Transcript Genetics pt 1 1314

Genetics
The study of heredity…whatever that means.
Heredity-The passing of traits from parents to
progeny (offspring…ummm…kids…do flowers
have kids?).
Who was Gregor Mendel?
He was a dude who studied peas in the
1850’s…WOW…that sounds exciting!
Actually, he experimented with pea plants to see
how traits were inherited (passed from parent to
offspring).
What did he do…exactly?
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Well…he crossed purebred plants (that
means the parents have similar traits so the
offspring always have the same trait as the
parent…blue eyed parent…blue eyed kid).
Then he started crossing different types
(like green with yellow instead of green with
green).
He figured out that individual factors
were controlling what he saw in the plants.
These are called…GENES!
Genes
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Remember that a GENE is a specific
sequence of nucleotides within the DNA
molecule.
So…a GENE contains the “code” for a
particular trait (like blue hair and blonde
eyes).
Also remember that when cells are dividing
(MITOSIS in the cell cycle), the DNA is
packed together forming a structure we call
a CHROMOSOME.
Alleles
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These are the various forms of a gene
(remember…genes control traits).
Alleles control the inheritance of traits.
There are two forms and they’re
represented by letters of the
alphabet.
Some traits are determined by one allele
and some are multi-allelic.
In sexual reproduction, one allele come
from the male and one comes from the
female, so…there will be two (2) alleles.
Let’s Start with the Simplest Type…
Complete Dominance…
one allele is dominant over another.
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DOMINANT (capital letters): If this
allele is there…the trait shows up.
Recessive (lower case letters): If this
allele is there…the trait won’t show up
if a dominant allele is also there.
Huh?
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Ok, let’s say that B = Brown fur and b=
white fur. What organism? Doesn’t
matter…let’s say the Alaskan Shortnose
Squeezle.
If mom and dad each contribute a B gene,
then the squeezle offspring has brown fur
(BB)
If mom gives up a B and dad a b, then the
squeezle kid still has brown fur…why?
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As long as the is a B…there will be brown
fur, because B is DOMINANT.
Now…if mom gives up a b and so does
dad (bb), then bingo…white furred
squeezle (and we all know how good
those are grilled).
bb…two recessive alleles.
Unfortunately…all of this junk has names
that you gotta know.
Fortunately…you already know a bunch of
them
Phenotypes & Genotypes
 Phenotype: the physical
characteristics of offspring (blue eyes,
straight hair, blood type).
 Genotype: the actual genetic
makeup of the offspring (Bb, rr, TT).
Genotypes can be as follows…
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Genotypes: Combinations of Alleles
Homozygous: two of the same
alleles…BB, RR, rr, ss…get it?
Homozygous Dominant…two dominant
alleles…QQ, LL, DD.
Homozygous Recessive…two recessive
alleles…dd, ss, ff.
Heterozygous: one of each allele, one
dominant and one recessive…Ff, Bb, Aa
Punnett Squares
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Used to determine the possible
outcomes based upon the GENOTYPE
of the parents.
You can determine the GENOTYPIC
RATIO & PHENOTYPIC RATIO from
this information.
They look like this:
Try These …
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Red flowers are dominant (R)
Yellow flowers are recessive (r)
Homozygous Dominant x
Heterozygous
Homozygous Recessive x
Homozygous Dominant
Heterozygous x Heterozygous