In the predatory Allosaurus a single gene with two alleles controlled tail lengt
ID: 58191 • Letter: I
Question
In the predatory Allosaurus a single gene with two alleles controlled tail length. The long tail allele (L) is dominant to the short tail allele (I). Give the genotypes and phenotypes of parents and offspring (also give expected ratios for offspring) for the following crosses: Pure- breeding long X Heterozygote Heterozygote X Heterozygote A tough one. You have a long tailed animal, but you aren't sure of its genotype. You crossed it to a short tailed animal and get some long and some short tailed offspring. What is its genotype? How do you know? Velociraptors are nasty! Actually they come in a whole range of nastiness, from sort of nasty to really, really nasty. What is the probable mechanism which determines nastiness in these beasts?Explanation / Answer
1. Let long tail phenotype has genotype LL for homozygous dominant and Ll for heterozygous dominant, and short tail has homozygous recessive allele ll
1a. Pure breeding long X Heterozygote ( LL X Ll):
P1 LL X Ll
F1 LL Ll Ll LL
All the offspring are long tail in ratio 2:2 ie; 1/2 are homozygous dominant, 1/2 are heterozygous dominant.
1b) Heterozygote X Heterozygote
P1 Ll X Ll
F1 LL LI LI ll
The offspring will be in the ratio 1:2:1 i.e; 1/4 are homozygous dominant, 1/2 are heretozygous dominant for long tail and 1/4 are homozygous short tail.
1c. An unknown genotype of long tail phenotype is crossed to homozygous short tail phenotype, the offspring are long and short.
When homozygous dominant for long tail LL is crossed to short tail ll all the offspring would be heterozygous for long tail Ll so the unknown genotype of the parent will be Ll for long tail
P1 Ll X ll
F1 Ll Ll ll ll
The ratio of offspring will be 2:2. 1/2 are heterozygous long Ll and 1/2 will be homozygous short.
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