UNIT 4 QCE BIO - Spermatogenesis & Oogenesis

Learning Goals: within the process of meiosis I and II: recognise the role of homologous chromosomes within the process of meiosis I and II: describe the processes of crossing over and recombination and demonstrate how they contribute to genetic variation within the process of meiosis I and II: compare and contrast the process of spermatogenesis and oogenesis (with reference to haploid and diploid cells). demonstrate how the process of independent assortment and random fertilisation alter the variations in the genotype of offspring. QCE BIOZONE Pages: 173-175

Spermatogenesis

the production of sperm

Oogenesis

the production of egg cells

Stages of Spermatogenesis

Spermatogonium → Primary Spermatocyte → Secondary Spermatocyte → Spermatids → Spermatozoa

Stages of Oogenesis

Oogonium → Primary oocyte → secondary oocyte → Egg cell (ovum)

When does spermatogenesis begin?

starts at puberty ad continues into old age

When are eggs cells made?

by 5 months gestation

How many sperm cells are made per division?

4 per division

How many sperm cells are made per day?

120 million per day

How many eggs cells are produced?

At birth, there are approximately 1 million eggs left. By the time you reach puberty, only about 300,000 remain. Will divide into 4 at meiosis

How many gametes are made from original spermatocyte

4

How many gametes are made from original oocyte

4 (1 good, rest bad)

Describe spermatocyte formation

Goes through cell division and meiosis, and then grow tail for motility

Describe oocyte formation

oogenesis starts with a germ cell, called an oogonium (plural: oogonia), but this cell undergoes mitosis to increase in number, eventually resulting in up to one to two million cells in the embryo.

Describe changes in ploidy during spermatogenesis

Gametes are haploid - one set of homologous chromosomes

Describe changes in ploidy during oogenesis

diploid oogonium go through mitosis until one develops into a primary oocyte, which will begin the first meiotic division, but then arrest; it will finish this division as it develops in the follicle, giving rise to a haploid secondary oocyte and a smaller polar body

other information about spermatogenesis

A cell differentiation process that ensures the production of fertilizing sperm, which ultimately fuse with an egg to form a zygote

other information about oogenesis

Will remain in prophase I until puberty, other pauses along the way. The Quality of human eggs get worse over time