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Biology > Topic 4-Meiosis > Flashcards

Topic 4-Meiosis Flashcards

1
Q

What is a diploid cell?

A

-A cell containing two of each chromosome

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2
Q

What is the diploid number?

A

2n

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3
Q

What are alleles?

A

Chromosomes that make up each pair are the same size and have the same genes although they could have different versions of those genes.

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4
Q

What are homologous chromosomes?

A

Pairs of matching chromosomes that are the same size but could have different alleles

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5
Q

How many homologous pairs does a human have?

A

23 pairs

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6
Q

What is the diploid number for humans?

A

46

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7
Q

What are gametes?

A

The sperm cells in males and egg cells in females

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8
Q

Do gametes have a haploid number of cells or diploid?

A

Haploid

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9
Q

What is a zygote?

A

-In sexual reproduction two gametes join togther in fertilisation
-It then divides and devolps into a new organism

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10
Q

What happens during fertilisation?

A

-A haploid sperm fuses with a haploid egg
-This makes a cell with the normal diploid number of chromosomes
-Half of these chromosomes are from the father and are from the mother

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11
Q

Is fertilisation random in sexual reproduction?

A

-Yes
-Any sperm cell can fertilise an egg

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12
Q

What does random fertilisation produce?

A

Zygotes with different combinations of chromosomes from both parents

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13
Q

What is the effect of mixing genetic material in sexual reproduction?

A

-Increases genetic diversity within a species

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14
Q

Where does meiosis take place?

A

-In the reproductive organs of multicellular eukaryotic organisms

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15
Q

Cells that divide during meiosis are diploid, to begin with, but what are the cells that are formed from meiosis? Why?

A

-Haploid
-The chromosome number halves

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16
Q

Does meiosis in humans and mammals produce gametes directly?

A

Yes

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17
Q

In other organisms are gametes produced directly?

A

-No
-It produces haploid cells which later divide by mitosis to become gametes

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18
Q

Without meiosis what would happen when the gametes fused?

A

-You would get double the number of chromosomes

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19
Q

Step 1: What happens before meiosis starts?

A

-The DNA unravels and replicates so there are two copies of each chromosome called chromatids
(Organelles and centrioles replicate)

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20
Q

What happens during interphase 1?

A

-The cell grows, organelles are produced and the cell carries out its normal functions

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21
Q

How is DNA arranged in interphase?

A

-Long, diffuse (spread-out) and chromosomes are not visible

22
Q

What happens during prophase 1?

A

-The chromosomes condense and become fatter
-The chromosomes appear as a double structure consisting of 2 sister chromatids joined by a centromere
-Centrioles begin to migrate towards the poles
-The spindle fibres begin to form extending from the centrioles
-The nuclear membrane and nucleolus breaks down in late prophase/ early metaphase
-Homologous chromosomes come together to form a bivalent (synapsis)

23
Q

What happens during metaphase 1?

A

-Centrioles reach the poles
-Microtubules extend between centrioles to form spindle fibres
-Bivalents line up on the equator and attach to the the centromere
-One homologous chromosome is attached by microtubules to one pole and the other is attached to the opposite pole

24
Q

What is the product of meiosis?

A

-Four haploid cells that are genetically different from each other

25
Q

What are the two ways genetic variation is created in gametes?

A

-Crossing over of chromatids
-Independent segregation

26
Q

When does crossing over occur?

A

-During prophase one

27
Q

What happens during crossing over?

A

-The chromosomes in each homologous chromosome pair twist around each other
-Chromatids break and rejoin
-The chromatids still contain the same genes but now have a different combination of alleles

28
Q

What is the result of crossing over?

A

-The four daughter cells formed from meiosis 2 contain chromatids with different alleles

29
Q

What happens during independent segregation?

A

-The homologous pair contains one maternal chromosome and one paternal chromosome
-When the homologous pair is separated in meiosis 1, it is completely random which chromosome from each cell ends up in each daughter cell
-So the four daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes

30
Q

When does independent segregation occur?

A

-Metaphase 1

31
Q

What happens during anaphase 1?

A

-Spindle fibres connected to the chromosomes contract
-This causes homologous chromosomes to separate apart and are pulled to opposite poles
-Sister chromatids are kept together

32
Q

What happens during telophase 1?

A

-spindle fibres break down
-Nuclear membrane forms
-around each set of chromosomes so there are 2 nuclei
-Cytokinesis occurs and 2 new cells are formed when the membrane pinches inward

33
Q

What happens during prophase 2?

A

-The chromosomes condense and become fatter
-The chromosomes appear as a double structure consisting of 2 sister chromatids joined by a centromere
-Centrioles begin to migrate towards the poles
-The spindle fibres begin to form extending from the centrioles
-The nuclear membrane and nucleolus breaks down in late prophase/ early metaphase
-Chromatids become visible

34
Q

What happens in metaphase 2?

A

-Centrioles reach the poles
-Microtubules extend between centrioles to form spindle fibres
-Bivalents line up on the equator and attach to the the centromere
-One homologous chromosome is attached by microtubules to one pole and the other is attached to the opposite pole

35
Q

What happens in anaphase 2?

A

–Spindle fibres connected to the chromosomes contract
-This causes the centromeres to divide and sister chromatids separate creating two sister chromosomes
-Daughter chromosomes are pulled to opposite poles

36
Q

What happens in telophase 2?

A

-spindle fibres break down
-Nuclear membrane forms
-around each set of chromosomes so there are 2 nuclei
-Cytokinesis occurs and 2 new cells are formed when the membrane pinches inward
-Chromosomes uncoil to form chromatin

37
Q

What are centrioles?

A

-A pair of organelles that organises microtubules into spindle fibres on which chromosomes are separated when cells divide

38
Q

What is the centromere?

A

-The region of a chromosome that holds sister chromatids together until they are separated at the beginning of anaphase

39
Q

What is a chromatid?

A

-One of two identical threads of DNA that are joined at a centromere to form a complete chromosome after DNA replication
-After replication they become daughter chromosomes

40
Q

What is chromatin?

A

-The substance that forms chromosomes consisting of DNA and associated proteins

41
Q

What is cytokinesis?

A

-The division of a cytoplasm immediately following telophase

42
Q

What is a diploid?

A

-A nucleus or cell that contains two complete sets of chomosomes one from each parent

43
Q

What is a gamete?

A

-A haploid sex cell resulting from meiosis and is capable of using with another gamete to form a zygote

44
Q

What is a haploid?

A

-A nucleus or cell with a single set of unpaid chromosomes

45
Q

What are homologous chromosomes?

A

-A pair of similar chromosomes (one maternal, one paternal) which pair up in meiosis 1

46
Q

What is independent assortment

A

-The chromosomes can align on the metaphase plate in different combinations

47
Q

What is meiosis?

A

-The process of cell division underlying reproduction in which one diploid cell divides to form 4 haploid daughter cells

48
Q

What are microtubules?

A

-Fibrous, hollow rods that function to help support and shape the cell
-They also function as routes along which organelles and cytoplasm can move using olecular motors

49
Q

What are spindle fibres?

A

-Microtubules that form between a cells poles, coordinating the movement of chromosomes during cell divison

50
Q

What is a zygote?

A

-A diploid cell formed from two haploid gametes during fertilisation

Biology (28 decks)

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