CH. 10 pt. 2 U5

ap bio

What is meiosis?

A type of nuclear division that reduces the chromosome number from diploid (2n) to haploid (n).

What does diploid (2n) refer to?

The total number of chromosomes in two sets, such as 46 chromosomes in humans.

What does haploid (n) mean?

A single set of chromosomes, which is half the diploid number, such as 23 chromosomes in humans.

What are gametes?

Reproductive cells (sperm and egg) that usually have the haploid number of chromosomes.

What is a zygote?

A diploid cell formed when haploid gametes merge during fertilization.

What is the consequence of not reducing the chromosome number during meiosis?

The chromosome number would double with each generation, leading to an unsustainable increase.

Who was Pierre-Joseph van Beneden?

A Belgian cytologist who first observed that gametes have a reduced chromosome number.

What are alleles?

Alternative forms of a gene that can produce variations in traits, such as hair color.

What happens during the S stage of the cell cycle?

DNA replicates, resulting in duplicated chromosomes composed of sister chromatids.

What is the purpose of the first division in meiosis?

To separate homologous pairs and reduce the chromosome number from 2n to n.

What occurs during the second division of meiosis?

The amount of DNA in n chromosomes is reduced to an appropriate amount for each gamete.

What is synapsis?

The process during meiosis I where homologous chromosomes come together and line up side by side.

What is a bivalent?

A structure formed during synapsis where homologous chromosomes are paired.

What is the end result of meiosis?

Four haploid gametes, each with n chromosomes.

What is the significance of homologous pairs in a zygote?

One chromosome of each pair is inherited from each parent, creating genetic diversity.

What is the role of meiosis in genetic variation?

it allows for the exchange of genes between homologous chromosomes, creating genetic mixtures.

How does meiosis contribute to evolution?

By generating genetic diversity through recombination and independent assortment of chromosomes.

What is the significance of the haploid number in gametes?

It ensures that when gametes fuse during fertilization, the resulting zygote has the correct diploid number.

What happens to the chromosome number in successive generations without meiosis?

The chromosome number would exponentially increase, leading to potential genetic instability.

How does meiosis differ from mitosis?

Meiosis involves two divisions and results in four haploid cells, while mitosis results in two diploid cells.

What is synapsis in meiosis?

The process where homologous chromosomes unite and stay in close association during the first two phases of meiosis I.

What happens to homologous pairs during meiosis I?

they align at the metaphase plate and then separate, reducing the chromosome number from 2n to n.

What is the significance of the bivalent in chromosome pairing?

It allows for genetic recombination through crossing-over between non-sister chromatids.

What is crossing-over?

An exchange of genetic material between non-sister chromatids of a bivalent during meiosis I.

What is independent assortment?

The random distribution of maternal and paternal chromosomes into gametes during meiosis.

What is the outcome of meiosis II?

Sister chromatids separate, resulting in four haploid daughter cells, each with a single chromatid.

What is parthenogenesis?

A form of asexual reproduction where new individuals are produced from unfertilized eggs.

What is the haploid number of chromosomes?

The number of chromosomes in a gamete, represented as n.

What occurs during the nucleoprotein lattice formation?

It holds the bivalent together during synapsis, allowing for proper alignment of homologous chromosomes.

How many crossovers typically occur during meiosis in humans?

An average of two to three crossovers occur between nonsister chromatids.

What happens to the chromosome number after meiosis I?

The chromosome number is reduced by half, resulting in haploid daughter cells.

What is the significance of the centromere count in meiosis?

It verifies the diploid number of chromosomes in the parent cell and helps track chromosome segregation.

What is the result of DNA replication before meiosis?

Each chromosome is duplicated and consists of two sister chromatids.

What is the fate of daughter cells in the plant life cycle after meiosis?

They become haploid spores that germinate to produce a haploid generation.

What happens to the genetic material during crossing-over?

Genetic material is exchanged between nonsister chromatids, leading to genetic recombination.

What is the relationship between meiosis and gamete formation?

Meiosis produces gametes, either sperm or eggs, which have half the chromosome number of the parent cell.

What is a potential disadvantage of parthenogenesis?

It may limit genetic variation, reducing the species' ability to respond to environmental changes.

How do some species, like honeybees, avoid the disadvantages of parthenogenesis?

By switching between parthenogenesis and sexual reproduction.

What is the significance of crossing-over in parthenogenic species?

It allows for some level of genetic variation despite being asexual.

How does parthenogenesis affect chromosome number before meiosis?

The species doubles the number of chromosomes, forming homologous pairs from a single parent.

How many possible combinations of chromosomes can be produced from a cell with three pairs of homologous chromosomes?

8 combinations (2^3).

What is the role of chiasmata during meiosis?

They are regions where nonsister chromatids are attached due to DNA strand exchange and crossing-over.