ZOO501 Lab Manual Updated 2020

Contents · S. No · Practical

P. No. Study of the structure of gametes in some representative cases, i.e. frog, fish and mammal Hen’s egg internal and external structural details Microscopic analysis of hen’s egg yolk, albumin and shell membranes Study of cleavage and subsequent development from prepared slides and/or models in various animals i.e., frog, mammals and chick etc. Study of fertilization, early development of frog/fish through induced spawning under laboratory conditions. Study of developmental stages of nematodes through microscopic analysis of animal dung Semen analysis Dactylography and its uses in developmental biology

Practical No: 1 Study of the structure of gametes in some representative cases, i.e. frog, fish and mammal

Male Gametes

The male gamete (sperm) is small and motile and only contributes the male’s haploid nucleus to the zygote.

Sperm

A typical human spermatozoon can be divided into three sections,

1. Head,
2. Mid-piece
3. Tail

Head region:

The head region contains three structures,

• A haploid nucleus
• An acrosome cap
• Paired centrioles

The haploid nucleus contains the paternal DNA (this will combine with maternal DNA if fertilization is successful)

• The acrosome cap contains hydrolytic enzymes which help the sperm to penetrate the jelly coat of the egg
• The centrioles are needed by a zygote in order to divide (egg cells expel their centrioles within their polar bodies)

Mid-piece:

The mid-piece contains high numbers of mitochondria which provide the energy (ATP) needed for the tail to move

Tail:

The tail (flagellum) is composed of a microtubule structure called the axoneme, which bends to facilitate movement. Fig 1.1: Detail of sperm

Female Gametes

A typical egg cell is surrounded by two distinct layers

1. The zone pellucida (jelly coat)
2. Corona radiate

Zone or Zona pellucida:

The zona pellucida is a glycoprotein matrix which acts as a barrier to sperm entry.

Corona radiate:

The corona radiata is an external layer of follicular cells which provide support and nourishment to the egg cell. Within the egg cell are numerous cortical granules, which release their contents upon fertilization to prevent polyspermy. Egg cells commonly include a haploid nucleus. The cytoplasm of the egg is called ooplasm. It contains a very little mount of yolk in human female and therefore it is alecithal. In animals where huge amount of yolk is present, the cytoplasm of egg consists of lipoproteins, pigment granules, water and along with other cytoplasmic organelles.

Fig 1.2: Detail of human egg Practical No: 2 Hen’s egg internal and external structural details

Chicken egg quality has been defined by Kramer (1951) as the properties of any given food that have an influence on the acceptance or rejection of this food by the consumer. Egg quality is a general term which refers to several standards which define both internal and external quality. External quality is focused on shell cleanliness, texture and shape, whereas internal quality refers to egg white (albumen) cleanliness and viscosity, size of the air cell, yolk shape and yolk strength.

Fig 2.1: Detail of egg

1. Eggshell

The outer eggshell is made almost entirely of calcium carbonate (CaCO3) and is covered with as many as 17,000 tiny pores. It is a semipermeable membrane, which allows air and moisture to pass through its pores. The shell also has a thin outermost coating called the bloom or cuticle that helps keep out bacteria and dust.

2. Outer shell membrane

3. Inner shell membrane

These two membranes – outer and inner – are just inside the shell surrounding the albumen (white). The two membranes provide an efficient defense against bacterial invasion and are made partly of keratin. The outer membrane sticks to the egg shell while the inner membrane sticks to the albumen. When an egg is first laid, it is warm. As it cools, the contents contract and the inner shell membrane separates from the outer shell membrane to form the air cell (see 14 below).

4. Chalaza

Chalaza is twisted in opposite directions and serves to keep the yolk centered. The more prominent the chalazae, the fresher the egg.

5. Exterior albumen (outer thin albumen)

The outer thin albumen is a narrow fluid layer next to the shell membrane.