Download Notes Pg.16 Complex Genetics PPT

NOTES PG. #16: COMPLEX
GENETICS
EQ: ARE THERE OTHER, MORE COMPLICATED,
TYPES OF INHERITANCE?
INCOMPLETE DOMINANCE
• Incomplete Dominance - Situation in which one
allele is not completely dominant over anotherphenotypes mix/blend.
• Example When straight hair and curly hair are crossed,
wavy hair results.
• Alleles:
• S= Straight (dominant)
• S’= Curly (recessive)
• Genotype=Phenotype:
• SS =Straight hair
• SS’=Wavy hair
• S’S’=Curly hair
INCOMPLETE DOMINANCE IN RATS
• If you crossed a white rat and a black rat using
incomplete dominance what offspring would you
get?
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EXAMPLE INCOMPLETE DOMINANCE
PUNNETT:
Red and white
flowers are
crossed and pink
flowers are
produced.
Genotype=Phenotype:
RR=Red
RR’=Pink
R’R’=White
YOU TRY: INCOMPLETE DOMINANCE
• #1: Cross a curly-haired mother with a wavy-haired
father, then summarize the genotype & phenotype
percentages:
Genotype=Phenotype:
SS =Straight hair
SS’=Wavy hair
S’S’=Curly hair
CODOMINANCE
• Codominance - Situation in which both alleles of
a gene contribute equally to the phenotype of
the organism.
• Example – A solid white cow is crossed with a solid black
cow and the resulting offspring are spotted black and
white (spotted is also called roan).
• Alleles: W=white, B=Black
• Genotype = Phenotype:
• WW=White cow, BB= Black cow, WB=White & Black spotted
cow [NOT gray!]
•
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EXAMPLE CODOMINANCE PUNNETT:
• If you cross a red and white flower, you get a flower
with red & white splotches.
Genotype = Phenotype:
• RR=Red
• WW=White
• RW=Red &
White spots
[NOT a mixNOT pink!]
CO-DOMINANCE IN RATS
• If you crossed a white rat and a black rat using
codominance what offspring would you get?
+
YOU TRY: CODOMINANCE
• #2: Cross a speckled “erminette” chicken with a white
chicken. Summarize the genotype and phenotype
results as percentages:
LABEL THE PICTURES
When you cross a red & white flower, what do you get?
1. If red is dominant
/with regular
[complete]
dominance?
2. With incomplete
dominance?
3. With
codominance?
CHECK YOURSELF: WHICH TYPE OF
INHERITANCE IS THIS?
CHECK YOURSELF: WHICH TYPE OF
INHERITANCE IS THIS?
CHECK YOURSELF: WHICH TYPE OF
INHERITANCE IS THIS?
CHECK YOURSELF: WHICH TYPE OF
INHERITANCE IS THIS?
Tall plant
Medium plant
Short plant
CHECK YOURSELF: WHICH TYPE OF
INHERITANCE IS THIS?
CHECK YOURSELF: WHICH TYPE OF
INHERITANCE IS THIS?
CHECK YOURSELF: WHICH TYPE OF
INHERITANCE IS THIS?
MULTIPLE ALLELES
• Multiple Alleles- Three or more alleles
of the same gene.
• Even though three or more alleles exist for
a particular trait, an individual can only
have two alleles - one from the mother
and one from the father.
EXAMPLES OF MULTIPLE ALLELES
1. Coat color in rabbits is determined
by a single gene that has at least
four different alleles. Different
combinations of alleles result in the
fur colors you see here.
EXAMPLES OF MULTIPLE ALLELES
2. Blood Type – 3 alleles
exist (IA, IB, and i),
which results in four
different possible blood
types
3. Hair Color – Too many
alleles exist to count
• There are over 20
different shades of
hair color.
MULTIPLE ALLELES:
HUMAN BLOOD TYPES
The 4 human blood types A, B, AB & O
made from 3 alleles: lA, lB, & i
• lA & lB are dominant to i
• lA & lB are codominant
HUMAN BLOOD TYPES
4 Human Blood Types:
Genotypes Surface Molecules
A
lA lA or lAi
B
lB lB or lBi
lA lB
A and B
None
ii
Phenotypes
A
B
AB
O
EXAMPLE: BLOOD TYPES
• What are the genotype &
phenotype chances for
this offspring?
YOU TRY: BLOOD TYPE PUNNETT
• Cross a Mother who is heterozygous for blood type
B, with a Father who has blood type AB:
• What are the genotype and phenotype
percentages?
MULTIPLE ALLELES
• There Are Always Multiple Alleles!
• Genetic inheritance is often presented with
straightforward examples involving only two
alleles with clear-cut dominance. This makes
inheritance patterns easy to see.
• But very few traits actually only have two alleles
with clear-cut dominance. As we learn more
about genetics, we have found that there are
often hundreds of alleles for any particular
gene.
• We probably know this already - as we look around
at other people, we see infinite variation.
POLYGENIC TRAIT
• Polygenic Trait - Trait
controlled by two or more
genes.
• Polygenic traits often show a
wide range of phenotypes.
• Example: The wide range of skin
color in humans comes about
partly because more than four
different genes probably control
this one trait... No wonder DNA is
soooo looooong!