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A level Biology > 6.2 Patterns of inheritance > Flashcards

6.2 Patterns of inheritance Flashcards

1
Q

define genotype

A

Genetic makeup of an organism

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2
Q

define phenotype

A

visible characteristic of an organism

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3
Q

define mutagen

A

agents which increase the rate of mutation

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4
Q

What are the three types of mutagens

A

physical agents
chemical agents
biological agents

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5
Q

Give examples of chemical mutagens

A

mustard gas
nitrous acid
aromatic amines

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6
Q

Give examples of physical mutagens

A

X-rays
gamma rays
UV light

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7
Q

Give examples of biological mutagens

A

viruses
food contaminants

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8
Q

What is a persistent mutation

A

can be transmitted through many generations without change

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9
Q

What is a random mutation

A

they are not directed by a need on the part of the organism in which they occur

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10
Q

What are the 5 types of chromosome mutations

A

deletion
inversion
translocation
duplication
non-disjunction

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11
Q

Describe deletion chromosomal mutation

A

part of a chromosome containing genes and regulatory sequences is lost

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12
Q

Describe inversion chromosomal mutations

A

A section of chromosome may break off, turn 180 degrees then join again

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13
Q

Why are inversion mutations harmful

A

although all the genes are still present some may now be too far away from their regulatory nucleotide sequences to be properly expressed

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14
Q

Describe translocation chromosomal mutations

A

a piece of one chromosome breaks off and then becomes attached to another chromosome

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15
Q

Describe duplication chromosomal mutations

A

a piece of chromosome may be duplicated and overexpression of genes may be harmful

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16
Q

Describe non-disjunction chromosomal mutations

A

one pair of chromosomes or chromatids fails to separate leaving one gamete with an extra chromosome.
When fertilized by a normal haploid gamete the resulting zygote has one extra chromosome

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17
Q

Define aneuploidy

A

the chromosome number is not an exact multiple of the haploid number as chromosomes or chromatids may fail to separate during meiosis - trisomy

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18
Q

Define polyploidy

A

if a diploid gamete is fertilised by a haploid gamete the resulting gamete the zygote will be triploid - have 3 sets of chromosomes

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19
Q

How dos sexual reproduction contribute to evolution

A

Genetic variation causes by random fusion of gametes, independent assortment of chromosomes during metaphase 1+2 and allele shuffling during prophase 1

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20
Q

Give examples of variation caused by environmental factors

A

speaking with an accent
scars
tattoos

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21
Q

Give examples of variation caused by genetic factors

A

eye colour
blood group

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22
Q

Give examples of variation caused by both environmental and genetic factors

A

skin colour
weight
height

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23
Q

Define heterozygous

A

having different alleles at a particular gene locus on a pair of homologous chromosomes

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24
Q

Define homozygous

A

True-breeding
having identical alleles at a particular gene locus on a pair of homologous chromosomes

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25
define monogenic
determined by a single gene
26
define sex-linked
gene present on one of the sex chromosomes
27
define autosome
the pairs are fully homologous - they match in length and contain the same genes at the same loci
28
why are the sex chromosomes slightly homologous
so that they can pair up during meiosis
29
How is XX different to XY in terms of alleles
If a female has one abnormal allele on one of her X chromosomes she will probably have a functional allele on the other X chromosome Whereas f a male inherits the abnormal allele on the X chromosome he will suffer from a genetic disease
30
Define codominance
where both alleles present in the genotype of a heterozygous individual contribute to the phenotype of an organism
31
Give an example of codominance
Red and white cows, when they mate can produce roan offspring Humans can have AB blood types
32
Give examples of sex linkage
Males suffer from haemophilia A whereas females dont Theyre are only female tortoise shell cats
33
Define multiple alleles
characteristic for which there are three or more alleles in the populations gene pool
34
give an example of a characteristic with multiple alleles
blood group
35
define autosomal linkage
gene loci present on the same autosome that are often inherited together
36
what is the mendeleian ratio for monohybrid inheritance
3:1
37
What are recombinant genes
when there is crossing over between two non-sister chromatids during prophase 1
38
What increases the chance of recombinant genes
the further the 2 gene loci are away from each other
39
describe inheritance of autosomally linked genes with no crossing over
they are always inherited as one unit
40
define dihybrid
involving two gene loci
41
what is the ratio in a dihybrid cross
9:3:3:1
42
When in autosomal linkage may there be more than the expected phenotypes
because the genes had crossed over
43
what can we deduce from dihybrid crosses
The alleles of two genes are inherited independently of each other so each gamete has one allele for each gene locus during fertilisation any one of an allele pair can combine with any one of another allele pair
44
How does epistasis differ from dihybrid crosses
although 2 gene loci are involved with epistasis there is only 1 phenotype expressed
45
Define epistasis
interaction of non-lined gene loci where one masks the expression of the other
46
What are some examples of genes working antagonistically
recessive and dominant epistasis
47
Define recessive epistasis
the homozygous presence of a recessive allele at the first locus prevents the expression of the other
48
what are the second gene loci called in epistasis
they are said to be hypostatic to those at the first locus
49
What is the ratio of recessive epistasis
9:3:4
50
Define dominant epistasis
The presence of a dominant allele at the first locus prevents the expression of another allele at the second gene loci
51
Give an example of recessive epistasis
inheritance of flower colour in salvia
52
What is the ratio for dominant epistasis
12:3:1 13:3
53
Give examples of dominant epistasis
feather colour in chicken
54
why might there be a ratio of 13:3 in dominant epistasis
when the first dominant allele may prevent colour from being present in chicken but in the second gene some alleles also may prevent colour being deposited as well basically only two phenotypes able to be expressed white or coloured
55
How may genes work in a complimentary fashion?
epistasis genes working to code for two enzymes that work in succession catalysing sequential steps for a metabolic pathway
56
Give an example of genes working in a complimentary action
coat colour in mice allele C present means the mice will have a black coat and not albino paired with allele A will create an agouti pattern
57
What are the ratios for complimentary gene action
9:7 - 2 phenotypes available for expression 9:3:4 9:3:3:1
58
What is the null hypothesis for the chi squared test
there is no statistically significant difference between the observed and expected data any difference is due to chance
59
Define discontinuous variation
where phenotype classes are distinct and discrete and discernible from eachother in a qualitative way monogenic or epistasis involved
60
Give an example of discontinuous variation
blood group gender
61
Describe continuous variation
Where genetic variation shows a range with a smooth gradation between intermediates polygenic
62
What are some examples of continuous variation
skin colour height tail length
63
Which variation is able to be influenced by the environment
continuous
64
Why might a 2:1 ratio be observed if 3:1 was expected
A pair of alleles may be lethal such as DD
65
Why can some alleles be said to be codominant
both alleles are expressed in the phenotype and neither is dominant or recessive to each other
66
By observing a graph how would you know that 2 genes are autosomally linked
the homozygous AB or ab are mostly produced from a heterozygous AaBb plant so for the alleles to be inherited together like this the 2 alleles must be on the same autosome
67
What is a phenotypic trait of a plant that is determined by plants
chlorosis lack of magnesium in soil
68
Define speciation
the splitting of a genetically similar population into two or more populations that undergo genetic differentiation and eventually reproductive isolation leading to the evolution of two or more new species
69
Define allopatric speciation
formation of two different species from one original species due to geographical isolation
70
Define sympatric speciation
formation of two different species from one original species due to reproductive isolation while the populations inhabit the same geographical location
71
What are the different isolating mechanisms
geography reproduction
72
Describe geographical isolation
populations separated by geographical features such as lakes experience different selective pressures and undergo independent allele changes and each population becomes adapted to its environment
73
describe reproductive isolation
biological or behavioural changes such as changes in time of activity or change in chromosome number or genitalia lead to speciation from reproductive isolation
74
How can change in the number of chromosomes lead to reproductive isolation
prevents gamete fusion zygote is less viable infertile hybrid offspring
75
Give example of evolution in action
tolerance to heavy metals in plants antibiotic resistance
76
define stabilising selection
normally occurs when the organisms' environment remains unchanged and the intermediate phenotype is favoured eg babies with a birth mass closer to 3.5 are more likely to survive
77
define disruptive selection
where both of the extreme phenotypes are favoured and the intermediate is selected against
78
define directional selection
if the environment changes there will be a gradual shift over generations of the optimum value of a trait
79
when does genetic drift arise
after a genetic bottleneck or as a result of the founder effect
80
Define genetic bottleneck
when population size shrinks then increases again eg after a catastrophic event
81
What occurs after a genetic bottleneck
genetic diversity within the population will be reduced loss of advantageous alleles or disproportionate frequency of harmful alleles putting the populations long term survival at risk
82
When might a genetic bottleneck be advantageous
if ones that survive have a particular advantage for example resistance to a particular pathogen it may improve the gene pool while also shrinking genetic diversity
83
Define the founder effect
if a new population is established by a very small number of individuals who originate from a larger population the new population is likely to experience loss of genetic diversity
84
Why might populations that are a result of the founder effect exhibit a loss of genetic diversity
The migrating populations will not be genetically representative of he parent population and so will have a small gene pool
85
What does the Hardy-Weinberg principle assume
population is large enough to make the sampling error negligible mating occurs at random there is no selective advantage for any genotype no mutation, migration or genetic drift
86
What 2 equations are used in the Hardy-Weinberg principle
p+q=1 P2+pq+Q2=1 where p=dominant q=recessive
87
What is the probability of gametes having two recessive or dominant alleles
p2 or q2
88
What is the probability of gametes having heterozygous alleles
2pq
89
Define artificial selection
selective breeding of organisms where humans are the agents of selection by choosing the desired phenotype and interbreeding phenotypes individually
90
define inbreeding depression
when related individuals are crossed and the chances of inheriting two copies of a harmful recessive allele are increased
91
Define hybrid vigour
outcrossing individuals belonging to two different varieties to obtain individuals that are heterozygous at many gene loci
92
What is the problem associated with artificial selection i plants
Reduces the organisms genetic diversity so they are more likely to succumb to the same pathogen e.g. if temperatures rise above 30C when wheat crops are flowering then their metabolism is disrupted and seeds do not form
93
What are some ethical considerations of artificial selection
domesticated animals may be less likely to be able to defend themselves and make them easy prey lean animals may succumb in winter desired traits in dogs may be disadvantageous in the wild

A level Biology (25 decks)

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