probability and punnett square. probability: likelihood that a specific event will occur. principle...
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Probability: likelihood that a specific event will occur.
Principle of probability: used to predict the outcomes of genetic crosses.
Two important points to remember with probabilities:
Past outcomes do not affect future events
Probabilities predict the average outcome of many events
Punnett Squares:
diagrams that model genetic crosses.
can be used to predict and compare the genetic variations that will result from a cross.
Homozygous: Organisms that have two identical alleles for a particular trait—TT,tt
Heterozygous: Organisms that have two different alleles for the same trait--Tt
Monohybrid Crosses
CrossBb x Bb
B b female gametes
B
b
male gametes
BB
Bb
Bb
bbPhenotypes
%75% Brown eyed, 25% Blue eyed
Ratio3 Brown eyed: 1 Blue eyed
Genotypes%
25% BB, 50% Bb, 25% bbRatios
1BB:2Bb:1bb
STEP
STEP
STEP
STEP
BB = brown eyes Bb = brown eyes bb = blue eyes
Cross two Alaskan huskies that are heterozygous for brown eyes (Bb).
DIHYBRID CROSSESCross: RrGg X RrGg
EXTRA STEP - Finding the possible gametes
(R r) (Gg)F.O.I.LFirstOuterInner Last
STEP
Incomplete Dominance
• In incomplete dominance, neither allele is Dominant-blending of traits when two different alleles for the same trait occur together.
• Colors blend together• heterozygous
individuals = 3rd phenotype
red whitepink
Incomplete Dominance
• Four O’ Clocks, if you cross a red RR (which is always pure)
with a white WW (that is also always pure) , you get a pink RW (which is always hybrid / heterozygous
RWRW
RW RW
Incomplete Dominance• In another flower, if red RR and
blue BB flowers are crossed, they produce a 3rd purple RB flower
• What would be the genotype ratio and phenotype ratio if you crossed two purple flowers?
• Cross of two purple flowers RB X RB
• What are gamete possibilities?• genotype ratio
• phenotype ratio
• Can you have a heterozygous red orhybrid blue flower?
B
R
R B
BBRB
RR RBred purple
purple blue
Codominance• Both alleles contribute to the phenotype of
the organism by showing up simultaneously (at the same time) in heterozygous individuals.
In cattle and horses, if
you cross a pure red (RR) with a pure white (WW), you get (RW) which produces the color roan.
Codominance• These cattle or horses actually have both
red and white hairs intermixed, or are spotted. Roan is a third phenotype.
• If you cross a roan with a white…
W
W
R W
WWRW
RW WWroan
roan
white
white
Codominance• Andalusian chickens also show this
pattern of inheritance.• If you cross a black (BB) chicken• With a white (WW) chicken• You get black+white speckled (BW) chicken