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Biology > 5 Chromosomes, genes and DNA > Flashcards

5 Chromosomes, genes and DNA Flashcards

1
Q

What is a diagram which shows our genetic make-up?

A
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2
Q

What is the chemical that is the basis of inheritance in nearly all organisms?

A

DNA.

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3
Q

What does DNA stand for?

A

Deoxyribonucleic acid.

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4
Q

What is DNA?

A

It is a chemical of which genes are made. Double helix composed of deoxyribose sugar, phosphates and four bases.

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5
Q

Where is DNA found?

A

In the nucleus of a cell.

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6
Q

Where exactly in the nucleus of the cell is DNA found?

A

In the chromosomes.

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7
Q

What are chromosomes?

A

They are thread-like structure found in the nucleus of a cell, made of DNA and protein. Contains the genetic
information (genes).

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8
Q

What is a small section of DNA that determines a particular feature called?

A

A gene.

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9
Q

What is a gene?

A

It is a part of a chromosome, the basic unit of inheritance. A length of DNA that controls a characteristic of an
organism by coding for the production of a specific protein.

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10
Q

How do genes determine features?

A

They determine features by instructing cells to produce particular proteins which then lead to the development of the feature.

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11
Q

Bearing that in mind, what can be a different definition for a gene?

A

So a gene can also be described as a section of DNA that codes for a particular protein.

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12
Q

What can DNA do?

A

It can replicate (make an exact copy of itself).

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13
Q

What happens when a cell divides by mitosis?

A

Each new cell receives exactly the same type and amount of DNA.

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14
Q

What are the names of the new cells formed?

A

The cells formed are genetically identical.

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15
Q

What does each chromosome contain?

A

One double-stranded DNA molecule.

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16
Q

How is the DNA arranged?

A

It is folded and coiled so that it can be packed into a small space.

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17
Q

What is the DNA coiled around?

A

Proteins called histones.

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18
Q

What are histones?

A

It is a protein associated with the DNA in a chromosome.

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19
Q

What happens due to the fact that a chromosome contains a particular DNA molecule?

A

It will also contain the genes that make up that DNA molecule.

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20
Q

What happens to another chromosome in terms of DNA?

A

Another chromosome will contain a different DNA molecule, and so will contain different genes.

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21
Q

How many chromosomes do nearly all human cells contain?

A

46 chromosomes.

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22
Q

What is an image that shows a man’s chromosomes?

A
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23
Q

Are the chromosomes arranged like this in the cell?

A

No they are not.

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24
Q

Why do the chromosomes then look like this in the photograph?

A

The original photograph has been cut up and chromosomes of the same size and shape ‘paired up’.

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25
Q

What does the cell from the male contain?

A

22 pairs of chromosomes and two that do not form a pair - the X and Y chromosomes.

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26
Q

What does a cell from a female contain?

A

It has 23 matching pairs, including a pair of X chromosomes.

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27
Q

What are the X and Y chromosomes?

A

They are the sex chromosomes.

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28
Q

What are the sex chromosomes?

A

They determine whether a person is male or female.

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29
Q

What are pairs of matching chromosomes called?

A

Homologous pairs.

30
Q

What is a homologous pair?

A

A pair of chromosomes that carry
genes controlling the same features at the same positions on each chromosome. The members of each homologous pair are the same size and shape.

31
Q

What do homologous pairs contain?

A

They carry genes for the same features, and these genes are arranged at the same positions and sequence along the chromosome.

32
Q

What is the name given to cells with chromosomes in homologous pairs?

A

Diploid cells.

33
Q

What are diploid cells?

A

Number of chromosomes found in
body cells. Diploid cells contain both chromosomes of each homologous pair.

34
Q

What is an image that shows how both chromosomes in a homologous pair have the same sequence of genes?

A
35
Q

Do all human cells have 46 chromosomes?

A

No.

36
Q

Which cells don’t have 46 chromosomes?

A
  • Red blood cells.
  • Sex cells.
37
Q

Why don’t red blood cells have 46 chromosomes?

A

Red blood cells have no nucleus
and so have none.

38
Q

Why don’t sex cells have 46 chromosomes?

A

Sex cells have only 23 – just half the number of other cells.

39
Q

How are sex cells formed?

A

They are formed by a cell division called meiosis

40
Q

What is meiosis?

A

Type of cell division that produces haploid cells (gametes).

41
Q

What does meiosis form?

A

Each cell formed has one chromosome from each homologous pair, and one
of the sex chromosomes.

42
Q

So what kind of cells are formed?

A

Diploid cells.

43
Q

What are diploid cells?

A

Number of chromosomes found in
body cells. Diploid cells contain both chromosomes of each homologous pair.

44
Q

When do two gametes fuse?

A

In fertilisation.

45
Q

What is fertilisation?

A

Fusion of male and female gametes to form a zygote

46
Q

What happens during fertilisation?

A

The two nuclei join to form a single diploid cell (a zygote).

47
Q

What is a zygote?

A

Single cell resulting from fusion of a male and female gamete.

48
Q

What happens to the cell after fertilisation has taken place?

A

This cell has, once again, all its chromosomes in homologous pairs and two copies of every gene. It has the normal DNA content.

49
Q

What is the entire DNA of an organisms known as?

A

Its genome.

50
Q

What is a genome?

A

The entire DNA of an organism (the amount present in a diploid cell)

51
Q

What is the human genome made up of?

A

The human genome is made up of about 3.2 billion base pairs.

52
Q

Do all genes code for proteins?

A

No.

53
Q

What do other genes do?

A

They have other functions, or functions yet to be discovered.

54
Q

What are genes?

A

They are sections of DNA that control the production of proteins in a cell.

55
Q

What does each protein do?

A

Each protein contributes towards a particular body feature.

56
Q

Is the feature that the protein codes for always visible?

A

Sometimes the feature is visible, such as eye colour or skin pigmentation. Sometimes the feature is not visible, such as the type of haemoglobin in red blood cells or the type of blood group antigen on the red blood cells.

57
Q

Do all genes have one form?

A

No, some genes have more than one form.

58
Q

What is an example of genes having multiple forms?

A

The genes controlling several facial features have alternative forms, which result in alternative forms of the feature.

59
Q

What is an image that shows the alternate forms of four facial features?

A
60
Q

What are the two forms of the gene for earlobe attachement?

A

The gene for earlobe attachment has the forms ‘attached earlobe’ and ‘free
earlobe’.

61
Q

What are these different forms of the genes called?

A

Alleles.

62
Q

What are alleles?

A

Different forms of a gene.

63
Q

How do homologous chromosomes carry genes?

A

Homologous chromosomes carry genes for the same features in the same sequence, but the alleles of the genes may not be the same.

64
Q

What is an image that shows a homologous pair of chromosomes that are different alleles?

A
65
Q

What does each cell with two copies of a chromosome also have in terms of genes?

A

Each cell with two copies of a chromosome also has two copies of the genes on those chromosomes.

66
Q

What is an example of having two copies of the genes on those chromosomes in reference to earlobes?

A

Suppose that, for the gene controlling earlobe attachment, a person has one allele for attached earlobes and one for free earlobes. What happens? Is one ear free and the other attached? Are they both partly attached? Neither. In this case, both earlobes are free.

67
Q

What is the name given to the ‘free’ allele?

A

Dominant.

68
Q

What is a dominant allele?

A

Allele of a gene that is expressed in
the heterozygote.

69
Q

What is the name given to the ‘attached allele’?

A

Recessive.

70
Q

What is a recessive allele?

A

Allele that is not expressed in the phenotype when a dominant allele of the gene is present (i.e. in the
heterozygote).

71
Q

What is the heterozygote?

A

An individual having two different alleles of a particular gene or genes, and so giving rise to varying offspring.

Biology (22 decks)

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