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Biology > Inheritance > Flashcards

Inheritance Flashcards

1
Q

What is a gene?

A

a sequence of dna that codes for a polypeptide

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2
Q

What is a locus?

A

A genes specific site on a chromosome

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3
Q

What is an allele?

A

A variant nucleotide sequence for a specific gene that codes for a different phenotype.
Basically different forms of the same gene
E.g. the allele for eyes could be blue or brown

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4
Q

What does homozygous mean?

A

It means the that alleles for a particular gene given from the parents are both the same.

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5
Q

What does heterozygous mean?

A

It means that the alleles for a particular gene given from the parents are different.

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6
Q

What is the genotype?

A

All the alleles an individual contains

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7
Q

What is the phenotype?

A

Characteristics, but it includes all hidden characteristics too like blood type

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8
Q

What determines the phenotype of an individual?

A

The environment and the genotype.

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9
Q

What is a dominant allele?

A

The allele that is always expressed

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10
Q

What is a recessive allele?

A

The allele that is expressed if there is not a dominant allele present.

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11
Q

What is monohybrid inhertiance?

A

Inheritance of a single gene

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12
Q

What contrasting characteristics are used to determine how they were inherited?

A

Characteristics controlled by single gene
controlled by genes on different chromosomes
clear-cut and easy to tell apart

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13
Q

What is a test/back cross?

A

A cross to show if a dominant characteristic is determined by 1 or 2 dominant alleles.

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14
Q

What is co-dominance and give an example

A

Where both alleles of a gene are expressed, e.g. speckled hens have black and white feathers OR
Blood type, a parent with A blood type and a parent with B blood type would produce offspring with AB blood type.

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15
Q

What is incomplete dominance and give an example

A

This is where the offspring phenotype is an intermediate between the two parental phenotypes.
Red carnations crossed with white carnations produce pink carnations.

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16
Q

What does unlinked mean?

A

Means that the alleles behave independently in relation to each other

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17
Q

What is dihybrid inheritance?

A

Inheritance of 2 unlinked genes, e.g. genes on different chromosomes

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18
Q

What is mendels ratio?

A

9:3:3:1

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19
Q

What is linkage/linked?

A

When genes are on the same chromosome and therefore do not segregate independently at meiosis, they are inherited together.
Basically they cannot move to opposite poles because they are on the same structure

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20
Q

What would lead to more recombinant gametes?

A

Genes further apart on a chromosome because there is more opportunity for a crossing over.

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21
Q

How would you recognise linkage?

A

When combinations of characteristics do not correspond to the mendelian ratio

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22
Q
A
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23
Q

What chromosome is longer?

A

X

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24
Q

What is autosome?

A

A chromosome that is not a sex chromosome

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25
Q

What chromosome determines sex?

A

The 23rd chromosome

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26
Q

What are heterosomes?

A

Chromosomes of different sizes, e.g. in males the chromosomes are XY, X chromosome is longer

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27
Q

Draw a chromosome pair and label PAR1 and PAR2

A

PG 172

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28
Q

What are the pseudoautosomal regions?

A

PAR 1 and PAR 2, they are homologous and can pair with each other at meiosis

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29
Q

What is one gene the Y chromosome posses that the X chromosome doesnt and what is its role?

A

SRY gene/sex determining region on the Y chromosome.
Its role is to switch on genes on other chromosomes

30
Q

What chromosome carries the gene for haemophilia?

A

The X chromosome

31
Q

What is haemophilia?

A

A blood clotting disorder where an individual cannot produce enough of one of the 13 blood clotting proteins.

32
Q

What blood clotting protein is not produced when the mutant X chromosome is expressed?

A

Factor VIII

33
Q

What is a carrier?

A

Where there is one normal dominant allele and one mutant recessive allele

34
Q

What does sex-linkage mean?

A

Where a gene is carried by a sex chromosome so that the characteristic is seen more in one sex

35
Q

Why is haemophilia more common in males?

A

Because there are only two possible genotypes for males, one being a male without haemophilia and the other a male with haemophilia

36
Q

How many genotypes for haemophilia are in females?

A

A female without haemophilia
A female that carries haemophilia A female with haemophilia

37
Q

What is duchenne muscular dystrophy caused by?

A

A X-linked recessive allele from the dystrophin gene

38
Q

What is a mutation?

A

A change in the amount, structure or arrangement of DNA or in viruses RNA.

39
Q

What are mutations described as?

A

Spontaneous, happen without a case
Random, they happen with equal probability

40
Q

What mutations can be inherited?

A

Those that happen in gamete cells

41
Q

What can cause mutations?

A

Ionising radiation, UV light etc.
Chemicals, like mustard gas, cigarette smoke

42
Q

How does radiation cause mutations?

A

Causes pyrimidine bases to join so that during replication DNA polymerase may insert an incorrect nucelotide

43
Q

What are gene point mutations and what can they be?

A

If DNA polymerase changes the base sequence they occur:
Addition of a base
Duplication of a base
Subtraction of a base
Substitution of a base
Inversion of a base

44
Q

What effect on the polypeptide can gene point mutations have?

A

Mutation may of coded for the same amino acid so no change to polypeptide, “silent mutation”
Similar polypeptides may be produced if a similar amino acid is added
If the polypeptide was an enzyme a mutation could destroy the active site

45
Q

Why are bacteria used in experiments?

A

Because they have a short life cycle and a high mutation rate

46
Q

How does sickle cell anaemia occur?

A

CTC codes for glutamate, it is large and hydrophilic. The T is substituted for A which produces Valine, it is small and hydrophobic.
This causes the cell membrane of the red blood cell to collapse, it becomes sickle cell shaped.
They are very fragile.

47
Q

What type of gene point mutation is sickle cell anaemia?

A

Substitution point, it is at position 7

48
Q

What are symptoms of sickle cell anaemia?

A

Less oxygen carried around the body
Joint pain
Organ damage

49
Q

What are chromosome mutations?

A

Changes in the structure of number of chromosomes in a cell

50
Q

How do mutations happen in the structure of chromosomes?

A

Mutations occur when the chromosome does not re-join correctly with its homologous partner after prophase 1.

51
Q

What is non-disjunction?

A

Where one daughter cell receives two copies of a chromosome and the other receives none

52
Q

What chromosome is affected in down syndrome?

A

Chromosome 21

53
Q

How does down syndrome occur?

A

If non-disjunction occurs in oogenesis, the secondary oocyte has either no chromosome 21 or it will have 2 copies.
The one without chromosome 21 cannot produce an embryo.
The oocyte with 2 copies of chromosome 21 produces an embryo with 3 copies of chromosome 21 because it has 1 from sperm.
This is downs syndrome

54
Q

What is downs syndrome also known as?

A

Trisomy 21

55
Q

How many chromosomes do people with down syndrome have?

A

47

56
Q

What is translocation downs syndrome?

A

Where a fragment of one chromosome has attached to another, the affected person has 46 chromosomes

57
Q

What chromosomes are affected in translocation downs syndrome and how does it happen?

A

A fragment of chromosome 21 attaches to chromosome 14, when this gamete fuses with a normal one it produces an embryo with 2 chromosome 21’s and an additional one attached to chromosome 14.

58
Q

What is polyploidy?

A

Where you have more than two sets of chromosomes

59
Q

What does euploid mean?

A

Cells with complete sets of chromosomes

60
Q

What does aneuploid mean?

A

Cells with either too few or too many chromosomes

61
Q

How does polyploidy arise?

A

2 diploid gametes fusing, producing a tetraploid.
A defect in the spindle at meiosis can cause all chromosomes to move to one pole.

62
Q

What is endomitosis?

A

The replication of chromosomes that is not followed by cytokinesis.

63
Q

Are hexaploids/ 6n fertile or non-fertile?

A

Fertile because they can make homologous pairs in meiosis.

64
Q

What is an oncogene?

A

A proto-oncogene with a mutation that results in cancer

65
Q

What is another name for the tumour supressing gene and what does it do?

A

TP53, this gene regulates mitosis and prevents cells dividing too quickly

66
Q

What does a mutant p53 protein do in TP53?

A

Doesn’t repair damaged DNA
Allows mutant cells to divide and undergo mitosis
Cells with damaged DNA go into S phase and are replicated

66
Q

When do proto-oncogenes cause cancer?

A

When they are permanently switched on

67
Q

When do tumour supressing genes cause cancer?

A

When they are turned off because they cannot control the division of cells which is cancer

68
Q

What is epigenetics?

A

Where the environment can alter the expression of genes without changing their nucleotide sequence.
Basically the genes are affected but the nucleotides are not

69
Q

What is DNA methylation?

A

Where cytosine can have a methyl or hydroxymethyl group added, this produces methylated cytosine.
This changes the way genes are expressed

70
Q

What are consequences of epigenetic changes?

A

Inactivated genes may be transferred to the next generation/ genomic imprinting.
X inactivation, where whole chromosomes are switched off

71
Q

What is a proto-oncogene?

A

A gene which mutates into an oncogene which causes uncontrolled cell division

Biology (26 decks)

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