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Biology IGCSE > Chapter #16 - Chromosomes, Genes and Proteins > Flashcards

Chapter #16 - Chromosomes, Genes and Proteins Flashcards

1
Q

Chromosomes

A

A length of DNA found in the nucleus. It contains genetic info in the form og different genes

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2
Q

Under what circumstances can chromosomes be observed?

A

They can be seen with a regular light microscope only when cells are dividing

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3
Q

What are chromososmes made of?

A

DNA in a double helix which is made up of genes

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4
Q

How do chromososmes vary within your body?

(depending on what part of the body they are in)

A

Every cell in the body has all of it’s DNA. However, the cells are specialized to “read” only the parts that are rfelevent to that part of the body

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5
Q

Draw a labled diagram of a chromosome

A
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6
Q

DNA

A

A molecule that contains genetic info in the form of genes.

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7
Q

What does DNA carry?

A

Each molecule of DNA carries a code whch the cell which proteins to make. So, each chromosome carries instructions for making diff proteins.

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8
Q

Gene

A

A length of DNA molecule that coede for one protein.

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9
Q

What do genes determine?

A

Many of our features such as:
* eye color
* hair color
* nose shape
* genetic diseases

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10
Q

Alleles

A

Alternative forms of the same gene.

Moste genes come in more than one form.

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11
Q

Homologous pair

A

A pair of chromosomes which are similar. In each pair, one is from the mother and the other from the father.

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12
Q

Heterozygous

A

Having 2 different alleles of a particular gene (e.g. Gg).

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13
Q

Homozygous

A

Having 2 identical alleles of a particular gene (e.g. GG or gg)

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14
Q

How many chromosomes do humans have?

A

Humans have 46 chromosomes in each of our cells. (23 homologous chromosomes)

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15
Q

Do all humans have the same types of alleles?

A

Humans have many genes in common but we differ in alleles. No 2 humans have the exact same combination of alleles (except for identical twins)

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16
Q

The 46 chromosomes in a human body cell nucleus are difficult to distinguish when packed inside the nucleus. How are the similar pairs in the 46 chromosomes identified by scientists?

A

So, scientists seperate them and arrange them according to size and appearence.

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17
Q

What chromosome pair does not match?

A

The sex chromosome. In males, the y chromosomes is smaller than the x chromosome.

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18
Q

How are chromosomes organized and identified by scientists?

A
  • Put into homologous pairs
  • Order from largest to smallest
  • They are numbered this way
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19
Q

What are homologous pairs made up of?

A

One chromosome is inherited by the mother and the other from the father.

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20
Q

Mitosis

A

The division of a cell nucleus resulting in 2 genetically identicle nuclei.

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21
Q

When is mitosis used by animal or plant cells?

A

To repair or grow (also in aesexual reproduction)

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22
Q

Replication

A

Before mitpsis begins, exact copies of all chromosomes are made.

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23
Q

What steps occure during mitosis?

A
  1. Each chromosome spilts (after replication)
  2. 2 daughter cells that are genetically identicle yo eachother are produced
  3. They are also genetically identicle to parent cell
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24
Q

Meiosis

A

The division of a diploid nucleus resulting in 4 genetically different haploid nuclei.

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25
Q

What else may meiosis be called?

A

Reduction division

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26
Q

Why is meiosis sometines called reduction division?

A

Because the number of chromososmes in the daughter cells is half that of in the parent cells.

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27
Q

Why is meiosis used?

A

To produce gametes (sex cells)

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28
Q
Complete the table
A
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29
Q

How many genes do humans have in their 46 chromosomes?

A

About 20000 human genes in our 46 chromosomes

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30
Q

What do chromosomes in a homologous pair have in common?

A

Each chromosome in a homologous pair contains genes for the same characteristics in the same position.

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31
Q

What does each gene contain?

A

Bases and therefore base pairs

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32
Q

What is the difference between a gene and an allele?

A

A gene specifies the trait, while the allele specifies which form of this trait the gene takes. (e.g. there could be a gene for eye color. The allele specifies that the eye color is brown.)

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33
Q

Genotype

A

The genetic makeup of an organism, including which alleles are used (e.g. bb or Bb or BB)

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34
Q

Phenotype

A

The observable features of an organism (e.g. brown eyes or blue eyes)

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35
Q

Dominant allele

A

An allele that is expressed if it is present (eg. G)

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36
Q

Recessive allele

A

an allele that is only expressed when there is no dominant allele present (eg. g)

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37
Q

Carriers

A

A recessive allele which is present but not expressed because of the precense of a dominant allele.

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38
Q

Codominance

A

alleles that are both present in the phenotype when they are both present.

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39
Q

What is an example of co-dominance?

A
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40
Q

What type of inheritance does the ABO blood group system demonstrate?

A

The ABO blood group system demonstrates codominance.

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41
Q

How is the gene for blood group represented, and how many alleles does it have?

A

The gene for blood group is represented with the capital letter I and has 3 alleles: I^A, I^B, I^O
.

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42
Q

What are the relationships between alleles for the blood group gene?

A

Both I^A and I^B are codominant and are both dominant to I^O

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42
Q

What is the blood group phenotype for the genotype I^A I^B

A

Blood group AB

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42
Q

What is the blood group phenotype for the genotype I^A I^O

A

Blood group O

42
Q

What is the blood group phenotype for the genotype I^A I^A

A

Blood group A

43
Q

What is the blood group phenotype for the genotype I^B I^B

A

Blood group B

44
Q

What is the blood group phenotype for the genotype I^B I^O

A

Blood group B

45
Q

What is the blood group phenotype for the genotype I^O I^O

A

Blood group O

46
Q

Explain how the alleles for blood groups in humans demonstrate both dominace and codominance.

A
47
Q

Inheritance

A

the transmission of genetic information from generation to generation​

48
Q

How can knowledge of genes and alleles help in inheritance?

A

Knowledge of genes and alleles can help make predictions about which characteristics will be passed on.

49
Q

How is genetic information transferred?

A

Genetic informaton is transferred in gametes. Each gamete only has one of the homologous chromosome pair instead of 2 (23 chromosomes instead of 46).
Therefore there is only one of each pair of alleles.

50
Q

What types of gametes would be produced by a male with genotype
𝐺𝑔?

A

Equal numbers of 𝐺 and 𝑔 sperm.

51
Q

What type of gametes would be produced by a female with genotype 𝑔𝑔?

A

Eggs with only the 𝑔 allele.

52
Q

What would happen if a 𝐺 sperm fertilizes a 𝑔 egg?

A

The resulting zygote would have the genotype 𝐺𝑔.

53
Q

What would happen if a
𝑔 sperm fertilized a 𝑔 egg?

A

The resulting zygote would have the genotype 𝑔𝑔.

54
Q

What determines the genotype of a zygote?

A

The genotype of the zygote is determined by the combination of alleles from the sperm and the egg during fertilization.

55
Q

What are genetic diagrmas used for?

A

Used to show how to predict the probability of genotypes and phenotypes of the offspring of two parents.​

56
Q

Monohybrid cross

A

A diagram that a cross where we consider the inheritance of only one gene. (The one drawn on a table)

57
Q

What is the monohybrid cross also referred as?

A

Punnet square diagram

58
Q

Dictionary

A

The record of descent of an animal, showing it to be pure-bred.

59
Q

Pedigree diagram

A

A chart used to show phenotypes (sometimes genotypes of family members in several generations.

60
Q

In a pedigree diagram, how do you know what organisms are male or female?

(when there is noe key)

A
61
Q

In a pedigree diagram, how do you know what organisms are affected, or not, or something else (state what it is)?

A
62
Q

What do the verticle lines in a pedigree diagrams represent?

A

They lead to offspring

63
Q

What do horizontal lines represent in a pedigree diagram?

A

They show parents

64
Q

What are the possible genotypes of an organism that expresses a dominant characteristic?

A

An organism that expresses a dominant characteristic could have two possible genotypes: homozygous dominant (e.g., 𝐴𝐴) or heterozygous (e.g., 𝐴𝑎).

65
Q

How do we find out weather the genotype of an organism is dominant homozygous or heterozygous?

A

We could find out the genotype by crossing the individual with a homozygous recessive organism. If any of the offspring express the recessive gene, the organism was heterozygous.

66
Q

What is the genetic makeup of pure-breeding organisms for a specific characteristic?

A

Pure-breeding organisms are always homozygous for the pure-breeding characteristic.

67
Q

Sex chromosomes

A

Chromosomes that determine sex

68
Q

X chromosome

A

The larger of the 2 sex xhromosomes in mammals

69
Q

Y chromosome

A

The smaller of the two sex chromosomes

70
Q

Each time someone has a child (regardless of how many children they have previously had) what is the chance of having a female or male?

A

50%

71
Q

Do the X and Y chromosomes only determine sex?

A

No, the X and Y chromosomes don’t just determine sex; they also have other genes on them.

72
Q

How do the X and Y chromosomes differ in size and number of genes?

A

The Y chromosome is tiny and contains only a few genes, while the X chromosome is larger and has many more gene

73
Q

Why don’t people necessarily have two sets of genes on their sex chromosomes?

A

The Y chromosome is tiny and contains only a few genes, while the X chromosome has many more. Therefore, unlike other homologous pairs of chromosomes, sex chromosomes do not always carry two sets of genes

74
Q

How do sex chromosomes differ from most homologous pairs of chromosomes? ( Show this in a diagram)

A

Most homologous pairs of chromosomes have identical sets of genes on both chromosomes. However, sex chromosomes (X and Y) differ:

  • The X chromosome contains many genes, including sex-linked genes.
  • The Y chromosome is smaller and contains genes that are not found on the X chromosome.
75
Q

What are sex-linked genes, and what do they produce?

A

Genes that are only found on sex chromosomes are called sex-linked genes. They produce characteristics that are more common in one sex than the other.

76
Q

What is an example of a sex-linked disease?

A

Red-green colour blindness

77
Q

: What does a sex-linked gene control in the retina?

A

A sex-linked gene controls the production of the 3 different kinds of cone cells found in the retina.

78
Q

What alleles makes someone red-green color-blind?

A

A sex linked gene controls the production of 3 diff. cone cells in the retina:
* A recessive allele of this gene = b = only 2 types of cone being made
* A dominant allele of this gene = B = all three are made.

79
Q

What makes someone red-green color blind?

A

Someone who is homozygous recessive and has the allele bb.

80
Q

How does red-green color-blidness affect males and females differently?

(what is the percentage of females which have the disease compared to ma

A

This disorder affects about 8% of men and about 1% of women.​

81
Q

How does being red-green color-blind affect someone?

A

Sufferers are unable to tell the difference between red and green.

82
Q

What is the role of nucleotide (base) sequences?

A

Sequences of nucleotides determine which amino acids are linked together to form a specific protein, and they also determine the protein’s features, such as its shape.

83
Q

How do sequences of nucleotides affect proteins?

A

Sequences of nucleotides determine which amino acids are linked together to form a specific protein, and they also determine the protein’s features, such as its shape.

84
Q

Where is DNA found?

A

In the nucleus

85
Q

Where is mRNA created?

A

mRNA is created in the nucleus

86
Q

What does mRNA do?

A

mRNA (messenger RNA) cerries information from DNA in the nucleus to ribosomes in the cytoplasm.

87
Q

mRNA is not made in what shape?

A

In a double helix

88
Q

What is a physical difference between DNA and RNA?

A

DNA is in a double helix while RNA is not. RNA is singke starnded.

89
Q

How does mRNA work in steps?

A

1.

90
Q

Why is it important that nucleotide sequences control the shapes of proteins?

A

So that functional enzymes are made with the right shapes to fit together (lock and key)

91
Q

What is the 1st step of how proteins are made using mRNA?

A
  • mRNA is created in the nucleus.
  • It makes a copy of the sequence of bases in the DNA that make up a gene.
  • The DNA stays in the nucleus.
92
Q

What is the 2nd step of how proteins are made using mRNA?

A

mRNA moves out of the nucleus and into the cytoplasm

93
Q

What is the 3rd step of how proteins are made using mRNA?

A

In a healthy person (eating a balanced diet) all the amino acids will be freely available in the cytoplasm.

The ribosome follows the code on the mRNA, and links together the necessary amino acids to form a chain (a protein.)

94
Q
Describe each stage of how proteins are made
A
  • mRNA is created in the nucleus.
  • It makes a copy of the sequence of bases in the DNA that make up a gene.
  • The DNA stays in the nucleus.
  • mRNA moves out of the nucleus and into the cytoplasm
  • In a healthy person (eating a balanced diet) all the amino acids will be freely available in the cytoplasm.
  • The ribosome follows the code on the mRNA, and links together the necessary amino acids to form a chain (a protein.)
95
Q

Stem cells

A

unspecialised cells that can divide by mitosis to form different types of specialized cells

96
Q

Where can unspecialized cells be found?

A
  • Newly formed embryos are made of stem cells
  • Bone marrow => blood cells
  • Brain cells => neurones
97
Q

Bone marrow

A

Where stem cells are constantly dividing to form specialized cells for our blood such as red blood cells, platelets and lymphocytes.

98
Q

Brain

A

Where stem cells divide to produce neurones

99
Q

Are all the cells in your body genetically identical?

A

Yes, all the cells in your body are genetically identical and have a complete copy of your DNA, except for red blood cells and gametes.

100
Q

Are all the cells in your body genetically identical, and do they use all the same genes?

A

Yes, all the cells in your body are genetically identical and have a complete copy of your DNA (except for red blood cells and gametes). However, they may only need to use some of the genes depending on their specific function.

101
Q

What does it mean when a gene is expressed?

A

When the information from a gene is used to make a protein.

102
Q

What is it called when the info. from a gene is used to make a protein?

A

We say the gene is expressed.

103
Q

What does it mean when a gene is expressed, and how does this relate to specialized cells?

A

When the information from a gene is used to make a protein, the gene is said to be expressed. Each specialized cell only expresses the genes it needs to carry out its specific function.

104
Q

How are newley formed embryo cells different from its cells in later stages?

A

Its cells have not yet developed and specialized, so they are stem cells.

105
Q
A

Biology IGCSE (20 decks)

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