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Biology > Grade 12 - Life at Molecular, Cellular and Tissue level - Chromosomes and Meiosis > Flashcards

Grade 12 - Life at Molecular, Cellular and Tissue level - Chromosomes and Meiosis Flashcards

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1
Q

What are chromosomes?

A
  • Long, thread-like structures
  • Strand of DNA wound around histone proteins
  • Called chromosomes or “coloured bodies” as they absorb dye easily
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2
Q

How many sets of chromosomes in somatic cells?

A
  • In somatic cells there are two sets – one from the mother; one from the father
  • Diploid (2n) – full set of chromosomes
  • Haploid (n) – half set of chromosomes
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3
Q

Define meiosis:

A

Cell division in reproductive organs producing gametes (sex cells)

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4
Q

Meiosis I

A

Crossing over of pieces of chromosomes
Leads to variation
Pairs of chromosomes separate

Reduction division which results in two cells being formed each with half the number of chromosomes of the parent cell i.e. the haploid (n) number.

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5
Q

Meiosis II

A

Copying division which involves the two haploid cells formed, each dividing again by mitosis to form 4 haploid cells.

Chromosomes split in half at the centromere
One half goes to each daughter cell

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6
Q

What is Meiosis?

A
  • Cell division in reproductive organs
  • Produces gametes
  • Reduces a full set of chromosomes(2n) to one set (n) in each daughter cell
  • The number of chromosomes is halved
  • One chromosome from each homologous pair
  • Male & female gametes (n) fuse to form the zygote during fertilisation
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7
Q

Where does meiosis take place in animals?

A
  • Reproductive organs :
  • Testes – spermatogenesis
  • Ovaries – oogenesis
  • Plants – formation of spores in sporangia
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8
Q

Where does meiosis take place in plants?

A
  • In the formation of spores in the sporangia. In seed-bearing plants:
  • microsporangia - pollen sacs in the male anthers
  • megasporangia - ovules in the female ovaries.
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9
Q

What phase does a cell spend most of its time in?

A
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10
Q

When were chromosomes discovered?

A

1888

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11
Q

Name the mass of interwoven threads found in the nucleus of interphase. (2 marks)

A

#

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12
Q

At which stage of the cell cycle does replication take place? (1 mark)

A

#

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13
Q

Why is replication of important? (3 marks)

A

Allows growth
#
Lifespan increased

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14
Q

What is another name for a cell body?

A

Somatic cell

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15
Q

Each body cell has two sets of chromosomes. What name is used to describe this and how is abbreviated? (2 marks)

A

1) Diploid
2) 2n

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16
Q

What do we call chromosomes inherited from the father? (1 mark)

A

Paternal chromosome.

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17
Q

What is meant by a chromosome number?

A

Page 149
Each species has a specific number of chromosomes in its somatic cells.
Some organisms - identical numbers but need not be related.
Similarities in the DNA of chromosomes - show relationships.

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18
Q

Define Early prophase 1

A
  • Chromosomes become short and fat and are visible as two chromatids joined by a centromere.
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19
Q

Define Late prophase 1

A
  • Chromosomes of homologous pairs lie along side one another, forming bivalent.
  • Spindle - made up of protein threads, develops across the cell from the two centrioles.
  • Crossing over takes place. (See page 154)
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20
Q

Define Anaphase 1

A
  • Centromeres do not split.
  • Bivalents separate and chromosomes (not chromatids) are pulled away from each other by contracting spindle threads.
  • Chromosomes move to opposite poles of the cell.
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21
Q

Define Telophase 1

A
  • Cytoplasm then divides (cytokinesis) to form two haploid cells, i.e. both the new cells only have one of each homologous pair of chromosomes.
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22
Q

What is Meiosis 2

A
  • A copying division
  • The two chromatids making up each chromosome needs to separate.
  • Each haploid cell will therefore divide again by mitosis.
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23
Q

What is crossing over?

A
  • The mutual exchange of pieces of chromosomes so that whole groups of genes are swapped between maternal and paternal chromosomes.
  • Takes place in late prophase of meiosis 1.
  • Synapsis to form Bivalents
  • Chiasmata / chiasma
  • Recombinant chromatid
  • Parentals
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24
Q

Explain why crossing over is important (4 marks)

A
  • Unique combination of genes -0 increase variation among daughter cells as there will be new combinations of genetic material.
  • Mutations during the exchange process. Sometimes beneficial.
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25
Q

Why is meiosis important?

A

1) Gametes are formed

2) Number of chromosomes is halved so the the chromosome number is kept constant from generation to generation.

3) Results in genetic variation through a) crossing over and b) random arrangement of chromosomes at the equator of the cell during metaphase.

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26
Q

Name the similarities between mitosis and meiosis?
STUDY TABLE PAGE 155 of your textbook!

A

1) Types of cell division

2) DNA of parent cell is replicated in interphase before the cell division starts

3) In early anaphase the chromosomes become short and fat and are visible as two chromatids joined by a centromere.

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27
Q

Discuss the difference between mitosis and meiosis with regards to:

1) Where the process occurs
2) The purpose of the process
3) Difference in the process.

A

Study table on page 155

28
Q

What is the result of abnormal meiosis?

A
  • Results in chromosome abnormalities and can take place in several different ways.
  • Chromosome non-disjunction occurs when chromosomes fail to separate correctly during meiosis.
  • aneuploidy
  • syndromes
  • cause and effects
  • Diagnosis
29
Q

What is chromosome non-disjunction?

A

Occurs when chromosomes fail to seperate correctly during meiosis.

30
Q

Explain aneuploidy

A

Occurs in the sex chromosomes (X and Y) fertilisation involving one of these abnormal gametes will result in a zygote with either an extra or missing chromosome.

31
Q

What are syndromes?

A

Occurs in the sex chromosomes (X and Y) fertilisation involving one of these abnormal gametes will result in a zygote with either an extra or missing chromosome. Affected individuals have a physical or mental characteristic called a SYNDROME

32
Q

Define diagnosis v prognosis

A

Identifying the nature of an event (e.g. an illness)

v

predicting how the event (as an illness) will develop.

33
Q

Discuss Klinefelter’s syndrome

A

Page 156 Textbook - Fill in

34
Q

Discuss Down syndrome (10 marks)

A

Page 156 Textbook - Fill in

35
Q

How does Down syndrome come about? Discuss

A

Page 156 Textbook FIll in

36
Q

What are Down syndrome characteristics?

A

1) Varying degrees of intellectual and development delay
2) Distinctive flattened facial features with slightly slanted eyes.
3) Short stubby fingers and toes - big toe widely spaced from second toe, largish head and ears
4) Heart defects
5) Happy, loving nature.
6) No cure

37
Q

How common is Down syndrome?

A

1 / 900 births
Increases with mother’s age
35 year old mom 1/350
Woman of 40 1/30 chance
Maternal age defect

38
Q

Discuss the aspects relevant to the abortion of a Down syndrome foetus.

A

Page 157 Fill in

39
Q

What is a karyotype?

A

A set of chromosomes in a cell is called a karyotype.

It shows the number, size and shape of the chromosomes during metaphase of mitosis.

40
Q

What are autosomes?

A

Page 157

41
Q

What are Karyotypes useful? (2 marks)

A

-Show whether a cell comes from a male or a female
-Abnormal chromosomes

42
Q

What is meant by trisomy? (2 marks)

A
43
Q

True or False: A centriole attaches two chromatids together.

A

#

44
Q

True / False: Meiotic division takes place in two stages, a reduction division and a copying division.

A

#

45
Q

True / False: In an animal cell a spindle is formed between two centromeres.

A

#

46
Q

True / False: Crossing over involves the exchange of segments of outer chromatids in a bivalent.

A

#

47
Q

True / False: All human somatic cells contains 23 chromosomes.

A

#

48
Q

Explain the relationship between chromatin network, chromosomes and chromatids.

A

When a cell is in Interphas (non-dividing phase), the chromosomes in the nucleus appear as a mass of threads = Chromatin Network

When a cell divides , the threads shorten, thicken and become visible = chromosomes

After replication has occurred, the chromosome (DNA and histones) consists of two identical units= chromatids, that are connected by a centromere.

49
Q

Define the term gene.

A

A segment of a DNA molecule.

50
Q

Define diploid chromosome number (2n)

A

The double set of chromosomes that appears in pairs in each body / somatic cell of an organism.

51
Q

Define homologous chromosome pair.

A

A set of two chromosomes that are similar in size and shape and carry corresponding genes that control the same characteristics. Thus it combines the characteristics of the mother and father in the new organism.

52
Q

Define gonosomes.

A

The sex chromosome that determine the sex of an individual e.g. in female the gonosomes are XX and in male XY.

53
Q

Define genome.

A

The complete set of genes in a particular organism.

54
Q

Define haploid chromosome number (n).

A

The single set of chromosomes found in sex cells (gametes) after meiosis occurred.

55
Q

Define autosomes.

A

The normal chromosomes that ar not involved in sex determination.

56
Q

Define karyotype.

A

The complete set of diploid chromosomes in a somatic cell, arranged in pairs according to size, shape and number.

57
Q

What type of cell division results in daughter cells with chromosome numbers identical to the mother cell?

A

Mitosis

58
Q

Name the differences between mitosis and meiosis.

A

See tables in both textbooks. Use following criteria:
1) Where the process occurs
2) Purpose of the process
3) Differences in the process

59
Q

Name four similarities between mitosis and meiosis.

A

1) Both are types of cell division
2) The DNA of the parent cells is replicated in interphase before cell division starts.
3) In early prophase the chromosomes become short and fat and are visible as two chromatids joined by a centromere.
4) ### (Answer book)

60
Q

What is meant by maternal age effect?

A

The risk of having a Down syndrome baby increases with maternal age as there is a greater chance that the chromosomes will not divide correctly. After 35 years of age, the risk increases dramatically.

61
Q

Give one word for the ‘deliberate termination of pregnancy’.

A

Abortion

62
Q

Do you think amniocentesis can cause har to the foetus? Explain.

A

1) Yes, an insufficiently trained medical person, or one that does not work accurately, can damage the foetus or the placenta

OR

2) No, well trained medical people work accurately and take all possible precautionary measures to ensure that the foetus is not harmed. I.e. it is safe if one goes to highly specialised medical experts.

63
Q

Define aneuploidy.

A
  • Abnormal meiosis results in chromosome abnormalities and it can place in several ways.
  • **Chromosome non-disjunction occurs when chromosomes fail to separate correctly during meiosis.
  • If this occurs in the sex chromosomes (X and Y) fertilisation involving one of these abnormal gametes will rusult in a zygote with either an extra or a missing chromosome.
  • This condition is known as aneuploidy.
  • Affectted individuals have physical and mental characteristics called syndromes.
  • Example : Klinefelter’s syndrome (Page 156)
64
Q

Define trisomy.

A

#

65
Q

During which phase of meiosis does this phenomenon of trisomy occur?

A

#

66
Q

Explain the concept polyploidy.

A

#

67
Q

Distinguish between non-disjunction and total non-disjunction.

A

#

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