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Life Science > CELL DIVISION (MEIOSIS) > Flashcards

CELL DIVISION (MEIOSIS) Flashcards

1
Q

WHAT ARE:
1. AUTOSOMES
2. GONOSOMES

A
  1. 44 ordinary chromosomes that are not involved in sex determination
  2. two sex chromosomes known as X and Y chromosomes. a female has two X-chromosomes, whereas a male has one X and one Y chromosome.
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2
Q

WHAT IS:
1. a homologous chromosome pair
2. the function of homologous chromosome pairs

A
  1. one chromosome of the pair comes from the mother of the organism (maternal) and the other from the father (paternal)
  2. these pairs ensure that the organism has characteristics of both parents
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3
Q

DEFINITION OF MEIOSIS

A

meiosis is a type of cell division that produces four different, haploid daughter cells (gametes in animals and spores in plants). it is known as the reduction division as the chromosome number is halved in the daughter cells (diploid to haploid)

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4
Q

WHAT IS THE DIFFERENCE BETWEEN THE FIRST AND SECOND MEIOTIC DIVISION

A

during the first meiotic division, the chromosome number is halved and genetic material is exchanged to produce genetic variation.
the second meiotic division proceeds like normal mitosis where the sister chromatids separate from each other

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5
Q

DIFFERENCE BETWEEN KARYOKINESIS AND CYTOKINESIS

A

division of the nucleus is called karyokinesis and division of the cytoplasm is called cytokinesis

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6
Q

WHAT IS THE PURPOSE OF MEIOSIS

also state where sperm and eggs are formed

A
  1. the purpose of meiosis is the formation of gametes in the sex organs of animals
  2. this process is called gametogenesis

sperm are formed in the testes by spermatogenesis
ova/eggs are formed in the ovaries by oogenesis

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7
Q

EXPLAIN THE PROCESS OF INTERPHASE

A
  1. DNA replication takes place
  2. chromosomes which are single threads become double
  3. each chromosome will consist of two chromatids joined by a centromere
  4. DNA replication helps to double the genetic material so that it can be shared by the new cells
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8
Q

EXPLAIN THE PROCESS OF PROPHASE 1

A
  • Nuclear membrane and nucleolus start to disappear.
  • Centrosome splits and the two centrioles move apart
    forming spindle fibres.
  • Chromatin network condenses into individual
    chromosomes and pairs of homologous chromosomes
    lie next to each other forming a bivalent.
  • Inner chromatids from each homologous chromosomes
    overlap and touch each other at a point called the
    chiasma (plural: chiasmata) in a process called
    crossing over
  • Chromatid segments break off and are exchanged,
    resulting in the exchange of genetic material.
  • This process is called crossing over and it brings
    about variation.
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9
Q

EXPLAIN THE PROCESS OF METAPHASE 1

A
  1. homologous chromosome pairs are arranged randomly on the equatorial plane of the cell with the centromere of the chromosome attached to the spindle fibre.
  2. this is called random arrangement and results in gametes having a different mix of paternal and maternal chromosomes
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10
Q

EXPLAIN THE PROCESS OF ANAPHASE 1

A
  • One whole chromosome from each pair is pulled to
    opposite poles by contraction of the spindle fibres
  • This separates the homologous chromosomes – one to
    each pole
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11
Q

EXPLAIN THE PROCESS OF TELOPHASE 1

A
  • A new nuclear membrane forms around the group of
    chromosomes at each pole.
  • Nucleolus returns.
  • Cytokinesis (division of cytoplasm) splits the mother
    cell into two daughter cells.
  • Each daughter cell now has half the number of chromosomes (i.e., is haploid) and each has a slightly different genetic make-up due to crossing over.
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12
Q

EXPLAIN THE PROCESS OF PROPHASE 2

A
  1. each chromosome of two recombinant chromatids joined by a centromere. there are no homologous pairs
  2. the nucleolus and nucleur membrane disappear
  3. a spindle forms consisting of centrioles at opposite poles joined by spindle fibres
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13
Q

EXPLAIN THE PROCESS OF METAPHASE 2

A
  1. the chromosomes move to the equator and align randomly in a single row on the equator
  2. some spindle fibres attach to the centromeres
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14
Q

EXPLAIN THE PROCESS OF ANAPHASE 2

A
  1. the centromere of each chromosome splits
  2. the two sister chromatids separate and move to opposite poles
  3. these single chromatids form V-shapes as the centromere is pulled by the spindle fibre
  4. cytokinesis begins to separate the cytoplasm
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15
Q

EXPLAIN THE PROCESS OF TELOPHASE 2

A
  1. the chromatids group at the poles and are known as unreplicated chromosomes
  2. these unreplicated chromosomes in each daughter cell are also known as recombinant chromatids as they have exchanged genetic material
  3. the spindle fibres disappear
  4. a nuclear membrane forms around each group of unreplicated chromosomes and a nucleolus forms in each nucleus
  5. the cytoplasm divides in cytokinesis
  6. cytokinesis is now complete and four daughter cells have been formed, each with the haploid chromosome number
  7. due to crossing over, the daughter cells are genetically different
  8. in males, the daughter cells develop into sperm
  9. in females, three of the daughter cells disintegrate and one develops into an egg/ovum
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16
Q

IMPORTANCE OF MEIOSIS

A
  1. production of haploid gametes/spores
  2. reduces the number of chromosomes by half, preventing the double effect of fertilisation
  3. genetic variation in gametes/spores is introduced
17
Q

EXPLAIN THE SOURCES OF VARIATION IN GAMETES AND SPORES

A
  1. crossing over of chromatids and the exchange of genetic material during prophase 1. a reshuffling of recombination of genes occurs which means every gamete formed by an individual has a different genetic composition
  2. random arrangement of chromosomes on the equator 1 & 2 results in genetic variation in the gametes/spores produced by meiosis. the paternal and maternal chromosomes/chromatids lie randomly on the equator before separating to form part of new combinations of genetic material in gametes/spores
18
Q

DEFINE RANDOM FERTILISATION

A

any sperm cell may fuse with any egg cell which increases the probability of variation within the offspring

19
Q

EXPLAIN THE PROCESS OF ABNORMAL MEIOSIS

A
  1. when meiosis does not proceed normally, changes in the chromosome number or structure of the chromosomes may occur
  2. these abnormalities are known as chromosome mutations or aberrations
  3. a condition, known as aneuploidy, may sometimes occur where there are extra chromosomes or missing chromosomes in a cell
  4. non-disjunction occurs when chromosome pairs do not separate during meiosis. two chromosomes move to one pole, and none to the other pole. gametes are formed with extra or missing chromosomes
20
Q

EXPLAIN WHAT HAPPENS TO THE CELLS IN DOWN SYNDROME DISORDER

A
  1. down syndrome is an example of aneuploidy, where there are 47 chromosomes instead of the usual 46 chromosomes in each somatic cell of the affected individual
  2. non-disfunction occurs in the production of eggs during meiosis when chromosome pair 21 does not separate during anaphase 1
  3. after meiosis 1, one daughter cell has an extra chromosome
  4. when the egg with 24 chromosomes fuses with a normal sperm during fertilisation, a zygote with 47 chromosomes is formed
  5. the zygote develops into an individual with 47 chromosomes in every somatic cell.
  6. this chromosomal abnormality is also known as trisomy 21
21
Q

DIFFERENCES BETWEEN MITOSIS AND MEIOSIS

A

MITOSIS:
1. occurs in damaged tissue
2. production of identical daughter cells, which are used for growth, repair and asexual reproduction
3. one division
4. no pairing of homologous chromosomes and no bivalents formed
5. no crossing over and exchange of genetic material occurs
6. the centromeres divide during anaphase

MEIOSIS:
1. occurs in the testes, ovaries and the sporangia of the sporophyte generation
2. introduces variation in the daughter cells
3. two divisions
4. homologous chromosomes arrange themselves in pairs and form bivalents when they are in contact with each other during prohase 1
5. crossing over between homologous chromosomes and exchange of genetic material occur during prophase 1
6. centromeres do not divide in anaphase 1, but they do divide during anaphase 2

22
Q

REPRESENTATION OF CROSSING OVER

A
  1. homologous chromosomes arrange themselves in pairs
  2. bivalent forms when the homologous chromosomes are in contact with each other
  3. identical sister chromatids are visible
  4. overlapping occurs between adjacent chromatids of a pair of homologous chromosomes
  5. crossing over and exchange of chromatid segments occur between adjacent chromatids at points called chiasmata
  6. homologous pairs remain as pairs after crossing over

Life Science (9 decks)

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