Lecture 3 - Review

Question 1

1. What distinguishes mitosis and meiosis?

Answer 1

Mitosis produces two genetically identical “daughter” cells from a single “parent” cell,
Meiosis produces cells that are genetically unique from the parent and contain only half
as much DNA.
Most cells in the body regularly go through mitosis, but some do so more often than others

Question 2

2. What are the stages of meiosis in human males?
   **Stems from spermatogenesis

Answer 2

Spermatogenesis: Begins at Puberty

1) Spermatogonium
2) Primary spermatocyte
3) Secondary Spermatocyte
4) Spermatid
5) Matured sperm

Detailed info
1. Spermatogonia are the cells that give rise to sperm cells. The spermatogonia divide by mitosis. One daughter cell remains a Spermatogonium that can divide again by
mitosis. The other daughter cell becomes a
primary spermatocyte.

2. The primary spermatocyte divides by meiosis to form secondary spermatocytes.
3. The secondary spermatocytes divide by meiosis to form spermatids.
4. The spermatids differentiate to form sperm cells
5. Sustentacular cells, in which the spermatogonia and developing sperm cells are embedded, maintain the blood-testis barrier.

Question 3

3. What are the stages of meiosis in human females?

** Stems from oogenesis

Answer 3

Oogensis: Beings during Embryogenesis

1) Oogonium
2) primary oocyte
3) secondary oocyte
4) ootid
5) matured egg-zygotete

Detailed info

In females, the process of meiosis is called oogenesis since it produces oocytes and ultimately yields mature ova(eggs).

In 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.

(4 polar bodies; 3 get discarded to leave one haploid secondary oocyte)

Question 4

4. What is nondisjunction?

Answer 4

Non-disjunction:

▪ The failure of chromosomes to
properly separate at either the
first or the second division in
meiosis is called nondisjunction.

▪ The result is an abnormal
number of chromosomes in
sperm or eggs.

▪ If these abnormal
gametes are involved in fertilization, the result can be a
a child with an abnormal number of chromosomes

Question 5

5. What conditions appear to increase chromosomal abnormalities?

Answer 5

Risk factors include:

• older age in the woman,
• a family history of genetic abnormalities
• a previous baby with a birth defect or miscarriage
• a chromosomal abnormality in one of the prospective parents.

Question 6

6. What can be done to detect chromosome abnormalities?

Answer 6

Four main types of screening tests for chromosome abnormalities are available:

• Early risk assessment (with or without “sequential screening”)
• quadruple screen
• cell-free DNA analysis (cfDNA),
• full fetal survey at the “nuchal translucency.” (This refers to fluid behind the neck of a fetus)

Question 7

7. What is the condition where a person has an extra chromosome 21?

Answer 7

Trisomy 21 (Nondisjunction)

Down syndrome is usually caused by an error in cell division called “nondisjunction.”

Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two.

Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate.

Question 8

8. What is the condition where someone with two X chromosomes has an extra Y chromosome

Answer 8

Turner syndrome: a condition that affects only females.

Results when one of the X chromosomes (sex chromosomes) is missing or partially missing.

Turner syndrome can cause a variety of medical and developmental problems, including short height, failure of the ovaries to develop and heart defects