One biology question in high school and one biology question in high school

a A person has 23 pairs of homologous chromosomes, one from the mother and one from the father.

d Except for sex chromosomes X and Y, which are long and short, the other pairs of homologous chromosomes are about the same shape and size.

Of course it's c.

Homologous chromosomes are one from the father and one from the mother, the same size and shape, and can be united. If it is not homologous chromosomes, it cannot be united, but if it can, it must be.

A is a random two from the father and the mother, and the size and form are not necessarily the same.

b Definitely not, not by the father and the mother respectively.

d shape and size, e.g. in option b, but no.

A is explicitly written in the biology book.

b is definitely not right, no need to explain.

c No, because the union is after the homologous chromosomes form tetrads.

d is correct, because there is also an xy chromosome, so the title says yes (generally) and not (all).

Select AA: ex vivo plant tissues, organs or cells - (dedifferentiation) - callus - (redifferentiation) - roots, shoots, embryoid bodies - seedlings - plants. So a pair.

B: Animals and plants are fine, and the specific explanation is as follows:

It's not that plants can't, but the somatic cells differentiated by plants grow in different environments from those in vivo under the condition of being in vitro, so there will be degradation after many passages, most of the cells can not be passed on after 10 generations, and a small number can be transmitted to 50 generations. However, because the cells at the growth points such as the root tip and stem tip are undifferentiated cells, their life activities are relatively vigorous and can be transmitted for a long time, but they are not indefinitely proliferated.

C: Plant cells have totipotency, but they can only exert their totipotency when they are out of the body. And the degree of cell differentiation varies in different parts.

D: The same mRNA does not necessarily exist.

dBecause the selective expression of genes is different, the proteins that need to be synthesized are different.

c and d are clearly wrong. cThe degree of cell differentiation and totipotency expression were different in different parts.

dNerve cells and islet cells of the same animal must express some genes that control basic functions (housekeeping genes) to produce the same mRNA.

In ex vivo culture, anther is pollen dedifferentiation to form callus. So, I think it's A.

Finally, mention is made to subparagraph b. Primary culture and subculture are for animal cell culture, and it is not appropriate to say whether plant cells can be subcultured.

c.Reason: a:

Pollen are sperm cells that do not have all the genetic material and cannot differentiate into calluses. B: Yes.

C: Plant cells are totipotent (the concept is written in the textbook) D: The same mRNA does not necessarily exist, not necessarily absent.