Gamete Formation (Nursing)

00:01 Welcome.

00:02 In this lecture we will be discussing the physiology of the male reproductive system.

00:09 But before we talk specifically about male reproductive physiology, let's look at an overview of gamete formation.

00:20 Most of our body cells contain 46 chromosomes.

00:25 This includes two sets of 23 pairs of chromosomes, where one of those chromosomes came from the mother or your maternal chromosomes, and one came from the father or the paternal chromosomes.

00:40 We refer to this pair as homologous chromosomes.

00:45 And 46 is referred to as our diploid number or a diploid chromosome number or our 2n.

00:56 Gamete cells are different from our body cells and that they only have 23 chromosomes, or our haploid chromosome number, because it is half of the 46 chromosomes found in the rest of the body.

01:13 In our gametes we only have one member of the homologous pair.

01:20 Formation of these haploid cells is going to require a process known as meiosis.

01:28 Before we talk about meiosis, however, let's do a quick recap of the other types of cell division, mitosis.

01:38 So recall that mitosis occurs when the nucleus of a cell divides, is going to result in the distribution of two sets of chromosomes into two separate nuclei.

01:52 We divide mitosis into four steps.

01:55 The first step is prophase, where the chromosomes have been replicated, and two copies are held together as sister chromatids.

02:04 In this process the cell prepares to divide by dissolving the nucleus away from the sister chromatids.

02:13 The next phase is metaphase.

02:16 And in this phase, all 46 duplicating chromosomes or sister chromatids line up along the midline of the cell.

02:26 After metaphase, we have anaphase, where the sister chromatids are now pulled apart toward opposite sides or poles of the cell.

02:38 Finally, after anaphase we have telophase, where we begin to form a nucleus around each new set of 46 unreplicated chromosomes.

02:52 Following telophase, we have cytokinesis.

02:56 Cytokinesis is when a cytoplasm is going to divide the two new nuclei that are formed from the daughter cells.

03:07 This process is going to occur in the body or in our somatic cells.

03:12 And results in the formation of two genetically identical cells from one cell.

03:22 Meiosis however, is going to involve a little bit of a different process.

03:28 And spermatogenesis, or the production of male gametes is going to require the process of meiosis .

03:36 So let's compare the two to see how they're different.

03:41 First, meiosis is going to involve two consecutive cell divisions, Meiosis I and Meiosis II, while there's only one round of DNA replication.

03:54 So in mitosis, we have 1 cell division and in meiosis, we have 2.

04:02 Secondly, we're going to produce four daughter cells in meiosis instead of the two daughter cells that we produce in mitosis.

04:13 Functionally, in meiosis the number of chromosomes are going to be cut in half from diploid to haploid, instead of remaining diploid in mitosis.

04:27 And when it comes to genetic diversity, meiosis is going to introduce genetic diversity as the daughter cells are going to be genetically different from the original cell.

04:39 In mitosis however, you're going to produce genetically identical daughter cells.