Sexual Reproduction in Flowering Plants Set-1

Q1. A flowering plant species has somatic chromosome number $2n = 14$. After normal double fertilization, what will be the chromosome numbers in the embryo and in the primary endosperm nucleus?

Q2. In a species with gametophytic self-incompatibility (GSI) there are three S‑alleles S1, S2 and S3 with frequencies $0.6,\;0.3,\;0.1$ respectively in the pollen pool. A pistil of genotype S2S3 receives a random pollen grain from the population. What is the probability that this pollen grain will be compatible on that pistil?

Q3. A mutation prevents fusion of the two polar nuclei in the central cell; during fertilization only one polar nucleus fuses with a sperm nucleus while the other polar nucleus degenerates. If the somatic chromosome number is $2n = 16$, what will be the chromosome numbers in the embryo and in the primary endosperm nucleus?

Q4. Consider reciprocal crosses between a diploid ($2x$) and a tetraploid ($4x$) plant. In Cross I the female is $4x$ and the male is $2x$; in Cross II the female is $2x$ and the male is $4x$. For each cross calculate the maternal:paternal genomic ratio in the primary endosperm nucleus and indicate which cross yields a ratio closer to the normal $2:1$ (maternal:paternal) and therefore is more likely to produce viable seeds.

Q5. An apomictic plant reproduces by apospory: an unreduced somatic cell gives rise to an embryo without fertilization (parthenogenesis), but endosperm formation requires fertilization by pollen (pseudogamy). If the somatic chromosome number is $2n = 20$ and pollen comes from a sexual diploid plant ($2n = 20$), what will be the chromosome numbers in the embryo and in the primary endosperm nucleus?

Q6. A flower has 6 stamens; each anther contains 4 microsporangia and each microsporangium contains 40 microsporocytes (pollen mother cells). After normal microsporogenesis (each microsporocyte gives 4 microspores) and pollen formation, how many pollen grains will be produced by all the anthers of that single flower?

Q7. A diploid plant ($2n$) is pollinated by a tetraploid plant ($4n$) that produces reduced male gametes. Assuming normal double fertilization (one sperm fuses with egg; the other with two polar nuclei), the ploidy level of the zygote (embryo) and the primary endosperm nucleus (PEN) will be:

Q8. Consider these interploidy crosses (reduced gametes, Polygonum-type embryo sac): P1 — $2n$ (♀) × $2n$ (♂); P2 — $2n$ (♀) × $4n$ (♂); P3 — $4n$ (♀) × $2n$ (♂); P4 — $4n$ (♀) × $4n$ (♂). Which of the following crosses are expected to produce endosperm with a maternal:paternal genome ratio close to the optimal $2:1$, and therefore most likely to give viable seeds?

Q9. In a Polygonum-type embryo sac one polar nucleus degenerates before fertilization so the central cell contains only a single polar nucleus ($n$). A normal sperm nucleus ($n$) fertilizes this central cell. What will be the ploidy of the primary endosperm nucleus (PEN) and the maternal:paternal genome ratio in the resulting endosperm?

Q10. In a cross between a diploid female ($2n$) and a tetraploid male ($4n$) viable hybrid embryos are sometimes formed but most seeds abort due to defective endosperm. Which of the following techniques is most appropriate to recover viable hybrid plants directly from such incompatible crosses?