Meiosis: Process, Phases, and Genetic Variation Chapter 13 (copy)

What are gametes in animals?

Gametes are reproductive cells called sperm and eggs.

What is the process called when gametes unite to form a new individual?

Fertilization.

What is meiosis?

Meiosis is a nuclear division that leads to the halving of chromosome number.

Why must gametes contain half the chromosome number?

To ensure that the full chromosome number is restored at fertilization.

What are sex chromosomes and how do they differ between males and females in many animals?

Sex chromosomes determine the sex of the individual; females typically have two X chromosomes, while males have one X and one Y chromosome.

What are autosomes?

Autosomes are non-sex chromosomes.

What is a karyotype?

A karyotype identifies the number and type of chromosomes in an organism.

What are homologous chromosomes?

Chromosomes of the same type that contain the same genes in the same position but may carry different alleles.

What does ploidy refer to?

Ploidy indicates the number of complete chromosome sets in a cell.

What is the haploid number (n) in humans?

In humans, the haploid number (n) is 23.

What is the diploid number (2n) in humans?

The diploid number (2n) in humans is 46.

What happens to chromosomes just before meiosis begins?

Each chromosome in the diploid parent cell is replicated, resulting in two identical sister chromatids.

What is the significance of sister chromatids during meiosis?

Sister chromatids remain attached and are considered a single replicated chromosome.

How many cell divisions occur in meiosis?

Meiosis consists of two cell divisions.

What is the role of microtubules during meiosis?

Microtubules attach to kinetochores at the centromere of each chromosome to coordinate chromosome movement.

What is Meiosis I known as and what does it accomplish?

Meiosis I is known as a reduction division that reduces the chromosome number.

What is produced from a diploid cell after meiosis in most plants and animals?

A diploid cell produces four haploid daughter cells.

What is gametogenesis?

Gametogenesis is the process by which daughter cells become eggs or sperm.

What is a zygote?

A zygote is a diploid cell formed after fertilization, restoring the full complement of chromosomes.

What is a bivalent in meiosis?

A bivalent consists of four chromatids from two homologous chromosomes.

What is the significance of chiasma in meiosis?

Chiasma is the point where non-sister chromatids exchange genetic material during crossing over.

What percentage of spontaneous abortions in humans is due to polyploid zygotes?

10% of spontaneous abortions in humans are due to the formation of polyploid zygotes.

What happens during Early Prophase I of meiosis?

The nuclear envelope begins to break down, chromosomes condense, and the spindle apparatus begins to form. Homolog pairs come together in a pairing process called synapsis, resulting in a bivalent or tetrad.

What occurs during Late Prophase I?

Homologs begin to separate but remain attached at chiasmata. Crossing over occurs between homologous non-sister chromatids, producing chromosomes with a combination of maternal and paternal alleles.

What is the role of the synaptonemal complex during meiosis?

The synaptonemal complex holds homologs together during synapsis and disassembles in Late Prophase I, leaving homologs held together only at chiasmata.

What happens during Metaphase I of meiosis?

The paired homologs line up at the metaphase plate in a random alignment.

What occurs during Anaphase I?

Paired homologs separate and migrate to opposite ends of the cell.

What is the outcome of Telophase I in meiosis?

Homologs finish migrating to the poles of the cell, and the cell divides through cytokinesis.

What occurs between meiosis I and meiosis II?

No chromosome replication occurs.

What happens during Prophase II?

The spindle apparatus forms, and one spindle fiber attaches to the centromere of each sister chromatid.

What occurs during Metaphase II?

Replicated chromosomes line up at the metaphase plate.

What happens during Anaphase II?

Sister chromatids separate, and the resulting daughter chromosomes begin moving to opposite sides of the cell.

What is the outcome of Telophase II?

Chromosomes arrive at opposite sides of the cell, a nuclear envelope forms around each haploid set of chromosomes, and each cell undergoes cytokinesis.

What is a bivalent or tetrad in meiosis?

A structure formed during synapsis that consists of two homologous chromosomes.

What are chiasmata?

Points where homologous chromosomes remain attached during meiosis, allowing for crossing over.

What is crossing over?

The exchange of genetic material between homologous non-sister chromatids during Late Prophase I.

What is the significance of random alignment during Metaphase I?

It contributes to genetic variation by ensuring that the distribution of maternal and paternal chromosomes to daughter cells is random.

What is cytokinesis?

The process by which the cell divides its cytoplasm and organelles to form two daughter cells.

What is the difference between sister chromatids and homologous chromosomes?

Sister chromatids are identical copies of a chromosome connected by cohesions, while homologous chromosomes are non-identical pairs, one from each parent.

What is the role of the spindle apparatus in meiosis?

It helps separate chromosomes during the various stages of meiosis by attaching to the centromeres and pulling them to opposite poles.

What is the chromosome total and chromatid total expected in the in-class assignment for Lecture 28?

Chromosome total = 828, and chromatid total = 1265.

What are the main differences between mitosis and meiosis in terms of daughter cells produced?

Mitosis produces two diploid daughter cells, while meiosis produces four haploid daughter cells.

What are the key processes that promote genetic variation during meiosis?

Crossing over, independent assortment, and random fertilization.

What is crossing over in the context of meiosis?

Crossing over is the random separation of homologous chromosomes that results in a variety of combinations of maternal and paternal chromosomes.

How does independent assortment contribute to genetic variation?

Independent assortment ensures that each gamete is unique by randomly distributing maternal and paternal chromosomes.

What is the significance of random fertilization in genetic variation?

Random fertilization contributes to genetic diversity by ensuring that offspring are genetically different from their parents.

What is the relationship between meiosis and natural selection?

Natural selection acts on the genetic variation produced by meiosis and fertilization, affecting the fitness of organisms in their environment.

What is nondisjunction and how does it occur during meiosis?

Nondisjunction occurs when both homologs or sister chromatids move to the same pole during anaphase, leading to abnormal products.

What is trisomy 21 and how is it related to meiosis errors?

Trisomy 21, or Down syndrome, is caused by an extra copy of chromosome 21, often resulting from nondisjunction during meiosis.

Why are errors in meiosis more common in females?

Errors are more common due to the long wait for oocytes to complete meiosis, which can be up to 50 years.

How does maternal age affect the incidence of Down syndrome?

The incidence of Down syndrome increases with maternal age, with higher risks at older ages.

What is the paradox of sex in relation to meiosis?

Despite the advantages of asexual reproduction, sexual reproduction persists due to the evolutionary benefits of increased genetic variation.

Why is sexual reproduction considered to have a 2-fold cost?

Sexual reproduction has a 2-fold cost because only half of the offspring produced are capable of reproducing (the males).

What happens to primary oocytes during female embryonic development?

Primary oocytes enter meiosis I and arrest in prophase I until sexual maturity is reached.

What is the role of genetic recombination in meiosis?

Genetic recombination creates new combinations of alleles, promoting genetic diversity among gametes.

What does random union of gametes ensure for offspring?

It ensures that offspring will be genetically different from each other and from their parents.

What is the expected outcome of meiosis in terms of gamete composition?

Meiosis results in four gametes with different chromosome compositions from each other and from the parent cell.

What is the significance of the changes in chromosomes produced by meiosis?

These changes are significant for evolution via natural selection, as they provide the variation necessary for adaptation.

What is the effect of oogenesis on the timing of meiosis completion in females?

Oogenesis leads to a delay in meiosis completion, which can increase the risk of errors such as nondisjunction.

How does the process of meiosis differ from mitosis in terms of genetic outcome?

Meiosis results in genetic variation through processes like crossing over and independent assortment, while mitosis produces genetically identical cells.

What is the overall purpose of meiosis in organisms?

The overall purpose of meiosis is to produce gametes for sexual reproduction, promoting genetic diversity.

What is the Purifying Selection Hypothesis?

Natural selection against deleterious alleles, where asexual reproduction leads to the inheritance of damaged genes by all offspring, while sexual reproduction allows for the potential loss of these alleles.

How do sexually reproducing individuals benefit in terms of deleterious alleles?

They are likely to have offspring that lack deleterious alleles present in the parent.

What was the test conducted to compare asexual and sexual reproduction in daphnia?

The test compared the same genes in two species of daphnia, one reproducing sexually and the other asexually, revealing that asexually reproducing individuals contained many more deleterious alleles.

What is the Changing-Environment Hypothesis?

Offspring from sexual reproduction are genetically different from their parents, increasing their likelihood of survival and reproduction in changing environments.

What is a potential risk for asexually produced offspring in changing environments?

All asexually produced offspring are likely to be susceptible to new environmental strains.

What was the test involving C. elegans meant to compare?

The rate of sexual vs. asexual reproduction in changing versus non-changing environments.

What is the significance of chronic wasting disease in relation to genotype?

Deer with a particular genotype are four times less likely to contract CWD and live 8.2 months longer if infected.

Why has sexual reproduction not been eliminated despite its costs?

It provides evolutionary benefits such as not always inheriting deleterious alleles and allowing for variation that may resist evolving pathogens.

What are homologous chromosomes?

Pairs of replicated chromosomes that consist of one maternal and one paternal chromosome.

What is the difference between mitosis and meiosis in terms of chromosome number?

Mitosis involves a diploid parent cell and maintains the chromosome number, while meiosis reduces the chromosome number by half.

What does '2n' represent in genetics?

It represents the diploid number of chromosomes, where 'n' is the number of unique chromosomes.

What happens during chromosome replication in a diploid parent cell?

The chromosomes are duplicated, resulting in sister chromatids.

What is the outcome of meiosis in terms of genetic variation?

Meiosis results in genetically diverse gametes due to crossing over and independent assortment.

What is the significance of genetic variation in offspring?

It increases the chances of survival in changing environments and helps resist pathogens.

What is the role of natural selection in purifying selection?

Natural selection acts against deleterious alleles, promoting the survival of individuals with beneficial traits.

How does sexual reproduction contribute to evolutionary success?

It allows for genetic diversity, which can enhance adaptability to environmental changes.

What are sister chromatids?

Identical copies of a chromosome that are connected at the centromere after DNA replication.

What is the relationship between genetic variation and pathogen resistance?

Genetic variation in offspring may provide some individuals with resistance to rapidly evolving pathogens.

What is the implication of low vs. high rates of outcrossing in C. elegans?

Low rates of outcrossing may lead to less genetic diversity, while high rates can enhance adaptability in changing environments.

What is the impact of environmental changes on asexual vs. sexual reproduction?

Sexual reproduction tends to yield offspring that can better adapt to environmental changes compared to asexual reproduction.

What does 'n' represent in genetic terms?

It represents the haploid number of unique chromosomes in a gamete.