Campbell Biology Chapter 10: Meiosis, Sexual Life Cycles & Genetic Variation

What are genes?

Units of heredity made up of segments of DNA.

How are genes passed to the next generation?

Via reproductive cells called gametes (sperm and eggs).

What is the total number of chromosomes in human somatic cells?

46 chromosomes.

What is a karyotype?

An ordered display of the pairs of chromosomes from a cell.

What are homologous chromosomes?

Chromosomes in a homologous pair that are the same length and shape and carry genes controlling the same inherited characters.

What determines the sex of an individual in humans?

The sex chromosomes, X and Y.

What is the diploid number of chromosomes in humans?

46 (2n = 46).

What is a haploid cell?

A cell that contains a single set of chromosomes.

What is the haploid number of chromosomes in humans?

23 (n = 23).

What is fertilization?

The union of gametes (the sperm and the egg).

What is a zygote?

The fertilized egg that is diploid, having one set of chromosomes from each parent.

What process produces haploid gametes?

Meiosis.

What is the role of mitosis in the human life cycle?

To produce somatic cells from the zygote and develop into an adult.

What is a clone?

An individual or group of genetically identical individuals produced asexually.

What is the difference between asexual and sexual reproduction?

Asexual reproduction involves one parent passing all genes, while sexual reproduction involves two parents contributing unique gene combinations.

What is the significance of meiosis in sexual life cycles?

Meiosis alternates with fertilization to maintain a constant chromosome number in a species.

What happens to chromosomes during DNA synthesis?

Each chromosome is replicated, resulting in two identical sister chromatids.

What are autosomes?

The 22 pairs of chromosomes in humans that are not sex chromosomes.

What is the role of gametes in the life cycle?

Gametes are the only types of human cells produced by meiosis and are involved in fertilization.

What occurs at sexual maturity in humans?

The ovaries and testes produce haploid gametes.

How do offspring acquire genes from their parents?

By inheriting chromosomes from both parents.

What is the relationship between meiosis and genetic diversity?

Meiosis creates unique combinations of genes, contributing to genetic diversity in offspring.

What is the main purpose of sexual reproduction?

To produce offspring with genetic variation.

What is the significance of the alternation of meiosis and fertilization?

It ensures the maintenance of chromosome number across generations.

What is the outcome of fertilization?

The formation of a diploid zygote.

What type of cells undergo mitosis?

Somatic cells.

What is the function of sister chromatids?

They are identical copies of a chromosome that are separated during cell division.

What is alternation of generations?

A life cycle that includes both a diploid and haploid multicellular stage.

What is the diploid organism in the alternation of generations called?

Sporophyte.

How does a sporophyte produce haploid spores?

By meiosis.

What does each haploid spore grow into?

A haploid organism called a gametophyte.

How are haploid gametes produced by a gametophyte?

By mitosis.

What is the result of fertilization of gametes?

A diploid sporophyte.

In most fungi and some protists, what is the only diploid stage?

The single-celled zygote.

How does the zygote produce haploid cells?

By meiosis.

What type of organism does each haploid cell grow into?

A haploid multicellular organism.

What is produced by the haploid adult?

Gametes by mitosis.

What is the key difference between haploid and diploid cells in terms of division?

Only diploid cells can undergo meiosis.

What is the primary outcome of the three types of life cycles?

Genetic variation among offspring.

What precedes meiosis?

Duplication of chromosomes.

How many sets of cell divisions occur in meiosis?

Two sets: meiosis I and meiosis II.

What is the result of the two meiotic divisions?

Four daughter cells, each with half the number of chromosomes as the parent cell.

What happens to homologous chromosomes during the first meiotic division?

They pair and separate.

What occurs during crossing over in Prophase I?

Nonsister chromatids exchange DNA segments.

What is formed at the metaphase plate during Metaphase I?

Homologous pairs of chromosomes line up.

What happens during Anaphase I?

Pairs of homologous chromosomes separate.

What is the outcome of Telophase I and Cytokinesis?

Two haploid daughter cells are formed.

What is the role of the spindle apparatus in Prophase II?

It forms to assist in chromosome movement.

How are sister chromatids arranged during Metaphase II?

At the metaphase plate.

What is a key feature of sister chromatids in Metaphase II?

They are no longer genetically identical due to crossing over.

What happens to sister chromatids during Anaphase II?

They separate and move toward opposite poles.

What occurs during Telophase II?

Four haploid cells are produced.

What occurs during Anaphase II of meiosis?

The sister chromatids separate and move toward opposite poles as individual chromosomes.

What happens during Telophase II and Cytokinesis?

Nuclei form, chromosomes begin decondensing, resulting in four genetically distinct daughter cells with haploid sets of unduplicated chromosomes.

What is synapsis in Prophase I?

The association of two homologous chromosomes along their length, forming a zipper-like structure called the synaptonemal complex.

What is crossing over?

The exchange of DNA segments between maternal and paternal chromatids during Prophase I, creating recombinant chromosomes.

How many cells does meiosis produce?

Meiosis produces four cells.

What is the primary difference between meiosis and mitosis?

Meiosis reduces the number of chromosome sets from two to one and produces genetically different cells, while mitosis conserves the number of sets and produces identical cells.

What are the three unique events of meiosis?

1. Synapsis and crossing over in Prophase I, 2. Alignment of homologous pairs at the metaphase plate in Metaphase I, 3. Separation of homologs during Anaphase I.

What happens to sister chromatids during meiosis I?

Sister chromatids stay together due to sister chromatid cohesion.

How does independent assortment contribute to genetic variation?

Homologous pairs of chromosomes orient randomly at Metaphase I, sorting maternal and paternal homologs independently into daughter cells.

What is the formula for the number of combinations possible due to independent assortment?

2^n, where n is the haploid number of chromosomes.

How many possible combinations of chromosomes exist for humans due to independent assortment?

About 8.4 million combinations.

What is the role of random fertilization in genetic variation?

Random fertilization allows any male gamete to fuse with any female gamete, contributing to genetic diversity.

How many diploid combinations can result from the fusion of gametes in humans?

About 70 trillion diploid combinations.

What is the significance of genetic variation in populations?

Genetic variation is crucial for natural selection and adaptation to changing environments.

What is the original source of genetic diversity?

Mutations in an organism's DNA.

What are alleles?

Different versions of genes created by mutations.

What contributes to genetic variation during sexual reproduction?

Independent assortment, crossing over, and random fertilization.

What happens to chromosomes during crossing over?

Chromosomes combine DNA from both parents, producing new combinations of alleles.

What is the evolutionary significance of sexual reproduction?

It contributes to genetic variation, which is essential for evolution and adaptation.