12. Meiosis

Life Cycle of Sexual Reproducers

In a tube-within-a-tube body plan, what is the interior tube derived from?
a. ectoderm
b. mesoderm
c. the coelom
d. endoderm

 No. At this point in the cell cycle, a cell would contain 92 chromosomes. 

 all gamete-producing cells after meiosis I 

 No. Cells are haploid at the end of meiosis I. 

Consider somatic cells.

Humans have 46 chromosomes. This number of chromosomes will be found in __________.

Types of Reproduction: Sexual versus Asexual Reproduction - iBiology & Youreka Science

GCSE Biology - Sexual vs Asexual Reproduction - What is Asexual Reproduction?  #71

True or false? New major animal body plans have continued to evolve since the Cambrian about 550 million years ago.

 No. Haploid gametes contain one chromosomal set. 

 No. Usually, human cells are not triploid. 

Contrast somatic cells with gametes.

Somatic cells in humans contain __________ set(s) of chromosomes and are therefore termed __________.

 gametes never resemble spores morphologically 

 No. This is not the basis of the distinction between the two. 

 gametes are always haploid whereas spores are diploid 

 only the formation of gametes contributes to genetic variation 

 No. Each cycle of chromosome halving and doubling contributes to genetic variation among offspring. 

 gametes are derived directly from sporophytes to form gametophytes 

 No. Sporophytes make spores by undergoing meiosis, and the spores divide by mitosis to form multicellular gametophytes. The gametophytes then make gametes by mitosis. 

 gametes can fuse to form a zygote, but spores can develop into independent organisms without first forming a zygote 

Consider the differences between plant and animal life cycles.

Spores and gametes are different in that __________.

What happens during fertilization?

The egg (ovum) of a rabbit contains 22 chromosomes. How many chromosomes are in the somatic (body) cells of a rabbit?

 No. Although this may be the genetic complement of a haploid organism, it is not what is meant by the term. 

 No. The term does not refer to an abnormality. 

 its cells have half of one set of chromosomes 

 its cells have a single set of chromosomes 

Contrast haploid with diploid.

When we say that an organism is haploid, we mean that __________.

 No. Meiosis reduces the number of chromosomes, but mitosis has no effect on chromosome number. 

 No. Fertilization doubles the chromosome number, but mitosis has no effect on it. 

 No. Meiosis reduces the number of chromosomes, but interphase, which precedes meiosis, has no effect on it. 

 No. Meiosis II follows meiosis I; together the two phases of meiosis produce a net reduction in chromosome number. 

Consider what happens to the chromosome number in each of the events.

In sexually reproducing species, the chromosome number remains stable over time because __________ and __________ always alternate.

 No. This process does not affect chromosome number. 

 when DNA is replicated during the S phase of the cell cycle 

 No. DNA replication doubles the amount of genetic material in the cell, but it does not change the chromosome number. 

 No. This is the last stage of a process that results in the formation of two diploid daughter cells from a diploid parental cell. 

 No. Embryonic development does not occur until after the diploid state has been restored. 

Consider which of these events reflects a doubling in chromosome number.

Nearly all life cycles have both haploid and diploid phases. Usually, the transition from haploid to diploid takes place __________.

 No. Primates, like all animals, represent a multicellular diploid form. 

 No. Plants follow the life cycle called "alternation of generations." 

 No. Prokaryotes are unicellular and do not reproduce sexually. 

 No. Fish, like all animals, represent a multicellular diploid form. 

Review the various types of life cycles.

A life cycle in which the only multicellular form is haploid is most typical of __________.

 No. However, humans have 23 pairs of chromosomes. 

 No. However, humans have two sex chromosomes. 

 No. However, humans have a single pair of sex chromosomes. 

 It depends on the sex of the individual. 

 No. Both sexes have the same number of autosomal pairs. 

Consider how many pairs of chromosomes a human has and how many of these pairs are not autosomes.

How many pairs of autosomes do humans have?

 they both give rise to genetically distinct offspring 

 No. Sexual reproduction produces genetically distinct offspring, but asexual reproduction produces genetically identical offspring. 

 No. Sexual reproduction involves two parents, whereas asexual reproduction requires only one. 

 they both require meiosis to complete the reproductive cycle 

 No. Sexual reproduction depends on meiosis, but asexual reproduction only involves mitosis. 

 in both cases, every parent transmits all of its genes to its progeny 

 No. Although this is true of asexual reproduction, in sexual reproduction each parent transmits only half of its genes. 

 they can both occur in multicellular organisms 

Cells produced by sexual and asexual reproduction (zygotes and clones, respectively) often multiply by mitosis.

Sexual and asexual reproduction are alike in that __________.

Asexual and Sexual Reproduction

Mitosis, gamete formation, and fertilization.

Mitosis, meiosis, gamete formation, and fertilization.

All eukaryotic sexual life cycles include:a) Mitosis, gamete formation, and fertilization.b) Mitosis, meiosis, gamete formation, and fertilization.c) Mitosis, meiosis, and gamete formation.d) Mitosis, fertilization, and meiosis.e) Mitosis, meiosis, apoptosis.f) Gamete formation, meiosis, mitosis.

 No. Mitosis keeps the same number of chromosomes, so it does not produce gametes. 

 No. Mitosis distributes a copy of all of the chromosomes to the two new daughter cells, keeping the chromosome number constant. 

 No. Mitosis produces two identical copies of the chromosomes, so it does not contribute to genetic variability. 

Contrast meiosis with mitosis.

Which of the following is a function of mitosis in humans?

 Multicellular haploid stage (gametophyte) 

 No. This statement is true, but there is a better answer. 

 Multicellular diploid stage (sporophyte) 

 All of the listed responses are correct. 

Think about what reproductive features might alternate between generations.

Which of the following is part of the life cycle called alternation of generations?

 a haploid zygote in some life cycles and a diploid zygote in others 

 No. Fertilization always involves the fusion of gametes. 

 No. Fertilization always involves the fusion of gametes and does not result in a haploid zygote. 

 a diploid zygote, except during the gametophyte stage of alternation of generations 

 No. The gametophyte phase culminates in the production of gametes that fuse during fertilization. 

 a multicellular haploid organism in a life cycle with an alternation of generations 

 No. The multicellular haploid organism that is part of the alternation of generations life cycle is a gametophyte, not a zygote. 

Think about the similarities and differences among the different types of life cycles.

Fertilization produces __________.

No. Fucus is not limited to mitosis.

 both mitosis and meiosis but not fertilization 

 No. This statement is true, but there is a better response. 

 both mitosis and fertilization but not meiosis 

No. Fucus is not limited to these two processes.

What is the significance of the fact that Fucus is diploid and reproduces sexually?

The sexual cycle of the diploid, multicellular algal genus Fucus involves __________.

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