Dihybrid Problems Recall that pigmented eyes (P) are dominant to non-pigmented (
ID: 132267 • Letter: D
Question
Dihybrid Problems Recall that pigmented eyes (P) are dominant to non-pigmented (p), and dimpled chins (D) are dominant to Non-dimpled chins (d). 4. A pigment-eyed, dimple-chinned man marries a blue-eyed woman without a dimpled chin. Their firstborn child is blue-eyed and has a dimpled chin. a. What are the possible genotypes of the father? b. What genotype is the mother? c. What alleles may have been carried by the father's sperm? 5. Suppose a dimple-chinned, blue-eyed man whose father lacked a dimple marries a woman who is homozygous recessive for both traits. a. What is the expected genotypic ratio of children produced in this marriage? b. What is the expected phenotypic ratio? 6. In his original work on the genetics of garden peas, Mendel found that yellow seed color (YY, Yy) is dominant over green seeds (vy) and that round seed shape (RR, Rr) is dominant over shrunken seeds (rr). Mendel crossed pure-breeding (homozygous) yellow, round-seeded plants with green, shrunken-seeded plants a. What will be the genotype and phenotype of the F1 progeny produced from such a cross? genotype phenotype b. If the F1 plants are crossed, what will be the expected phenotypic ratio of the F2 generation?Explanation / Answer
4. (a) According to the given allelic information about dominant and recessive traits, the genotype of the father can be traced using the following table.
Pigment eye P is dominant to non-pigment eyes p; dimpled chins (D) dominant to non-dimpled chin (d). Since the phenotype of the father is pigmented eyes (PP/Pp) and dimpled chin (DD/Dd), the genotype can either be PpDd/ PPDD). Similarly, mother possessing blue eyes (pp) and non-dimpled chin (dd) would have ppdd genotype.
The child born has blue eyes (pp) and dimpled chin (Dd/DD) would have the genotype (ppDd/ ppDD). If we obtain all the possible genotypes obtained upon crossing of th father and mother genotypes according to the Mendelian dihybrid cross, the possible genotype of the father can be deduced.
Assuming the genotype of father be PpDd and that of mother be ppdd
Upon crossing,
the genotype highlighted in the bold in above table indicates the genotype of the child.
In another assumption for the genotype of father, based on phenotypic characteristics and the allelic information,
In the second assumption; PPDD (father) X ppdd (mother) , the genotype of the progenies would be
In the above scenario, none of the possible phenotypes match with that inherited by the child born. Thus, the most appropriate genotype of the father is PpDd.
(b) Since the mother possess both the recessive traits, the genotype could be ppdd.
(c) The alleles bein carried by the father's sperm are as follows:
PD (Pigment eyes, dimpled chin)
pD (blue eyes, dimpled chin)
Pd (pigmented eyes, non-dimpled chin)
pd (non-pigmented eyes, non-dimpled chin)
5.
(a) According to the given phenotypes of the two parents,
ppDd X ppdd
Thus, the genotypic ratio would be 1:1.
(b) the phenotypic ratio equals the genotypic ratio, i.e. 1:1.
6. According to the question with the alleic information on dominance and recessiveness,
the parental population is YYRR X yyrr
(a) YYRR X yyrr
F1 progeny : YyRr (Yellow and round seeds)
(b) Upon crossing of F1 progeny,
YyRr X YyRr; teh progenies obtained have bene presented in the table below.
The expected phenotypic ratio of F2 population = 9:3:3:1
pd PD PpDd pD ppDd Pd Ppdd pd ppdd