meroblastic : lines of segmentation do not completely pass through egg & remain confined to a part of egg. megalecicithal : very large amount of yolk. discoidal : disc of cells is produced at animal pole of zygote. as birds has megalecicithal eggs, the yolk provides resistance to cleavage, hence the cleavage is meroblastic & discoidal. meroblastic cleavage occurs in insects & reptiles also but it is not discoidal, it is suferficial (having centrolecithal eggs).
Full Answer
Why is cleavage in bird Meroblastic and Discoidal?
Meroblastic cleavage takes place in those eggs where the amount of yolk is high, which leads to the partial or incomplete cleavage. It is basically of two types spherical and discoidal. The discoidal type of cleavage takes place in the reptiles and birds whose eggs are telolecithal in nature.
Why is cleavage called Discoidal in birds?
The cleavage remains limited in eggs of Birds, Reptiles and egg-laying mammals, to the disc-shaped area of cytoplasm, the blastodisc. The animal pole yolk is not divided. Such incomplete cleavage is known as discoidal cleavage.
What is Discoidal Meroblastic cleavage?
Medical Definition of discoidal cleavage : meroblastic cleavage in which a disk of cells is produced at the animal pole of the zygote (as in bird eggs)
Do birds have Meroblastic cleavage?
Like fish eggs, the yolky eggs of birds undergo discoidal meroblastic cleavage.
What type of cleavage do birds have?
Discoidal cleavageDiscoidal cleavage is commonly found in monotremes, birds, reptiles, and fish that have telolecithal egg cells (egg cells with the yolk concentrated at one end).
What is the difference between Holoblastic cleavage and Meroblastic cleavage?
Holoblastic cleavage – is a complete cleavage meaning it completely penetrates the egg. Meroblastic cleavage – is incomplete or partial cleavage meaning it does not penetrate the egg completely.
Why cleavage in chick is Discoidal type?
The cleavage in the chick is called discoidal because it is limited to the blastodisc. EXPLANATION: Post-fertilization changes in the chicken egg are caused by several mitotic divisions. The entire egg at a point of development is divided into two poles, the vegetal pole and the animal pole.
In which animal Meroblastic cleavage occurs?
Hint: Meroblastic cleavage is a type of cleavage that occurs in very yolky eggs like birds in which the egg cytoplasm and not the yolk divides (incomplete division) .
What is Discoidal?
Medical Definition of discoidal : of, resembling, or producing a disk especially : having the villi restricted to one or more disklike areas.
What is different in the reproduction of birds and mammals?
There is a major difference between birds and mammals is the female reproductive system as birds produce large yolk filled eggs. The precursors of the yolk are synthesized by the liver. Another difference is that there is a single ovary and oviduct in birds.
Are humans Holoblastic or Meroblastic?
HoloblasticIt is the general case of cleavage in the human zygote. However, other organisms lay eggs under meroblastic cleavage, which is a partial embryo development case. Humans undergo Holoblastic division as they do not have egg yolk. As a result, different cells combine to form a compact mass which we call a morula.
What animals show Holoblastic cleavage?
The holoblastic type of cleavage is commonly seen in eggs containing moderate to sparse amount of yolk. Examples of animals with eggs that divide holoblastically include the amphibians, mammals, echinoderms, annelids, flatworms, nematodes, etc.
What is Discoidal?
Medical Definition of discoidal : of, resembling, or producing a disk especially : having the villi restricted to one or more disklike areas.
What is Discoidal shape?
Definitions of discoidal. adjective. having a flat circular shape. synonyms: disc-shaped, disclike, discoid, disk-shaped, disklike circular, round. having a circular shape.
What do you mean by Centrolecithal egg?
Centrolecithal egg is an egg in which the yolk is concentrated near the centre of the egg cell, as is the case in many of the insects.
What do you mean cleavage?
Cleavage is a word for a kind of splitting or separation: it's mainly used for the split between a woman's breasts. We can talk about many kinds of cleavage, such as the splitting of a cell or a hunk of wood.