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.