For each problem I need to know the following plus whatever specifics the proble
ID: 69834 • Letter: F
Question
For each problem I need to know the following plus whatever specifics the problem requests:
Key: (Which symbol stands for which allele) – Use the same letter for a gene using a capital to designate dominant and lower case to show recessive.
Parental genotypes
Possible gametes for each parent
The Punnett Square
1. In guinea pigs black coat color is dominant to brown coat color. A black guinea pig (from a long line of black guinea pigs) is bred to a brown guinea. If one of these offspring is then bred to a different brown guinea pig, what are the expected genotypes and phenotypes of their offspring?
2. In pea plants tall stems are dominant to short stems and purple flowers are dominant to white flowers. A true breeding plant with tall stems and white flowers is crossed with a true breeding plant having short stems and purple flowers. The offspring from this cross are grown up and allowed to interbreed. What are the expected genotypes and phenotypes of their offspring?
3. In dogs, black is dominant to golden. You have a black Labrador retriever you would like to stand at stud, but first you want to know if it is homozygous black or heterozygous. You make a testcross to determine this. What are the expected genotypes and phenotypes if your dog is heterozygous? If it is homozygous?
4. Color-blindness is X-linked in humans. A color-blind man marries a woman whose father was color-blind. What are the expected genotypes and phenotypes of their children?
Explanation / Answer
Solution:
Black colour of guinea pigs –B allele
Brown colour – b allele
Assuming that dominant pure bred black (BB) is crossed with recessive pure bred brown (bb), then the phenotype of the offspring would be black and the genotype would be Bb.
If the offspring(Bb) is bred with another brown guinea pig(bb) , then the resulting offspring would be in the ratio: Black(Bb): Black(Bb): brown(bb):brown(bb)
If the offspring (Bb) is bred with heterozygous brown pig (Bb), then the resulting offspring would be in the ratio of: Back (BB): Black (Bb): Black (Bb): Brown (bb)
2.
Allele for Tall gene in Pea – T and short – t
Allele forPurple - P and white – p
When true breeding tall white plant (TTpp) is crossed with true breeding shortpurple(ttPP), the resulting phenotype of the offspring is Tall Purple(TtPp).
When this offspring is interbreed we get the following results:
TP
Tp
Pt
pt
TP
TTPP(TALL PURPLE)
TTPp(TALL PURPLE)
TtPP(TALL PURPLE)
TPtp(TALL PURPLE)
Tp
TTPp(TALL PURPLE)
TTpp(TALL WHITE)
TtPp (TALL PURPLE)
Ttpp (TALL WHITE)
Pt
TtPP(TALL PURPLE)
TtPp(TALL PURPLE)
TtPP (short PURPLE)
TtPp(short PURPLE)
pt
TtPp(TALL PURPLE)
Ttpp(TALL WHITE)
TtPp (SHORT PURPLE)
Ttpp (SHORT WHITE)
Phenotypic ratio: 9:3:3:1genotypic : Tall(12) : Short(4) : purple(12): white(4)
3. Dominant Black – BB or Bb
Golden -bb
Testcross between heterozygous (Bb) will give the following result in the ratio: Black(Bb) : Black(Bb) : Golden(bb) : Golden(bb)
Testcross between homozygous (BB) will give the following result in the ratio : Black(Bb) : Black(Bb) : Black(Bb): Golden(bb)
4. the male offspring of the parents will be colourblind while the females will be carriers.
TP
Tp
Pt
pt
TP
TTPP(TALL PURPLE)
TTPp(TALL PURPLE)
TtPP(TALL PURPLE)
TPtp(TALL PURPLE)
Tp
TTPp(TALL PURPLE)
TTpp(TALL WHITE)
TtPp (TALL PURPLE)
Ttpp (TALL WHITE)
Pt
TtPP(TALL PURPLE)
TtPp(TALL PURPLE)
TtPP (short PURPLE)
TtPp(short PURPLE)
pt
TtPp(TALL PURPLE)
Ttpp(TALL WHITE)
TtPp (SHORT PURPLE)
Ttpp (SHORT WHITE)
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