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Inherited change 2 Flashcards

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1
Q

What are homologous chromosomes?

A

They are a pair of chromosomes in a diploid cell that have the same structure as each other, with the same genes (but not necessarily the same alleles of those genes) at the same loci, and that pair together to form a bivalent during the first division of meiosis

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2
Q

What is a gene?

A

A length of DNA that codes for a particular protein or polypeptide

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3
Q

What is an allele?

A

A particular variety of a gene

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4
Q

What is a locus?

A

The position at which a particular gene is found on a particular chromosome; the same gene is always found at the same locus

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5
Q

What is a genotype?

A

A genotype is the alleles possessed by an organism

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6
Q

What does homozygous mean?

A

Having two identical alleles of a gene

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7
Q

What does heterozygous mean?

A

Having two different alleles of a gene

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8
Q

What is an organism’s phenotype?

A

It’s characteristics, often resulting from an interaction between its genotype and its environment

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9
Q

What is a dominant allele?

A

Is one whose effect on the phenotype of a heterozygote is identical to its effect in a homozygote

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10
Q

What is a recessive allele?

A

One that is only expressed when no dominant allele is present

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11
Q

What are codominant alleles?

A

Both have an effect on the phenotype of a heterozygous organism

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12
Q

What is the F1 generation?

A

The F1 generation is the offspring resulting from a cross between an organism with a homozygous dominant genotype, and one with a homozygous recessive genotype

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13
Q

What is the F2 generation?

A

The offspring resulting from a cross between two F1 (heterozygous) organisms

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14
Q

What is a test cross?

A

A test cross is a genetic cross in which an organism showing a characteristic caused by a dominant allele is crossed with an organism that is homozygous recessive; the phenotypes of the offspring can be a guide to whether the first organism is homozygous or heterozygous

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15
Q

What is linkage?

A

Linkage is the presence of two genes on the same chromosome, so that they tend to be inherited together and do not assort independently

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16
Q

What does the nuclei of eukaryotic cells contain?

A

Chromosomes and that the number of chromosomes is characteristic of the species

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17
Q

What is a karyogram? How are they prepared?

A
  • Definition

- They are prepared by cutting out individual chromosomes from a picture and rearranging them

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18
Q

Describe a karyogram chromosome

A
  1. There are 22 matching pairs of chromosomes and these are called homologous chromosomes, each pair is given a number
    - In the original zygote one of each pair came from the mother, and one from the father
    - There is also a non-matching pair labelled X and Y, there are therefore two sets of 23 chromosomes, and one set of 23 from the father and a set of 23 from the mother
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19
Q

What are the non-matching X and Y chromosomes?

A
  1. The non-matching X and Y chromosomes are the sex chromosomes, which detainee the sex of the individual
  2. All the other chromosomes are called autsomes
    - It is conventional to position the two sex chromosomes to one side in a karyogram, so that the sex of the organism can be recognised quickly
  3. In humans, females have two X chromosomes and males have one X and one Y chromosome
    - The Y chromosome has protons missing and is therefore smaller than the X chromosome
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20
Q

How can the pairs of chromosomes be distinguished?

A

-The pairs of chromosomes can be distinguished not only by size and shape, nut because each pair has a distinctive banding pattern when stained with certain stains

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21
Q

What does each chromosome have?

A
  • A characteristic set of genes which code for different features
  • Scientists are gradually identifying which genes are located on which chromosome and what their precise functions are e.g. we now know that the gene for the genetic disorder cystic fibrosis is located on chromosome 7
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22
Q

How many gene loci does each chromosome have?

A
  • Each chromosome typically has several hundred to several thousand gene loci
  • The total number of different genes in humans is thought to be about 20000-25000
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23
Q

Describe alleles

A
  1. Each member of a homologous pair possess genes controlling the same characteristics
  2. A gene for a given characteristic may exist in different forms (alleles) which are expressed differently
    - E.G the gene for eye colour has two forms, or alleles, one coding for blue eyes and one for brown eyes, an individual could possess both alleles, one on the maternal chromosome and the other on the paternal chromosome
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24
Q

What are diploid cells?

A
  • Cells that contain two complete sets of chromosomes
  • This is represented as 2n where n=the number of chromosomes in one set of chromosomes
  • E.G. normal body cells
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25
Q

What are haploid cells?

A
  • A cell which contains only one complete set of chromosomes
  • This is represent as n
  • E.G gametes
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26
Q

What is the type of nuclear division for growth?

A
  1. When a diploid zygote, which os one cells grows into an adult with millions of cells, the new cells must be genetically identical, with the same number of chromosomes as the cells that divided to produce them
  2. This type of nuclear division that achieves this is mitosis
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27
Q

What is the type of nuclear division for sexual reproduction?

A
  1. For the life cycle to contain sexual reproduction, there must be a point before fertilisation takes place when the number of chromosomes is halved
  2. This results in the gametes containing only one set of chromosomes, rather than two sets
  3. If there were no point in the life cycle when the number of chromosomes halved, then the number of chromosomes would double every generation
  4. The type of nuclear division that halves the chromosome number is called meiosis
    - Gametes are always haploid as a result of meiosis
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28
Q

Why is meiosis sometimes described as reduction division?

A

-The number of chromosomes is reduced

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29
Q

What does meiosis also do rather than just halve the number of chromosomes?

A
  • Introduces genetic variation into the gametes and therefore the zygotes that are produced
  • Genetic variation may also arise as a result of mutation, which can occur at any stage in a life cycle
  • Such variation is the raw material on which natural selection has worked to produce the huge range of species that live on earth
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30
Q

What is genetic variation?

A

The occurrence od genetic differences between individuals

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31
Q

What does the Hb stand for and subscript A and S?

A
  • Hb stand for the locus of the haemoglobin gene

- A and S stand for particular alleles of the gene

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32
Q

What are the different haemoglobin genotypes and phenotypes?

A
  • In a human cell which is diploid there are two copies of the beta goblin polypeptide gene and the two copies may be: (with two different alleles, there are three possible genotypes)
    1. HbAHbA (homozygous) (all of haemoglobin will be normal) (normal)
    2. HbAHbS (heterozygous) (half normal haemoglobin and glad sick cel haemoglobin) (normal but with sickle cell trait)
    3. HbSHbS (all of person’s haemoglobin will be sickle cell haemoglobin which is insufficient at transporting oxygen) (sickle cell anaemia)
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33
Q

What is an example of codominance?

A
  • A snap dragon with genotype CRCW has some red colour and somewhat colour, so that the flowers appear pink
  • Alleles that behave like this are said to be codominant
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34
Q

What is sickle cell anaemia?

A

A genetic diseases caused by a faulty gene coding for haemoglobin in which haemoglobin tends to precipitate when oxygen concentrations are low

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35
Q

What is sickle cell trait?

A

A person who is heterozygous for the sickle cell allele is said to have sickle cell trait; there are normally no symptoms, except occasionally in very severe conditions of oxygen shortage

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36
Q

What is multiple alleles?

A
  • Most genes have more than two alleles
  • E.G gene for human blood groups
  • The existence of three or more alleles of a gene, as, for example in the determination of A,B,O blood groups
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37
Q

What are sex chromosomes?

A

The pair of chromosomes that determine the sex of an individual; in humans they are X and Y chromosomes

38
Q

What are autosomes?

A

All the chromosomes except the X and Y (sex) chromosomes

39
Q

What does the X chromosomes contain?

A

-Many different genes for example the genes that codes for the production of the protein needed for blood clotting, factor VIII

40
Q

What are the two alleles of the factor VIII?

A
  • Two alleles of this gene
    1. Dominant one H producing normal factor VIII
    2. Recessive one h resulting in a lack of factor VIII
  • The restive allele causes haemophilia in which blood fails to clot properly
41
Q

How does the fact that the gene is on the X chromosome affect thing?

A
  1. The fact that the gene for haemophilia is on the X chromosome, and not on an autosome, affects the way that it is inherited
  2. Females who have two copies of the gene
  3. Males only have one X chromium, and so have only one copt of the gene
  4. Therefore the possible genotypes for men and mean are different
    XHXh XHXh XhXh (lethal) XHY XhY (haemophilia)
    -Factor VIII gene is said to be sex linked
42
Q

What is a sex linked gene?

A
  • One that is found on a part of the X chromosome not matched by the Y, and therefore not found on the Y chromosome
  • Genotypes, including sex-linked genes are always represented by symbols that should they are on the X chronometer and not on Y
43
Q

Describe independent assortment

A

-In meiosis to produce gametes, the pairs of homologous chromosomes line up independently of each other on the equator during metaphase 1
-There are two ways in which the two pairs of chromosomes can do this
0If there are many such cells undergoing meiosis, then the chromosomes in roughly half of them will probably line up in one way and other half will line up in another way

44
Q

What is the ratio of a typical dihybrid cross between two heterozygous organisms where the two alleles snow complete dominance and where the genes are on different organisms?

A

9:3:3:1

45
Q

What are some of the interactions between alleles at the same locus?

A
  1. Codominant alleles in flower colour in snapdragons
  2. Dominant and receive alleles in tomato plant stem colour
  3. Multiple alleles in the inheritance of the ABO blood groups
46
Q

What is an example of a case when different loci interact to affect one phenotypic character?

A
  • Inhertiance of feather colour in chickens, where there is an interaction between two gene loci I/I C/c
  • I white
  • C coloured
47
Q

What happens to the ratio when you cross a IICC and iicc?

A

-All IiCc and all white
-Then breed IiCc together:
13 white: 13 coloured

48
Q

What is the ratio in the interaction shown by the inheritance of flower colour in Salvia?

A
  • A pure breeding pink crossed with pure breeding white. offspring had purple flower
  • Interbreeding these offspring to give another generation resulted in purple, pink and white flowered plants in a ration 9:3:4
49
Q

What are the chromosomes in Salvia with two loci A/a and B/b on different chromosomes? What is the impact?

A

AB: purple
Abb: pink
aaB: white
aabb: white
-The homozygote recessive aa affect the B/b locus
-Neither the dominant allele B for purple flower colour, nor the recessive alleles b for pink flower can be expressed in the absence of a dominant A allele

50
Q

What happens if genes are linked?

A
  • When two or more gene loci are on the same chromosome, they do not assort independently in meiosis as they would if they were on different chromosomes (the genes are said to be linked)
  • Genes on a chrome other than the sex chromosomes are said to be autosomal linked
51
Q

What is linkage?

A

The prescience of two genes on the same chromosome, so that they tend to be inherited together and do not assort independently

52
Q

What is an example of linkage?

A
  • The fruit fly drosophila normally has a stripped body and antennae with a feathery artista
  • The gene for body colour and the gene for antennal shape are close together on the same chromosome and so are linked
  • A black body with not tried results from a recessive alleles called ebony
  • A recessive allele for antennal shape called ‘aristoppedia’ gives antenna looking like a drosophila leg with two claws on the end
53
Q

How do you write linked alleles?

A

(EA)(EA) and not EEAA which would indicate that the genes were not on the same chromosome

54
Q

How does the dihybrid cross of linked alleles behave?

A

As a monohybrid cross and the alleles that went into the costs together remained together

55
Q

Describe linkage

A
  • The genes of any organism fall into a number of linkage groups equal to the number of pairs of homologous chromosomes
  • Total linkage is very rare
  • Almost always, the linkage groups ar broken by crossing over during meiosis
  • In male drosophila was test crossed to show the effect of linkage since there is no crossing over in Male drosophila
56
Q

What is crossing over?

A
  1. During prophase I of meiosis a pair of homologous chromosomes (a bivalent) can be joined by chiasmata
  2. The chromatids of a bivalent may break and reconnect to another, non-sister chromatid
  3. This results in an exchange of gene loci between a maternal and paternal chromatid
57
Q

What happens as you test cross female drosophila?

A
  1. Large number of parental type of flies are produced in a 1:1 ratio
  2. Smaller numbers of recombinant flies are produced
    - These result from crossing over and ‘recombine’ the characteristic of the original parents into some flies that have a striped body and abnormal antenna and other and ones with ebony body and normal antennae
  3. The two recombinant classes are in a 1:1 ratio
58
Q

What is the cross over value?

A
  1. The percentage of offspring that belong the recombinant class e.g. 6% + 6% = 12%
  2. This is a measure of the distance apart of the two gene loci on their chromosomes
  3. The smaller the cross-over value, the closer the loci are together
  4. The change of a cross over taking place between two loci is directly related to their distance apart
59
Q

Describe genes and alleles

A
  • Most genes have several variants called alleles
  • A gene is made up of a sequence of nucleotides each with its own base
  • The different alleles of a gene contain slightly different sequences of bases
60
Q

What did these different alleles originally rise from?

A

Mutation

61
Q

What is a mutation?

A
  • An unpredictable change in the genetic material of an organism
  • Mutations may occur randomly with no obvious cause
62
Q

What is a gene mutation?

A

A change in the structure of a DNA molecule producing a different allele of a gene

63
Q

What is a chromosome mutation

A

A change in the structure or number of whole chromosomes in a cell

64
Q

What is an example an environmental factor that significantly increases the chances of a mutation occurring?

A
  1. All types of ionising radiation can damage DNA molecules, altering the structure of the bases in them
  2. ultraviolet radiation, mustard gas
65
Q

What is a mutagen?

A

A substance that increases the chance of mutation occurring

66
Q

What re the three different ways in which the sequence of bases in a gene can be altered?

A
  1. Base substitution, where one base simply takes the place of another e.g. CAG t GTG
  2. Base addition, w ere one or more extra bases are added to the sequence CCT GAG to CCA TGA
  3. Base deletion, where one or more bases are lost from the sequence CCT GAG to CCG AGG
67
Q

What is the effect of base addition or deletions?

A
  • Very significant effect on the structure and therefore the function of the polypeptide that the allele codes for
  • Base addition or deletions always have large effects because they alter every set of three bases that ‘follows’ them int he DNA molecule
  • Often the effects are os large that the protein made may be useless or may introduce a ‘stop’ triplet so that a complete protein is not made
68
Q

What do base additions or deletions cause?

A

Frame shifts in the code

69
Q

What do base substitutions cause?

A
  • Often have no effect at all
  • Often silent mutations because many amino acids have more than one triplet code, so even if one base is changed, the same amino acid is coded for
  • Base substitutes can have large effects as may change to stop triplet so the synethesis of the protein may stop from this point
70
Q

What is a silent mutation?

A

A mutation that has no apparent effect on an organisms

71
Q

What type of mutation is in sickle cell anaemia?

A
  1. Base substitution

2. Base sequence CTT is replaced by CTT so Glu goes to Val

72
Q

What does this difference in amino acid sequence in sickle cell anaemia?

A
  • Makes little difference to haemoglobin molecule when combined to oxygen
  • When not combined to oxygen makes haemoglobin less soluble
    1. The molecules tend to stick to each other forming long fibres inside red blood cells
    2. The rbc are pulled out of shape into a sickle shape
    3. When this happens the distorted cells become useless at transporting oxygen
    4. They also get stuck in small capillaries stopping any unaffected cells from getting through
  • A person with this unusual beta glib can suffer every anaemia (lack of oxygen transported to cells) and may die, it is more common in Africa and India
73
Q

What is albanism?

A
  • The dark pigment melatonin is missing completely or partially from eyes skin and hair
  • So pale blue or pink irises in eye and very pale skin and hair and the pupils appear red and often associated with poor vision, by rapid and jerky movements of the eyes and by tendency to avoid bright light
74
Q

What causes albanism?

A
  • Mutations at several loci but classical an autosomal recessive and individuals are homozygous for the recessive allele
    1. Mutations in the gene for the enzyme tyrosinase results in absence of it or inactive form in the cells repsosnbile for melatonin production
    2. In these melanocytes, the first two steps of the conversion of the amino acid, tyrosine into melanin cannot take place
    3. Tryosine cannot be converted into DOPA and dopaquinonine
75
Q

What is tyrosinase?

A
  • An oxidase and has two copper atoms in its active site which bind an oxygen molecule
  • It is a transmembrane protein and is found in the membrane of large organelles in the melanocytes called melanosomes
  • Most of the protein, including the active side is inside the melanosome
  • Tyrosinases also occur in plant as well as in animal tissues, the action of the enzyme can be seen in the blackening of a slice of port left exposed to the air
76
Q

What is Huntington’s disease?

A
  • A mutation that is inherited as a dominant allele
  • A neurological disorder resulting in involuntary movements (chorea) and progressive mental deterioration
  • Brain cells are lost and the ventricles become larger
  • Age of onset mostly middle age
77
Q

What causes Huntington’s?

A
  1. The mutation is an unstable segment in a gene on chromosome 4 coding for a protein Huntingtin
  2. In people who do not have HD, the segment is made up of a small number of repeats of the triplet of bases CAG
  3. People with HD have a larger number of repeats of the CAG triplet and this is called a ‘stutter’
  4. There is a rough inverse correlation between the number of times the triplet of bases is repeated and the age of onset of the condition: the more stutters the earlier the condition appears
78
Q

What is factor VIII?

A

One of the several substances that must be present in blood in order for clotting to occur

79
Q

What is haemophilia?

A

A genetic disease in which there is an insufficient amount of a clotting factor such as factor VIII in the blood

80
Q

What is a sex linked gene?

A

A gene that is carried on an X chromosome but not on a Y chromosome

81
Q

What is a monohybrid crosses?

A

A cross in which the inheritance of one gene is considered

82
Q

What is a dihybrid crosses?

A

A genetic cross in which two different genes are considered

83
Q

What is a chiasmata?

A

The physical effect(s) of crossing over

84
Q

What is a gene mutation?

A

A change in the base sequence in part of a DNA molecule

85
Q

What is a chromosome mutation?

A

A random and unpredictable change in the structure or number of chromosomes in a cell

86
Q

What is a mutagen?

A

A substance that can cause mutation

87
Q

What is a silent mutation?

A

A mutation in which the change in the DNA has no discernible effect on an organism

88
Q

What is an operon?

A

A group of structural genes headed by a non-coding sequence of DNA called the operator

89
Q

What is a sex linked gene?

A
  • sex linked: gene carried on one sex chromosome and not the other
  • gene: section of DNA that codes for a specific protein
90
Q

What is dominat?

A

Always expresses itself (in the phenotype when present)

91
Q

Why might people not want to take a blood test?

A
  • dear of needles
  • dear of positive results
  • fear of effect of result on other members of the family
  • no desire to have children
  • financial / insurance concerns
  • possibility of false result
  • costs of tests
  • not worth having test as no treatment

Z A Level Biology 2 (18 decks)

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