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biology - component 2 > inheritance > Flashcards

inheritance Flashcards

1
Q

define gene

A

a sequence of DNA bases that occupies a specific locus (position) on a chromosome

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2
Q

what are the main characteristics of genes?

A
  • they code for polypeptide
  • they can mutate
  • they can separate and divide
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3
Q

define alleles

A

alternative forms of genes occupying a similar locus on homologous chromosomes

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4
Q

what are the three different allele combinations for any one gene?

A

heterozygous: two different alleles for a given gene

homozygous dominant: having two dominant alleles

homozygous recessive: having two recessive alleles

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5
Q

define gene pool

A

all the alleles in a population at any one time

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6
Q

define genotype

A

all the alleles that an individual has

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7
Q

define monohybrid inheritance

A

inheritance of a single gene, such as that controlling plant height or seed colour

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8
Q

why might peas have been a useful choice for inheritance experiments for Mendel?

A
  • easy to grow
  • can self or cross fertilise
  • produce flower and fruit in the same year
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9
Q

how would Mendel ensure that offspring produced were only from the parents above?

A

pollen transferred by hand - receiving flower, could be in a bag to prevent further cross-pollination
- remove anthers before they mature so no self-pollination

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10
Q

what is Mendel’s first “law of inheritance”?

A

The characteristics of an organism are determined by (factors) alleles, which occur in pairs
Only one allele of a pair is present in each gamete

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11
Q

describe continuous variation

A
  • controlled by a number of genes
  • e.g if an individual has inherited a number of alleles for tallness, they have the potential to grow tall
  • the characteristic often has a range of values
  • usually the bell-shaped normal distribution curve
  • environmental factors have an effect
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12
Q

describe discontinuous variation

A
  • controlled by a single gene
  • these characteristics have distinct categories
  • environmental factors have no effect
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13
Q

define pure breeding

A

two organisms of the same phenotype that will only produce offspring of the same phenotype when bred together (homozygous)

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14
Q

describe test cross (or ‘backcross’)

A

a method used in genetics to determine whether a particular dominant characteristic observed in an organism is controlled by one or two dominant alleles
- the unknown is always crossed with a recessive phenotype

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15
Q

describe codominance

A

a condition in which both alleles for a gene are expressed when present in a heterozygote
e.g cattle can have a red, white or roan (red&white coat)
- both alleles written using a capital letter

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16
Q

describe incomplete dominance

A

heterozygous individuals produce a phenotype intermediate of the parental phenotype
- the heterozygous condition is somewhere in between
e.g flowers can be red, white or pink
- capital letters are used

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17
Q

describe dihybrid inheritance

A
  • involves the inheritance of two unlinked genes (genes found on different chromosomes)
  • independent assortment of these genes produces recombinants
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18
Q

outline Mendel’s second law (law of independent assortment)

A

either of a pair of alleles may combine randomly with either of another pair

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19
Q

define expected, in terms of chi squared

A

based on ratios gained through genetic crosses

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20
Q

define observed, in terms of chi squared

A

actual ratios

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21
Q

define null hypothesis

A

there is no significant difference between the observed and the expected

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22
Q

describe the null hypothesis

A
  • if there is no significant difference between the observed and expected ratios then we accept our null hypothesis
  • if there is a significant difference between the observed and the expected then we reject the null hypothesis - other factors must be having an influence
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23
Q

what is the degree of freedom?

A

one less than the number of categories (i.e phenotypes)

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24
Q

when do accept or reject null hypothesis?

A
  • if the chi squared value is less than the value in the table we accept the null hypothesis
  • if the chi squared value is greater than the value in the table we reject the null hypothesis
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25
Q

what are the two types of chromosome?

A

autosome
sex chromosome

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26
Q

define autosome

A

any chromosome that is not a sex chromosome

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27
Q

define sex chromosome

A

a chromosome concerned in determining the sex of an organism, typically one of two kinds.
they are similar in females and dissimilar in males

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28
Q

why does the Y chromosome carry fewer genes?

A

it is smaller in size

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29
Q

describe haemophilia

A

an individual with haemophilia cannot produce enough of one particular blood clotting protein

30
Q

describe duchenne muscular dystrophy

A
  • caused by a sex-linked recessive allele of the dystrophin gene
  • the gene codes for the protein dystrophin, which stabilizes cell membranes of muscle fibres
31
Q

what are the symptoms for duchenne muscular dystrophy?

A

loss of muscle mass and muscle weakness

32
Q

why might there be a low number of children who have sex-linked diseases through affected parents?

A

affected parents might die before they can reproduce
OR
they decide they do not wish to conceive and pass the disease onto offspring

33
Q

when do Mendel’s ratios apply?

A

when genes are not linked

34
Q

describe linkage

A
  • genes are inherited together
  • crossing over is very unlikely to separate them as the genes are too close together on the same chromosome
35
Q

describe incomplete linkage

A
  • genes are on the same chromosome, but are far apart
  • genes could be separated due to crossing over and not be inherited together but this is rare (only 5-10% of the time)
36
Q

in what stage of meiosis does crossing over occur?

A

prophase I

37
Q

define mutation

A

an unpredictable change in the genetic material of an organism

38
Q

what are the two types of mutation?

A
  1. gene mutations
  2. chromosome mutations
39
Q

describe gene mutations

A

affect single genes

40
Q

describe chromosome mutations

A

causes changes in the structure or number of whole chromosomes

41
Q

explain the importance of mutations

A

mutations are spontaneous random events that provide an important source of genetic variation

42
Q

in what case are mutations more frequent?

A

in organisms with short life cycles and frequent cell division

43
Q

when do chromosomes mutations occur?

A

during crossing over in prophase I
and
non-disjunction during anaphase I and anaphase II

44
Q

what causes mutation rates to increase?

A

mutagens

45
Q

define mutagens

A

factors in the environment that increase the frequency of mutation in an organism

46
Q

why is it incorrect to say that mutagens cause mutations?

A

mutagens do not cause mutations but increase exposure to mutagens increases the rate of mutations occuring

47
Q

state some examples of mutagens

A

UV and gamma radiation
polycyclic hydrocarbons

48
Q

define carcinogens

A

mutagens that increase the rate of cancer

49
Q

define proto-oncogenes
- what are they called when they are mutated?

A

gene which can mutate to form cancer
- ocogenes

50
Q

define tumour-suppressor genes

A

regulate cell division within humans

51
Q

what harmful chemicals are in tobacco smoke?

A
  • tar
  • nicotine
  • carbon monoxide
52
Q

describe tar

A

tar contains carcinogens that affect the DNA in the cells of the alveoli.
- if a mutation occurs in a proto-oncogene or a tumour suppressor gene, lung cancer may develop

53
Q

what do gene mutations affect?

A

single bases within a gene

54
Q

what could be the result of a change in the single base of a gene?

A
  • change in DNA base sequence
  • resulting in a change in triplets/codon for amino acids
  • different amino acid sequence produced in translation
  • bonds form in different places and result in a different shaped protein (may not function)
55
Q

describe gene mutation in the haemoglobin gene

A
  • the replacement of only one base pair in the DNA results in the change of just one amino acid in two of the polypeptide chains making up the haemoglobin molecule
  • the abnormal haemoglobin causes the red blood cells to become sickle-shaped
  • this affects the ability of the haemoglobin to bind to oxygen
  • this results in anaemia and may be fatal
56
Q

sickle cell trait also confers some resistance to the malaria parasite, why is this?

A

the malarial parasites (plasmodium) reproduce inside red blood cells but cannot reproduce inside sickle shaped cells

57
Q

define chromosome mutations

A

mutations causing changes in the structure or number of whole chromosomes
- many genes are affected

58
Q

what are the three types of chromosome mutations?

A
  1. changes in chromosome structure
  2. changes in whole sets of chromosomes - polyploidy
  3. changes in chromosome number - nondisjunction
59
Q

describe changes in chromosome structure

A

errors occur when chromosomes exchange sections of DNA during crossing over at prophase I

60
Q

describe changes in whole sets of chromosomes

A

if a gamete receives two sets of chromosomes during a failed meiotic division the gametes will be diploid rather than haploid
- this is common in flowering plants (e.g tomatoes and wheat)
- if it occurs in animals they do not survive

61
Q

describe nondisjunction

A

nondisjunction is a process in which faulty cell division results in one daughter cell getting two copies of a chromosome, whilst one daughter cells gets none

62
Q

state some features of down’s syndrome?

A
  • open facial features
  • small shaped ears
  • low muscle tone
  • some degree of learning disability
63
Q

describe down’s syndrome

A
  • chromosome 21 is affected
  • during meiosis in the female ovary, an oocyte with two copies of chromosome 21 is produced and survives
  • if this oocyte is fertilised, the zygote would have 3 copies of chromosome 21 - two from the mother and one from the father
  • the resulting individual will have down’s syndrome
64
Q

explain how trisomy such as trisomy 16 in mice can occur in a zygote

A
  • homologous chromosomes fail to separate; nondisjunction
  • at anaphase I in oogenesis
  • secondary oocyte has 2 copies of chromosome 16
  • third chromosomes is added from sperm at fertilisation
65
Q

define epigenetics

A

the control of gene expression by modifying DNA or histone protein without affect the DNA nucleotide sequence

66
Q

what are the two method of epigenetics?

A
  1. addition of methyl group
  2. modification of histone protein
67
Q

outline the addition of the methyl group

A
  • adding a methyl group to nitrogenous bases
  • this prevents the bases from being recognised and therefore reduces the ability of the whole gene to be transcribed (expressed)
  • if transcription does not occur translation will not occur and the polypeptide and eventual protein will not be produced
68
Q

what is the correlation between methylation, gene expression and transcription

A

methylation increases
transcription decreases
therefore, gene expression decreases

69
Q

outline the modification of histone proteins

A
  • histone proteins are used to organize the DNA in a chromosome
  • if the DNA becomes more tightly coiled around the histone proteins, this can prevent gene expression
  • if coiled more loosely, it can increase gene expression
70
Q

where can epigenetic modification occur?

A
  • in cells of the same tissue
  • in different tissues of the same organism

biology - component 2 (7 decks)

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