4 Dihybrid Cross Presentation Pigs

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Piggy Problem
Piggy Problem
• You are to predict the types and possible ratios of
traits in the offspring resulting from the cross
between a male and female pig.
• In pigs, curly tails (C) are dominant over straight tails
(c). Pink color (P) is dominant over gray (p).
• A male homozygous dominant pig is crossed with a
female pig that is homozygous recessive for tail type
and heterozygous for color.
If you follow the necessary steps in solving genetic problems with
Punnett Squares, your Punnett life will be a breeze for you.
It is very important that you follow the necessary steps!
1. Determine how to assign letters to represent all
alleles.
This was given to you:
Curly tails is dominant over straight tail, so curly tail = C
and straight tail = c
Pink color is dominant over gray color, so pink = P and
gray = p
2. Fill in the P1 cross with the correct alleles:
P1: ________ x ________
Since the male pig is homozygous dominant for both traits, the
letters assigned for both traits must be capital letters. Remember,
it takes 2 letters (alleles) to represent each trait.
The female pig is homozygous recessive for type of tail (2 lowercase
letters) and heterozygous for color (one capital and one lowercase
letter).
P1: _CCPP_ x
_ccPp_
3. Determine possible gamete combinations from each parent:
Remember that you will need one allele from each parent for EACH trait.
Male: CCPP = only CP (no other combinations)
Female: ccPp = cP and cp
4. Fill in the sides of the Punnett square with the parent
allele combinations.
Male
CP
cP
Female
cp
cP
cp
CP
CP
CP
5. Complete the Punnett square by taking the letters that
correspond with each box and bring them into the boxes.
(Remember that capital letters always go on front of lower case
letters since they dominate over them.)
Male
CP
cP
Female
cp
cP
cp
CP
CP
CP
5. Complete the Punnett square by taking the letters that
correspond with each box and bring them into the boxes.
(Completed)
Male
CP
CP
CP
CcPP
CcPP
CcPP
CcPP
CcPp
CcPp
CcPp
CcPp
cP
CcPP
CcPP
CcPP
CcPP
cp
CcPp
CcPp
CcPp
CcPp
CP
cP
Female
cp
6. Punnett square results.
There are two factors to examine:
genotypes and phenotypes.
PHENOTYPE = appearance
CURLY and PINK (all 16 = curly and all 16 = pink)
Ratios: 16/16 = 100% curly and pink
GENOTYPE = gene make-up
CcPp and CcPP (8 = CcPp and 8 = CcPP)
Ratios: 8 CcPp/8CcPP = 50% CcPp, 50% CcPP
NO Straight tails or gray color
Summary
• We can predict that when a male pig that is
homozygous dominant for both curly tail and pink
color is crossed with a female pig that is homozygous
recessive for tail type and heterozygous for color,
that you will get all curly-tailed pink babies!
Now, calculate your own Punnett Square:
A male heterozygous (both traits) pig is
crossed with a female pig that is
homozygous recessive for tail type and
heterozygous for color.
What are the probabilities of genotypes
and phenotypes? SHOW WORK!
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