Meiosis: how does sexual reproduction lead to genetic variation?
at the end of meiosis 1, two cells have been produced. How many replicated chromosomes are in each of these cells?
2
How many replicated chromosomes does the cell contain during prophase?
4
If there were three sets of homologous chromosomes in the cell, how many possible arrangements would there be for the tetrads in late prophase 1?
8
Calculate the number of possible genetic combinations due to independent assortment.
8,388,604
Consider what you already know about mitosis in cells, what event must take place during interphase before the cell proceeds to division?
DNA replication
Considering what you know about DNA replication and meiosis, is either arrangement equally likely during the formation of tetrads in late prophase 1?
DNA replication occurs randomly within the nucleus. when the homologous chromosomes come together as tetrads, they are just as likely to line up on one side of the cell as another.
At the end of meiosis 2 are four daughter cells. Are they haploid or diploid?
Haploid because there is half the original chromosome number. Each chromosome contains a complete set of genes.
Considering the genetic makeup of the homologous pairs, will the cells at the end of telophase 1 be genetically identical to each other?
No because the alleles on each homologous pair are not identical.
In what type of organs are the cells that enter meiosis I found?
Sex organs: ovaries/testes
Explain the origin of the chromosomes found in the zygote.
a zygote receives 46 chromosomes, however, 23 are supplied by the sperm and 23 from the egg. Homologous pairs are chromosomes that are identical. In the human cell, there are 23 pairs of homologous chromosomes.
Meiosis and sexual reproduction each lead to variation in the genetic make-up of every person. Explain how meiotic events, as well as the random fertilization of eggs and sperm, together lead to this genetic variation.
alleles combinations are of chromosomes are shuffled, and varies the chromosomes that end up in the egg and sperm after meiosis 2. Random fertilization of eggs and sperm means that when zygotes are formed, the gene combination will be different each time, even if they come from the same two parents
What are the cross over points called?
chiasma
What is the ploidy of the zygote produced by fertilization - haploid or diploid?
diploid
Cells with a full set of chromosomes are referred to as diploid or 2n, whereas cells with half the chromosomes are haploid or n. At which stage(s) of meiosis 1 are the cells diploid and at which stage(s) are they haploid?
diploid - prophase, metaphase, anaphase haploid- telophase after the cell splits
During meiosis 2, the secondary oocyte divides unevenly, which one cell (the ovum) receiving half of the chromosomes and nearly all the cytoplasm and organelles, while the other cell, the polar body, is much smaller and eventually degenerates. Explain why the secondary oocyte divides in this way.
fertilization is only possible for the one daughter cell that gets the most cytoplasm when meiosis has finished - the other polar bodies eventually disintegrates.
Before fertilization, what happens to the secondary oocyte?
goes through meiosis 2
In meiosis 1, during anaphase 2, which structures separated?
homologous chromosomes
At which stage in meiosis 1 do the pairs of homologous chromosomes come together?
late prophase 1
What do these cells (from the previous question) eventually become?
mature sperm
During fertilization which two cells come together?
mature sperm and secondary oocyte
Where did each of the cells come from that started meiosis 2?
meiosis 1
Are the genes on a recombinant chromatid the same as the original chromatid?
no because they have new DNA from the other chromatid.
Are the alleles on a recombinant chromatid the same as the original chromatid?
no they are mixed
At which stage of meiosis are the chromosomes?
prophase 1
What phase is used to describe the chromatids after crossing over takes place and the homologous chromosomes separate?
recombinant chromatids
What is the name given to the cells produced at the end of meiosis 1 in females?
secondary oocyte
What is the name given to the cells produced at the end of meiosis 1 in males?
secondary spermatocyte
In meiosis 2, during anaphase 2, which structures separated?
sister chromatids
What two structures make up a single replicated chromosome?
sister chromatids
At the end of meiosis 2 in males, what cells are produced?
spermatids
Once the chromosomes have formed a pair, what are they called?
tetrads
Describe what happens to the chromatids during crossover.
the chromosomes tetrad get some new DNA and keep some of their DNA.
Describe the relationship between the cells at the end of meiosis 2 and the original cell.
the new cells have one copy of half the genetic information in the original cell.
Describe the relationship between the cells at the end of telophase 1 and the original cell.
the new cells have two copies of half of the genetic information in the original cell.
What would the ploidy of the zygote be if the egg and sperm were produced by mitosis rather than meiosis? How would this affect the ploidy of each successive generation?
the ploidy of the zygote would be genetically identical to the parent cells. since mitosis doesn't reduce the number of chromosomes by half, each successive generation would have twice as many chromosomes as the last.
