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.

1. Determine how to assign letters to represent all alleles. 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

P1: ________ x ________ P1: _CCPP_ x _ccPp_   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_

Male: CCPP = only CP (no other combinations) 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 CP CP cP cp Female 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 CP CP cP cp Female 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 CP CcPP CcPp cP cp Female cP 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!