Meiosis & Genetic Diversity (College Board AP® Biology): Flashcards
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Define meiosis.
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Define meiosis.
Meiosis is a form of nuclear division that produces haploid gamete cells from a diploid cell, forming daughter cells with half the number of chromosomes of the parent.
Define haploid.
Haploid describes a cell that contains a single set of chromosomes, half the number found in a diploid parent cell.
How many divisions occur during meiosis, and what are they called?
Two divisions: meiosis I and meiosis II.
Why does meiosis help maintain the correct chromosome number in offspring?
Meiosis produces haploid gametes, so when two gametes fuse the resulting diploid zygote has the full chromosome number restored.
During prophase I, the exchange of genetic material between non-sister chromatids of homologous chromosomes is called over.
During prophase I, the exchange of genetic material between non-sister chromatids of homologous chromosomes is called crossing over.
What happens to homologous chromosomes during metaphase I?
Homologous pairs of chromosomes line up along the equator of the cell at the metaphase plate, with spindle fibers attached to their centromeres.
What is separated during anaphase I of meiosis?
Homologous chromosomes are pulled to opposite poles, while the sister chromatids remain attached (the centromeres do not divide).
True or False?
DNA is replicated again between meiosis I and meiosis II.
False.
There is no interphase between the two divisions, so the DNA is not replicated before meiosis II.
What is separated during anaphase II of meiosis?
Sister chromatids are pulled apart to opposite poles of the cell, creating four groups of chromosomes.
At the end of meiosis, cytokinesis produces a total of haploid cells.
At the end of meiosis, cytokinesis produces a total of four haploid cells.
Define cytokinesis.
Cytokinesis is the division of the cytoplasm that separates a cell into daughter cells, distributing organelles between them.
How do mitosis and meiosis differ in the number and genetic content of the daughter cells produced?
Mitosis produces two diploid cells that are genetically identical to the parent.
Meiosis produces four haploid cells that are genetically different from the parent and each other.
True or False?
Mitosis and meiosis both use a spindle apparatus to move chromosomes.
True.
Both processes use a spindle apparatus to move chromosomes, but they differ in the number of cells produced and their genetic content.
What is the biological purpose of mitosis compared with meiosis?
Mitosis supports growth and replaces damaged cells by producing identical body (somatic) cells.
Meiosis produces genetically different gametes for sexual reproduction and genetic diversity.
What happens to homologous chromosomes during meiosis I?
Homologous chromosomes (one maternal and one paternal) pair up and then separate, so each resulting cell receives one chromosome from each pair, giving a haploid (1n) set.
What separates during meiosis II?
Sister chromatids of each chromosome separate, producing gametes that still contain a haploid set but now with one chromatid from each chromosome.
Define nondisjunction.
Nondisjunction is the failure of homologous chromosomes (in meiosis I) or sister chromatids (in meiosis II) to separate correctly, producing gametes with the wrong number of chromosomes.
True or False?
When nondisjunction occurs, the resulting gametes are still haploid.
False.
Nondisjunction produces gametes with too many or too few chromosomes (e.g. n+1 or n–1), so they are no longer haploid. This is called aneuploidy.
Which condition can result from a gamete carrying an extra chromosome 21?
Down syndrome (trisomy 21), caused by nondisjunction during meiosis.
Define crossing over.
Crossing over is the process by which non-sister chromatids of homologous chromosomes exchange alleles, increasing the genetic diversity of gametes.
Crossing over occurs during of meiosis I.
Crossing over occurs during prophase I of meiosis I.
Define chiasmata.
Chiasmata are the points at which non-sister chromatids cross over and become entangled during prophase I, where a section of chromatid may break and rejoin with another.
Define independent assortment.
Independent assortment is the random alignment of homologous pairs along the equator of the spindle during metaphase I, producing different combinations of alleles in the daughter cells.
True or False?
The orientation of one homologous pair during metaphase I affects the orientation of the other pairs.
False.
Each homologous pair aligns independently of the others, so the orientation of one pair does not affect any other pair.
How does random fertilization increase genetic variation?
During fertilization, any male gamete can fuse with any female gamete. This random fusion of gametes means each zygote has a unique combination of alleles, creating variation between zygotes.
The random fusion of a male and female gamete at fertilization produces a genetically unique .
The random fusion of a male and female gamete at fertilization produces a genetically unique zygote.
Name three processes in sexual reproduction that increase genetic variation.
Crossing over
Independent assortment (random assortment of chromosomes during meiosis)
Random fertilization of gametes
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