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