biology - component 2 > inheritance > Flashcards

inheritance Flashcards

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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
  • 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
what are the two types of chromosome?
autosome sex chromosome
26
define autosome
any chromosome that is not a sex chromosome
27
define sex chromosome
a chromosome concerned in determining the sex of an organism, typically one of two kinds. they are similar in females and dissimilar in males
28
why does the Y chromosome carry fewer genes?
it is smaller in size
29
describe haemophilia
an individual with haemophilia cannot produce enough of one particular blood clotting protein
30
describe duchenne muscular dystrophy
- 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
what are the symptoms for duchenne muscular dystrophy?
loss of muscle mass and muscle weakness
32
why might there be a low number of children who have sex-linked diseases through affected parents?
affected parents might die before they can reproduce OR they decide they do not wish to conceive and pass the disease onto offspring
33
when do Mendel's ratios apply?
when genes are not linked
34
describe linkage
- genes are inherited together - crossing over is very unlikely to separate them as the genes are too close together on the same chromosome
35
describe incomplete linkage
- 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
in what stage of meiosis does crossing over occur?
prophase I
37
define mutation
an unpredictable change in the genetic material of an organism
38
what are the two types of mutation?
1. gene mutations 2. chromosome mutations
39
describe gene mutations
affect single genes
40
describe chromosome mutations
causes changes in the structure or number of whole chromosomes
41
explain the importance of mutations
mutations are spontaneous random events that provide an important source of genetic variation
42
in what case are mutations more frequent?
in organisms with short life cycles and frequent cell division
43
when do chromosomes mutations occur?
during crossing over in prophase I and non-disjunction during anaphase I and anaphase II
44
what causes mutation rates to increase?
mutagens
45
define mutagens
factors in the environment that increase the frequency of mutation in an organism
46
why is it incorrect to say that mutagens cause mutations?
mutagens do not cause mutations but increase exposure to mutagens increases the rate of mutations occuring
47
state some examples of mutagens
UV and gamma radiation polycyclic hydrocarbons
48
define carcinogens
mutagens that increase the rate of cancer
49
define proto-oncogenes - what are they called when they are mutated?
gene which can mutate to form cancer - ocogenes
50
define tumour-suppressor genes
regulate cell division within humans
51
what harmful chemicals are in tobacco smoke?
- tar - nicotine - carbon monoxide
52
describe tar
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
what do gene mutations affect?
single bases within a gene
54
what could be the result of a change in the single base of a gene?
- 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
describe gene mutation in the haemoglobin gene
- 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
sickle cell trait also confers some resistance to the malaria parasite, why is this?
the malarial parasites (plasmodium) reproduce inside red blood cells but cannot reproduce inside sickle shaped cells
57
define chromosome mutations
mutations causing changes in the structure or number of whole chromosomes - many genes are affected
58
what are the three types of chromosome mutations?
1. changes in chromosome structure 2. changes in whole sets of chromosomes - polyploidy 3. changes in chromosome number - nondisjunction
59
describe changes in chromosome structure
errors occur when chromosomes exchange sections of DNA during crossing over at prophase I
60
describe changes in whole sets of chromosomes
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
describe nondisjunction
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
state some features of down's syndrome?
- open facial features - small shaped ears - low muscle tone - some degree of learning disability
63
describe down's syndrome
- 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
explain how trisomy such as trisomy 16 in mice can occur in a zygote
- 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
define epigenetics
the control of gene expression by modifying DNA or histone protein without affect the DNA nucleotide sequence
66
what are the two method of epigenetics?
1. addition of methyl group 2. modification of histone protein
67
outline the addition of the methyl group
- 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
what is the correlation between methylation, gene expression and transcription
methylation increases transcription decreases therefore, gene expression decreases
69
outline the modification of histone proteins
- 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
where can epigenetic modification occur?
- in cells of the same tissue - in different tissues of the same organism
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