The chromosomal mutation in the zygote can be traced back to which of the following? (4.3, 4.4)Immersive Reader
1 answer:
The chromosomal mutation in the zygote can be traced back to "Chromosome 6 in the egg cell".
<u>Option: B</u>
<u>Explanation:</u>
In germ cells i.e. egg or sperm cells, the mutations in chromosome often happen during the meiosis phase. The number of chromosomes in egg cells or sperm cells must be haploid, so that diploid chromosomes form zygote on fertilization. Chromosome mutation in meiosis leads in an additional set of chromosomes or structural defects in the chromosome.
Chromosomal mutations are often caused by chemical agents or by mutagens. The homologous chromosomes are segregated from sister chromatids throughout cell division, any abnormality at this point allows the chromosomes to be unequally divided or not disjuncted, same is observed in the situation seen in egg cell chromosome 6.
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Answer:
Pollen grain lands on stigma
Explanation:
A) Pollen grain lands on stigma
- pollen tube grows down the style
- generative cell divides, forming two sperm
- two sperm are discharged to them female gametophyte
- sperm fuse with the egg and two polar nuclei
- zygote forms and divides into a terminal cell and a basal cell
- cells of embryo differentiate into three tissue types---- seed dries out and becomes dormant.
B)
- During pollination, a pollen grain is transferred from an anther to a stigma. Once the pollen grain lands on a suitable stigma, it germinates and forms a pollen tube, a structure that grows down through the style to the ovary.
- Once in the pollen tube, the generative cell from the pollen grain divides by mitosis, forming two sperm. The sperm travel down the pollen tube and are discharged into the female gametophyte. In a process called double fertilization, one sperm fertilizes the egg, forming the zygote; the other sperm fuses with two polar nuclei in the female gametophyte, forming a triploid (3n) nucleus. The zygote develops into the plant embryo, and the triploid nucleus divides and gives rise to the endosperm. Double fertilization prevents the waste of the plant's resources by ensuring that the nutrient-rich endosperm only develops if the egg is fertilized.
- After double fertilization, the ovule starts to develop into a seed containing the plant embryo. As the embryo develops, the three tissue systems are established, and the cotyledons (seed leaves) form. The seeds of many species dry out as they mature. These dry seeds lie dormant until suitable germination conditions occur.
