22 .In plants Tall (T) is dominant to short (t) and green (G) is dominant to yel

ID: 99374 • Letter: 2

Question

22.In plants Tall (T) is dominant to short (t) and green (G) is dominant to yellow (g) and round (R) is dominant to wrinkled (r). You have a Tall yellow round plant. You have the following plants available. Which one could be used to determine the precise genotype of your Tall yellow and round plant?
(a) Tall green round plant

(b) Tall yellow round plant

(d) Short green wrinkled

(e) none of the above

KEY:22. D

23.Through mutagenesis you have isolated 2 drosophila mutants that both have an extra set of legs bodies (d and l). After isolating a purebreeding specimens of each mutation. What would be the complementation test to determine if they are the same gene or not assuming they are both recessive?

(a) d/d x l/l

(b) D/d x L/l

(d) D/D x x L/L

(e) d/d x L/L

23: KEY..A

Please give a good explanation to your answer, will give a thumbs up, thank you. (visual learner)

Explanation / Answer

22. The dominant and recessive alleles for different plant characteristics are as follows:

Height – T(Tall) for dominant and t(short) for recessive

Seed Shape – R (Round) for dominant and r (wrinkled) for recessive

Seed Colour – G(Green) for dominant and g( yellow) for recessive

The three pairs of characters can be considered in a trihybrid cross

i) tall plant vs short plant

ii) green seed versus yellow seed

iii) round seed versus wrinkled seed

The parents TTYYRR and ttyyrr will give to the F1 hybrids TtYyRr which are heterozygous for the three genes. There will be eight gametes in equal proportions on both male and female side.

A trihybrid cross between Tall, yellow and Round and short, Green and wrinkled plants

TTyyRR * ttYYrr

(tall,yellow and round) (short, green and wrinkled)

Gametes

F1 - TtYyRr

F1 Gametes –

Out of 64 combinations, 9 genotypes will be – Tall, Yellow, Round i.e, TTyyRR =1, TTyyRr = 2, TtyyRR = 2, TtyyRr =4.

23. The complementation tests are also known as cis-trans test. This test determines whether two mutations associated with a phenotype represents the two different allele of same gene or are the variations of two different genes. The term cis is used to describe mutation on the same chromosome and trans is used to describe mutation occurring on different chromosomes.

The heterozygotes with one mutated chromosome and one normal chromosome in which one parent bears both mutations are created in cis test. In this test a functional protein is always produced whether the mutation is present on same gene or different genes.

The heterozygotes with different mutations from different parents are created in trans test. In this test functional protein is produced only if the mutations are on different genes.

The complementation test is relevant for recessive traits- the traits that are not expressed in the phenotype due to masking by dominant allele.

While performing a complementation test an investigator can start with large number of mutants all with same phenotype and then complementation groups are formed with mutant alleles of different genes. The complementation groups are equivalent to a gene. Each mutation in complementation group represents a mutant allele of the gene. The product of each gene when altered will produce the phenotype which is the basis for initial screening. The number of complementation groups or genes gives approximately the number of products (polypeptides or RNA) utilized in generating the cellular function.

The complementation groups of different mutants can be determined through the complementation assay in which the haploids are mated together to form diploids.

If the resulting diploid is wild type then it is assumed that the mutations are in different gene and the mutants complement each other.

If the mutation is in the same gene the mutants fail to complement each other.

Based on the information provided the complementation test in the pure breeding strains to determine whether the mutations are present on the same gene will be d / d * l / l.