Transcript File

Genetics
The study of heredity; how traits are passed
from parent to offspring.
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Heredity- passing of physical
characteristics from parents to offspring
Fertilization- A new organism begins to
form when egg and sperm join. Happens
in plants and animals.
Hybrid- Organism who has 2
different alleles for a trait.
Purebred-Organism is the
offspring of many generations
that have the same trait.
The study of heredity started
with the work of Gregor Mendel and his
pea plant garden
Mendel was an Austrian Monk that lived
in the mid 1800’s
Genetics: The Science of Heredity - Mendel’s Work
Crossing Pea Plants
Gregor Mendel crossed pea plants that had different traits.
The illustrations show how he did this.
Mendel noted that the size of pea
plants varied. He cross-bred these
pea plants to find some surprising
results.
Mendel’s cross between tall pea plants yielded all
tall pea plants. His cross between small pea plants
yielded all small pea plants.
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Mendels’ cross between tall pea plants and small pea
plants yielded all tall pea plants.
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Genetics: The Science of Heredity - Mendel’s Work
Mendel’s Experiments
In all of Mendel’s crosses, only one form of the trait appeared
in the F1 generation. However, in the F2 generation, the “lost”
form of the trait always reappeared in about one fourth of the
plants.
Genetics: The Science of Heredity - Mendel’s Work
Dominant and Recessive Alleles
Mendel studied several traits in pea plants.
Traits are different forms of a characteristic, such as stem height or
seed color
Mendel’s work led him to the understanding
that traits such as plant height are carried in
pairs of information not by single sets of
information.
-Carrying the information are chromosomes.
-Chromosomes are made up of sections
called genes.
-Genes are made up of DNA
DNA
D.N.A. - Deoxyribonucleic Acid
Molecule made of:
1. Deoxy Sugar
2. Combination of four nitrogen bases
Either: a. Guanine
b. Cytocine
c. Thymine
d. Adenine
The sum total of combinations that these
four bases are capable of creating are
greater than all the stars visible in the night
time sky
DNA
• Nitrogen bases pair up
– Cytosine & Guanine
– Thymine & Adenine
• Pairing creates a ladder shape
• Angle of bonds creates a twist
Ladder and Twist produces the famous
“Double Helix”
DNA
Cell
• DNA resides in all cells
– Inside the nucleus
• Each strand forms a chromosome
Nucleus
DNA
DNA
DNA is found in all living cells
– It controls all functions
inside a cell
– It stores all the genetic
information for an entire
living organism
– Single cell like an amoeba
– Multi cell like a human
Genetics
Small sections of DNA are responsible for a
“trait”. These small sections are called
“Genes”.
– Gene - A segment of DNA that codes for a
specific trait
– Trait - A characteristic an organism
can pass on to it’s offspring
through DNA
Gene
Genetics
There are three basic kinds of genes:
– Dominant - A gene that is always
expressed and hides others
– Recessive - A gene that is only
expressed when a dominant gene
isn’t present
Genetics
Dominant and Recessive Genes
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A dominant gene will always
mask a recessive gene.
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A “widows peak” is dominant,
not having a widows peak is
recessive.
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If one parent contributes a
gene for a widows peak, and the
other parent doesn’t, the offspring will have a widows peak.
Widows Peak
Genetics
Punnet Square - A tool we use for predicting
the traits of an offspring
– Letters are used as symbols to designate genes
– Capital letters are used for dominant genes
– Lower case letters are used for
recessive genes
– Genes always exist in pairs
– Alleles are different forms of a gene, like having
a widows peak or no widows peak.
Genetics
A Widows Peak, dominant, would be symbolized
with a capital “W”, while no widows peak,
recessive, would be symbolized with a
lower case “w”.
Father - No Widows Peak - w
Mother - Has a Widows Peak - W
Genetics: The Science of Heredity - Probability and Heredity
Percentages
One way you can express a probability is as a percentage. A
percentage (%) is a number compared to 100. For example,
50% means 50 out of 100.
Suppose that 3 out of 5 tossed coins landed with heads up.
Here’s how you can calculate what percent of the coins
landed with heads up.
1. Write the comparison as a fraction.
3 out of 5 = 3/5
2. Multiply the fraction by 100% to express it as a
percentage.
3/5 x 100%/1 = 60%
Genetics: The Science of Heredity - Probability and Heredity
Percentages
Practice Problem
Suppose 3 out of 12 coins landed with tails up. How can you
express this as a percent?
25%