Lecture 8 - Prenatal Development

Question 1

What is the largest cell in the human body?

Answer 1

The ovum.

Question 2

What is interphase and is it a part of Meiosis?

Answer 2

Interphase in the stage PRIOR to meiosis (and mitosis). It involves the replication of the the 46 chromosomes. Because there are still on 46 centromeres, and we measure chromosome number by number of centromeres, we do not say there are now 92 chromosomes. Rather, there are 46 sets of replicated chromosomes - known as sister chromatids.
The phases of meiosis are prophase I, metaphase I, anaphase I, telophase I + cytokinesis, prophase II, metaphase II, anaphase II, telophase II and second cytokinesis.

Question 3

What are homologous chromosomes?

Answer 3

Homologous chromosomes are chromosomes of a similar length/size that contain genes for the same proteins.

Question 4

What is DNA recombination and when does it occur and why does it occur?

Answer 4

DNA recombination is one of the defining characteristics of meiosis compared to mitosis.
DNA recombination occurs in the prolonged prophase I stage of meiosis. Whilst the spindles are forming the duplicated pairs homologous chromosomes exchange genetic material and in doing so create whole new/novel combinations of genetic material. These recombined chromosomes then go through metophase, anaphase, telophase and cytokinesis to produce daughter cells with 23 pairs of duplicated and recombined chromosomes. At the end of Meiosis II the daughter cells, which become gametes, only have 23 chromosomes as well, but this time there are only 23 chromatids. This is how haploid cells, known as gametes, are formed.

Question 5

How is genetic diversity created during meiosis?

Hint: recombination and 23 chromosomes.

Question 6

Why is genetic variation important?

Question 7

What sex chromosomes do the spermatozoa contain?
What sex chromosome does the ovum contain?

Question 8

What is different between spermatogenesis and oogenesis?

Question 9

What are spermatids and ovids?

Question 10

What is the difference between when spermatozoa and ova are produced?

Hint: one is during fetal development and one is everyday (after puberty).

Question 11

On average how many sperm are there per ejaculation and how many sperm tend to make it close to the ovum?

Question 12

What are some reasons not all/so few sperm make it to the ovum?

Hint: we learned about three

Question 13

What are the three phases of prenatal development?
When are these phases defined?
What are these phases characterised by?

Question 14

Within how many hours does the first round of mitosis occur for the the zygote?

Question 15

What is a zygote?

Question 16

What is the difference between meiosis and mitosis?

Question 17

What is a blastocyst?

Question 18

How many zygotes fail to implant successfully into the uterine wall and what can impair/prevent implantation?

Question 19

What are the three layers of the inner cell mass of the blastocyst?
And, what do these different cell types become?

Answer 19

Ectoderm, mesoderm and endoderm.

Question 20

What are 4 major support structures for the developing embryo/fetus?

Question 21

Are there different levels of activity between different fetuses and if so, does this correlate with activity levels of infants/children postnatally?

Question 22

What stimulation is present for the fetus that helps with the development of the sensory nervous system?

Question 23

What kind of fetal learning occurs prenatally?

Question 24

What percentage of pregnancies fail/do not progress past 3 weeks?

Answer 24

45%

Question 25

Define Teratogen.

Question 26

What are critical periods for different organs in regards to teratogens and fetal development?

Question 27

What is an example of a disease that a carrying parent could have that would impair fetal development?

Answer 27

Rubella.

Question 28

What are two examples of teratogens?

Answer 28

Alcohol and Thalidomide.

Question 29

The effect that teratogens will have on a developing fetus depends on what?

Question 30

What are sleeper effects? What is an example of this?

Question 31

Is Meiosis I or Meiosis II most similar to mitosis?

Answer 31

Meiosis II is most similar to mitosis, as there is no recombination of DNA.

Question 32

After meiosis I how many chromosomes and sister chromatids do the daughter cells have?

Answer 32

After meiosis I the daughter cells have 23 chromosomes, which each have two sister chromatids, which are not identical because they have undergone DNA recombination in prophase I. So, there are 46 chromatids, but only 23 chromosomes (23 centromeres).