What is the diploid number of chromosomes in the organism represented in the diagram?
Click to see answer
2n = 6.
Click to see question
What is the diploid number of chromosomes in the organism represented in the diagram?
2n = 6.
What happens during Anaphase I?
Homologous chromosomes separate and move towards opposite poles, while sister chromatids remain attached at the centromere.
What happens to the nucleolus and nuclear envelope during prophase II?
They disintegrate.
How are spindle fibers attached to chromosomes during prophase II?
They are attached to the centromeres via the kinetochore.
What is the significance of crossing over in prophase I?
The sister chromatids of each chromosome will not be genetically identical.
What happens during anaphase II?
Centromeres divide, and sister chromatids separate and move towards opposite poles.
Why is it unlikely for two gametes to be genetically identical?
Due to the billions of sperm and hundreds of eggs produced, leading to vast genetic variation.
What do chromosomes decondense into during Telophase II?
Chromatin.
What occurs to the spindle fibers during Telophase II?
They disintegrate.
What structures reform during Telophase II?
The nuclear envelope and nucleolus.
What can result from non-disjunction during meiosis?
A change in chromosome number, leading to aneuploidy or polyploidy.
What happens to DNA prior to meiosis?
DNA is replicated during the S phase of interphase, resulting in chromosome duplication.
What is a diploid cell?
A cell with 2 sets of chromosomes (2n), one set from each parent.
What happens during fertilization in terms of chromosome number?
Haploid gametes fuse to restore the diploid number of chromosomes.
What happens to chromosomes during Telophase II?
Chromosomes reach opposite poles.
What occurs during Metaphase I of meiosis?
Pairs of homologous chromosomes (bivalents) are arranged along the equator (metaphase plate).
What replicates just before meiosis I in animal cells?
Centrioles.
How many daughter nuclei are formed at the end of Telophase II?
4 daughter nuclei.
How many cycles of nuclear and cell divisions are involved in meiosis?
Two cycles: Meiosis I and Meiosis II.
What are chromosomal aberrations?
Alterations in the structure or number of chromosomes, including numerical aberrations like aneuploidy and structural aberrations like translocation, duplication, inversion, and deletion.
How many chromosomes do human haploid sperm and ovum each contain?
23 chromosomes.
When does the number of DNA molecules per nucleus decrease?
When the nucleus has divided during telophase I and II or when the cell has divided during cytokinesis.
What occurs during crossing over?
There is a breakage and re-joining of DNA molecules in the non-sister chromatids, resulting in an exchange of genetic materials.
What occurs after telophase I in some species before meiosis II?
Cells enter a brief interphase.
What type of cells are formed at the end of cytokinesis in Telophase II?
4 haploid daughter cells (gametes).
What occurs during fertilization that contributes to genetic variation?
The random fusion of male and female gametes from each parent.
What is the result of the random fusion of gametes during fertilization?
A genetically variable zygote, leading to genetically variable offspring.
How are spindle fibers attached to chromosomes during Prophase I?
Spindle fibers are attached to the centromeres of the chromosomes via the kinetochore.
What structures are formed between non-sister chromatids during synapsis?
Chiasmata are formed between the non-sister chromatids of a pair of homologous chromosomes.
When does the number of chromosomes increase in meiosis?
When sister chromatids separate during anaphase II.
What is the outcome of crossing over?
New combinations of alleles in the non-sister chromatids, which become chromosomes of the daughter cells.
What is independent assortment in meiosis?
The random orientation of bivalents at the equator during metaphase I, leading to random separation of homologous chromosomes.
During which process does meiosis occur?
During the formation of gametes (e.g., sperm and ovum).
What is a gene mutation?
A change in the nucleotide sequence of a gene, which can involve substitution, addition, or deletion of nucleotides.
What is an example of numerical aberration?
Aneuploidy, such as trisomy 21 (Down syndrome).
What is the significance of meiosis in sexual reproduction?
It prevents the doubling of chromosomes by producing haploid gametes.
What shape characterizes the movement of sister chromatids during anaphase II?
A distinct 'V' shape.
What is the result of meiosis in terms of gametes?
Formation of haploid gametes due to the separation of homologous chromosomes during anaphase I.
What is the significance of chiasmata during Prophase I?
Chiasmata enable crossing over between non-sister chromatids.
During which stage of meiosis do homologous chromosomes pair with each other?
Prophase I.
In what form is DNA present during interphase?
Thread-like chromatin.
What is another term for meiosis?
Reduction division.
How do the daughter cells compare genetically to the parent cell?
Each daughter cell is genetically different from the parent cell and from each other.
What is the haploid number of chromosomes in humans?
How many possible combinations of chromosomes are there in human gametes?
2^23.
How does meiosis contribute to genetic variation?
Through processes like crossing over and independent assortment.
What is a bivalent (or tetrad) in Meiosis I?
A bivalent (or tetrad) is formed by a pair of homologous chromosomes.
What happens to the number of chromosomes per nucleus during cell division?
It decreases when the nucleus has divided during telophase I and II or when the cell has divided during cytokinesis.
What happens to the DNA content during meiosis?
It is halved during the formation of gametes.
How does the chromosome number change from the start of meiosis to the formation of gametes?
It decreases from 6 to 3.
What occurs during Telophase I?
Homologous chromosomes reach opposite poles, spindle fibers disintegrate, and the nuclear envelope reforms, resulting in 2 daughter nuclei.
What role do centrioles play during Prophase I?
Centrioles move to opposite poles and spindle fibers form.
What happens during prophase I of meiosis?
Homologous chromosomes pair up and exchange genetic material through crossing over.
What occurs during the S phase of interphase?
DNA replicates.
What are some symptoms of Cri du chat syndrome?
High-pitched cry, intellectual disability, delayed development, small head size, low birth weight, and weak muscle tone.
What is the formula for the number of possible combinations of maternal and paternal homologues?
2^n, where n is the number of homologous pairs.
What forms during prophase II in animal cells?
Centrioles move to opposite poles and spindle fibers form.
Where are chromosomes arranged during metaphase II?
Along the equator or metaphase plate.
What is the significance of the meiotic cell cycle?
It prevents the doubling of chromosomes in sexual reproduction and generates genetic variation.
What is synapsis in the context of Prophase I?
Synapsis is the process where homologous chromosomes pair up.
What is the outcome of meiosis?
Four genetically diverse haploid cells.
What can happen to homologous chromosomes during prophase I of meiosis?
They may become intertwined, leading to structural aberrations.
What is meiosis?
A type of nuclear division that forms 4 genetically different daughter nuclei, each with half the number of chromosomes of the parent cell.
What characterizes the shape of chromosomes during Anaphase I?
Chromosomes form a distinct 'V' shape with centromeres pointing towards opposite poles.
What is the ploidy of daughter nuclei formed at the end of meiosis I?
Haploid, with only 1 set of chromosomes.
What is the formula for the possible combinations of chromosomes in gametes due to independent assortment?
2^n, where n is the number of chromosomes per gamete.
What are the main stages of meiosis?
Meiosis I and Meiosis II, which include prophase, metaphase, anaphase, and telophase for each.
What contributes to the increase in genetic variation during fertilization?
Meiosis (crossing over and independent assortment) and random fusion of gametes.
What is the result of crossing over in terms of genetic variation?
Non-sister chromatids may contain new combinations of alleles due to the exchange of genetic materials.
What is the chromosome number before meiosis begins?
6 chromosomes.
What genetic disorder is caused by a deletion in chromosome 5?
Cri du chat syndrome.
What is independent assortment in the context of Metaphase I?
The direction in which each chromosome faces in a bivalent is independent of the other bivalents.
Is there DNA replication before meiosis II?
No, there is no S phase or DNA replication prior to meiosis II.
How does crossing over affect genetic variation?
It results in non-identical sister chromatids due to the exchange of genetic materials, increasing genetic variation.
What is produced at the end of the meiotic cell cycle?
Genetically variable gametes.
What is a haploid cell?
A cell with 1 set of chromosomes (n), such as gametes formed at the end of meiosis.
What are homologous chromosomes?
Pairs of chromosomes that come from each parent in a diploid cell.
What are the separated chromatids considered after anaphase II?
They are now considered individual chromosomes.
What forms during crossing over?
Chiasmata between homologous chromosomes.
What are homologous chromosomes?
Pairs of chromosomes that have the same size, with centromeres in the same position, and the same genes arranged in identical sequences.
What is the chromosome number in gametes after meiosis?
3 chromosomes.
What is non-disjunction in meiosis?
Failure in the separation of homologous chromosomes in anaphase I or sister chromatids in anaphase II.
What happens if maternal and paternal homologues contain different alleles?
Different combinations of homologues result in different combinations of alleles in the gametes.
What does ploidy level refer to?
The number of sets of chromosomes in the nucleus of a cell.
What happens to chromatin during Prophase I of Meiosis I?
Chromatin condenses into chromosomes, while the nucleolus and nuclear envelope disintegrate.
What would happen if meiosis did not occur before fertilization?
The fusion of male and female gametes would result in a doubling of the chromosome number for each successive generation.
What is crossing over in meiosis?
The exchange of genetic materials between non-sister chromatids of homologous chromosomes during prophase I.
What is the role of homologous chromosomes in meiosis?
They pair up during meiosis, allowing for genetic recombination and independent assortment.
How does meiosis generate genetic variation?
By creating new combinations of alleles in gametes.
When does the number of DNA molecules increase in a cell?
Only when DNA replicates during the S phase.
