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Biology SB > SB3 Genetics > Flashcards

SB3 Genetics Flashcards

1
Q

What do offsprings normally look like?

A

A blend of their parents.

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2
Q

Who developed the modern ideas about genes?

A

Gregor Mendel.

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3
Q

What do genes control?

A

Inherited characteristics.

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4
Q

What did Gregor Mendel observe?

A

The characteristics in pea plants from parent pea plants which were either present or absent, never blended.

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5
Q

What did Mendel do to observe this?

A

Bred pea plants together using a paintbrush to move pollen from one plant to the flower of another. he planted the seeds that formed and observed the characteristics.

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6
Q

Why did he place a bag over the flower of the plant and seal it?

A

So the moved pollen doesn’t get blown away and so the pollen of a unwanted plant didn’t get on the plant.

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7
Q

What do inherited ‘factors’ control?

A

variation of characteristics.

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8
Q

What are different versions of genes called?

A

Alleles.

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9
Q

Plants with two of the same factors were called?

A

True - Breeding.

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10
Q

What are Mendel’s three laws of inheritance?

A
  1. each gamete receives only one factor for a characteristic.
  2. the version of a factor that a gamete receives is random.
  3. Some alleles are more dominant and always have an effect on the offspring.
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11
Q

Why were Mendel’s ideas ignored?

A

~couldn’t be seen
~couldn’t be linked to Darwin’s theory of Evolution.

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12
Q

If you cross breed a white sweet pea and purple sweet pea, what will the offspring look like?

A

Depends on the alleles. If white is dominant then all offspring will be white, if purple is dominant then all the offspring will be purple.

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13
Q

What is an example of a allele?

A

Hair colour - brunette, blonde
Eye colour - blue, brown, green

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14
Q

What does dominant and recessive mean?

A

~dominant - stronger allele, always expressed (B)
~recessive - weaker allele, only expressed if two copies are present (b)

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15
Q

What does homozygous and heterozygous mean?

A

~Homozygous - two of the same allele (BB, bb)
~Heterozygous - different alleles (Bb)

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16
Q

What is phenotype and genotype?

A

~Phenotype - physical appearance coded for by genotype.
~Genotype - combination of alleles the individual has.

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17
Q

How do most animals and plants reproduce sexually?

A

By fertilisation of gametes.

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18
Q

What are the two types of sex chromosones for male and female?

A

Male - XY
Female - XX

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19
Q

How do some organisms reproduce asexually?

A

By producing clones that are genetically identical to the parent.

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20
Q

Why are carriers of diseases not affected by them?

A

They have a copy of the dominant, healthy allele.

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21
Q

What is very rare in vertebrates?

A

Asexual reproduction.

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22
Q

What is common in invertebrates?

A

Asexual reproduction.

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23
Q

Explain how the sperm cell is responsible for the determination of sex in humans?

A

If a y sperm fertilises the egg a male will be born but if a X sperm feritilises a egg a female will be born.

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24
Q

In summer, why do female aphids produce offspring asexually via mitosis?

A

Because conditions are favourable.

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25
Q

What does someone need if the lose a lot of blood?

A

A blood transfusion of the same blood type.

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26
Q

Advantages of sexual reproduction? (3)

A

.Combines characteristics from both parents, producing offspring that are different from each other.​
.This variation is advantageous if environmental conditions change.
.Variation means some offspring will be better suited to the new conditions so will be more likely to survive and reproduce.

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27
Q

What happens if someone gets given the wrong blood type in a blood transfusion?

A

The blood cells can clump together which can be fatal.

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28
Q

What are the three blood types?

A

A,B and O.

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29
Q

What are the 4 blood groups?

A

A, AB, B or O.

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30
Q

What are the alleles responsible for the ABO markers?

A

lA, lB, lO

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31
Q

How many copies of alleles do humans have, and why?

A

Two copies so could be homozygous or heterozygous.

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32
Q

What allele for blood groups is recessive?

A

lo

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33
Q

If someone has the alleles lA and lB what blood group will they be and why?

A

AB because the alleles are equally dominant, codominance.

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34
Q

What is the word for alleles being equally dominant to each other?

A

Codominance.

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35
Q

Which sex chromosome is missing genes?

A

Y chromosome.

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36
Q

Are men or women more likely to develop sex - linked genetic disorders and why?

A

Men because they only need one X chromosome to inherit the disease whilst women need two diseased X chromosomes to inherit it, meaning they can have one healthy and one diseased chromosomes and not be affected.

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37
Q

Explain why colour blindness tends to be more common in males than females?

A

Men only have one copy of the X chromosome so if they inherit the colour blind allele, they will develop the disorder. Women would need two copies of the recessive allele to be colour blind.

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38
Q

Why is it an advantage to have brown eyes in a hot country?

A

The colour brown is a result of high concentration of melanin in the iris causing more light to be absorbed then reflected, giving them more protection from the sun?

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39
Q

What are mutations caused by?

A

A mistake in copying DNA during cell division.

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40
Q

Why can mistakes in copying DNA during cell division occur?

A

By radiation or by exposure to toxic substances.

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41
Q

What can mutations cause? (3)

A

~Cause a protein to be made incorrectly.
~Have no effect.
~Can cause major changes in how the body functions.

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42
Q

What is all the DNA in a living organism called?

A

Genome.

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43
Q

What is the human genome project?

A

Project to map the human genome.

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44
Q

How can information about an individual’s human genome be useful in medicine? (3)

A

~Identification of new genes.
~Genes analysed for mutations causing disease. - predict diseases in humans.
~To target medicines for the diseases.

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45
Q

What are some human genomes negatives?

A

~People may be put under pressure to not have children or terminate the pregnancy.
~Embryo has no choice.
~May lead to ‘designer babies’ with selection for specific fashionable characteristics. e.g. Stormi baby
~May lead to discrimination with jobs.

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46
Q

Explain how mutation can lead to variation in the phenotype?

A

A mutation can change the DNA base sequence. this causes a change in the amino acid sequence which creates a different protein and this changes the phenotype.

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47
Q

What is the sickle cell allele an example of?

A

A genetic mutation.

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48
Q

What are people with the sickle cell allele more likely to survive?

A

Malaria.

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49
Q

How was the sickle cell allele passed on?

A

Many people with this trait lived long enough to reproduce and pass on the allele to their children.

50
Q

What is the disadvantage of the sickle cell allele?

A

It is possible that children may be born with sickle cell anaemia if both parents are sickle cell carriers.

51
Q

Disadvantages of sexual reproduction? (1)

A

Need to find mate to reproduce.

52
Q

Advantages of asexual reproduction? (2)

A

.Much faster than sexual reproduction as there is no need to find a mate.​
.Plants grow rapidly in the summer so aphids reproduce asexually to make the most of all the available food.

53
Q

Disadvantage of asexual reproduction? (2)

A

.Reduce variety of species
.Cloned animals have short life spans

54
Q

How is a zygote formed?

A

The nuclei of two gametes (sex cells) fuse during fertilisation.

55
Q

The zygote divides by mitosis to form what?

A

An embryo.

56
Q

Why does the zygote divide by mitosis?

A

So that all the cells in the embryo (stem cells) are genetically identical.

57
Q

State the name of humans gametes?

A

Sperm and egg.

58
Q

How many chromosome are in a human sperm cell?

A

23.

59
Q

How many chromosome are in a human liver cell?

A

46.

60
Q

How many chromosome are in a human zygote?

A

46.

61
Q

What is meiosis?

A

a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell.

62
Q

What is the purpose of meiosis?

A

to produce gametes.

63
Q

How may chromosomes do human diploid cells have?

A

46.

64
Q

Body cells are diploid which means?

A

they contain two copies of each chromosome (2n).

65
Q

How many chromosomes do human gametes have?

A

23.

66
Q

Gametes are haploid which means?

A

they contain one set of chromosomes (n).

67
Q

Gamete production process?

A
  1. The gamete-making cell has two set of chromosomes. It is diploid (2n).
  2. The chromosomes replicate (and the copies stay stuck to one another).
  3. Cell divides into two.
  4. Cell divides into two again. Each of the final four daughter cells have a copy of one chromosome from each pair. They are haploid (n).
68
Q

What is a genome?

A

the DNA of an organism.

69
Q

Where is the human genome found?

A

in 46 chromosomes.

70
Q

What is a section of DNA called?

A

a gene and codes to make protein.

71
Q

Around how many genes do humans have?

A

20 000.

72
Q

Compare mitosis and meiosis.

A

.Mitosis = body cell division, 2 daughter cells (46) diploid chromosomes.​
.Meiosis = sex cell division, 4 daughter cells (23) haploid chromosomes.​
.Both forms of cell division

73
Q

What is the human genome made up of?

A

our DNA.

74
Q

What is DNA like inside the nucleus of a cell?

A

tightly coiled into chromosomes.

75
Q

What does DNA containing two strands form?
What are the two strands hold together by?

A

a double helix.
bases.

76
Q

DNA is a polymer which is what?

A

a long molecule made from joining repeating units.

77
Q

Each DNA nucleotide is made up of what three points?

A

-phosphate​
-sugar​
-base

78
Q

What are the four complementory base pairs?

A

Adenine which pairs with Thymine​.
Cytosine which pairs with Guanine.

79
Q

Each base is attached to a sugar and phosphate group to form what?

A

the backbone of DNA.

80
Q

What is DNA made up of?

A

many similar units and is therefore a polymer.

81
Q

What do DNA bases have?

A

a slight electrical charge so are weakly attracted to each other.

82
Q

What type of bonds does cytosine and guanine have?

A

3H-

83
Q

What type of bonds does adenine and thymine have?

A

2H-

84
Q

What do differences in the order of our DNA bases cause?

A

they cause us to produce different proteins and therefore have different characteristics.

85
Q

How can DNA analysis be used?

A

to compare DNA bases and see if people are related.

86
Q

Describe the structure of DNA (3) ?

A

Double helix shape with a sugar/phosphate backbone joined by complementary bases pairs and hydrogen bonds.

87
Q

Who worked out the genetic code?

A

Watson, Crick and 22 other scientists.

88
Q

What is the genetic code?

A

the order of DNA bases caused by amino acids joined in a certain order to make a protein.

89
Q

During transcription what are the DNA bases used to make?

A

a strand of RNA (ribonucleic acid).​

90
Q

What does an enzyme, RNA polymerse, attach itself to?

A

the front of a gene in a non-coding region of DNA.​

91
Q

What does non-coding mean?

A

does not code for a protein / amino acid.

92
Q

An enzyme breaks the hydrogen bonds between bases, separating the strands to form what?

A

two template strands.

93
Q

What does the RNA polymerase move along?

A

the DNA template strand adding complementary RNA nucleotides.

94
Q

RNA contains the same bases as DNA other than what?

A

uracil which replaces thymine.

95
Q

What do the RNA nucleotides join together to make?

A

a strand of messenger RNA (mRNA) which leaves the nucleus.​

96
Q

mRNA leaves the nucleus, through small holes in the membrane called what?

A

nuclear pores.

97
Q

What does mRNA travel to?

A

ribsosomes in the cytoplasm.

98
Q

What does the ribosome move along?

A

an mRNA strand, three bases (a triplet) at a time.

99
Q

What is each triplet of bases called?

A

a codon.

100
Q

What happens at each mRNA codon?

A

a molecule called transfer RNA (tRNA) with complementary bases attaches.

101
Q

What does each tRNA molecule carry?

A

a specific amino acid.

102
Q

What happens as the ribosome moves along the mRNA?

A

more tRNA molecules attach, joining the amino acids in order.

103
Q

What do joined amino acids form?
What is this process called?

A

a polypeptide.
translation.

104
Q

What does the ploypeptide chain fold to form?

A

a protein (such as an enzyme) with a specific shape.

105
Q

What are some proteins made up more of?

A

one polypeptide chain.

106
Q

Who worked out which codons coded for each amino acid?

A

Indian born scientist Har Gobind Khorana.

107
Q

What creates a mutation (or genetic variation)?

A

a change in the bases of a gene

108
Q

What causes a change in the bases of a gene?

A

when DNA is not copied correctly in cell division or by environmental factors.​

109
Q

What can be caused by multiple mutations?

A

one gene having many alleles.

110
Q

What are your characteristic determined by?

A

the alleles you inherit.

111
Q

What does haemoglobin contain?

A

four polypeptides, two α and two β.

112
Q

What is haemoglobin?

A

a spherical protein that carries oxygen.

113
Q

There are different alleles of the β-polypeptide gene.
What happens at alleles 1?

A

result in the correctly folded protein.​

114
Q

What happens at allele 2?

A

folds incorrectly, causing sickle cell disease.​

115
Q

What happens at allele 3?

A

folds incorrectly, causing red blood cells to break apart causing shortness of breath.

116
Q

What does RNA polymerase attach itself to?

A

DNA bases in front of a gene.

117
Q

What might a mutation in the DNA bases in front of a gene prevent?
What can this mutation cause?

A

RNA polymerase binding correctly, reducing transcription.
β-thalassaemia, where a lack of β-polypeptide is made causing tiredness, weakness and shortness of breath.​

118
Q

What can other non-coding mutations increase?

A

RNA polymerase binding, producing more mRNA.

119
Q

What is haemophilia?

A

an inherited disorder in which the blood doesn’t clot easily. People with haemophilia are unable to produce an enzyme that is needed in the blood clotting process.

120
Q

What kind of molecule is an enzyme?

A

a protein.

121
Q

What is one genetic varient causing haemophilia?

A

loss of a single base in the part of the DNA just before the gene that codes for the enzyme.

122
Q

What does the loss of one base in the part of the DNA just before the gene for the blood-clotting enzyme mean?

A

the RNA polymerase cannot bind to the DNA.

Biology SB (4 decks)

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