DNA and
Genetics
Genetics and Heredity
See what you remember.
Directions: Fill in the blanks with vocabulary terms from the list below.
All organisms reproduce, or make more organisms that are similar to themselves.
______________________ also involves the passing of traits from one parent to
offspring. The passing of traits from parents to offspring is called
_____________________________. A _____________ is a set of instructions for
an inherited trait. For example, a gene may contain the instructions that determine
the color of a person’s eyes. The genes are located on structures inside a cell called
_____________________________. After scientists recognized that chromosomes
store the genetic information, they began an intensive search to learn more about
the structure and chemical composition of chromosomes.
Chromosomes are made from a chemical compound called ______________________
___________, abbreviated as ______________________. The genes that are
passed from generation to the next are made of DNA. Knowing the structure of
DNA would help scientists understand how DNA functions to control the
development of traits in an individual. This is exactly what James Watson and
Francis Crick were trying to do in the early 1950’s. Watson and Crick used data that
other scientists obtained about the chemical composition of DNA to figure out its
three-dimensional ___________.
Vocabulary Terms
•
•
•
•
•
•
•
Chromosomes
Deoxyribonucleic acid
DNA
Gene
Heredity
Reproduction
Structure
ANSWER KEY
All organisms reproduce, or make more organisms that are similar to
themselves. REPRODUCTION also involves the passing of traits from
one parent to offspring. The passing of traits from parents to offspring
is called HEREDITY. Heredity is controlled by genes. A GENE is a set of
instructions for an inherited trait. For example, a gene may contain the
instructions that determine the color of a person’s eyes. The genes are
located on structures inside a cell called CHROMOSOMES. After
scientists recognized that chromosomes store the genetic information,
they began an intensive search to learn more about the structure and
chemical composition of chromosomes.
Chromosomes are made from a chemical compound called
DEOXYRIBONUCLEIC ACID abbreviated as DNA. The genes that are
passed from generation to the next are made of DNA. Knowing the
structure of DNA would help scientists understand how DNA functions
to control the development of traits in an individual. This is exactly
what James Watson and Francis Crick were trying to do in the early
1950’s. Watson and Crick used data that other scientists obtained
about the chemical composition of DNA to figure out its threedimensional STRUCTURE.
Reproduction-113
• The process of making more of one’s own kind
• Each species reproduces only its own kind.
• Reproduction is essential for the survival of
the species.
• There are two types of reproduction:
– Sexual
– Asexual
Sexual Reproduction-114
Asexual Reproduction
• Reproduction without sperm and egg.
• It involves only one parent organism.
Plants
Egg cells form in the
ovary. A long
tube, or pistil,
grows out from
the ovary.
Surrounding the
pistil are stamens.
Stamen produce
pollen, a dust-like
material that
contains sperm
cells.
The Structure of DNA
Chromosomes are
made of DNA. Each
chromosome
contains thousands
of genes. The
sequence of bases in
a gene forms a code
that tells the cell
what protein to
produce.
A Complex Molecule
• The shape of the molecule is like a twisted
zipper. It is called a double helix.
• The scientist that discovered DNA and its
shape realized that smaller molecules of DNA
bond together and form this double helix
shape.
The Genetic Code
• Genes and DNA: A gene is a section of DNA
molecule that contains the information to code
for one specific protein.
• Order of the Bases: The order of the nitrogen
bases along a gene forms a genetic code that
specifies what type of protein will be produced.
Adenine (A) Cytosine (C) Thymine (T) Guanine (G)
The Human Genome-117
• Humans have thousands of different genes.
• They are located on 23 pairs of chromosomes.
Twins and Cloning
• Identical twins are two individuals that formed
from one egg fertilized by one sperm.
• Fraternal twins are offspring formed when
two different egg cells are fertilized by
different sperm cells at the same time.
• Cloning can be used to produce offspring hat
are genetically identical to their parent.
Gregor Mendel
• A 19th century priest who
revolutionize the study of heredity.
• HEREDITY is the passing of physical characteristics
from parents to offspring.
• This is why we “look” the way we do.
– Why we have certain characteristics from one parent and
other characteristics from the other parent.
Dominant and Recessive Alleles
• Mendel reached several conclusions on the
basis of his experimental results. He reasoned
that individual factors, or sets of genetic
“information,” must control the inheritance of
traits in peas. The factors that control each
trait exist in pairs. The female parent
contributes one factor, while the male parent
contributes the other factor. Finally, one factor
in a pair can mask, or hide, the other factor.
The tallness factor, for example, masked the
shortness factor.
• An organism’s traits are controlled by the
alleles it inherits from its parents. Some alleles
are dominant, while other alleles are
recessive.
• A dominant allele is one whose trait always
shows up in the organism when the allele is
present.
• A recessive allele , on the other hand, is
hidden whenever the dominant allele is
present. A trait controlled by a recessive
allele will only show up if the organism does
not have the dominant allele.
Symbols for Alleles: Geneotypes
Geneticists use letters to represent alleles. A dominant
allele is represented by a capital letter. For example,
the allele for tall stems is represented by T.
A recessive allele is represented by the lowercase
version of the letter. So, the allele for short stems
would be represented by t.
When a plant inherits two dominant alleles for tall
stems, its alleles are written as TT. When a plant
inherits two recessive alleles for short stems, its
alleles are written as tt.
When a plant inherits one allele for tall stems and one
allele for short stems, its alleles are written as Tt and
is a hybrid. A hybrid organism has two different
alleles for a trait.
Punnett Squares-123
B=dominant for brown eyes
b=recessive for blue eyes
Here are some practice sites:
• Traits Activities
http://learn.genetics.utah.edu/content/inheritance/activities/
• Learn. Genetics, Genetic Science Learning Center: The Basics and Beyond
http://learn.genetics.utah.edu/content/begin/tour/
• Science Kids at Home: Genetics–What are Genes? (tutorial for students)
www.sciencekidsathome.com/science_topics/genetics-a.html
• Genetics for Kids Mini-lecture and Punnett’s Square Activity
http://exploringnature.org/db/detail.php?dbID=22&detID=2290
• The Wonderful World of Genetics. WebQuest.
www.uni.edu/schneidj/webquests/spring05/genetics/index.html
• Gregor Mendel (1822–1884)
www.accessexcellence.org/RC/AB/BC/Gregor_Mendel.php
• Mendel’s Genetic Laws
http://anthro.palomar.edu/mendel/mendel_1.htm