Download aren`t completely dominant

Genetics Rules
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Rule #1?
Rule #2: Incomplete dominancesome alleles
aren’t completely dominant so they BLEND
Rule #3: Codominancesome alleles dominate
together so BOTH ARE SEEN
Rule #4: sex-linked genesALL alleles on a
male’s X chromosome (X-linked) are expressed.
Complete Dominance
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Rule #1—some alleles completely
dominate over others:
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B=brown eyes
b=blue eyes
Bb= brown eyes, so B is completely
dominant.
Incomplete Dominance
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Rule #2—some alleles
DON’T COMPLETELY
DOMINATE, so they
blend:
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RR= red flowers
rr = white flowers
Rr = pink flowers
PINK FLOWERS!!!
BLENDING!!!
Codominance
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Rule #3—some alleles dominate
TOGETHER so they BOTH are shown
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H = brown hair on horses
H’ = white hair on horses
HH’ = both brown and white hairs, so the
horse is roan color.
Blood types are like this, too.
Roan Horse
Blood Types
Antigens-markers on cells
Blood type determined by your
carbohydrate markers on your
red blood cells
4 blood group phenotypes:
Type A has A antigens
Type B has B antigens
Type AB has A and B antigens
Type O has no antigens
Multiple Alleles
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Multiple alleles- 3 different
forms of the gene code for
blood types IA, IB, and i
A
 Allele I makes an “A”
antigen
B
 I makes a “B” antigen
 i makes none
6 blood group genotypes
Complete dominance- IA and IB
dominate over i
Codominance- IAIB genotype
shows BOTH A and B carbs
Blood Types
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Reactivity to blood transfusions and
organs:
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Antibodies-proteins produced by your
immune system to fight off things that look
“foreign.”
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Type A (makes anti-B antibodies)
Type B (makes anti-A antibodies)
Type AB (makes NO antibodies—universal
receiver)
Type O (makes anti-A and anti-B antibodies—
universal donor)
Free Write Journal Entry
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Why? Take time to absorb the
material and think about and
process the information.
What should you do?

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Take a couple of minutes to write down
any thoughts, questions, or ideas at the
bottom of your notes.
There are no right or wrong entries, as
long as you try.
Sex-Linked Genes
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Rule #4: sex-linked genesALL alleles on
a male’s X chromosome (X-linked) are
expressed.
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Male sex chromosomes?_________
Female sex chromosomes?_________
We also call sex-linked genes by another
name, X-linked, because the X chromosome
has the majority of the genes.
Sex-Linked Genes
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In males, EVERY gene on their X chromosome is
expressed. The Y doesn’t have the same genes.
In females this is not the case because they have
another copy on their other X chromosome to
overcome it.
Sex-Linked Genes
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Examples of sex-linked disorders:
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Colorblindness
Hemophilia
Fragile X Syndrome
Duchene Muscular Dystrophy
Cleft Palate
Vitamin D Resistant Ricketts
3 types of deafness
Male Pattern Baldness
Sex-Linked Genes
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The genes that occur on the sex
chromosomes must be written with X’s
and Y’s to show this special situation.
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For example: red-green colorblindness is a
recessive trait. It is found on the X
chromosome, not the Y.
We write the alleles (forms of the gene)
this way:
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XC = colorblindness
XC = normal
Sex-Linked Genes
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Try to complete this
table:
Phenotypes
Normal Male
Colorblind Male
Normal Female
Normal “carrier”
Female
Colorblind female
Genotypes