:

    • Victor uses clear features to categorize four African cat species.

    • Initial Question Example: "Does it have spots?"

    • Focuses on significant, unchanging traits rather than variables that can change with age.

Similarities and Differences in Species

  • Feature Stability:

    • Keys are effective if male and female animals share the same characteristics.

  • Example Question to Distinguish Cats:

    • Are its spots in groups (leopard) or separate (cheetah)?

    • Are its ears rounded (lion) or pointed (caracal)?

17.2 What Makes Us Different?

  • Identical Twins: Priyanka and Juvina's similarities and differences stem from genetics and environment.

  • Inheritance:

    • Characteristics such as skin color and blood group are inherited; others, like voice, develop later.

  • Embryonic Development:

    • Fertilization joins sperm and egg nuclei, forming an embryo and subsequently more cells, all with identical genes.

Genes and Cell Nucleus

  • Gene Storage:

    • Genes in the nucleus dictate growth and development; half come from each parent during fertilization.

    • Identical twins arise from a split fertilized egg, sharing genetic makeup.

Environmental Influence on Traits

  • Environmental Factors:

    • Factors like diet and surroundings modify genetic traits; for example, Priyanka's healthy lifestyle versus Juvina's unhealthy habits resulted in differences in height and weight.

17.3 Chromosomes

  • Chromosome Structure:

    • Chromosomes made of DNA; 23 pairs in human cells, inherited from both parents.

  • Sex Chromosomes:

    • Determine gender: XX for females, XY for males.

17.4 Investigating Inheritance

  • Mendel's Work:

    • Studied inheritance in pea plants, discovering dominant (T) and recessive (t) genes.

  • Gene Dominance:

    • Traits from dominant genes manifest, while recessive ones require two copies.

17.5 Selective Breeding

  • Definition:

    • Selective breeding manipulates breeding to enhance desired traits over generations.

  • Steps Involved:

    1. Identify traits to improve.

    2. Choose parent plants/animals with these traits.

    3. Select and continue breeding the best offspring.

17.6 Developing a Theory

  • Darwin's Contribution:

    • Developed evolution theory via natural selection.

  • Observations:

    • Noted variations and adaptations in species during his travels, leading to the theory of evolution.

17.7 Darwin's Theory of Evolution

  • Core Concepts:

    1. Many offspring produced; few survive.

    2. Variations provide survival advantages.

    3. Traits become prevalent over generations via successful reproduction.

17.8 Moving Genes

  • Genetic Engineering:

    • Involves adding new genes into organisms; quicker than selective breeding.

    • Examples include creating genetically modified mice and bacteria to produce insulin.

17.9 Using Genes

  • Selective Breeding vs. Genetic Engineering:

    • Both methods aim for practical applications in medicine, agriculture, and more.

  • Challenges of Malaria Treatment:

    • The resistance development of protozoa led scientists to use artemisinin derived from artemisia plants.