Gamete formation and fertilization in angiosperms

Question

Explain what is different about gamete formation and fertilization in angiosperms (compared to vertebrates) that results in the fruit containing triploid endosperm when triploid tissues are not found in vertebrates. 

Answer 1

This question has a couple different parts that must be addressed. I will keep the answer general, but the actual mechanisms are quite complex.

Gamete formation (gametogenesis)

In both instances gamete formation begins with the duplication of chromosomes during interphase. Take the somatic number (chromosome number in body cells) and multiply it by two.

In order for sexual recombination to occur, this number has to be reduced. This happens during anaphase I & II.

In most invertebrates, homologous chromosomes (the chromosome pairs that come from mom & dad) will be equally divided into daughter cells during anaphase I. They will then be divided equally again during anaphase II. For example (interphase 2n->4n) (anaphase I 4n->2n) (anaphase II 2n->n).

In the angiosperm example mentioned, there is an unequal division of chromosomes into daughter cells during anaphase. I

will let you ponder whether this happens during anphase I, II, or both. Hint: it depends on the somatic number of the organism. You should be able to figure it out with some simple algebra.

Fertilization

Fertilization is pretty simple. The purpose is to create a cell that has the proper number of chromosomes required for somatic cells. For humans this would be a diploid cell with 46 chromosomes, 23 from mom and 23 from dad.

The somatic number varies from organism to organism, but suffice to say the purpose of fertilization is to take the reduced chromosome number in gametes and recombine into the somatic chromosome number of that species.