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Chapter 11: Problem 28

How are spores produced in haploid-dominant and alternation of generation life cycles? a. by gametophytes b. by germ cells c. through mitosis d. through meiosis

Short Answer

Expert verified
Spores are produced through meiosis.

Step by step solution

01

- Understanding Life Cycles

First, recognize that 'haploid-dominant' and 'alternation of generation' refer to different types of life cycles in organisms. Haploid-dominant cycles are seen in organisms like fungi, while alternation of generations is observed in plants and some algae.
02

- Haploid-Dominant Life Cycle

In a haploid-dominant life cycle, the organism spends most of its life cycle in the haploid state. Spores are produced by meiosis in the diploid zygote. Therefore, in haploid-dominant organisms, spores are produced through meiosis.
03

- Alternation of Generations

In alternation of generations, organisms alternate between haploid gametophyte and diploid sporophyte phases. The sporophyte produces spores by meiosis. Thus, in alternation of generations, spores are also produced through meiosis.
04

- Analyzing Answer Choices

Choices (a) and (b) are incorrect because gametophytes produce gametes (not spores) and germ cells are involved in gamete formation. Choice (c) is incorrect because spores are not produced through mitosis. Thus, the correct answer is (d) through meiosis.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

haploid-dominant life cycle
A haploid-dominant life cycle is common in many fungi and some algae. In this type of life cycle, the organism mostly exists in a haploid state. The process begins with a diploid zygote, which undergoes meiosis to produce haploid spores. These spores then grow into mature haploid organisms. This means that meiosis is critical even though the organism spends very little time in the diploid phase. Remember, the diploid zygote is just a fleeting stage created by the fusion of haploid gametes. Once meiosis occurs, the cycle continues with the haploid individuals that populate the environment.
alternation of generations
The alternation of generations is a type of life cycle seen in plants and some types of algae. In this cycle, organisms switch between two stages: the haploid gametophyte and the diploid sporophyte.

  • The gametophyte stage produces gametes (sperm and eggs) through mitosis.
  • When these gametes fuse, they form a diploid zygote, starting the sporophyte stage.
  • The sporophyte undergoes meiosis to produce haploid spores, which then develop into new gametophytes.
These stages alternate consistently, hence the name 'alternation of generations.' This cycle allows for genetic diversity through sexual reproduction, while also enabling the organism to exploit different ecological niches.
meiosis
Meiosis is a key process in the life cycles of organisms that reproduce sexually. It ensures genetic diversity and maintains the stability of chromosome numbers across generations. Meiosis consists of two successive divisions: meiosis I and meiosis II.

  • Meiosis I: During this stage, homologous chromosomes pair up and exchange segments in a process called crossing over. This results in the separation of homologous chromosomes into different cells.
  • Meiosis II: The second division separates the sister chromatids, producing four haploid cells from the original diploid cell.

These haploid cells, when functioning as spores or gametes, are vital for the continuation of an organism's life cycle in both haploid-dominant and alternation of generations systems.

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Most popular questions from this chapter

Explain how the orientation of homologous chromosomes during metaphase I of meiosis contributes to greater variation in gametes. a. The random alignment of homologous chromosomes at the metaphase plate ensures the random destination of the chromosomes in the daughter cells. b. Because homologous chromosomes dissociate from the spindle fibers during metaphase I, they move randomly to the daughter cells. c. The homologous chromosomes are paired tightly during metaphase I and undergo crossover as the synaptonemal complex forms a lattice around them. d. Recombination of maternal and paternal chromosomes occurs in metaphase I because the homologous chromosomes are not connected at their centromeres.

What is a disadvantage of sexual reproduction over asexual forms of reproduction? a. Half the population is capable of carrying offspring. b. Identical offspring are not produced. c. Adaptation to rapidly changing environments is more difficult. d. Mutation rates are slower.

Describe what happens to the tetrads after they form. a. Prophase I of meiosis forms the tetrads. They line up at the midway point between the two poles of the cell to form the metaphase plate. There is equal chance of a microtubule fiber to encounter a maternally or a paternally inherited chromosome. Orientation of each tetrad is independent of the orientation of other tetrads. b. Prophase II of meiosis forms the tetrads. They line up at the midway point between the two poles of the cell to form the metaphase plate. There is equal chance of microtubule fiber to encounter maternally or paternally inherited chromosome. Orientation of each tetrad is independent of the orientation of other tetrads. c. Prophase I of mitosis forms the tetrads. They line up at the midway between the two poles of the cell to form the metaphase plate. There is equal chance of a microtubule fiber to encounter a maternally or a paternally inherited chromosome. Orientation of each tetrad is independent of the orientation of other tetrads. d. Prophase I of meiosis forms the tetrads. They line up at the midway between the two poles of the cell to form the metaphase plate. There is a chance of microtubule fiber to encounter maternally inherited chromosome. Orientation of each tetrad is independent of the orientation of other tetrads.

Which of the following distinguishes metaphase I from metaphase II? a. Metaphase I occurs when chromosomes appear in homologous pairs on the spindle. Metaphase II has a single line of chromosomes on the spindle. A Pair of chromosomes is pulled apart and migrate towards pole in anaphase I, while in anaphase II sister chromatids separate. Telophase I reconstitutes the nucleus and loosen the chromosomes, while telophase II mimics telophase I. b. Prophase I condenses the chromosomes and eliminates the nuclear membrane. The microtubules arrange in a spindle. Prophase II mimics prophase I. Metaphase I occurs when chromosomes appear in homologous pairs on the spindle. Metaphase II has a single line of chromosomes on the spindle. Pairs of chromosomes are pulled apart and migrate towards the poles during anaphase I, while in anaphase II sister chromatids separate. Telophase I reconstitutes the nucleus and condenses the chromosomes, while telophase II mimics telophase I. c. Prophase I condense the chromosomes and add nuclear membrane. The microtubules arrange in a spindle. Prophase II mimics prophase I. Metaphase I occurs when chromosomes appear in homologous pairs on the spindle. Metaphase II has a single line of chromosomes on the spindle. Pair of chromosomes are pulled apart and migrate towards the poles in anaphase I, while in anaphase II sister chromatids separate. Telophase I reconstitutes the nucleus and loosens the chromosomes, while telophase II mimics telophase I. d. Prophase I condenses the chromosomes and eliminates the nuclear membrane. The microtubules arrange in a spindle. Prophase II mimics prophase I. Metaphase I occurs when chromosomes appear in homologous pairs on the spindle. During Metaphase II, the chromosomes line up in a double line across the spindle. Each pair of chromosomes is pulled apart and migrate towards the poles in anaphase I, while in anaphase II sister chromatids separate. Telophase I reconstitutes the nucleus and loosen the chromosomes, while telophase II mimics telophase I.

At which stage of meiosis are sister chromatids separated from each other? a. anaphase I b. anaphase II c. prophase I d. prophase II
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