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Biology > Unit 1.6 - Meiosis + Mitosis > Flashcards

Unit 1.6 - Meiosis + Mitosis Flashcards

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1
Q

When do chromosomes become visible?

A

Only at the onset of cell division

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2
Q

Before cell division begins, what do DNA molecules do?

A

Make copies of themselves

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3
Q

What are chromatids?

A

2 identical DNA threads that lie parallel to each other

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4
Q

Where are chromatids joined?

A

Only in specialized regions called the centromere

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5
Q

How many chromosomes do humans have?

A

46 homologous pairs
- Called the diploid number

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6
Q

Where do humans get their chromosomes from?

A

Gametes, 23 from mom and 23 from dad
- Called the haploid number

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7
Q

What does mitosis produce?

A

Two genetically identical daughter cells

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8
Q

What are the cell cycles of mitosis?

A

Prophase
Metaphase
Anaphase
Telophase
- THERE IS NO INTERPHASE IN MITOSIS

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9
Q

What occurs during the interphase of the cell cycle? [7]

A
  • Replication of DNA
  • Replication of organelles which have their own DNA e.g mitochondria and chloroplasts
  • Making new organelles
  • Synthesis of ribosomal material
  • Synthesis of ATP
  • Synthesis of proteins
  • Increase in cell size (NOT GROWTH)
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10
Q

Describe Prophase in MITOSIS

A
  • First stage
  • DNA condenses forming chromosomes
  • Chromatids are visible
  • chromosomes are already duplicated and each ‘X’ is composed of sister chromatids joined at the centromere
  • nuclear membrane breaks down
  • centrioles migrate to the poles of the cell, creating the mitotic spindle
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11
Q

Describe metaphase in MITOSIS

A
  • chromosomes line up on the metaphase plate which is half way between the 2 poles
  • the chromosomes are joined to the spindle by kinetochores
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12
Q

Describe anaphase in MITOSIS

A
  • Very rapid stage
  • Centromere splits
  • Spindle fibers contract
  • Chromatids separate and are pulled to opposite poles in the cell
  • The centromere leads the way
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13
Q

Describe telophase in MITOSIS

A
  • Final stage
  • Chromatids have reached the poles of the cells and are referred to as chromosomes again
  • Chromosomes uncoil and lengthen
  • Spindle breaks down
  • Nucleolus reappears and the nuclear membrane reforms
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14
Q

How does cytokinesis occur in animal cells?

A

Occurs by constriction of the center of the parent cell from the outside inwards.

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15
Q

How does cytokinesis occur in plant cells?

A

A cell plate forms across the equator of the parent cell from the center outwards and a new cell wall is laid down.

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16
Q

Why is DNA doubled during the interphase?

A

To ensure that DNA content is maintained after cytokinesis

17
Q

Why is mitosis essential?

A
  • Growth and repair
  • Replacement of dead or worn out tissues
  • Asexual reproduction
18
Q

What is an advantage [2] and a disadvantage [1] of asexual reproduction?

A
  • Offspring are genetically identical to the parent
  • The ability to increase numbers quickly and to take advantage of an ideal environment
  • Lack of genetic variation leading to the inability to adapt to environmental changes
19
Q

What is a result of uncontrolled mitosis?

A

Cancer.
- Cancerous cells divide repeatedly out of control with the formation of tumors.
- Tumors prevent the normal function of body organs
- Cancers are inherited when mutations occur in genes that control cell division

20
Q

Describe prophase I in MEIOSIS

A
  • The same as prophase in mitosis
  • However the chromatids are joined at the chiasmata (chromosomes are half paternal and half maternal)
  • At the chiasmata the chromatids may break and recombine with different but equivalent chromatids
  • This swapping of chromosomes is called crossing over and is a source of genetic variation
21
Q

Describe metaphase I in MEIOSIS

A
  • Homologous chromosome arrange themselves randomly on the equator of the spindle
  • Chance determines how the homologous chromosomes are arranged on the equator
  • This random distribution and consequent independent assortment of chromosomes produces new genetic combinations
  • The homologs remain in their bivalente pairs at this stage
22
Q

Describe anaphase I in MEIOSIS

A
  • Very rapid state
  • Spindle fibers contract
  • Chromosomes in each bivalent separate and are pulled to opposite poles of the cell
  • Random arrangement of homologous pairs at the metaphase I means that each pole has a random mixture of paternal and maternal chromosomes
23
Q

Describe telophase I in MEIOSIS

A
  • Marks the end of the first meiotic division
  • Chromosomes have reached opposite poles
  • Nuclear envelope reforms around each group of haploid chromosomes
  • THE CHROMOSOMES REMAIN IN THEIR CONDENSED FORM
  • In animal cells cytokinesis occurs after this phase
24
Q

Describe prophase II in MEIOSIS

A
  • In animal cells the new spindle develops at right angles to the old spindle
  • Many plant cells do not need to form a new spindle as the old one remains
25
Q

Describe metaphase II in MEIOSIS

A
  • Chromosomes line up separately on the spindle fibers at the equator
  • Each chromosome is attached to the spindle by its centromere
26
Q

Describe anaphase II in MEIOSIS

A
  • Spindle fibers contract
  • Centromere splits
  • Chromatids are pulled to opposite poles
27
Q

Describe telophase II in MEIOSIS

A
  • On reaching the poles the chromatids lengthen and are indistinct
  • The spindle disappears
  • Nuclear membrane reforms
  • End of telophase II, cytokinesis takes place
28
Q

Compare mitosis and meiosis [5 differences]

A

Mitosis is one division resulting in 2 daughter cells
Meiosis is two divisions resulting in 4 daughter cells
Mitosis has a number of chromosomes unchanged
Meiosis has a number of chromosomes halved
Mitosis - homologous chromosomes do not associate in pairs
Meiosis - homologous chromosomes pair up to form bivalents
Mitosis crossing over does NOT occur
Meiosis crossing over DOES occur and chiasmata forms
Mitosis daughter cells are genetically identical (no genetic variation)
Meiosis daughter cells are genetically different

Biology (7 decks)

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