The document provides a history of genetics from ancient times to modern day. It discusses: 1) Early ideas about inheritance from ancient Greeks and inheritance of acquired traits. 2) Gregor Mendel's experiments in the 1800s which laid the foundations of genetics through principles of segregation and independent assortment. 3) Major discoveries in the 20th century including DNA's role as the genetic material, Watson and Crick determining DNA's double helix structure, and cracking of the genetic code.

1. HISTORY OF GENETICS
People have known about inheritance for a long time.
 Children resemble their parents
 Domestication of animals and plants, selective breeding for good characteristics
 Sumerian horse breeding records
 Egyptian data palm breeding
 Ability to indentify a person as a member of a particular family by certain physical traits

2. OLD IDEAS
Despite knowing about inheritance in general, a number of incorrect ideas had
to be generated and overcome before modern genetics could arise.
1. All life comes from other life. Living organisms are not spontaneously generated
from non-living material. Big exception: origin of life.
2. Species concept: offspring arise only when two members of the same species
mate. Monstrous hybrids don’t exist.

3. MORE OLD IDEAS
3. Organisms develop by expressing information carried in their hereditary material.
As opposed to “preformation”, the idea that in each sperm (or egg) is a tiny,
fully-formed human that merely grows in size.
4. The environment can’t alter the hereditary material in a directed fashion. There is
no “inheritance of acquired characteristics”. Mutations are random events.

4. MORE OLD IDEAS
5. Male and female parents contribute equally to the offspring.
 ancient Greek idea: male plants a “seed” in the female “garden”.
 alleged New Guinea belief: sex is not related to reproduction.

5. GREEK PHILOSOPHERS
Theophrastus proposed that male flowers caused
female flowers to ripen
Hippocrates speculated that “seeds” were produced
by various body parts and transmitted to
offspring at the time of conception
Aristotle though that male and female semen mixed
at conception
Aeschylus proposed the male as the parent with the
female as a “nurse for the young life sown within
her”

6. DIFFERENT OLD THEORIES EXPLAINED
THE SIMILARITIES AND DISSIMILARITIES
BETWEEN INDIVIDUALS
 Blending theory
The mixture of sperm and egg resulted in progeny that were
a “blend” of two parent’s characteristics.
 Acquired characters inheritance (Jean Baptiste
Lamarck)
Individuals inherit traits are strengthened by their parents
 Pangenesis (Charles Darwin)
The cells excreted gemmules then collected and
concentrated in the reprodutive organ. Fathers and
mother gemmules blended to form an embryo

7. DIFFERENT OLD THEORIES EXPLAINED
THE SIMILARITIES AND DISSIMILARITIES
BETWEEN INDIVIDUALS
 Performation and Epigenesis
Organism develop by expressing information carried
in their heredity material
 Cell Theory (Hooke, Leewenhoek, Schleiden,
Schwann, Virchow)
1. All living things are composed of one or more cells
2. Cells are the basic units of structure and function in living
things (Schleiden and Schwann, 1839)
3. New cells are produced from existing cells (Virchow,
1858)

8. MID 1800’S DISCOVERIES
Three major events in the mid-1800’s led directly to the development of modern genetics.
1859: Charles Darwin publishes The Origin of
Species, which describes the theory of
evolution by natural selection. This theory
requires heredity to work.
1866: Gregor Mendel publishes Experiments in
Plant Hybridization, which lays out the basic
theory of genetics. It is widely ignored until
1900.
1871: Friedrich Miescher isolates “nucleic acid”
from pus cells.

9. GENETICS - The study of the way animals & plants pass on to their
offspring such as:
eye color, hair color, height, body build, blood types,
intelligence, gender, etc.
HEREDITY - Characteristics that a child receives from both parents

10. CELL: Basic unit of all living matter (Adult = over 10 trillion
cells)
NUCLEUS: Central point of
cell / contains genetic coding for
maintaining life systems and
issuing commands for growth &
reproduction
CYTOPLASM: Substance of a cell outside of
the nucleus
CHROMOSOMES:
46 in each Nucleus (23 pairs)
GENES: bands on
chromosomes (thousands of genes)
DNA on genes (billions of
DNA)

11. ? ? ? ? ? ? ? ?
How many chromosomes are there in each
cell?
46 CHROMOSOMES or 23 PAIRS
How many chromosomes are in
Reproductive (egg & sperm) or Germ
cells?
23 CHROMOSOMES
 (combined = the 46 chromosomes)

12. CELL DIVISION
MITOSIS: Cell divides by copying the DNA - cell
splits - new cell with normal number of
chromosomes (Cell growth & repair)
MEIOSIS: Creates 1/2 sets of
chromosomes
 Women = 23 Men = 23 Combined = 46

13. Female Sex Cells XX (Ovum or Egg)
Male Sex Cells XY (Sperm)
Baby Girl = XX Baby Boy = XY
 Conception is the union of an OVUM and the SPERM
Gender is determined by the father!
 Someone should have told King Henry VIII!

14. DOMINATE Gene: More powerful - trait seen in person
RECESSIVE Gene: Weaker and hides in the background. Trait can
only determine when two of them are present - may show
up in future generations.
CARRIER: Has a recessive gene that is not visible
SEX-LINKED: Mother passes the recessive X to son
 Color-blind male receives the trait from his mother.
 The mother is usually not color-blind herself.
B = BROWN eyes (dominate) b = BLUE eyes
(recessive)
BB = BROWN eyes
bb = BLUE eyes
Bb = BROWN eyes but carry the recessive BLUE eye gene

15. MULTIPLE BIRTHS
ZYGOT: the cell that is formed when a sperm fertilized
an egg (ovum)
MONOZYGOT: Identical Twins 1 Egg + 1 Sperm
 Fertilized ovum splits into 2 identical cells - Always the same gender
DIZYGOT: Fraternal Twins 2 Eggs + different Sperm
 Will look different - May be different or the same gender
MULTIPLE BIRTHS: More than 2
 May be identical, fraternal or both - May be different or the same
gender
CONJOINED (Siamese) TWINS: Ovum splits apart, but the
separation is not completed. Babies are joined at some part
of their bodies.

16. WHAT 4 FACTORS MAY CONTRIBUTE
TO MULTIPLE BIRTHS?
1) History in the family
2) Increased hormones naturally
 More than 1 egg released
3) Fertility Drugs
 More than 1 egg released
4) Age 32-36
Likelihood of multiple pregnancies in the United States
 Twins: Blacks- 1 in 73 Whites 1 in 93
 Triplets: 1 in 10,000
 Quadruples: 1 in 620,000

17. GREGOR MENDEL (1822-1884)
Systematically recorded
results of crosses
Theorized on nature of
hereditary material
Postulate mechanism
of transfer of
"Elementen"
governing traits

18. MENDEL’S WORK WITH PEAS
a. He selected strains that differed in
particular traits (e.g., smooth or
wrinkled seeds, purple or white
flowers)
b. After making genetic crosses, he
counted the appearance of traits in
the progeny and analyzed the
results mathematically.
c. He concluded that each organism
contains two copies of each gene,
one from each parent, and that
alternative versions of the genes
(alleles) exist

19. 4. He deduced that the factors (now called genes) segregate
randomly into gametes (Mendel’s first law, the Principle of
Segregation).
5. The two factors for a particular trait assort independently of
factors controlling other traits (Mendel’s second law, the
Principle of Independent Assortment).
6. An example is seed color in peas:
i. True-breeding plants with yellow seeds (YY) are crossed
with true-breeding plants with green seeds (yy).
ii. The progeny (F1) have yellow seeds, and a heterozygous
genotype (Yy).
iii. When the progeny self-pollinate, the F2 contains 3
yellow:1 green, with genotypic ratios of 1 YY : 2 Yy : 1 yy.
Mendel’s Work with Peas

20. MAJOR EVENTS IN THE 20TH CENTURY
1900: rediscovery of Mendel’s work by Robert Correns,
Hugo de Vries, and Erich von Tschermak .
1902: Archibald Garrod discovers that alkaptonuria, a
human disease, has a genetic basis.
1904: Gregory Bateson discovers linkage between genes.
Also coins the word “genetics”.
1910: Thomas Hunt Morgan proves that genes are
located on the chromosomes (using Drosophila).
1918: R. A. Fisher begins the study of quantitative
genetics by partitioning phenotypic variance into a
genetic and an environmental component.

21. THOMAS HUNT MORGAN
Thomas Hunt Morgan: early 1900’s
Worked at Columbia University; later at
CalTech
Studied fruit fly eye color, determining that
trait was sex-linked
Won the Nobel Prize in 1933 for his work
on chromosomes and genetics

22. THOMAS HUNT MORGAN

23. THOMAS HUNT MORGAN
By this point, it was known that genetic
material was located on a chromosome
This genetic material was in discrete
units called genes
It was NOT known whether the gene
was simply a protein, or whether it was
composed of DNA

24. MORE 20TH CENTURY EVENTS
1926: Hermann J. Muller shows that X-
rays induce mutations.
1944: Oswald Avery, Colin MacLeod and
Maclyn McCarty show that DNA can
transform bacteria, demonstrating that
DNA is the hereditary material.
1953: James Watson and Francis Crick
determine the structure of the DNA
molecule, which leads directly to
knowledge of how it replicates

25. MORE 20TH CENTURY EVENTS
1966: Marshall Nirenberg solves the
genetic code, showing that 3 DNA
bases code for one amino acid.
1972: Stanley Cohen and Herbert Boyer
combine DNA from two different
species in vitro, then transform it into
bacterial cells: first DNA cloning.
2001: Sequence of the entire human
genome is announced.

26. JAMES WATSON AND
FRANCIS CRICK

27. JAMES WATSON AND
FRANCIS CRICK
Used wire models to conform with
the measurements that Franklin
and Wilkins had come up with
Determined the structure to be a
double helix
Lead to understanding of mutation
and relationship between DNA and
proteins at a molecular level
1959 – “Central Dogma”
 DNARNAprotein

28. CENTRAL DOGMA OF BIOLOGY