Thomas Morgan conducted famous fruit fly experiments in the early 20th century. His discoveries led to the understanding that genes are located on chromosomes and are duplicated during cell division. This work established the foundations of genetics and paved the way for later discoveries of genetic mutations, gene flow between populations, and genetic drift within populations. Morgan's experiments showed that traits are passed from parents to offspring via alleles located on homologous chromosomes.

1. Thomas Morgan
Jennifer Wood

2. Thomas Morgan (What is natural selection)
Thomas Hunt Morgan:
(1866-1945)
Discovered that genes are carried within chromosomes while
conducting his famous fruit fly experiment. This led to the discovery
that hereditary material is then duplicated in a thing called cell
division. His discoveries in his experiment gave way to the discovery
of mutations, gene flow, and genetic
Drift. (Larsen, 43)

3. At this point in time scientists knew that
there were two alleles, one coming from
the mother and one from the father,
Morgan was able to identify that the alleles from one gene pool could also flow to
another gene pool causing them to flow from one population to the next. The image
abo above represents the movement of alleles from one
a population to another. And the image below presents
he the idea of a gene flow into an area that that a certain
g organism couldn’t occupy before. ( Larsen, 44)
b
Gene Flow

4. Genetic Drift
Genetic drift was able to be discovered
when studying populations and their ability
to be affected especially within a smaller
population. Eventually the populations will discover they have less of one gene which
creates the lesser chance of that gene’s ability to be passed down. This leads to the
possible elimination of that specific gene. Both of these images are meant to show the
genes that are most vulnerable to not be passed down again. In this bottom image the
vulnerable gene would be the red one which eventually stops being able to be passed
down. (Larsen, 44)

5. DNA
The discovery of chromosomes allowed scientists to
discover DNA and its structure, leading to the high-
quality images of DNA that were then produced. These
images allowed for the identification of genes that carry
certain diseases and disorders that could be passed down
into the next generations. (Larsen, 44)
The image to the right shows
how the alleles and genes are
passed down from the mother
and father to the children. Some
of the children have the DNA
carrying the disease and some
don’t.

6. Mutations
Darwin couldn’t identify the origin of a variation between two species- mutations are
responsible. Mutations can cause diseases that ruin the chance to have healthy
offspring. Some mutations can enable the carrier to live longer and better with the
ability to pass onto offspring. Mutations can happen spontaneously or they can be
caused by exposure to radiation or chemical agents. Scientists can now even
manipulate genes to create new species. The images below show what a mutation in
DNA look like, and what it can cause. (Larsen, 44)

7. Sources
Larsen, C. S. (2008). Discovering Physical Anthropology; Our Origins. New York , New
York : W. W Norton & Company, Inc.