Meiosis Flashcards
Why is meiosis required?
In order to produce four genetically different gametes with half the normal amount of chromosomes. This reduction is critical- without it, fertilisation would result in cells with twice the normal number of chromosomes
What is the main difference between meiosis in males and females?
In males, it produces four sperm, and in females, it produces one egg and three polar bodies
Why do two divisions take place in meiosis?
The first division splits the genetic material between 2 daughter cells; the second gives half of the genetic material to each of two more daughter cells. The result is 4 daughter cells, each with half of the genetic material of the mother cell.
When does the DNA replicate in meiosis?
Like with mitosis, DNA replication occurs during interphase
Describe the stages of meiosis I and II.
Meiosis I:
Prophase: Chromosomes condense, homologues align, and exchange homologous segments; chromosomes begin to separate
Metaphase: Nuclear membrane disappears, chromosomes align in middle
Anaphase: Separation
Telophase: Cell splits into two
Meiosis II:
Normal Prophase, metaphase, anaphase, and telophase
What are the consequences of meiosis?
Each chromosome will typically have three or more segments of alternating parental origin
There is very little chance that two gametes are exactly the same
Define the term ‘aneuploidy’
Aneuploidy is a condition where an abnormal number of chromosomes are present
What can happen during meiosis that can lead to aneuploidy?
During meiosis, two members of a homologous pair may not segregate normally, resulting in one daughter cell with both chromosomes and the other with none. Upon fertilisation, the resulting zygote has either 47 or 45 chromosomes
Give an example of aneuploidy
Down syndrome, which is also known as trisomy 21 as three chromosome 21 are present
What are the two phases of gamete formation in males?
Spermatogenesis
Spermiation
Define the term ‘spermatogenesis’
The process by which Type A dark spermatogonia (the main stem cell in the seminiferous tubule) form spermatozoa
Define the term ‘spermiation’
The process by which mature spermatids are released into the seminiferous tubule lumen
Describe the three stages involved in spermatogenesis
1) Mitotic proliferation to produce large reservoir of identical cells (spermatogonia proliferate and form primary spermatocytes)
2) Meiotic division to give rise to haploid gametes and increase genetic diversity (primary spermatocytes undergo meiosis to form spermatids)
3) Spermiogenesis to produced specialised germ cells (spermatids form spermatozoa)
