Sexual Reproduction in Flowering Plants Set-5

Q1. In a flowering plant with somatic chromosome number $2n=14$, what will be the chromosome number of the primary endosperm nucleus formed after normal double fertilisation?

Q2. In a species exhibiting gametophytic self-incompatibility (GSI), a pistil has genotype $S_1S_2$ and receives pollen from a plant with genotype $S_2S_3$. Pollen grains from the donor are haploid $S_2$ or $S_3$ in equal proportion. What fraction of the donor's pollen grains will be compatible on this pistil?

Q3. A style is $6\ \text{mm}$ long. Self-pollen tube grows at $0.5\ \text{mm h}^{-1}$ and cross-pollen tube at $1.0\ \text{mm h}^{-1}$. Self pollen lands on the stigma $2$ hours before cross pollen. Assuming constant growth rates and continuous growth after landing, which pollen's sperm will reach the ovule first?

Q4. In a flowering plant with somatic chromosome number $2n=18$, one polar nucleus fails to reduce and remains $2n$ while the other polar nucleus is normal $(n)$. If a normal haploid male gamete fertilises the central cell, what will be the chromosome number of the primary endosperm nucleus?

Q5. In a diploid species with $2n=14$, an error during megasporogenesis produces an unreduced egg cell $(2n)$ and the central cell contains one unreduced polar nucleus $(2n)$ and one normal polar nucleus $(n)$. If fertilisation occurs by a normal haploid male gamete $(n)$, what will be the chromosome numbers of the resultant zygote and the primary endosperm nucleus respectively?

Q6. In a flowering plant with haploid chromosome number $n=8$, a pollen grain fertilizes the egg cell and the second sperm fuses with the two polar nuclei (double fertilization). What are the chromosome numbers in the zygote and in the primary endosperm nucleus respectively?

Q7. In a species with gametophytic self‑incompatibility (GSI) a pollen grain is rejected if its haploid $S$‑allele matches any $S$‑allele present in the stigma/style. Given four plants with genotypes P1($S_1S_2$), P2($S_2S_3$), P3($S_1S_3$) and P4($S_3S_3$), which of the following pollinations will be completely incompatible (no pollen grain can fertilize the ovule)?

Q8. A flowering plant has somatic chromosome number $2n=18$. In Polygonum‑type (monosporic) embryo sac development an 8‑nucleate embryo sac is formed and normal double fertilization occurs. What are the chromosome numbers in (i) each egg cell and each synergid, (ii) each polar nucleus, and (iii) the primary endosperm nucleus after fertilization?

Q9. Normal endosperm development in most angiosperms requires the maternal:paternal genomic ratio in the primary endosperm nucleus to be approximately $2:1$. Using ploidy notation where somatic cells are $2x$ (diploid), $4x$ (tetraploid), $6x$ (hexaploid), etc., which of the following crosses is most likely to produce normal seeds based on endosperm genome ratio?

Q10. In a species each pollen grain landing on a receptive stigma independently germinates and produces a pollen tube that reaches the embryo sac with probability $p=0.30$. Double fertilization requires at least one pollen tube to reach the embryo sac. Using the expression for success probability $P(N)=1-(1-p)^N$, what is the minimum integer number $N$ of pollen grains that must land on the stigma so that $P(N)\ge 0.95$?

Q11. In a flowering plant with somatic chromosome number $2n$, a normal double fertilization occurs. What are the ploidy levels of the resulting zygote (embryo) and the primary endosperm nucleus?

Q12. A tetraploid plant ($4n$) is used as the female parent and a diploid plant ($2n$) as the male parent in a cross. Assuming normal meiosis and typical double fertilization, what will be the chromosome number (ploidy) of the embryo and the primary endosperm nucleus in the seed?

Q13. A plant species exhibits gametophytic self-incompatibility (GSI). A pistil with genotype $S_1S_2$ receives pollen grains produced equally by two different plants with genotypes $S_1S_3$ and $S_2S_4$. If all pollen grains are equally likely to land on the stigma, what fraction of pollen grains will be compatible (able to fertilize the pistil)?

Q14. Assertion (A): Self-incompatibility mechanisms in flowering plants promote outcrossing and thereby increase genetic diversity.
Reason (R): In many species SI is controlled by multiple alleles at a single $S$-locus.

Q15. A diploid plant heterozygous for a gene ($A/a$) self-pollinates. Embryo sac development is of the monosporic (Polygonum) type so both polar nuclei derive from the same megaspore and are genetically identical. What is the probability that the primary endosperm nucleus will be homozygous for $A$ (genotype $A\;A\;A$, i.e., two maternal $A$ alleles plus one paternal $A$ allele)?