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IGCSE Biology - Extended > Inheritance > Flashcards

Inheritance Flashcards

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1
Q

What is inheritance?

A

Inheritance is the transmission of genetic information from generation to generation

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2
Q

Where are chromosomes located?

A

Chromosomes are located in the nucleus of cells

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3
Q

What are chromosomes?

A

They are thread-like structures of DNA, carrying genetic information in the form of genes

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4
Q

What is a gene?

A

A gene is a short length of DNA found on a chromosome that codes for a specific protein (characteristic)

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5
Q

What is an example of a gene?

A

This could be a structural protein such as collagen found in skin cells, an enzyme or a hormone

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6
Q

What do genes control?

A

Genes control our characteristics

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7
Q

How do genes control our characteristics?

A

they code for proteins that play important roles in what our cells do

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8
Q

What is an allele?

A

Alleles are different versions of a particular gene

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9
Q

How many DIFFERENT chromosomes do humans have?

A

All humans have 23 different chromosomes in each cell

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10
Q

How many chromosomes do people have in general?

A

In most body cells, we have 2 copies of each chromosome, leading to a total of 46 chromosomes

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11
Q

What cells are an exception to having 46 chromosomes? How many do they have?

A

The gametes (egg and sperm cells) only have one copy of each chromosome, meaning they have a total of 23 chromosomes in each cell

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12
Q

What does it mean if a cell has a DIPLOID NUCLEI?

A

Nuclei with two sets of chromosomes are known as diploid nuclei

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13
Q

What does it mean if a cell has a HAPLOID NUCLEI?

A

Nuclei with one set of unpaired chromosomes are known as haploid nuclei

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14
Q

What is sex determined by?

A

Sex is determined by an entire chromosome pair (as opposed to most other characteristics that are just determined by one or a number of genes)

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15
Q

What sex chromosomes do females have?

A

XX

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16
Q

What sex chromosomes do males have?

A

XY

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17
Q

Who is responsible for determining the sex of the child?

A

As only a father can pass on a Y chromosome, he is responsible for determining the sex of the child

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18
Q

How can you show the inheritance of sex?

A

The inheritance of sex can be shown using a genetic diagram (known as a Punnett square)

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19
Q

What is different between a genetic diagram for sex inheritance and inheritance of other features?

A

the X and Y chromosomes taking the place of the alleles usually written in the boxes

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20
Q

What happens before a cell divides?

A

When cells divide their chromosomes double beforehand

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21
Q

Why do the chromosomes in a cell double before cell division?

A

This ensures that when the cell splits in two, each new cell still has two copies of each chromosome (is still diploid)

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22
Q

When is mitosis used?

A

This type of cell division is used for growth, repair of damaged tissues, replacement of cells and asexual reproduction

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23
Q

What is the definition of mitosis?

A

Mitosis is defined as nuclear division giving rise to genetically identical cells

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24
Q
  1. What is the first step to prepare for mitosis?
A

Just before mitosis, each chromosome in the nucleus copies itself exactly (forms x – shaped chromosomes)

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25
Q
  1. What happens after the chromosomes double before mitosis?
A

Chromosomes line up along the centre of the cell

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26
Q
  1. What happens to the chromosomes once they line up along the centre of the cell?
A

cell fibres pull them apart

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27
Q
  1. What happens once the cell fibres pull the chromosomes apart?
A

The cell divides into two; each new cell has a copy of each of the chromosomes

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28
Q

Why is mitosis so important?

A

All cells in the body (excluding gametes) are produced by mitosis of the zygote

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29
Q

What does mitosis replace?

A

Mitosis is important for replacing cells e.g, skin cells, red blood cells and for allowing growth (production of new cells e.g. when a zygote divides to form an embryo)

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30
Q

What 3 processes does mitosis occur in?

A

Growth
Repair
Asexual reproduction

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31
Q

How does mitosis help in growth?

A

mitosis produces new cells

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32
Q

How does mitosis help in repair?

A

to replace damaged or dead cells

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33
Q

How does mitosis help in asexual reproduction?

A

mitosis produces offspring that are genetically identical to the parent

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34
Q

What do all tissues in the human body contain?

A

Many tissues in the human body contain a small number of unspecialised cells

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35
Q

What are unspecialised cells called?

A

These are called stem cells

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36
Q

What is the function of stem cells?

A

their function is to divide by mitosis and produce new daughter cells that can become specialised within the tissue and be used for different functions

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37
Q

What type of cells does meiosis produce?

A

Meiosis is a type of nuclear division that gives rise to cells that are genetically different

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38
Q

What is meiosis used to produce?

A

It is used to produce the gametes (sex cells)

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39
Q

What must

meiosis result in?

A

The number of chromosomes must be halved when the gametes (sex cells) are formed

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40
Q

Why must the number of chromosomes be halved before meiosis?

A

Otherwise there would be double the number of chromosomes after they join at fertilisation in the zygote (fertilised egg)

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41
Q

What is meiosis described as?

A

This halving occurs during meiosis, and so it is described as a reduction division in which the chromosome number is halved from diploid to haploid, resulting in genetically different cells

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42
Q
  1. What happens at the beginning of meiosis?
A

It starts with chromosomes doubling themselves as in mitosis and lining up in the centre of the cell

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43
Q
  1. What happens after the chromosomes have lined up?
A

recombination occurs and then cell fibres will pull the pairs apart, each new cell will have one of each recombinant chromosome pair

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44
Q
  1. What happens in the second division?
A

chromosomes will line up along the centre of the cell, cell fibres will pull them apart (as with mitosis)

45
Q
  1. How many cells does meiosis form and how can they be described?
A

Because of this double division, meiosis produces four haploid cells

46
Q

What are examples of cells produced by meiosis?

A

Production of gametes e.g. sperm cells and egg cells, pollen grains and ovum

47
Q

What does meiosis help with?

A

Increases genetic variation of offspring

48
Q

How does meiosis increase genetic variation?

A

Meiosis produces variation by forming new combinations of maternal and paternal chromosomes every time a gamete is made, meaning that when gametes fuse randomly at fertilisation, each offspring will be different from any others

49
Q

What is the difference between mitosis and meiosis in the number of cells produced?

A

MI - two cells produced (known as daughter cells)

ME - four cells produced (known as daughter cells)

50
Q

What is the difference between mitosis and meiosis in the daughter cells?

A

MI - diploid

ME - haploid

51
Q

What is the difference between mitosis and meiosis in the genetic differentiation of the daughter cells?

A

MI - genetically identical to each other and to the parent cell
ME - genetically different from each other and the parent cell

52
Q

What is the difference between mitosis and meiosis in the number of divisions?

A

MI - one cell division occurs

ME - two cell division occurs

53
Q

How many copies of each chromosome do we have?

A

2

54
Q

How many copies do we have of each gene?

A

2 copies

55
Q

How many copies do we have of each allele (for each gene)?

A

2

56
Q

Why do we have 2 different alleles?

A

One of the alleles is inherited from the mother and the other from the father

57
Q

What is a phenotype?

A

The observable characteristics of an organism (seen just by looking – like eye colour, or found – like blood type) is called the phenotype

58
Q

What is a genotype?

A

The combination of alleles that control each characteristic is called the genotype

59
Q

What 2 types of allele can there be?

A

Alleles can be dominant or recessive

60
Q

What is the difference between recessive and dominant alleles in relation to the phenotype?

A

A dominant allele only needs to be inherited from one parent in order for the characteristic to show up in the phenotype

A recessive allele needs to be inherited from both parents in order for the characteristic to show up in the phenotype.

61
Q

What happens if there is only one recessive allele?

A

If there is only one recessive allele, it will remain hidden and the dominant characteristic will show

62
Q

What does it mean if a person is homozygous?

A

If the two alleles of a gene are the same, we describe the individual as being homozygous

63
Q

What two different types of homozygous can a person be?

A

homozygous recessive

homozygous dominant

64
Q

What does it mean if a person is homozygous recessive?

A

having two copies of the recessive allele

65
Q

What does it mean if a person is homozygous dominant?

A

having two copies of the dominant allele

66
Q

What does it mean if a person is heterozygous?

A

If the two alleles of a gene are different, we describe the individual as being heterozygous

67
Q

What letter represents a dominant and recessive allele in a genetic diagram?

A

The dominant allele is given a capital letter and the recessive allele is given the same letter, but lower case

68
Q

Can we tell the genotype from a person’s phenotype?

A

We cannot always tell the genotype of an individual for a particular characteristic just by looking at the phenotype

69
Q

Why can’t we always tell a persons genotype from the phenotype?

A

a phenotype associated with a dominant allele will be seen in both a dominant homozygous and a dominant heterozygous genotype

70
Q

What offspring will be produced if identically homozygous individual reproduce?

A

If two individuals who are both identically homozygous for a particular characteristic are bred together, they will produce offspring with exactly the same genotype and phenotype as the parents

71
Q

Why is crossing two homozygous individuals called pure-breeding?

A

We describe them as being ‘pure breeding’ as they will always produce offspring with the same characteristics

72
Q

Can heterozygous individuals participate in pure breeding?

A

A heterozygous individual can pass on different alleles for the same characteristic each time it is bred with any other individual and can therefore produce offspring with a different genotype and phenotype than the parents – as such, heterozygous individuals are NOT pure breeding

73
Q

What is a monohybrid inheritance?

A

Monohybrid inheritance is the inheritance of characteristics controlled by a single gene (mono = one)

74
Q

What does a punnett square show?

A

A Punnett square diagram shows the possible combinations of alleles that could be produced in the offspring

75
Q

What is the ratio D to R when two heterozygous individuals are crossed?

A

There is more variation in this cross, with a 3:1 ratio of tall : short, meaning each offspring has a 75% chance of being dominant and a 25% chance of being recessive

76
Q

What is the ratio D to R when one homozygous recessive individual and one heterozygous individual are crossed?

A

In this cross, there is a 1:1 ratio of dominant to recessive, meaning a 50% chance of the offspring being dominant and a 50% chance of the offspring being recessive

77
Q

How can you find an unknown genotype?

A

Breeders can use a test cross to find out the genotype of an organism showing the dominant phenotype

78
Q

What does a test cross involve?

A

This involves crossing the unknown individual with an individual showing the recessive phenotype – if the individual is showing the recessive phenotype, then its genotype must be homozygous recessive

79
Q

How can we tell if the individual is heterozygous or homozygous from the test cross?

A

By looking at the ratio of phenotypes in the offspring, we can tell whether the unknown individual is homozygous dominant or heterozygous

80
Q

How can we tell from the test cross that the organism is homozygous dominant?
tall and short plants

A

If the tall plant is homozygous dominant, all offspring produced will be tall

81
Q

How can we tell from the test cross that the organism is heterozygous?
tall and short plants

A

If the tall plant is heterozygous, half the offspring will be tall and the other half will be short

82
Q

What are family pedigree diagrams used to show?

A

Family pedigree diagrams are usually used to trace the pattern of inheritance of a specific characteristic (usually a disease) through generations of a family

83
Q

What can we find out by a family pedigree?

A

This can be used to work out the probability that someone in the family will inherit the genetic disorder

84
Q

What is an example of codominance?

A

Inheritance of blood group

85
Q

What alleles are dominant and codominant in blood groups?

A

Alleles IA and IB are codominant, but both are dominant to IO

86
Q

What does the letter I represent in blood group alleles?

A

I represents the gene and the superscript A, B and O represent the alleles

87
Q

What does IA produce in the blood?

A

IA results in the production of antigen A in the blood

88
Q

What does IB produce in the blood?

A

IB results in the production of antigen B in the blood

89
Q

What does IO produce in the blood?

A

IO results in no antigens being produced in the blood

90
Q

What does it mean if a characteristic is sex-linked?

A

When alleles that control a particular characteristic are found on the sex chromosomes, we describe the inheritance that results as ‘sex linked’

91
Q

On which chromosome are the alleles usually on and why?

A

In almost all cases, there are only alleles on the X chromosome as the Y chromosome is much smaller

92
Q

Why are males more likely to inherit sex-linked conditions?

A

Because males only have one X chromosome, they are much more likely to show sex-linked recessive conditions (such as red-green colour blindness and haemophilia)

93
Q

Why are females less likely to inherit sex-linked conditions?

A

Females, having two copies of the X chromosome, are likely to inherit one dominant allele that masks the effect of the recessive allele

94
Q

What is a woman known as if she has one recessive allele?

A

A female with one recessive allele masked in this way is known as a carrier; she doesn’t have the disease,

95
Q

What is the chance that a female carriers offspring will have a sex-linked condition?

A

she has a 50% chance of passing it on to her offspring

If that offspring is a male, he will have the disease

96
Q

What would be the result of a male who is colourblind a female carrier crossing?

A

In the cross above, there is a 25% chance of producing a male who is colourblind, a 25% chance of producing a female carrier, a 25% chance of producing a normal female and a 25% chance of producing a normal male

97
Q

What are proteins made by?

A

Proteins are made by ribosomes

98
Q

What forms proteins and what are they controlled by?

A

the sequence of amino acids controlled by the sequence of bases contained within DNA

99
Q

Can DNA travel outside the nucleus? Why?

A

DNA cannot travel out of the nucleus to the ribosomes (it is far too big to pass through a nuclear pore)

100
Q

How is the base code copied from the nucleus if it can’t leave the nucleus?

A

the base code of each gene is transcribed onto an RNA molecule called messenger RNA (mRNA).

101
Q

What happens once the base code has been transcribed to mRNA?

A

mRNA then moves out of the nucleus and attaches to a ribosome

102
Q

What does the ribosome do once it receives the mRNA?

A

The ribosome ‘reads’ the code on the mRNA in groups of three

103
Q

What does each triplet of bases do?

A

Each triplet of bases codes for a specific amino acid

104
Q

What does the ribosome do with the sequence of bases?

A

In this way the ribosome translates the sequence of bases into a sequence of amino acids that make up a protein

105
Q

What happens once the amino acid has been assembled?

A

Once the amino acid chain has been assembled, it is released from the ribosome so it can fold and form the final structure of the protein

106
Q

What does DNA control and how?

A

DNA controls cell function by controlling the production of proteins

107
Q

What are examples of proteins?

A

The proteins may be enzymes, antibodies, or receptors for neurotransmitters

108
Q

Why are some genes in certain cells not expressed?

A

Although all body cells in an organism contain the same genes, many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs

IGCSE Biology - Extended (22 decks)

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