REPRODUCTION AND DEVELOPMENT

Biology: Reproduction And Development

Reproduction And Development

Introduction

In the chapters 26, we have studied sexual reproduction: a reproductive system in which two differentiated cells (called gametes) fuse to give rise to a new individual single cell (the zygote) that will be developed by successive mitosis as multicellula. This definition of sexual reproduction leads to break down some concepts involved in it: (Bacon, 1999).

The gametes: they are differentiated cells, a process of meiosis, have decreased the number of chromosomes in half. They also called gametic cells, as opposed to other body cells (called somatic cells). While somatic cells have 2n chromosomes (2n cells or cells are diploid) gamete or gamete cells have n chromosomes (n or haploid cells are), that is, while somatic cells have pairs of homologous chromosomes, gametes have only A copy of each partner (Bacon, 1999).

Usually the male gametes are small and mobile, and large and immobile female.

Gametes arise from diploid cells undergo meiosis (from a cell obtained 2n n 4 cells). "The male animal gametes or sperm (n) are formed in the process of spermatogenesis from spermatogonia (2n), as we have studied.”The female animal gametes or ova (n), arise in the process of oogenesis from oogonia (2n). In the case of plants, male gametes are called anterozoides, and female oospheres.

Fertilization: the fundamental operation in reproduction. Is the union of two gametes (male and female) to give rise to a new individual.

The zygote, zygote or egg cell called the result of fertilization. It is a new individual with its own chromosome (different from parents) and complete (ie, 2n). For subsequent mitosis will develop as multicellular (all multicellular cells have the same genetic information as the egg cell or zygote) (Weiber, 2001).

The embryonic development is the development of new individual from the zygote stage to birth. This process will be the subject of detailed study in this issue (Weiber, 2001).

Embryonic development

The embryonic development of animals is an ongoing process. However, as was the case with cellular mitosis and meiosis, for study is usually divided into three periods:

Segmentation: repeated division of the zygote but the resulting cells undergoes displacement sensitive.

Gastrulation: blastodermic formation or embryonic leaves, with displacement of the cells, which come to occupy certain parts of the embryo.

The organogenesis, differentiation of organs, apparatuses and systems.

a) Types of eggs and segmentation

In the zygote are two parts: the pure active plasma or cytoplasm (which give rise to the embryo) and ...