Question

A human zygote has
A)46 chromosomes
B)23 chromosomes
C)47 chromosomes
D)48 chromosomes

Answer 1

Hint: A zygote is a eukaryotic cell that is produced by two gametes by a fertilization event. The genome of the zygote is a mixture of the DNA in each gamete and contains all the genetic material required to produce a new organism. The earliest embryonic stage is the zygote of multicellular organisms.

Complete answer:
In case of human fertilization, a released ovum (a haploid secondary oocyte with replicated chromosome copies) and a haploid sperm cell (male gamete) are merged to build a single 2n diploid cell known as the zygote.

The division of the second meiosis is achieved before the single sperm enters the oocyte, producing a haploid daughter with only 23 chromosomes, almost half the cytoplasm, and the sperm with its own pronucleus. The other result of meiosis is the second polar body with only genes but no ability to replicate or survive. In the fertilized daughter, DNA is then repeated in the two distinct pronuclei formed from the sperm and ovum, making a short 4n diploid of the zygote chromosome number. After about 30 hours from the time of fertilization, pronucleus fusion and immediate mitotic division produce two 2n diploid daughter cells called blastomeres.

Note: A Chlamydomonas zygote incorporates chloroplast DNA (cpDNA) from both parents; these cells are typically uncommon because cpDNA is usually inherited uniparentally from the parent of the mt+ mating form. These rare biparental zygotes allowed chloroplast genes to be mapped by recombination. In the Amoeba, replication happens by the parent cell's cell division: first, the parent's nucleus breaks into two, then the cell membrane also cleaves, forming two "daughter" Amoeba.