Chapter 10 Flashcards
Define Meiosis
The type of nuclear divison that reduces the number of chromosomes from diploid to haploid numbers
In humans, what is the diploid, and the haploid number?
The diploid number is 2n, while the haploid number is n
What are gametes?
The reproductive cells~The sperm and egg
When gametes fuse, what is it call?
A Zygote
Does a zygote have a diploid, or a haploid number of chromosomes?
A Diploid number
In diploid body cells, how do chromosomes occur?
They occur in pairs
What are homologous chromosomes?
They are the members of the pair of chromosmes. They look alike, have the sme length and centromere position, as well as banding patterns (because they contain the same genes and traits)
Although the genes are the same in the homologous chromosomes, do they necessarily code for the same thing?
No. They could code for alternate forms of the gene
What are alternate forms of the gene called?
They are called alleles
Why does the zygote have two chromosomes of each kind?
Because there is one inherited from each parent.
How many divisions does meiosis require? What is the result?
It requires two nuclear divisons The result is four haploid daughter cells
What kinds of chromosomes do the daughter cells recieve? Do they necessarily need to be the same as the ones the parent has?
The daughter cells recieve one of each kind of parental chromosomes, but in different combinations. So no, they’re not necessarily identical to the parent cell
Prior to meiosis I, has DNA replication occured?
Yes, therefore each chromosome has two sister chromatids
What is synapsis?
It is the process by which the homologous chromosomes come together and line up side by side (due to an attraction)
What does synapsis result in?
A Bivalent (two) homologous chromosomes that stay close together during the first four phases of meiosis
What term can be used instead of bivalent?
Tetrad
What happens after synapsis?
The homologous pairs align at the metaphase plate and then the members of each pair separate
What does the separation of homologous chromosomes mean?
It means that only one duplicated chromosome from each homologous pair reaches a daughter nucleus
Is DNA replication done between meiosis I and meiosis II?
NO
During meiosis II, what happens?
Sister chromatids separate, becoming daughter chromosomes that move to opposite poles
What does meiosis provide a way to do?
I tprovides a way to keep the chromosome number constant
How do asexual organisms get genetic variations?
Usually through mutations
What are the two ways that meiosis brings genetic variation?
It brings genetic variatin via crossing over and independent assortments of homologous chromosomes
What does crossing over?
Crossing over is the exchange of genetic material between nonsister chromatids of a bivalent (homologous chromosomes) during meiosis I
What is the estimated number of crossing overs that occur per human chromosome?
2-3
What mechanism holds the homologous chromosomes together so they are aligned?
A nucleoprotein lattice
As a result of the nucleoprotein lattice, what can occur?
Crossing over
When the lattice holding the homologous chromosomes together breaks down, what temporarily holds the chromosomes together?
chiasmata regions where the nonsister chromatids are attached due to crossing over
After crossing over, are the chromatids held together by a centrosome identical?
No, they have different instructions (for the same genetic traits)
What is gene recombination?
It is the result of crossing over. Because of this, the offspring have different sets of genes than their parents
What happens during independent assortment?
The homologous chromosome pairs separate independently, in a random manner
When teh homologues align on the metaphase plate (after independent assortment), what pole are they oriented towards?
They are oriented towards either pole
Why is meiosis important?
It is important because it encourages genetic variation, which is very important in the long term survival of the species
How many phases of meiosis are there?
2
What happens in prophase I to the nucleus, centrosomes, and nucleolus?
A spindle forms as the centrosomes migrate away from one another. The nuclear envelope fragments, and the nucleolus disappears.
What happens to homologous chromosomes during prophase I?
The undergo synapsis to form bivalents. Crossing over between nonsister chromatids occur. Chromosomes condense
During metaphase I, what are the bivalents held together by?
They are held together by chiasmata
What happens during metaphase I?
The bivalents (held together by chiasmata) move towards the metaphase plate. The spindle has fully formed, kinetochores are seen, and the two kinetochores of a duplicated chromosome are attached to the kinetochore spindle fiber
What happens during anaphase I?
The homologues of each bivalent separate and move towards opposite poles. Sister chromatids ARE NOT separated. Each chromosome has two chromatids
Is the completion of telophase I necessary during meiosis?
No.
What happens during telophase I?
The spindle disappears, new nuclear evelops NEED NOT FORM.
Is telophase I accompanied by cytokinesis?
Not necessarily
What is interkinesis?
It is a process that is similar to interphase between mitotic divisions except DNA replication doesn’t occur
What is there at the beginning of meiosis II?
Two daughter cells contain the haploid number of chromosomes (one chromosome from each pair)
During metaphase II, what happens?
Chromsomes align at the metaphase plate, but DO NOT align in homologous pairs
During anaphase II, what happens?
sister chromatids separate, becoming daughter chromosomes that are not duplicated. Daughter chromosomes move toward the poles.
Telophase II and Cytokineses ~ What is the result after both of these
Foru haploid cells
What does meiosis result in plants?
spores
What are teh FUNDAMENTAL differences between meiosis and mitosis ( 4 of them)
1) Meiosis requires 2 nuclear divisons, while mitosis requires 1
2) Meiosis produces fourdaughter cells, while mitosis produces 2 daughter cells
3) The 4 daughter cells from meiosis are haploid,while the 2 daughter cells from mitosis are diploid
4) Mitosis produces identical daughter cells, while the daughter cells produced in meiosis are different
When does meiosis occur, compared to mitosis?
Meiosis occurs only at certain times in teh life of a sexually reproducing being, while Mitosis occurs a lot because it is needed for growth and repair
Prophase I vs. Prophase
Prophase 1- Pairing of homologous chromosomes
Prophase: No pairing
Metaphase I vs. Metaphase
Metaphase I-Bivaletns at metaphase plate
Metaphase- Duplicated chromosomes at metphase plate
Anaphase I vs Anaphase
Anaphase 1- Homologues of each bivalent separate and duplicated chromosomes move to poles
Anaphase: Sister chromatids separated, become daughter chromosomes that move to the poles
Telophase I vs Telophase
Telophase I- Two haploid daughter cells, not identical to the parent cell
Telophase- Two haploid daughter cells identical to the parent
Prophase II vs Prophase
Both have no pairing of chromosomes
Metaphase II vs Metaphase
Metaphase II- Haploid number of duplicated chromosomes at metaphase plate
Metaphase-Diploid number of duplicated chromosmes at metaphase plate
Anaphase II vs Anaphase
Anaphase II- Sister chromatids separate, become daughter chromosomes that move to the poles
Anaphase- Sister chromatids separate, becoming daughter chromosomes that move to the poles
Telophase II vs. Telophase
Telophase II- Four haploid daughter cells, not genetically identical
Telophase- Two diploid, genetically identical diploid cells
What does the term life cycle refer to?
All the reproductive events that occur from one generation to the next similar generation
What is the differnce between animal (humans as well) and plant life cyle?
The individual in animals is always diploids, and meiosis produces gametes,w hile in plants, they have haploid phase that alternates with diploid phase
What are the haploid/diploid generations known as in plants?
Gemetophyte (Haploid)- May be larger or smaller than the diploid generation
Diploid-Sporophyte
Name the process of meiosis in male and female animals?
Spermatogenesis and Oogenesis
What does spermatogenesis result in? Oogenesis?
4 sperm cells/1 egg, 3 polar bodies
