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ESA1 - Medical Cell Biology and Genetics > Mitosis And Meiosis > Flashcards

Mitosis And Meiosis Flashcards

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1
Q

How many DNA molecules are in a replicated chromosome (2 sister chromatids)?

A

Two

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2
Q

What are the two sister chromatids held together by?

A

Centromere

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3
Q

What are found on the ends of chromosomes?

A

Telomeres

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4
Q

What are the two arms of chromatids?

A 
P arm (short)
Q arm (long)
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5
Q

What are telomeres?

A

Telomeres are repeated nucleotide sequences at the end of each chromosome/chromatid

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6
Q

What is the function of telomeres?

A

They protect the DNA from degradation

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7
Q

What is the telomere sequence in humans?

A

TTAGGG

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8
Q

What happens to the telomeres each time the cell divides?

A

They get shorter. Eventually, if the telomere is not long enough, this results in the degradation of the DNA

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9
Q

What is the centromere?

A

The centromere links the sister chromatids and consists of repetitive sequences. Can be in different positions on different chromosomes.

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10
Q

What are the positions in which centromeres can be on chromosomes called?

A

Metacentric, submetacentric, acroscentric and telocentric

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11
Q

How are chromosomes grouped together?

A

By their size and shape (groups A-G). Eg X is C group and Y is G group

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12
Q

What is mitosis?

A

The cell division for somatic cells leading to the production of two identical daughter cells with the same chromosomal content as the parent cell.

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13
Q

What happens in prophase in mitosis?

A
  • Nuclear membrane starts to disintegrate
  • Chromosomes condense and become visible
  • Microtubule spindle starts to form
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14
Q

What happens in prometaphase in mitosis?

A
  • The disruption of the nuclear envelope allows for the mitotic spindles to gain access to the mature kinetochores on the centrosomes.
  • Microtubule spindle attaches to centromeres
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15
Q

What happens in metaphase in mitosis?

A
  • Chromosomes line up at the metaphase plate (in the middle)

- The order in which they line up is random - there is no recognition of homologous pairs

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16
Q

What happens in anaphase in mitosis?

A
  • Microtubule spindles contract and pull the chromatids apart to opposite poles

Note - when sister chromatids are separated, they are now called chromosomes as they are daughter chromosomes

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17
Q

What happens in telophase in mitosis?

A
  • Spindle disintegrates
  • Nuclear membrane reforms
  • Cleavage in the middle to form two daughter cells (cytokinesis)
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18
Q

What is cytokinesis?

A

This is where the cytoplasm divides and two daughter cells with identical genetic information are formed.

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19
Q

Where are the chromosomes/chromatids during interphase?

A

Still there! We just can’t see them because they are not condensed

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20
Q

What is a pair of homologous chromosomes?

A

Homologous chromosomes are made up of chromosome pairs of approximately the same length, centromere position, and staining pattern, for genes with the same corresponding loci. One homologous chromosome is inherited from the organism’s mother and the other is inherited from the organism’s father.

They have the same DNA sequence - same genes

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21
Q

What are sister chromatids?

A

Identical chromatids formed by the replication of a single chromosome, with both copies joined together by a common centromere.

  • Identical DNA, same alleles
22
Q

What is an allele?

A

Different variants of the same gene

23
Q

What are non-sister chromatids?

A

These chromatids have the same genes but may have different alleles (one maternal and one paternal)

24
Q

What is meiosis?

A

This is a special cell division for germ line cells that leads to the production of four non-identical daughter cells with half the chromosome content of the parent cell

25
Q

How does meiosis achieve half the chromosome count?

A

One round of replication, two rounds of division (meiosis I and II). Diploid (2n) is reduced to haploid (n). Production of egg and sperm.

26
Q

What happens in prophase I of meiosis I?

A

At the start of prophase I, the chromosomes have already replicated.

  • Nuclear membrane disintegrates
  • Chromosomes become visible, they condense as they coil and become shorter/thicker
  • Homologous chromosomes pair up
  • Crossing over occurs
27
Q

How do homologous chromosomes ‘find each other’ in prophase I of meiosis?

A

They are identical in sequence

28
Q

What is crossing over?

A

This is when homologous chromosomes exchange parts of their genetic sequence. The contact between two chromatids that will undergo crossing-over is known as a chiasma.

29
Q

What happens in metaphase I of meiosis I?

A

Homologous pairs line up on the metaphase plate.

30
Q

What is a tetrad?

A

Two homologous chromosomes aligned

31
Q

What happens in anaphase I of meiosis I?

A

Spindle contracts and homologous pairs separate, migrating to opposite poles.

32
Q

What happens in telophase I of meiosis I?

A

Nuclear membrane reforms, spindle disintegrates, cleavage in the middle to form two daughter cells with 23 chromosomes each.

33
Q

What happens in prophase II of meiosis II?

A

Nuclear membrane disintegrates, spindle begins to form

34
Q

What happens in metaphase II of meiosis II?

A

Chromosomes line up on metaphase plate

35
Q

What happens in anaphase II of meiosis II?

A

Spindle contracts and chromatids are pulled apart

36
Q

What happens in telophase II of meiosis II?

A

Nuclear membrane reforms, spindle disintegrates, cleavage in the middle. End result is 4 haploid daughter cells (23 chromosomes each)

37
Q

What are the consequences of meiosis?

A
  • Maintains a constant chromosome number from generation to generation
  • Generation of genetic variability via random assortment of homologous pairs and crossing over
38
Q

What is aneuploidy?

A

This is an error in cell division that results in the daughter cells having the wrong number of chromosomes

39
Q

Why does aneuploidy of the sex chromosomes have fewer adverse effects than aneuploidy of autosomes?

A

This is because only one X chromosome is expressed even if there are more than one so the others would just become genetically inactive

40
Q

What is anaphase lag?

A

This is where one homologous chromosome in meiosis or one chromatid in mitosis fails to connect to the spindle apparatus, or is tardily drawn to its pole and fails to be included in the reforming nucleus. This usually results in aneuploidy.

41
Q

What is nondisjunction?

A

The failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.

42
Q

How many chromosomes does every human somatic cell contain in G2, just before mitosis?

A

46 - made up of 2 sister chromatids

43
Q

How many chromosomes does every human somatic cell contain in G1, just after mitosis?

A

46 - made up of single chromatids

44
Q

How many chromatids are there in a human cell that is about to undergo meiosis 1?

A

92 chromatids, sister chromatids are paired up to give 46 chromosomes

45
Q

How many DNA molecules are there in a human cell that is about to undergo meiosis 1?

A

92 DNA molecules, as 1 chromatid is 1 DNA molecule

46
Q

How many DNA molecules are there in a human somatic cell at the end of G1?

A

46 DNA molecules as the DNA has not yet replicated

47
Q

During which phase of the cell cycle are chromosomes replicated?

A

S phase

48
Q

If you are told that in a cell division of human cells, 23 unduplicated structures are seen travelling to each pole, is this mitosis or meiosis?

A

Meiosis II because in mitosis there would be 46 unduplicated structures and in Meiosis I there are 23 pairs moving to separate poles so these are duplicated

49
Q

What is the function of the SRY gene?

A

The SRY gene is found on the Y chromosome. The sex-determining region Y protein produced from this gene attaches to specific regions of DNA and helps control the activity of particular genes.

(Causes a foetus to develop male gonads and prevent development of female reproductive structures)

50
Q

What is mosaicism?

A

Presence of two or more cell lines in an individual.

Degree of mosaicism depends on when (whether it was first mitotic division or later)

Can result from non-disjunction, anaphase lag etc

ESA1 - Medical Cell Biology and Genetics (18 decks)

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