Which of the following sequences accurately represents the order of development?

Fertilisation -zygote-cleavage-morula-blastula-gastrula .

The correct answer is Option (1)- Fertilisation -zygote-cleavage-morula-blastula-gastrula .

Explanation:

• Fertilisation:The process of fusion of a sperm with an ovum is called fertilisation.
• Zygote: The haploid nucleus of the sperms and that of the ovum fuse together to form a diploid zygote.
• Cleavage: The mitotic division starts as the zygote moves through the isthmus of the oviduct called cleavage towards the uterus and forms 2, 4, 8, 16 daughter cells called blastomeres.
• Morula: The embryo with 8 to 16 blastomeres is called a morula.
• Blastula: A hollow ball of cells formed as the morula undergoes further cell division and rearrangement.
• Gastrula: Formation of three primary germ layers (ectoderm, endoderm, and mesoderm) through a process called gastrulation.

So, Option 1 correctly represents the chronological order of developmental stages.