Number of chromosomes
Arabidopsis plants have 10 chromosomes (5 pairs) in their somatic cells. How many chromosomes are present in each of the following: (a) egg cell nucleus in the female gametophyte, (b) generative cell nucleus in a pollen grain, (c) fertilized endosperm nucleus, (d) fertilized egg nucleus?
(a) Egg cells are haploid. Sperm and egg cells are haploid. Somatic cells are diploid which means they contain two sets of chromosomes that are inherited from each parent. Therefore, 5 chromosomes are present in egg cell of the female gametophyte.
(b) Generative cell nucleus in a pollen grain of flowering plant is one of the haploid nuclei present in pollen grains. It enters the pollen tube and divides by mitosis and forms male gamete nucleus that fertilizes with the female egg cell. Therefore, 5 chromosomes are present in generative cell nucleus in a pollen grain.
(c) In flowering plants, fertilization is known as double fertilization because two male nuclei from the pollen grain fuses with the egg and polar nuclei and forms diploid zygote and triploid endosperm respectively. Therefore, 15 chromosomes are present in fertilized endosperm nucleus.
(d) In fertilized egg nucleus 10 chromosomes are present. If sperm fertilizes the egg then it results in diploid number of chromosomes.
In a basic language, it can be said that DNA is in gene and the genes are on chromosomes. But, to comprehend the enigma of the creation of life, one needs to study about DNA, genes and chromosomes relationship.
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