6.1.2 - Patterns of inheritance Flashcards
1
Q
Define genotype
A
This is the genetic make up of an organism in respect to that gene
2
Q
Define phenotype
A
Observable characteristics of an organism
3
Q
What is a dominant allele ?
A
The version of the gene that will always be expressed if present in an organism
4
Q
What does showing the dominant characteristic mean ?
A
They could have one or two copies of the dominant gene
5
Q
What is a recessive allele ?
A
Will only be expressed if two copies of the allele are present in this organism
6
Q
What does showing the recessive characteristic mean ?
A
They must have two alleles coding for the recessive phenotype
7
Q
What is variation?
A
- Differences in characteristics within species
- Can be interspecific or intraspecific
8
Q
Define intraspecific variation
A
Differences between individuals within the same species
9
Q
Define interspecific variation
A
Differences between individuals that are from a different species
10
Q
What are the 2 causes of variation?
A
Environmental and genetic
11
Q
Are environmental effects heritable?
A
No
12
Q
Give 2 examples of environmental effects
A
- Hair dye
- Diet
13
Q
Are genetic factors heritable?
A
Yes
14
Q
Give 4 causes of genetic variation
A
- Presence of a different allele
- Random fertilisation of gametes
- Meiosis
- Independent assortment and crossing over specifically
- Mutations
15
Q
What are the two sources of variation in meiosis?
A
- Crossing over
- Independent assortment
16
Q
What are the two types of variation?
A
Continuous and discontinuous
17
Q
What is continuous variation?
A
- Variation from one possible extreme to another, can be anywhere between both ends of the spectrum
- It can be plotted to give a normal distribution curve
18
Q
Give 2 examples of continuous variation
A
- Height
- Weight
19
Q
What is discontinuous variation?
A
- Discrete groupings of individuals
- Presented as a bar chart
20
Q
Give an example of discontinuous variation
A
Blood group
21
Q
Why does continuous variation occur?
A
Due to the inheritance of 2 or more genes
22
Q
Why does discontinuous variation occur?
A
Result of inheritance of one gene with 2 or more alleles
23
Q
Is continuous variation influenced by the environment?
A
It can be
24
Q
Is discontinuous variation influenced by the environment?
A
No
25
What is a polygenic characteristic ?
A characteristic that is controlled by two or more genes
26
What is a multifactorial characteristic ?
A characteristic that involves both genetic and environmental factors
27
Define monogenic inheritance
When the inheritance of a single gene is shown
28
When does codominance occur ?
Codominance occurs when two different alleles occur for a gene - both of which are equally dominant
29
What is the result of codominance ?
Both alleles of the gene are expressed in the phenotype of the organism if present
30
Give an example of codominance
- The colour of snapdragon flowers
- Two equally dominant alleles exist, each of which codes for the colour of the flower (red and white)
- The three colours that can be produced are red, white and pink
31
How are alleles represented in codominance ?
- A letter is chosen to represent the gene
- The different alleles are then represented using a second letter which is shown as superscript
32
What are genes with more than two versions called ?
Multiple alleles
33
How many alleles can be present in an individual ?
Only two, because there are two versions of the gene (one on each of the homologous chromosomes)
34
What allele codes for blood group ?
Immunoglobulin gene
35
What are the different versions of the immunoglobulin gene ?
- Ia
- Ib
- Io
36
What is the combination of alleles for blood group A ?
IAIA or IAIO
37
What is the combination of alleles for blood group B ?
IBIB or IBIO
38
What is the combination of alleles for blood group AB ?
IAIB
39
What is the combination of alleles for blood group O ?
IOIO
40
What is the 23rd pair of chromosomes called ?
Sex chromosomes
41
What do females have on the 23rd chromosome ?
XX
42
What do males have on the 23rd chromosome ?
- XY
43
What does the Y chromosome carry ?
- Carries a gene that causes the embryo to develop as a male
- Therefore the sex of the offspring will be determined by whether the sperm fertilising the egg contains a Y chromosome or an X
44
What are sex linked genes ?
Genes that are carried on the sex chromosomes
45
Which chromosome is smaller, X or Y ?
Y chromosome is smaller than the X chromosome
46
What are dihybrid crosses used to show ?
The inheritance of two different characteristics, caused by two genes, which may be located on different pairs of homologous chromosomes
47
What is dihybrid inheritance ?
Inheritance of two genes
48
What is the expected result of a heterozygous dihybrid cross ?
9,3,3,1
49
Why may the actual ratio of results vary from expected ?
- Fertilisation is random
- If there is no crossing over, alleles for 2 characteristics will be inherited together if on the same chromosome
50
What are linked genes ?
These are genes that are both on the same chromosome
51
Why may numbers from dihybrid crosses vary from the expected numbers ?
- This is due to the fact that the process is random
- The differences should not be large
52
What is one of the reasons that the ratios in dihybrid crosses vary largely from what they should be ?
- Linkages
- This means that the genes are located on the same chromosome
53
What is autosomal linkage ?
- Autosomal linkage refers to when the genes that are linked are found on one of the other pairs of chromosomes
- Any chromosome that isnt a sex chromosome
54
How are linked genes inherited ?
They are inherited as one unit
55
What are some examples of linked characteristics ?
Body colour and wing length in fruit flies
56
What can cause separation of some of the linked genes ?
- Crossing over
- Prophase 1
- Meiosis 1
57
What are genes on the same autosome said to be ?
Linked - this is because they stay together during independent assortment
58
What are recombinant offsprings ?
- They have different combinations of alleles than either parent
- Can be caused by crossing over - chiasmata etc
59
How is genes being closer on the chromosome beneficial ?
They are less likely to be separated during crossing over and there will be fewer recombinant offspring produced
60
What is the recombination frequency ?
Measure of the amount of crossing over that has happened in meiosis
61
What is the equation for recombination frequency ?
Number of recombinant offspring / total number of offspring
62
What does a recombination frequency of 50 % indicate ?
Indicates that there is no linkage and the genes are on separate chromosomes
63
What does a recombination frequency of less than 50% indicate ?
There is gene linkage and the random process of independent assortment has been hindered
64
What happens as the degree of crossing over decreases ?
The recombination frequency also gets smaller
65
What is epistasis ?
Interaction of genes at different loci
66
What are some examples of epistasis ?
- Gene regulation - regulatory genes control the activity of structural genes
- Gene interaction - occurs in biochemical pathways involving only structural genes
67
How are some genes said to interact ?
Epistatically
68
What does genes interacting epistatically mean ?
The genes interact together to display a said phenotype
69
What are the characteristics that show continuous variation controlled by ?
Multiple gene control and epistasis occurs frequently
70
What is a hypostatic gene ?
Gene that is affected by another gene
71
What is an epistatic gene ?
Gene that affects the expression of another gene
72
How can an epistatic gene influence the activity of other genes ?
As a result of the presence of dominant or recessive alleles
73
What is recessive epistasis ?
If two recessive alleles at a gene locus led to the lack of something
74
What will the ratio be if you cross homozygous parents in recessive epistasis ?
9:3:4 ratio in the F2 generation
75
What is dominant epistasis ?
When dominant alleles at a gene locus lead to something being shown
76
Why does dominant epistasis occur ?
If a dominant allele results in a gene having an effect on another gene
77
What will happen if one of the epistatic alleles is dominant ?
Then having one copy of it will mask the expression of the other gene
78
What will the ratio be if you cross homozygous parents in dominant epistasis ?
12:3:1
79
What is the ratio for a monohybrid cross ?
3:1
80
What is the ratio for a dihybrid unlinked cross ?
9:3:3:1
81
What is the ratio for a dihybrid linked cross ?
3:1
82
What is the ratio of an epistatic recessive cross ?
9:3:4
83
What is the ratio of an epistatic dominant cross ?
12:3:1
84
What is a 1:0:0:1 ratio ?
Linked traits
85
How can you tell if two genes are linked ?
They wont fit the expected ratio
86
Define Gene Pool
The sum total of all the genes in a population at any given time
87
Define Allele Frequency
The frequency of a particular allele in a population
88
What does p represent when calculating allele frequency ?
The frequency of the dominant allele (A)
89
What does q represent when calculating allele frequency ?
The frequency of the recessive allele (a)
90
What is the short equation to work out allele frequency ?
p + q = 1
91
What does the Hardy-Weinberg principle model ?
It models the mathematical relationship between the frequencies of alleles and genotypes in a theoretical population that is stable and not evolving
92
What does the Hardy-Weinberg principle state ?
In a stable population with no disturbing factors, the allele frequency will remain constant from one generation to the next and there will be no evolution
93
What is the equation for the Hardy-Weinberg principle ?
p2 + 2pq + q2 = 1
94
What does p2 represent ?
Frequency of homozygous dominant genotype in the population
95
What does 2pq represent ?
Frequency of heterozygous genotype in the population
96
What does q2 represent ?
Frequency of homozygous recessive genotype in the population
97
What are the assumptions with the Hardy-Weinberg principle ?
- Random mating
- No mutations
- No selection pressure
- Large and isolated population
98
Are the assumptions of the principle likely to happen in real life ?
No
99
What are the factors that can affect the rate of evolution ?
- Mutations
- Sexual selection
- Gene flow
- Genetic drift
- Natural selection
100
How can mutations affect the rate of evolution ?
Leads to genetic variation
101
How can sexual selection affect the rate of evolution ?
Leads to an increase in the frequency of alleles which code for characteristics that improve mating success
102
How can gene flow affect the rate of evolution ?
- It is the movement of alleles between populations
- Due to immigration and emigration
103
How can genetic drift affect the rate of evolution ?
- This is a change in allele frequency due to the random nature of mutation
- The appearance of a new allele will have a greater impact in a smaller population
104
How can natural selection affect the rate of evolution ?
- Leads to an increase in the number of individuals that have characteristics that improve their chances of survival
- Reproduction rates of these individuals will increase as will the frequency of the allele that codes for the characteristics
105
What are the two types of limiting factors that can limit or decrease the size of a population ?
- Density dependent factors
- Density independent factors
106
What are density dependent factors ?
They are dependent on population size and include competition, predation, parasitism and communicable disease
107
What are density independent factors ?
They affect populations of all sizes in the same way including - climate change, natural disasters, seasonal change and human activities
108
What are population bottlenecks ?
Large reductions in population size which last for at least one generation
109
What can be the effect of population bottlenecks ?
The gene pool and therefore genetic diversity is greatly reduced and the effects will be seen in future generations
110
What is a positive aspect of a genetic bottleneck ?
A beneficial mutation will have a much greater impact and lead to the quicker development of a new species
111
What is the founder effect ?
- Small populations arising due to the establishment of new colonies by a few isolated individuals
- Extreme example of genetic drift
112
What happens as a result of the founder effect ?
- These small populations have much smaller gene pools than the original population and display less genetic variation.
- If carried to the new population, the frequency of any alleles that were rare in the original population will be much higher in the new, smaller population and so they will have a much bigger impact during natural selection.
113
What does a bell shaped curve represent ?
Normal distribution
114
What is stabilising selection ?
The norm/average is selected and the extremes are not selected
115
What does stabilising selection result in ?
A reduction in the frequency of alleles at the extremes and an increase in the frequency of average alleles
116
When does directional selection occur ?
When there is a change in the environment and the normal phenotype is no longer more advantageous
117
What happens in directional selection ?
- Organisms which are less common and have more extreme phenotypes are positively selected.
- The allele frequency then shifts towards the extreme phenotypes and evolution occurs
118
What happens in disruptive selection ?
- The extremes are selected for and the norm selected against
- This is opposite to stabilising selection where the norm is positively selected
119
What is speciation ?
Speciation is the formation of new species through the process of evolution.
120
What is an important characteristic of a species ?
- Species are able to interbreed and produce fertile offspring
- After speciation this cannot occur
121
What events occur leading up to speciation ?
- Members of a population become isolated and no longer interbreed with the rest of the population resulting in no gene flow between the two groups.
- Alleles within the groups continue to undergo random mutations.
- Different characteristics will be selected for or against because there are different selection pressures
- The members of the different populations become so different that they are no longer able to interbreed (to produce fertile offspring).
- They are now reproductively isolated and are different species
122
What is allopatric speciation ?
- Allopatric speciation is the more common form of speciation
- Happens when some members of a population are separated from the rest of the group by a physical barrier - they are geographically isolated.
123
What allows for allopatric speciation to occur ?
- The environments of the different groups will often be different and so will the selection pressures resulting in different physical adaptations.
- Separation of a small group will often result in the founder effect leading to genetic drift further enhancing the differences between the populations.
124
What is sympatric speciation ?
Speciation that occurs within populations that share the same habitat
125
How frequently does sympatric speciation occur ?
It happens less frequently than allopatric speciation and is more common in plants than animals
126
When can sympatric speciation occur ?
It can occur when members of two different species interbreed and form fertile offspring - this often happens in plants.
127
What are characteristics of the hybrid formed from sympatric speciation ?
- The hybrid formed, which is a new species, will have a different number of chromosomes to either parent and may no longer be able to interbreed with members of either parent population.
- This stops gene flow and reproductively isolates the hybrid organisms.
128
What can cause organisms to be reproductively isolated ?
- Disruptive selection
- Mating preferences
- Other behavioural differences
129
What can interfere with the process of speciation ?
Gene flow, as they still live in the same habitat
130
What are reproductive barriers ?
Barriers to successful interbreeding that can occur before or after fertilisation
131
What are prezygotic reproductive barriers ?
They prevent fertilisation and the formation of a zygote
132
What are postzygotic reproductive barriers ?
- They are often produced as a result of hybridisation
- They reduce the viability or reproductive potential of offspring
133
What are polymorphic populations ?
They display more than one distinct phenotype
134
What is a wild type allele ?
The allele coding for the most common characteristic
135
What are mutants of the wide type allele ?
They are different forms of the wild type allele
136
What is artificial selection (selective breeding) ?
Fundamentally the same as natural selection except for the nature of the selection pressure applied
137
What is the difference between artificial selection and natural selection ?
Instead of changes in the environment leading to survival of the fittest, it is the selection for breeding of plants or animals with desirable characteristics by farmers or breeders.
138
How does artificial selection occur ?
- Individuals with the desired characteristics are selected and interbred
- Offspring from this cross showing the best examples of the desired traits are then selected to breed.
- The process is repeated over many generations resulting in changes to the frequency of alleles within the population and eventually speciation.
139
What is inbreeding ?
The breeding of closely related individuals
140
What are some problems associated with inbreeding ?
- Limiting the gene pool and so decreasing genetic diversity reduces the chances of a population of inbred organisms evolving and adapting to changes in their environment.
- Organisms that are closely related are genetically similar and are likely to have the same recessive alleles.
- The breeding of closely related organisms therefore results in offspring which have a greater chance of being homozygous for these recessive traits and being affected by genetic disorders.
- Over time this reduces the ability of these organisms to survive and reproduce.
141
What is the role of seed banks ?
- They keep samples of seeds from both wild type and domesticated varieties
- They are an important genetic resource
142
What are gene banks ?
- They store biological samples, other than seeds, such as sperm and eggs
- These are usually frozen
143
What is outbreeding ?
Alleles from gene banks being used to increase genetic diversity
144
What is another form of outbreeding ?
- Breeding unrelated or distantly related varieties
- This reduces the occurrence of homozygous recessives and increases the potential to adapt to environmental change
