Early Development of Zygote

Question 1

What occurs on day 1 of early development of the zygote?

2

Answer 1

Fertilisation occurs on day 1

Zygote is formed

Question 2

What is a zygote?

Answer 2

A fertilised egg

Question 3

How many chromosomes are present in a fertilised egg?

Answer 3

46 chromosomes

Question 4

Where do the 46 chromosomes in a fertilised egg come from?

Answer 4

23 from the egg

23 from the sperm

Question 5

What is the origin of most of the zygotes cytoplasm and all of its mitochondria?

Answer 5

The egg

Question 6

What part of the zygote comes entirely from the egg?

Answer 6

The mitochondria

Question 7

What part of the zygote comes mostly from the egg?

Answer 7

The cytoplasm

Question 8

What happens during the first three days?

Answer 8

The zygote divides rapidly by a series of mitotic divisions to produce two cells, then four etc.

Question 9

What occurs on day 3 after fertilisation?

Answer 9

After 3 days of mitotic division a solid clump of cells called the morula is formed

Question 10

Define a morula.

Answer 10

A morula is a solid ball of cells formed from a zygote by mitosis

Question 11

When is the morula formed?

Answer 11

It is formed on day 3 (after 3 days of mitotic division)

Question 12

What happens on the fifth day after fertilisation?

Answer 12

The morula forms a hollow ball of a few hundred cells called a blastocyst

Question 13

When is the blastocyst formed?

Answer 13

It is formed on the fifth day after fertilisation

Question 14

Define a blastocyst.

Answer 14

A blastocyst (or blastula) is a hallow ball of cells formed from a morula

Question 15

What does the outer cells of the blastocyst form?

Answer 15

The trophoblast

Question 16

What part of the blastocyst forms the trophoblast?

Answer 16

The outer cells of the blastocyst

Question 17

What does the trophoblast form?

Answer 17

It will later form the membranes around the embryo

Question 18

What forms the membranes around the embryo?

Answer 18

The trophoblast

Question 19

What are the inner cells of the blastocyst called?

Answer 19

They are called the inner cell mass

Question 20

What does the inner cell mass form?

Answer 20

It will later form the embryo

Question 21

What part of the blastocyst will later form the embryo

Answer 21

The inner cell mass

Question 22

What part of the blastocyst will later form the membranes around the embryo?

Answer 22

The trophoblast

Question 23

The stages in the development of the zygote can be discussed based on 7 headings, name these headings.

Answer 23

Day 1 
Day 3
Day 5 
Day 10
Development up to 8 weeks 
Development up to 3 months
Gestation