16.3 The Formation of Gametes Flashcards
What are the two key outcomes of Meiosis?
Reduction Division
Recombination
What is Reduction Division?
When cell division produces daughter cells with fewer chromosomes than the parent cells
What is recombination?
When the products of meiosis have different combinations of genes that give rise to genetic offspring that are genetically distinct from one another and their parents
What are the phases of Meiosis I?
Prophase I
Metaphase I
Anaphase I
Telophase I
What are germ cells?
Gamete producing cells
What phase do gamete producing cells undergo that is the same of body cells?
The interphase and Prophase, Metaphase, Anaphase, Telophase
What is the interphase?
A period of growth and synthesis that occurs before meiosis begins
What does a germ cell contain at the start of meiosis?
Duplicated chromosomes
What do duplicated chromosomes consist of?
2 sister chromatids that are joined together at the centromere
What happens in the Prophase I of Meiosis?
Each pair of homologous chromosomes align side by side
What is Synapsis?
The alignment of homologous chromosomes in the Prophase I
What are homologous chromosomes?
Chromosomes that are not identical but contain the same genes
What is the name for the pairs of chromosomes that align during the Prophase I?
A tetrad
What is a Tetrad?
The four chromatids that align with each other during the Prophase I
What is a Tetrad made up of?
A pair of sister chromatids synapsed with another pair of sister chromatids
What are non-sister chromatids?
Two homologous but non-identical chromatids
What happens is the Metaphase I?
A spindle fiber attaches to the centromere of each chromosome. A spindle fibre from each pole attaches to opposite pairs of sister chromatids in the tetrad and guid each tetrad to the equator of the cell
What happens after each Tetrad is guided to the equator in the Metaphase I?
The chromosomes line up as homologous pairs so that in each pair one homologous chromosome is positioned on either side of the cell’s equator
What happens during Anaphase I?
The spindle fibres shorten which causes the homologous chromosomes to separate from one another to opposite poles. This results in each chromosome (made of 2 sister chromatids) from each homologous pair move to each pole of the cell
What happens during Telophase I?
The homologous chromosomes begin to uncoil and the spindle fibres disappear and the cytoplasm is divided and the nuclear membrane forms around each group of homologous chromosomes. Two cells are formed
What do the two new cells formed at the beginning of Telophase I contain?
One set of sister chromatids and is known as a haploid cell
What happens during Meiosis II?
The cell proceeds through Prophase II, Metaphase II, Anaphase II, and Telophase II
What is the result at the end of Meiosis II?
The daughter cells are haploid but contain single unreplicated chromosomes
What is the outcome of Meiosis?
The formation of genetically distinct distinct haploid gametes
What are the 2 ways that genetic variation is ensured?
By the creation of Gametes that that carry different variations of maternal and paternal chromosomes and by the exchange of genetic material between maternal and paternal chromosomes
How does independent assortment take place?
During Metaphase I when chromosomes are arranged in a line next to their homologous pair, some maternal chromosomes are facing one way and some paternal chromosomes are facing the same or opposite way which results in variation
What is Crossing over?
When during Prophase I, homologous pairs exchange genetic information from their chromosomes
What is Nondisjunction?
When chromosomes or chromatids do not separate as they should during Meiosis?
Where does Nondisjunction occur?
At Anaphase I and II of Meiosis
How does nondisjunction occur in Anaphase I?
When homologous pairs are not separated to opposite pole and one pair is pulled toward the same pole together
How does nondisjunction occur in Anaphase II?
When sister chromatids do not separate to opposite poles and both sister chromatids are pulled toward the same pole together
What happens as a result of nondisjunction?
It produces gametes that have either too few or too many chromosomes
What is Monosomy?
When a chromosome is lost due to nondisjunction. So a Gamete is missing on chromosome of a homologous pair
What is Trisomy?
The gain of an extra chromosome
What are the products of meiosis?
Haploid Gametes
What is the process of sperm production called?
Spermatogenesis
What is the process of egg production called?
Oogenesis
What does the process of spermatogenesis begin with?
A diploid germ cell called a spermatagomium
What is a spermatogonium?
The diploid cell that spermatogenesis begins with
What stimulates the Spermatogonium to divide?
Puperty
How does the spermatogonia divide?
First it divide by Mitosis to form 2 daughter cells, one of which becomes a spermatogonium and the other becomes the primary spermatocyte
How does the Primary Spermatocytes divide?
It undergoes Meiosis I to form two secondary spermatocytes. The secondary spermatocytes then undergo Meiosis II to form spermtids
What are Spermatids?
The end process of Spermtogenesis
What happens after a spermatid is produced?
The nucleus and certain enzymes are arranged into a head region and the parts of the sperm develop
What does Oogenesis begin with?
A diploid germ cell called oogonium.
How does each Oogonium divide?
It undergoes mitosis to form two primary oocytes. This occurs before a baby is born
How long do the Primary Oocytes last?
Until puberty
What happens every month after puberty?
One primary oocyte undergoes meiosis
What is different between Spermatogenesis and Oogenesis?
Oogenesis involves unequal division of the cytoplasm called asymmetrical cytokinesis
What happens as a result of asymmetrical cytokinesis?
Because the cytoplasm is not equally divided at the end of Meiosis I, the cell that receives most of the cytoplasm called the secondary oocyte and the other cell is called the first polar body
What happens to the first polar body?
The first polar body may or may not go to through a second division but they cells degenerate anyways
What happens to the secondary oocyte?
It undergoes meiosis II and the cell that contains the most cytoplasm will become a mature egg. The second polar body degenerates
How many gametes are produced from Oogenesis?
1
How many years separates Meiosis I and Meiosis II in women?
About 10 years
What state is the primary oocytes suspended in?
Prophase I until puberty. Hormones signal one oocyte to continue a month
Where is the secondary oocyte suspended at?
Metaphase II until it comes into contact with sperm
