BIOL1010 - Genetics and Molecular Bio - Lecture 2

Lecture 2

Introduction

• Nobel Prize Season: Time of year for Nobel Prize announcements, a significant event for scientists.

• Recent Nobel Prize in Physiology or Medicine awarded to Victor Ambrose and Gary Rivkin for the discovery of small RNA molecules that regulate gene expression.

• They used C. elegans (a type of small worm) as a model organism for their research.

• Encouragement to read the press release on their findings, which outlines how observations lead to major discoveries in science.

Overview of Cell Division

• Last class covered mitosis: the process by which somatic cells (non-reproductive cells) reproduce, resulting in two genetically identical cells.

• Today’s focus: reproduction, beginning with asexual reproduction.

• Asexual Reproduction Types:

  • Budding: Example organism: Hydra. A bud develops on the side and, after detachment, grows into a new organism.

  • Fragmentation: Example organism: Planaria. Fragmentation allows cutting the organism into pieces, each capable of growing into a new organism.

    • Important detail: Genetic material in offspring is identical to that of the parent, making them clones.

Cloning Experiments in Frogs

• 1970s experiment aimed at understanding whether a differentiated animal cell nucleus could create a new organism.

• The first part involved using a frog egg cell exposed to intense UV light to render its nucleus non-functional.

  • The nucleus from a frog embryo was transplanted into the egg cell, resulting in the production of a tadpole.

• The second part of the experiment used an intestinal cell nucleus from a tadpole, resulting in only a 2% success rate in producing tadpoles.

  • This demonstrated that as cells differentiate, their ability to contribute to a whole organism decreases, largely due to gene regulation by microRNAs.

Dolly the Sheep Cloning

• The phenomenon of cloning was exemplified by the famous case of Dolly the sheep (1997), cloned from an adult somatic cell nucleus.

• Dolly’s cloning success came after hundreds of trials, emphasizing the challenges of cloning vertebrates.

• Health issues and premature aging led to Dolly being euthanized at six years old, a reminder of complications arising from cloning processes.

Introduction to Sexual Reproduction

• Transitioning to sexual reproduction, which is more complex than asexual reproduction.

• Key terms: Gametes (sperm and eggs) carry a haploid set of chromosomes.

• Fusion of gametes leads to fertilization, producing a diploid zygote.

• Notable process: only one sperm enters the egg through a complex mechanism involving calcium waves.

The Meiosis Process

• Comparison of mitosis and meiosis:

  • Meiosis reduces the diploid complement of chromosomes to haploid gametes.

  • Meiosis has two main stages: Meiosis I (homologous chromosomes separate) and Meiosis II (sister chromatids separate).

• The importance of crossing over in Prophase I, which mixes genetic material from homologous chromosomes.

• The concept of Independent Orientation: During meiosis, the way in which chromosomes are segregated leads to thousands, if not millions, of combinations of genetic material.

Genetic Variation Importance

• Emphasis on the significance of genetic variation in populations: Asexual reproduction can lead to detrimental results during environmental changes due to lack of variation.

• Sexual reproduction introduces beneficial genetic mixes that enhance survival and adaptability of offspring.

Mendelian Genetics: History and Principles

• Introduction to Mendel's experiments with pea plants and key historical contributions to understanding heredity.

• Mendel established the laws of inheritance:

  • Law of Segregation: Alleles for a trait segregate during gamete formation.

  • Law of Independent Assortment: Genes for different traits are passed independently of one another.

• Important definitions:

  • Characters (general traits) vs. traits (specific variations of a character).

  • Use of Punnett Squares to predict offspring genotypes and phenotypes based on parental combinations.

Types of Dominance

• Dominant vs. Recessive Traits: Mendel's terms related to whether an allele masks the presence of another.

  • Example: Purple flowers (dominant) vs. white flowers (recessive) in pea plants.

• The practical application of this theory leads to improved understanding of genetics in various organisms.