A metallic blue-colored Indian blue peahen with long pinion feathers is crossed
ID: 142512 • Letter: A
Question
A metallic blue-colored Indian blue peahen with long pinion feathers is crossed with a dull brown-colored Indian blue peacock with short pinion feathers. Half of the resulting peacocks are metallic blue with short pinions and half the resulting peacocks are metallic blue with long pinions. Half of the resulting peahens are dull brown with short pinions and half the peahens are dull brown with long pinions. Long pinions are the result of a functional protein. A) Which gene is sex-linked? B) What are the genotypes of each parent and each type of offspring?
Step 1: Determine whether either of the genes are sex-linked. For this type of a question, if you aren’t told, then the thing for which to look is whether when looking only at the offspring one of the phenotypes sorts out by sex.
In this example, Half of the resulting peacocks are metallic blue with short pinions and half the resulting peacocks are metallic blue with long pinions. Half of the resulting peahens are dull brown with short pinions and half the peahens are dull brown with long pinions.
This suggests what is sex-linked, why?
Step 2: Determine the correct sex chromosomes (if needed) for the species. Step 3: put down allelic place holders for each individual
Peacock Father: _/_ _/_ Peahens Mother: _/_ _/_
Peacock Boys: _/_ _/_ Peahens Girls: _/_ _/_
Step 4 Figure out which allele is functional for each gene. To do this, look at individuals that will be heterozygous for alleles from mom and dad. For sex-linked traits, that would be the homogametic sex (ZZ or XX). For autosomal traits, all offspring will be informative
Step 5: Fill in what you know for sure based on phenotype:
Peacock Father: _/_ _/_ Peahens Mother: _/_ _/_
Peacock Boys: _/_ _/_ Peahens Girls: _/_ _/_
Step 6: Apply Rules 1 & 2 to deduce the unknown alleles:
Peacock Father: _/_ _/_
Peahens Mother: _/_ _/_
Peacock Boys: _/_ _/_
Peahens Girls: _/_ _/_
What are the genotypes of each parent and each type of offspring? Parents genotypes :
Offspring genotypes:
Explanation / Answer
Answer (A) There are no sex-linked genes in the given question.
Explanation for the answer:
Sex-linked genes show phenotypic expression of alleles related to allosomes or sex chromosomes of an individual. These genes show distinct contrasting characteristics in males different from females or vice versa, determining sex-linked traits. In the case of peacocks and peahens, the ZZ-ZW sex determination occurs. The peahens show ZW genotype and the peacocks show ZZ genotype. So, in this case, the genes present on Z or W are termed as sex-linked. In the given question, there is no gene that is sex-linked, because in the resultant progeny both the peacock boys and the peahen girls are having similar types or colors and feathers.
Answer (B) Genotype for parents are BbLl for peahen and bbll for peacock. In the resultant progeny, the genotype for offsprings are BbLl, Bbll, bbLl, bbll.
Explanation for the answer:
Suppose, the metallic-blue color is dominant and depicted by 'B' and the dull-brown color is recessive and depicted by 'b'; the feature of long pinion feathers is dominant and depicted by 'L' and the trait for short pinion feathers is recessive and depicted by 'l'.
Then, the possible genotypes for the parents would be:
Metallic blue colored peahen with the long pinion feathers = BbLl (gametes- BL, Bl, bL, bl)
Dull brown colored peacock with the short pinion feathers = bbll (gametes- bl, bl, bl, bl)
For the genotype of progeny, according to the results of the cross depending on the Mendelian law of independent assortment,
Therefore, the possible genotypes of the offsprings peacock boys and peahen girls would be:
Metallic blue colored with long pinion wings: BbLl
Metallic blue colored with short pinion wings: Bbll
Dull brown colored with long pinion wings: bbLl
Dull brown colored with short pinion wings: bbll
BL Bl bL bl bl BbLl Bbll bbLl bbll