1. Genetics
An Introduction

2. Genetics
Genetic information directs cellular function, largely determines an organism’s external appearance and serves as a link between generations in every species

3. What does genetics mean?
Genetics is the branch of biology concerned with heredity and variation
Involves the study of cells, individuals, their offspring and the populations within which organisms live
Geneticists investigate all forms of inherited variation as well as the molecular basis underlying such characteristics

4. What is the center of heredity in a cell?
Eukaryotic organisms the nucleus contains the genetic material in the form of genes present on chromosomes

5. What is a gene?
The gene is a functional unit of heredity residing at a specific point along the chromosome
An informational storage unit capable of undergoing replication, expression, and mutation
The gene has been found to be a very complex element
The length of DNA that specifies a product or action

6. What is a chromosome?
A long, usually circular DNA molecule organized into genes
Most eukaryotes have many chromosomes that are composed of linear DNA molecules intimately associated with proteins
These contain many nongenic regions

7. How many chromosomes does an organism have?
Members of most eukaryotic species have a specific number of chromosomes in each somatic cell
Diploid number (2n)
Example: humans have a diploid number of 46
These chromosomes are found to occur in pairs
Homologous chromosomes: the members of each pair are identical in their length and in the location of the centromere
Also contain the same sequence of gene sites

8. Chromosomal Theory of Inheritance
Inherited traits are controlled by genes that reside in chromosomes, which are faithfully transmitted through gametes to future generations

9. History of Genetics

10. Prehistoric Times
We don’t know when people first recognized the existence of heredity
Various types of archeological evidence provides insight
Evidence documents the successful domestication of animals and cultivation of plants thousands of years ago
Between 8000 and 1000 BC: horses, camels, oxen, and various breeds of dogs were domesticated to serve various roles
BC: cultivation of plants (maize, wheat, rice, date palm)
This supports the hypotheses that our ancestors learned that desirable and undesirable traits are passed to successive generations
By influencing their breeding, many desirable varieties of animals and plants could be obtained

11. The Greek Influence
During the Golden Age of Greek culture, philosophers directed much attention to heredity
Focus: how heredity relates to the origin of humans and to their reproduction
Evidence: writings of Hippocratic school of medicine ( BC) and Aristotle ( BC)

12. 1600-1850: The Dawn of Modern Biology
300BC-1600AD:
Theoretical understanding of genetics was not extended by significant new ideas
Roman times: plant grafting and animal breeding were common
Middle Ages: aware of the impact of heredity on organisms they studied
1600s: William Harvey wrote a treatise on reproduction and development (patterned after Aristotle’s work)
He is credited with the earliest statement of the theory of epigenesis
An organisms is derived from substances present in the egg, which differentiate into adult structures during embryonic development

13. : Continued
The theory of epigenesis as written by Harvey conflicts with the 17th century theory of preformation
Sex cells contain a complete miniature adult called homunculus
Preformation was popular into the 18th century
Casper Wolff and others clearly disproved the preformation theory
He was convinced that several structures were not initially present in the earliest embryos he studied, but instead were formed later during development
1808: John Dalton expounded his atomic theory
All matter is composed of small, invisible units called atoms

14. : Continued
1830: Matthias Schleiden and Theodor Schwann proposed cell theory
All organisms are composed of basic visible units called cells, which derived from similar preexisting structures
The fixity of species was also prevalent
Animal and plant groups remain unchanged in form from the moment of their appearance on Earth
Supported by Carolus Linnaeus
Work of Joseph Gottlieb Kolreuter and his work with tobacco

15. Charles Darwin and Evolution
Darwin published in 1859 the book On the Origin of Species
Statement of his evolutionary theory
Observations convinced him that existing species arose by descent with modification from other ancestral species
Led to his formulation of the theory of natural selection
1868: published Variations in Animals and Plants under Domestication
Attempted to provide a more definitive explanation of how heritable variation arises gradually over time

16. Mendel
As Darwin’s work ensued, Gregor Johann Mendel conducted his experiment between 1856 and 1863
Published in 1866
Demonstrated a number of statistical patterns underlying inheritance and developed a theory involving hereditary factors in the germ cells to explain these patterns
Early part of the 20th century: chromosomes were discovered and support for the epigenetic interpretation of development had grown considerably