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BSCI 1511 > Meiosis > Flashcards

Meiosis Flashcards

1
Q

How does genetic variation in gametes arise?

A

It arises from the independent assortment of chromosomes, crossing over, and random fertilization.

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2
Q

How does meiosis affect the number of chromosomes from parent to daughter cells?

A

Meiosis reduces the number of chromosome sets from diploid to haploid.

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3
Q

What is the role of gametes in plants and animals that reproduce sexually?

A

Reproductive cells called gametes are the vehicles that transmit genes from one generation to the next.

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4
Q

How do fertilization and meiosis cause unique offspring?

A

During fertilization, male and female gametes unite, passing genes from both parents to their offspring. Because genes are inherited from two parents, the offspring has a unique combination. This uniqueness is in large part due to meiosis followed by fertilization.

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5
Q

Are gametes diploid or haploid?

A

Haploid.

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6
Q

What is a karyotype?

A

A display of the chromosome pairs of a cell, arranged by size and shape.

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7
Q

Describe the characteristics of the human karyotype.

A

There are 46 chromosomes: 2 chromosomes of each of 23 types. The homologous chromosomes have the same length, centromere position, and gene arrangement.

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8
Q

What are autosomes?

A

The autosomes are the non-sex chromosomes (1-22).

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9
Q

What are homologous chromosomes?

A

A couple of homologous chromosomes are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. They have the same length, centromere position, and gene location (though the genes are not identical).

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10
Q

How do somatic cells reproduce?

A

In humans, somatic cells (2n) divide by mitosis and contain 23 pairs of chromosomes (46 in total)–a maternal set and a paternal set–and are diploid (2n).

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11
Q

How do germ cells reproduce?

A

In humans, germ cells (2n) divide by meiosis and result in gametes that contain a single set of chromosomes: gametes are haploid (n).

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12
Q

How does a zygote divide?

A

Through mitosis.

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13
Q

What are sister chromatids?

A

A sister chromatid refers to the identical copies formed by the DNA replication of a chromosome, with both copies joined together by a common centromere. In other words, a sister chromatid may also be said to be ‘one-half’ of the duplicated chromosome.

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14
Q

What is the difference between sister chromatids and non-sister chromatids?

A

Sister chromatids are the duplicated chromosome themselves, and they contain the exact same alleles. Non-sister chromatids are the chromatids of the homologous chromosome, and they may contain different alleles.

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15
Q

What happens in interphase?

A

In interphase (S phase), chromosomes duplicate, yielding sister chromatids.

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16
Q

What happens in prophase I?

A

The centrosomes move, the spindle forms, duplicated chromosomes pair, and crossing over happens.

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17
Q

What happens in metaphase I?

A

Pairs of homologous chromosomes attach to the metaphase plate. Independent assortment happens here.

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18
Q

What happens in anaphase I?

A

Homologous chromosomes separate and move toward opposite poles–the sister chromatids remain paired.

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19
Q

What happens in telophase I and cytokinesis?

A

The cytoplasm divides, and the cleavage furrow forms–each chromosome consists of two sister chromatids.

20
Q

What is the overall goal of meiosis I?

A

To separate homologous chromosomes.

21
Q

What is crossing over?

A

Crossing over is a mechanism by which you can add additional genetic variation because the chromosome from mom and the chromosome from dad are swapping information.

22
Q

What is independent assortment?

A

Independent assortment is the process where the chromosomes move randomly to separate poles during meiosis. A gamete will end up with 23 chromosomes after meiosis, but independent assortment means that each gamete will have 1 of many different combinations of chromosomes.

23
Q

In which phase of meiosis does the cell go from diploid to haploid?

A

Teleophase I/cytokinesis.

24
Q

Which processes in meiosis introduce genetic variation?

A

Crossing over and independent assortment.

25
Q

What happens in prophase II?

A

The spindle forms.

26
Q

What happens in metaphase II?

A

Chromosomes attach to the metaphase plate; because crossing over happened, the two sister chromatids are not identical.

27
Q

What happens in anaphase II?

A

Sister chromatids separate and move toward opposite poles.

28
Q

What happens in telophase II/cytokinesis?

A

Nuclei form, the chromosomes begin to decondense, cytokinesis occurs, and the cleavage furrow forms.

29
Q

Why are the sister chromatids not identical in metaphase II?

A

Crossing over made them non-identical.

30
Q

Why does crossing over happen?

A

Crossing over during prophase I produces recombinant chromosomes: individual chromosomes that carry DNA derived from two parents.

31
Q

What is a chiasma?

A

A chiasma is the point of contact, the physical link, between two chromatids belonging to homologous chromosomes. At a given chiasma, an exchange of genetic material can occur between both chromatids.

32
Q

In which phase does the breakdown of proteins holding sister chromatid arms together occur?

A

Anaphase I.

33
Q

What would the result be if crossing over did not occur?

A

If crossing over did not occur, when you separate the sister chromatids, they would be identical. Therefore, two of the haploid cells would be the same, and two wouldn’t

34
Q

What holds sister chromatids together?

A

Cohesins.

35
Q

What is the role of the synaptonemal complex?

A

It holds the homologs together, stabilizing them and allowing for chiasma formation and crossover. This alignment is called synapsis.

36
Q

How do enzymes play a role in crossing over?

A

Enzymes come in and break the DNA at a specific point in both sister chromatids. Because the cell wants to repair that point, parts from each chromatid cross over.

37
Q

How is the number of possible combinations for the assortment of chromosomes related to the diploid number of the organism?

A

The number of possible combinations increases with the diploid number of the organism and equals 2^n, where n is the haploid number. For humans, this is 2^23 (8.4 million possibilities).

38
Q

Determine if the event occurs in mitosis or meiosis: crossing over.

A

Meiosis

39
Q

Determine if the event occurs in mitosis or meiosis: homologous chromosomes pair at the metaphase plate.

A

Meiosis

40
Q

Determine if the event occurs in mitosis or meiosis: the production of diploid cells.

A

Mitosis

41
Q

Determine if the event occurs in mitosis or meiosis: the production of genetically identical cells.

A

Mitosis

42
Q

Determine if the event occurs in mitosis or meiosis: homologs separate.

A

Meiosis

43
Q

What does it mean when a fruit is parthenocarpic?

A

It means the fruit can develop without fertilization. The fruit is seedless, and propagation is via side shoots.

44
Q

What is the problem with commercial bananas?

A

The Cavendish strain is parthenocarpic, meaning that every plant is a clone; there is no genetic variation. The fungus “Tropical Race 4” is threatening the Cavendish with extinction.

45
Q

What does it mean to be triploid?

A

Two sets of chromosomes come from one original parent and one set from the other.

46
Q

Why don’t bananas form gametes?

A

Because they are triploid, homologous chromosomes cannot pair properly during metaphase I, and meiosis fails. So, no gametes are formed.

BSCI 1511 (32 decks)

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