Meiosis

Are the g̲e̲n̲e̲s̲ on a recombinant chromatid the same as the original chromatid?

Yes, each chromosome in the homologous pair contains the same genes in the same place on the chromosome, so a switch between chromosomes would not affect the genes present.

After fertilization, what is the name given to the cell produced by the fusion of the two cells via fertilization?

Zygote

Diploid vs. Haploid

Cells with a full set of chromosomes are referred to as 𝙙𝙞𝙥𝙡𝙤𝙞𝙙 or 2𝙣, whereas cells with half the chromosomes are 𝙝𝙖𝙥𝙡𝙤𝙞𝙙 or 𝙣.

When the chromosomes come together as homologous pairs, the arms of the sister chromatids may cross over. What are these crossover points called?

Chiasma

After cytokinesis, how many cells have been formed from the parent cell?

4

If there were three sets of homologous chromosomes in the cell in Model 5, how many possible arrangements would there be for the tetrads in late prophase I?

8 (2x2x2=8)

what event must take place during interphase before a cell proceeds to division?

DNA replication

What is the 𝙥𝙡𝙤𝙞𝙙𝙮 of the zygote produced by fertilization-haploid or diploid?

Diploid

How does 𝙖𝙣𝙖𝙥𝙝𝙖𝙨𝙚 𝙄𝙄 differ from anaphase I?

During anaphase I, whole chromosomes are pulled to opposite sides of the cell. During anaphase II, the chromosomes are split and sister chromatids are pulled to opposite sides of the cell.

Why do you think egg cells are large and sperm cells are small?

Egg cells have the potential to grow into an organism, so they need the nutrients and supplies from the cytoplasm to do so. Sperm cells only need to transfer genetic material to an egg cell, so they do not require any additional materials.

In meiosis I, during anaphase I, which structures separated-homologous chromosomes or sister chromatids?

Homologous chromosomes

What would the ploidy of the zygote be if egg and sperm were produced by mitosis rather than meiosis? How would this affect the ploidy of each successive generation?

If the egg and sperm were produced by mitosis, each would be diploid so the zygote would be tetraploid (four sets of chromosomes). If this tetraploid organism produced tetraploid egg and sperm, the next generation would be octoploid (eight sets of chromosomes), and this doubling would continue with each generation.

How does anaphase I in meiosis differ from anaphase in mitosis?

In mitosis, sister chromatids are pulled apart in anaphase. In meiosis, homologous chromosomes are pulled apart (sister chromatids stay together) in anaphase I of meiosis.

Are the a̲l̲l̲e̲l̲e̲s̲ on a recombinant chromatid the same as the original chromatid?

No, the chromosomes in the homologous pair can have different alleles for each gene, so a switch in a portion of the chromosome would affect the information in that chromatid.

Considering the genetic makeup of the homologous pairs, will the cells at the end of telophase be genetically identical to each other?

No, they will not be genetically identical to each other because the homologous pairs separated and the alleles on each homologous pair are not necessariIly identical.

For the female cell, proceed through meiosis until you reach the end of anaphase I. Up to this point, did you notice any differences between the development of male and female gametes?

No. Meiosis has so far proceeded the same way as in male cells.

What is the name given to the female cells that is not fertilized.

Polar body

How do the random distribution of chromosomes and crossovers create more variation in the resulting gametes?

Random distribution of chromosomes allows for different combinations of chromosomes in the resulting gametes (here it brings the possible gamete total from two to four). Crossovers further randomly mix up the alleles that each gamete would receive, creating almost unlimited numbers of different combinations.

What phrase 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 I in females?

Secondary oocyte

What is the name given to the cells produced at the end of meiosis I in males?

Secondary spermatocyte

Describe what happens to the chromatids during crossover.

Sections of the homologous pair switch places on the chromatids.

In meiosis II, during anaphase II, which structures separated-homologous chromosomes or sister chromatids?

Sister chromatids

What two structures make up a single replicated chromosome?

Sister chromatids

At the end of meiosis II in males, what cells are produced?

Spermatid

Once the chromosomes have formed a pair, what are they called?

Tetrads

What happens to the cell at the beginning of interphase?

The cell grows and synthesizes mRNA and proteins

Why is it necessary for the cell to grow and duplicate its DNA before the start of meiosis?

The cell grows so that it has enough materials to undergo replication and duplicates its DNA so the daughter cells will receive the correct amount.

At the end of the meiosis II are four daughter cells. Are they haploid or diploid?

The cells are still haploid They each contain one chromosome (sister chromatid) from each homologous pair. Each chromosome contains a complete set of genes.

Proceed through telophase I and cytokinesis I. What do you notice about the size of the two resulting cells? (FEMALE)

The cells did not divide evenly. There is one large cell and one small cell.

Describe what would happen if cytokinesis did not occur.

The cells do not split in two. This would result in a cell with two nuclei and double the amount of genetic material.

Describe what would happen if the chromosomes did not attach to spindle fibers during metaphase I.

The chromosomes do not segregate properly. The daughter cells may have inconsistent or missing genetic material.

Describe what would happen if sister chromatids were not pulled apart at anaphase II.

The chromosomes do not segregate properly. The sister chromatids may end up in the same gamete, leaving some cells without a full complement of chromosomes.

the statement that explains the origin of the chromosomes found in the zygote.

The homologous pairs of chromosomes found in the zygote have come from each parent. One half of each pair is maternal in origin and the other half is paternal in origin.

How does this compare to the two cells at the end of telophase I and cytokinesis I in male cells?

The male cells divided evenly but the female cells did not.

Which of the statements below correctly describes the relationship between the cells at the end of meiosis II and the original cell?

The new cells have one copy of half of the genetic information in the original cell.

Which of the statements below correctly describes the relationship between the cells at the end of telophase I and the original cell?

The new cells have two copies of half of the genetic information in the original cell.

Describe what happens when you click on the chromosomes during telophase I.

The nuclear envelope reforms and the chromosomes begin to unravel

What must happen in the original cell so that each of the daughter cells has a complete set of 𝙘𝙝𝙧𝙤𝙢𝙤𝙨𝙤𝙢𝙚𝙨?

The orginial cell must copy it's DNA so that each of the daughter cells have a complete set of chromosomes.

Chromosomes are distributed randomly during anaphase I. What is/are the possible chromosome combination(s) in the two daughter cells?

any combination of green and purple

Anaphase I

diploid

Prophase I Diploid OR Haploid

diploid

metaphase I Diploid OR Haploid

diploid

telophase I

haploid

Are all of the cells the same size?

yes

calculate the number of possible genetic combinations in a human gamete due to independent assortment.

2²³ = 8,388,608 possible combinations

At the end of anaphase I (meiosis), how many chromosomes are on each side?

2

At the end of anaphase II, how many chromatids are on each side of the cell?

2

At the end of meiosis I, two cells have been produced. How many replicated chromosomes are in each of these cells?

2

explain how meiotic events, as well as the random fertilization of eggs and sperm, together lead to this genetic variation.

Independent assortment leads to multiple different maternal and paternal gene combinations being produced in the cells at the end of meiosis 1. Chiasma formation between homologous pairs of chromosomes leads to blocks of genes being swapped between nonsister chromatids during separation at anaphase 1. This leads to allele combinations on the chromosomes being shuffled and further varies the chromosomes that end up in egg and sperm after meiosis II 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.

At which stage in meiosis I do the pairs of homologous chromosomes come together?

Late Prophase I

What do these male cells (from the previous question above) eventually become?

Mature sperm

During fertilization which two cells come together?

Mature sperm and Secondary oocyte

During meiosis II, the secondary oocyte divides unevenly, with one cell (the ovum) receiving half of the chromosomes and nearly all the cytoplasm and organelles, while the other cell, the pola rbody, is much smaller and eventually degenerates. With your group, propose an explanation to explain why the secondary oocyte divides in this way.

The ovum will receive more organelles, such as mitochondria for making energy, which will provide the zygote with all of its cytoplasm and organelles (note that the sperm contains only scant cytoplasm, a few mitochondria and haploid chromosomes), but nuclear division is necessary to produce the correct number of chromosomes in the oocyte.

How do the chromosomes separate in anaphase I?

The pairs of homologous chromosomes are pulled apart and each intact chromosome pair is pulled to the opposite side of the cell.

Describe what would happen if meiosis occurred without DNA replication.

The parent cell does not start with enough DNA, so the gametes may be missing some or all of their genetic material.

Describe what happened during cytokinesis.

The ring shrinks, pinching the membrane inward. This splits the cell into two cells.

During sexual reproduction, two sex cells fuse to create a fertilized cell with a complete set of chromosomes. What must be true about the number of chromosomes in each sex cell?

The sex cells will have half the number of chromosomes as the fertilized cell.

what do the resulting cells look like (FEMALE)?

There is one big and three small cells.

Before prophase II begins, does the DNA in the cell duplicate itself?

no

During metaphase II, do homologous chromosomes pair up as in metaphase I?

no

According to Model 1, in what type of organs are the cells that enter meiosis I found?

ovaries and testies

what is the large cell called?

ovum (egg cell)

what are the small cells called?

polar bodies