Mendel found that round ( R ) seed is dominant over wrinkled ( r ) seed, and yel
ID: 189345 • Letter: M
Question
Mendel found that round (R) seed is dominant over wrinkled (r) seed, and yellow (G) seed is dominant over green (g) seed. The following crosses were made between plants of known phenotypes but unknown genotypes:
a) Using the same symbols as defined above, list the genotypes of the parent plants in each cross.
1 round, yellow X round, yellow
2 round, yellow X round, yellow
3 round, yellow X wrinkled, green
b) Which of the above crosses is a testcross?
Offspring and ratio 3/4 round, yellow 1/4 wrinkled, yellow 9/16 round, yellow 3/16 round green 3/16 wrinkled, yellow 1/16 wrinkled, green 1/4 round, yellow 1/4 round, green 1/4 wrinkled, yellow 1/4 wrinkled, green Cross 1) round, yellow X round, yellow 2) round, yellow X round, yellow 3) round, yellow X wrinkled, greenExplanation / Answer
A) 1)
Genotype of round, yellow X round, yellow.
As the offsprings do not have any recessive phenotype that is green seed, so yellow genotype is GG
Wrinkled seed observed in phenotype so it the genotype is Gg
A 2) in second case the phenotype shows both recessive and dominant traits.
So the genotype of one parent is R/r ; G/g
Genotype of second parent is R/r ; G/g
a 3) round, yellow X wrinkled, green
As wrinkled and green is recessive so it has to be homozygous to be shown in phenotype.
So 2nd parent's genotype is rr;gg
1st parent's genotype is Rr; Gg
As there are recessive phenotypes shown in the offspring so the 1st parent cannot be homozygous.
B) the third cross is the test cross.
A test cross is the one in which the genotype of one parents is determined by crossing it with a recessive 2nd parent