Introduction to Genetics

Introduction to Genetics

• Genetics is the scientific study of genes and heredity.
• It explores how traits are passed from parents to offspring through changes in DNA sequence.
• The transmission of traits between generations is called inheritance, or heredity.
• Offspring are not identical copies of their parents or siblings.
• Variation exists alongside inherited similarity.

Gregor Mendel

• Gregor Mendel, an Augustinian monk, conducted experiments using pea plants in the 1860s.
• His experiments laid the foundation for the understanding of genetics.
• His work is fundamental to the field of genetics.

Chromosomal Theory of Inheritance

• Inherited traits are controlled by genes residing on chromosomes.
• Chromosomes faithfully transmit traits through gametes.
• This maintains genetic continuity across generations.

Alleles and Mutations

• Alleles are alternative forms of a gene.
• The variant eye color gene found in Drosophila is an allele.
• Mutations are heritable changes that are the source of genetic variation.

Thomas Hunt Morgan

• Thomas Hunt Morgan received the Nobel Prize in Physiology or Medicine in 1933.
• His work focused on the role of chromosomes in heredity.
• He was affiliated with Caltech at the time of the award.
• Born in 1866 and died in 1945.

Genotype and Phenotype

• Different alleles produce observable differences, or phenotypes, in an organism.
• The set of alleles for a given trait is called the genotype.
• Environment influences the expression of the phenotype.

Cell Division

• Mitosis involves copying and distributing chromosomes to ensure that each daughter cell receives a full diploid set.
• Meiosis, involved in gamete (sex cell) formation, reduces the number of chromosomes.
• Researchers in the late 1800s documented the behavior of chromosomes during mitosis and meiosis.

DNA as Hereditary Material

• Scientists determined that DNA, not proteins, carries genetic information.
• Experiments revealed that proteins are the most abundant molecules in cells.
• Their widespread distribution in both the nucleus and cytoplasm led many researchers to believe they held the key to genetic inheritance.

Griffith's Experiment

• Griffith's experiments helped identify DNA as the hereditary material to solve controversy on which molecule played central role in heredity.
• Experiments showed that a non-harmful (R) strain of bacteria could be transformed into a harmful (S) strain by exposure to a heat-killed S strain.
• This transformation remained even after destroying the proteins, but ceased after destroying the DNA.

Avery, MacLeod, and McCarty Experiment

• Avery, MacLeod, and McCarty further solidified DNA's role in heredity via a series of experiments.
• Their research provided crucial evidence supporting Griffith's conclusions.
• They isolated a substance from the S strain and successfully transformed the R strain to an S strain.
• They found that the transforming principle was DNA.

Hershey-Chase Experiment

• The Hershey-Chase experiment used bacteriophages (viruses that infect bacteria) to demonstrate DNA carries genetic information.
• The experiment tracked which components of the phage (DNA or protein) entered the bacterial cells and directed the assembly of new phages.
• The experiment confirmed that DNA, not protein, was the genetic material in phages.