Download introduction to genetics

INTRODUCTION TO
GENETICS
Before we start, did you know….
• Humans are 99.9% genetically
identical – only 0.1% of our genetic
make-up differs.
• Our genes are remarkably similar to
those of other life forms. For
example, we share 98% of our genes
with chimpanzees, 90% with mice,
85% with zebra fish, 21% with worms,
and 7% with a simple bacterium such
as E. coli.
We share DNA…..with THEM?!
Purpose of today’s class:
• To understand how Mendel began
the study of genetics.
• To understand how genes lead to
physical characteristics.
3 Questions!
Background to Genetics
GREGOR MENDEL:
- priest who tended to
a garden at his
monastery.
- Asked himself why
different pea plants
had different
characteristics.
Ex. Color, height, seed
- THUS BEGAN GENETICS!
QuickTime™ and a
decompressor
are needed to see this picture.
Mendel’s Experiments
• Mendel cross-pollinated
two purebred pea
plants:
QuickTime™ and a
decompressor
are needed to see this pict ure.
=He took the pollen from
one plant and used it to
fertilize another plant,
giving him control of
fertilization.
Crossing Pea Plants
• By crossing two purebred pea plants,
Mendel was able to study the heredity of
certain traits.
Heredity= passing of physical characteristics
from parent to offspring.
Trait= each form of a characteristic. For ex.
Characteristic= seed color
Traits = yellow, green
DIAGRAM of Mendel’s Cross
Parent Generation= P
= pink purebred crossed
with white purebred.
QuickTime™ and a
decompressor
are needed to see this picture.
1st Filial Generation= F1
= all pink flowers produced
??If parent generation had
two separate traits (purple
and white), why did the F1
generation have only ONE
trait (just purple)?
What determines Physical Traits?
• GENE: a segment of DNA on a
chromosome that determines/controls a
physical trait.
• ALLELE= different forms of a gene. You
get one allele of a gene from each
parent. Alleles are represented by a
letter.
• Physical traits are determined by the
DOMINANT alleles= the allele that always
shows up in an organism when present.
(If there is no dominant allele present, then the
recessive allele is expressed.)
For Example, in Mendel’s Cross…
Physical Characteristic= flower color
Trait= purple or white
Alleles:
purple= dominant because the F1
generation was all purple.
white= recessive because it was hidden in
F1 generation (none were white).
Symbols for Alleles
• Capital letters represent dominant alleles.
(P= purple)
• Lowercase letters represent recessive
alleles. (p= white)
*As long as one capital letter is present, the
physical trait is the dominant form.
*Same letter must be used for the same
allele. The letter is chosen based on the
dominant form. That is why the recessive allele isn’t “w”
For Example:
The letter “P” represents flower color.
PP = purple (inherited dominant alleles from
both parents).
Pp= purple (inherited one dominant and
one recessive, but trait is still purple).
This is a hybrid= one of each allele.
pp= white (inherited recessive alleles from
both parents, and trait is now white).
*Look at Allele symbols in the above cross-pollinations.
Homozygous & Heterozygous
• Homozygous = purebred for a trait.
-both alleles are dominant (PP)
or
-both alleles are recessive (pp)
• Heterozygous = hybrid for a trait
-alleles are different (Pp)
-heterozygous traits take on the
dominant form
Do you understand…
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Gregor Mendel
Heredity
Trait
Characteristic
Cross-pollination
Purebred
Gene
Allele
P generation
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F1 Generation
Dominant
Recessive
Symbols for alleles
PP
Pp (hybrid)
pp