Ch. 5.5 Meiosis Flashcards
Why does Meiosis occur?
To produce gametes and gemetes are haploid
What cells undergo Meiosis?
Germ cells in testis or ovary (in mammals)
What is the resulf of Meiosis in humans?
Sperm and eggs are results; Sperm fetilize egg to produce zygote which is the first stage of eukaryotes)
What divisions does Meiosis involve?
Meiosis l and Meiosis ll
When does DNA replicate?
Only before Meiosis l
What does Meiosis l do?
Meiosis l separates homoglous paris
What does Meiosis ll do?
Meiosis ll separates sister chromatids
What is the result when Meiosis is complete?
The result is one diploid cell becomes one haploid egg and four haploid sperms
When does male begin to produce sperms and how many gemates do males produce?
Males begin to produce sperms during puberty and it continues through life of their time; Males produce milliions gemates per day
When does female begin to produce egg and how many gemates do females produce
Females produce egg before birth and meiosis is completed when the egg is fertilized; Females produce one egg per month
What is prophase l?
Homologues begin to pair up and exchange segments (Crossing Over)
What is metaphase l?
The paired homologues chromosomes align at the equotorial plane
What is anaphase l?
Homologues separate from pairing and move to opposite poles
What is telophase l?
Individual chromosomes gather at each of two poles
What is prophase ll?
After a brief interphase with no DNA replication, new spindle
fibres form
What is metaphase ll?
The sister chromatids align at the equatorial plane
What is anaphase ll?
Sister chromatids separate from the pairing and move to
opposite poles
What is telophase ll?
Individual chromosomes gather at each of the two poles, and a
new nuclear envelope form
Where do crossing over occur?
between two non-sister chromatids of
homologous chromosomes
How does crossing over occur and what is the result of crossing over?
The chromatids break in the same place and a section of each
chromosome is swapped with the other
The result is a hybrid chromosome
How is homologous paired?
The pairing is held together by the cohesin between sister chromatids
and the cross-overs
What is independent assortment?
the process where the chromosomes move randomly to separate poles during meiosis as a result in gemate
What are two unique features of meiosis that are not found in mitosis?
- Synapsis 2. Reduction division
What is synapsis?
The process of drawing together homologous
chromosomes down their entire lengths so that crossing over
can occur
What is reduction division?
Because meiosis involves two nuclear divisions but only one
replication of DNA, the final amount of genetic material passed
to the gametes is halved (2n–>n)
What are 3 mechanisms that help genetic variety through sexual reproduction?
- Independent assortment
- Crossing over
- Random fertilization—one of 8 million different sperm can fertilize
the egg
