Question(12 age pattern may be restricted (ventral wing surface white, dorsal wi

Question

Question(12 age pattern may be restricted (ventral wing surface white, dorsal wing surface neck ring whre -breeding lines exist for each type. The table below shows the results of crosses In mallard ducks tite in males), dusky C ard ducks the pumales), dusky (ventral and dorsal wing surface colored, no neck ringn ot between the three lines. Fr TestcrosS Parents restricted x mallard restricted x dusky mallard x dusky restricted restricted mallard 1 restrict:1 mallard 1 restrict: 1 dusky 1 mallard : 1 dusky A. How many genes appear to determine the plum age pattern? Explain. alleles determine the plumage pattern? What are the allelic relationships? Explain. restricted from cross 1 are crossed to the Fi restricted from cross 2, what types of progeny dete B. How many c.lfthe Fi phen explain. otypes would be produced and in what ratio would they be produced? Use appropriate symbols to

Explanation / Answer

A.) In the cross of parents with different plummage patterns progeny produced have a single phenotype and after test cross only two distinct phenotypes and their is no intermediate between these phenotypes. This is a feautre of qualitative traits which ae controlled by one or only a few genes For example qualitative mendelian trait height is controlled by a single gene and progeny of a cross between tall and dwarf parents are all tall and progeny of a cross between heterozygous tall (Tt) plants is 3/4 tall and 1/4 dwarf. There are only two phenotypic extremes with no intermediates between them.

The number of genes controlling a trait can be determined by using 2n + 1 = number of phenotypic classes formula, where n is the number of gene pairs . There are 3 phenotypic classes : restricted, mallard and dusky

2n + 1 =3

2n = 2

n =1

Therefore 1 gene pair is controlling plummage pattern

B.) There are 3 different alleles for plummage pattern as there are 3 different phenotypes mallard, restricted and dusky. A single gene can cause 3 different phenotypes when it has a different alleles for each phenotype.

In the restricted (RR) cross mallard (MM) all F1 (RM) are restricted which suggest that restricted is dominant over mallard. Mallard is recessive as it expressed only in homozygous recessive conditon when restricted allele is present.

Simillarly in restricted (RR) cross dusky (DD) all F1 (RD) are restricted which indicates restricted is also dominant over mallard.

In mallard (MM) cross dusky (DD) all F1 (MD) are mallard which indicates mallard is dominant over dusky.

C.) Corss 1 : Restricted x mallard

RR X MM

F1 : RM (restricted)

Cross 2 : Restricted x dusky

RR x DD

F1 : RD (restricted)

RM (restricted from cross 1 ) X RD (restricted from cross 2 )

gametes by RM : R and M

gametes by R and D

Progeny : RR( restricted) ,RD ( restricted), RM ( restricted) , MD (mallard)

Phenotypic ratio is 3 restricted : 1 mallard

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