Q38-5TYU. - Campbell Biology

Question

Some dioecious species have the XY genotype for male and XX for female. After double fertilization, what would be the genotypes of the embryos and endosperm nuclei? 

(A)    embryo XY/endosperm XXX or embryo XX/endosperm XXY 

(B)    embryo XX/endosperm XX or embryo XY/endosperm XY 

(C)    embryo XX/endosperm XXX or embryo XY/endosperm XYY 

(D)    embryo XX/endosperm XXX or embryo XY/endosperm XXY

Step-by-Step Solution

Answer

(A)    The statement “embryo XY/endosperm XXX or embryo XX/endosperm XXY” is false. 

(B)    The statement “embryo XX/endosperm XX or embryo XY/endosperm XY” is false. 

(C)    The statement “embryo XX/endosperm XXX or embryo XY/endosperm XYY” is false.  

(D)    The statement “embryo XX/endosperm XXX or embryo XY/endosperm XXY” is true.

Step 1: Dioecious plants

There are male and female groups in the plant kingdom as well. The plants with male and female groups are called dioecious, while those lacking this sexual differentiation are monoecious. Date palm and papaya are examples of dioecious plants.

Step 2: Explanation of option (A)

Fertilization in plants occurs when one of the two sperms cells entering the female reproductive part fuses with the egg forming zygote. When this event is assisted with merging one of the sperm cells with the polar nuclei, the phenomenon is called double fertilization. 

When the embryo formed is XY, then the endosperm cannot be XXX.

Thus, when the embryo is XY, the endosperm cannot be XXX.

Therefore, the given statement is false.

Step 3: Explanation of option (B)

Double fertilization in plants can result in the formation of triploid endosperm, which nourishes the developing embryo. When the XY male and XX female form an embryo, a triploid (3n) endosperm is formed, with three sex chromosomes instead of two.

Thus, the endosperm arising from double fertilization is triploid instead of diploid.

Therefore, the given statement is false.

Step 4: Explanation of option (C)

Along with egg cells, there are two polar nuclei in the ovule. The process of double fertilization occurs when the sperm cell fuses polar nuclei. There should be two XX in the triploid endosperm composition instead of two Y as Y is absent in polar nuclei.

Thus, the endosperm cannot have YY in their genotype in this case.

Therefore, the given statement is false.

Step 5: Explanation of option (D)

Plant biological advancements enable certain plant species to incorporate certain specific traits generally not found in their species. Plant biotechnology can form newer and more advanced plant strains. This technology is extensively used for agricultural advancements.

 

Thus, the embryo can be XX with XXX endosperm or XY with XXY endosperm.

Therefore, the given statement is true.