Introduction
Chapter 1
Interesting Story…
•Albinism among the Hopi Native Americans
–Albinism is a defect in one of the enzymes
responsible for producing the pigment melanin.
•Why is it interesting?
–Unique feature is the high frequency of albinism is
their population. In most populations it is rare, in
the Hopis it is 100x greater than in most
populations
Interesting Story…
•What accounts for the high frequency?
–For Hopis with albinism there was special
treatment in everyday activities:
•Mating advantages – males with albinism were the
only ones around females in the daytime during
the growing season. This helped spread the albino
genes.
•Exclusion from farming – males with albinism were
excused from farming and avoiding the increased
probability of skin cancer and poor eyesight.
–The small population size of the Hopi tribe
Albinism in the Hopi Native Americans
Introduction
•This chapter introduces you to genetics and
reviews some concepts that you may have
learned in previous courses. The three major
areas covered are:
1. The importance of genetics
2. The history of genetics and how the field
developed
3. The fundamental terms and principles of
genetics used throughout the book
Genetics Is Important to Individuals, to
Society, and to the Study of Biology
• Genes influence our lives
– Genes affect our
susceptibility to many
diseases and disorders
– Genes contribute to
personality
– Genes are fundamental to
who and what we are
• Genes are important in agriculture
– The rise of agriculture began when people
started to apply genetics to the domestication
of plants and animals.
• Genes are important in biotechnology and
medicine
– Molecular genetic techniques are used to
develop and mass produce substances of
commercial value
• Examples: growth hormone, insulin,
antibiotics, vaccines, drugs
• Genes are important in many areas of biology
– Evolution, developmental biology, taxonomy,
ecology, animal behavior
Genetic Diversity and Evolution
•Despite all the diversity among living
organisms, the common feature is they all use
similar genetic systems
•The coding system for genomic information is
common to all life
A genome is a complete set of genetic instructions
for any organism.
o Either RNA or DNA
o
Genetic Diversity and Evolution
•Evolution involves 2 steps:
–Inherited differences arise randomly
–Then the proportion of individuals with particular
differences either increases or decreases
•Genetic variation is the of all evolutionary
change and the basis for all life
Divisions of Genetics
• Transmission genetics
– The basic principles of heredity and how traits
are passed from one generation to the next.
• Molecular genetics
– How genetic information is encoded, replicated
and expressed. Includes replication,
transcription, translation and gene regulation.
• Population genetics
– Considers the genetic makeup of populations
(groups of individuals of the same species) and
how that changes over time.
Model Genetic Organisms
• Model genetic organisms are organisms with
characteristics that make them useful for
genetic analysis:
o
o
o
Short generation time
Production of numerous offspring
The ability to be reared in a laboratory
environment
• Six have been intensively studied genetically.
– See Figure 1.7
– We will revisit these throughout the term.
Humans Have Been Using Genetics for
Thousands of Years
•10,000–12,000 years ago: domestication of
plants and animals
–Ancient people in the Middle East
•Ancient Jewish writing: understanding of
genetics of hemophilia
• Early concepts of heredity (all incorrect!):
– Pangenesis – genetic information travels from
different parts of the body to reproductive organs
and transferred to the gametes (sperm & egg). (See
Figure 1.10a)
– Inheritance of Acquired Characteristics – Acquired
traits become incorporated into hereditary
information.
– Preformationism – Miniature organism found inside
the sex cells; all traits were inherited from one
parent.
– Blending Inheritance – Genes from parents blend
and mix
• Current Concepts of Heredity (all correct!):
– Germ-plasm theory – all cells contain a complete
set of genetic information. (See Figure 1.10b)
– Cell theory – all life is composed of cells and cells
come from pre-existing cells
– Mendelian inheritance – traits are inherited
according to specific principles proposed by
Mendel (more on this later)
The Rise of the Science of Genetics
•The following are early scientists that
contributed to the study of genetics with their
discovery:
–Gregor Mendel: Principles of Heredity
–Schleiden and Schwann: Cell theory
–Flemming: Chromosomes
–Darwin: Heredity as a fundamental concept of
evolution
The Rise of the Science of Genetics
–Weismann: Germ-plasm theory
–Sutton: Genes are located on chromosomes
–Watson, Crick, Franklin, & Wilkins – the 3-D
structure of DNA
Other important scientists will be discussed later.
The Future of Genetics
• Some continued and future applications of
genetics:
– Sequencing the genomes of different species
– Noninvasive prenatal testing
– Identifying key genes for specific agricultural
characteristics
– Identifying key genes affecting the risk of specific
diseases
– Evolutionary history among organisms
– Epigenetic regulation of gene expression
Fundamental Concepts in Genetics
Review these concepts that were learned in
previous biology classes:
•Eukaryotic vs. prokaryotic
–Cells are of 2 basic cell types
•Genes are the fundamental unit of heredity
–Gene is an informational unit that encodes
a genetic trait.
•Genes come in multiple forms called alleles
–Alleles are alternate form of a gene
Fundamental Concepts in Genetics
•Genes confer phenotypes
–Genotype is the genetic information an
organism possesses that determines the
phenotype which is the trait or physical
appearance.
•Genetic information is carried in DNA and
RNA
–DNA and RNA are nucleic acids made up of
nucleotides.
Fundamental Concepts in Genetics
(continued)
• Genes are located on chromosomes
– Chromosomes consist of DNA and protein. Each
species has a characteristic number of
chromosomes.
Fundamental Concepts in Genetics
(continued)
•Chromosomes separate through mitosis and
meiosis
–Mitosis is the separation of replicated
chromosomes in the division of somatic cells.
Meiosis is the pairing and separation of replicated
chromosomes in the production of gametes.
•Gene expression
–Genetic information is first transcribed from DNA
to RNA, and then translated from RNA to protein.
Fundamental Concepts in Genetics
(continued)
•Mutations can cause permanent changes
–Gene mutations affect the genetic information of a
single gene. Chromosomal mutations alter the
structure and number of chromosomes usually
affecting many genes.
•Some traits are affected by multiple factors
–Many traits are affected by multiple genes as well
as environmental factors.
Fundamental Concepts in Genetics
(continued)
•Evolution is genetic change
–Evolution causes change in populations due to
genetic variation.
Concept Check 1
What are some of the implications of all
organisms having similar genetic systems?
a. That all life forms are genetically related
b. That research findings on one organism’s gene
function can often be applied to other organisms
c. That genes from one organism can often exist and
thrive in another organism
d. All of the above
Check the end of the chapter in your textbook for the answer!
Concept Check 2
Would the horse make a good model genetic
organism? Why or why not?
Concept Check 3
How did developments in cytology in the nineteenth
century contribute to our modern understanding of
genetics?