6.2- Patterns of inheritance Flashcards
1
Q
Describe phenotype
A
- the appearance of an organism
- influenced by both genotype and environment
2
Q
Name Genetic factors that cause phenotypic variation
A
1) Gene Mutations
2) Chromosome mutations
3) Sexual reproduction
3
Q
What us he name of agents that increase rate of mutation, name different categories
A
Mutagens:
- physical agents
- chemical agents
- biological agents
4
Q
List physical agents (mutagens)
A
- X-rays
- Gamma rays
- UV light
5
Q
List chemical agents (mutagens)
A
- Benzopyrene (found in tobacco smoke)
- Mustard gas
- Nitrous oxide
- aromatic amines (in some synthetic dyes)
- Reactive oxygen species- free radicals
- Colchicine
6
Q
List biological agents (mutagens)
A
Biological agents
* Some viruses
* Transposons- jumping genes, remnants of viral nucleus acid that have become incorporated into our genomes
* Food contaminants such as mycotoxins from fungi, e.g. aflatoxins in contaminated nuts, chemicals in charred meat,, alcohol
7
Q
Describe the effects of gene mutations
A
Can be harmful, advantageous, or neutral
8
Q
Describe the characteristics of mutations that occur during gamete formation
A
- Persistent- can be transmitted through many generations without change
- Random- not directed by a need on the part of the organism in which they occur
9
Q
When do chromosome mutations occur, name different types
A
Occur during meiosis. Include:
* Deletion
* Inversion
* Translocation
* Duplication
* Non-disjunction
* Aneuploidy
* Polyploidy
10
Q
Outline deletion (chromosome mutation)
A
Part of a chromosome, containing genes and regulatory sequences, is lost
11
Q
Outline inversion (chromosome mutation)
A
- A section of a chromosome may break off, turn through 180 degrees, and then join again
- Although all the genes are still present, some may now be too far way from their regulatory nucleotide (control site) to be properly expressed
12
Q
Outline translocation (chromosome mutation)
A
- A piece of one chromosome breaks off and then becomes attached to another chromosome
- May also interfere with regulation of genes on the translocated chromosome
13
Q
Outline duplication (chromosome mutation)
A
- a piece of a chromosome may be duplicated
- Overexpression of genes can be harmful, because too many of certain proteins or gene-regulating nucleic acids may disrupt metabolism
14
Q
Outline Non-disjunction (chromosome mutation)
A
- One pair of chromosomes or chromatids fails to separate, leaving one gamete with an extra chromosome
- When fertilised by a normal haploid gamete, the resulting zygote has one extra chromosome- e.g. Down syndrome (Trisomy 21) is caused by non-disjunction
15
Q
Outline aneuploidy (chromosome mutation)
A
- The chromosome number is not an exact number if the haploid number for that organism
- Sometimes chromosomes or chromatids fail to separate during meiosis (e.g. trisomy)
16
Q
Outline polyploidy (chromosome mutation)
A
- If a diploid gamete is fertilised by a haploid gamete, the resulting zygote will be triploid (has 3 sets of chromosomes)
- The fusion of 2 diploid games can male a tetraploid zygote
- Doesn’t occur in animals
- Many cultivated plants are polyploid (they have more than 2 sets of chromosomes)
17
Q
Describe how genetic variation occurs in sexual reproduction
A
Has contributed to evolution:
- allele shuffling during crossing over in P1
- independent assortment of chromosomes in M/A1
- independent assortment of chromatids in M/A2
- random fusion of genetically dissimilar haploid gametes (only contain one of each our of homologous chromosomes and one allele for every gene)
18
Q
Describe examples of variation caused only by the environment
A
- Speaking regional dialect- offspring don’t inherit, but learnt by listening to others
- Losing a limb or scarring following injury
19
Q
Describe an example of Variation caused by environment interacting with genes in plants
A
- If plants are kept in dim light after germination, or if the soil in which they are grown contains insufficient magnesium, then the leaves do not develop enough chlorophyll and are yellow or yellow-white
- The plant is described as chlorotic, or suffering from chlorosis
- The plant cannot photosynthesise
- Chlorotic plants have the genotype for making chlorophyll, but environmental factors are preventing the expression of these genes
20
Q
Nam different causes of variation
A
- genetic
- environmental
- combination of the two
21
Q
Briefly outline the history of artificial selection
A
- humans have been practicing animal and plant breeding via AS for around 10,000 years- since beginning of settled agriculture
22
Q
What is the agent of selection in natural vs artificial selection
A
- natural- environment
- artificial- humans
23
Q
Outline the process of artificial selection
A
- breeders select individuals with the desired traits and allow them to interbreed
- at the same time, they prevent those without the the desired characteristics from breeding
24
Q
name examples of species humans have domesticated
A
- cereals
- potatoes
- vegetables and fruits
- cattle
- pigs
- sheep
- goats
- horses
- oxen
- dogs
- cats
- pigeons
- poultry
25
Describe desirable characteristics in plants (artificial selection)
- increased yield
- pest and disease resistance
26
Describe desirable characteristics in animals (artificial selection)
- docility
- placidity
- ability to be trained
- animals that normally live in social groups (herds) with a dominance hierarchy may also be able to be trained to accept a man as the pack leader, and to tolerate being penned with other animals
27
What does artificial selection produce
new breeds of organisms
28
Table of organisms and their desirable traits/examples of use by humans
29
Describe how new breeds can be produced (artificial selection)
- selective breeding programmes
- e.g. breeders may grow many plants of a particular type under the conditions they wish these plants to withstand e.g. low temperatures, high salinity
- they will then select those individuals that grow best under these conditions and cross pollinate them, collect and sow the seeds, and repeat this process over many generations
- selective breeding programme takes around 20 years
30
Describe the term for the issue with inbreeding
Inbreeding depression
31
Outline inbreeding depression
- at each stage of selective breeding, the individuals with the desirable characteristics and no/few desirable characteristics are selected
- inevitably, the genetic diversity ins the gene pool of the selective breed is reduced
- if related individuals are crossed, inbreeding depression can result- the chances of an individual inheriting 2 copies of a recessive harmful allele are increased
32
Describe how growing plants in specific desirable conditions aids in artificial selection
- it is random mutations giving rise to new phenotypes - happens independently of the selection process
- growing one environment that being made to withstand doesn't directly contribute to this- just allows us to see which plants have a mutation that makes them able to tolerate the conditions
33
Describe hybrid vigour
When breeders outcross individuals belonging to 2 different varieties to obtain individuals that are heterozygous at many gene loci
34
How do breeders obtain individuals that are heterozygous at many gene loci
Hybrid vigour
35
Describe what has happened to the number of commercially grown varieties of crops over the last 50-100 years, why
greatly reduced:
- selective breeding reduces the organisms genetic diversity
- all commercial varieties are genetically similar- if a pathogen was introduced, most plants would succumb to the infection
36
How do breeders overcome the issue of commercial plants being genetically similar
- outcross the cultivated varieties with varieties more like their wild ancestors to increase hybrid vigour
- samples of such wild ancestor types need to be conserved- often in gene banks
37
What are gene banks, name examples
Store genomes, but in their organisms:
- rare breed farms
- wild populations of organisms
- crops in cultivation
- botanic gardens and zoos
- seed banks
- sperm banks
- cells in tissue culture
- frozen embryos
38
Describe an example of the necessity of gene banks in the UK
- Much of the wheat grown in the UK has a dwarfing allele introduced from a Japanese variety of wheat
- If given extra fertiliser, the wheat does not grow taller and fall over in the wind, but uses the extra nutrients to increase seed size and yield
- However, if the environmental temperature rises above 30 °C, the effect of this allele is changed and yield is decreased
- If climate change is likely to produce higher temperatures during the British summer, a new breed of wheat will have to be developed
- Wheat breeders are looking, in a gene bank, for different dwarfing alleles
39
Describe ethical considerations of artificial selection
- domesticated animals may retain many juvenile characteristics, making them friendly, docile and playful BUT makes them less able to defend themselves- loss of nervous disposition may make them easy prey
- livestock animals e.g. pigs selected to have more lean meat and less fat BUT might succumb to low environmental temperatures during winter off they were not housed
- dogs have been domesticated for many thousands of years and used by humans for hunting, companionship, protection, herding , transport, guide dogs, and for aesthetic qualities BUT may put dogs at selective disadvantage if they had to survive in the wild, some breeds through inbreeding from a limited number of pedigree dogs have susceptibility to disease, and some coat colours would camouflage the animals
40
Conditions to which different dog breeds are susceptible to table
41
Who first investigated genetics
Gregor Mandel
42
What type of organisms did Mendel study
- easy to grow
- naturally self fertilising, but easy to cross-fertilise artificially
43
What is the monohybrid cross
- involves only 1 characteristic with 1 pair of contrasting crates
- mates 2 parent strains (P1 generation) with different phenotypes- produces F1(first filial) generation
- then breed F1 1to produce F2
44
Describe what is meant by a chacteristic that is monogenic
- governed by one gene
= the one gene has 2 distinct alleles
45
Describe different types of allele
- dominant- when present in homozygous or heterozygous individuals, produces the dominant phenotype
- recessive- will only produce recessive phenotype if homozygous- two recessive alleles with no dominant allele present
46
Describe the meaning of heterozygous
- having different alleles ay a particular gene locus on a pair oh homologous chromosomes
- not true breeding
47
Describe the meaning of homozygous
- having identical alleles at a particular gene locus on a pair of homologous chromosomes
- true breeding
48
What is a punnet square
- all possible gametes are assigned to a row
- those of the female parent go in the vertical column, male goes in horizontal row
- genotypes of the next generation are predicted by combining the male and female genotypes- represents all possible random fertilisation events
49
Punnet square example- monogenic inheritance
50
What is used to work out the genotypes of phenotypically similar individuals
The test cross
51
Describe the test cross for monogenic inheritance
- used to work out whether e.g. tall plants are TT or Tt- tall (T) is dominant so both genotypes could produce tall phenotype
- the organism exhibiting the dominant pheonotype (but of unknown genotype) are crossed with an individual showing the recessive phenotype (homozygous recessive genotype)
- if any of the individuals have the recessive phenotype, the dominant phenotype organism Is heterozygous (Tt)
52
Monogenic inheritance tests cross example
53
Define codominance
- where both alleles present in the genotype of a heterozygous individual contribute two the individuals genotype
- the phenotype of heterozygotes is different from the phenotype of homozygotes
54
List examples of co-dominance
- coat colour in shorthorn cattle- gene for coat colour has 2 alleles- homozygous for each (red or white) are red/white respectively, but if heterozygous have a roan coat (with red and white)
- MN blood roups- GM and GN blood groups (code for different versions of proteins on surface of erythrocytes)- if one parent with M and other with N, will be MN blood group
- ABO blood groups
- sickle cell anaemia- caused by mutation of gene that codes for B-globin chain of haemoglobin- heterozygous leads to half normal haemoglobin and half abnormal- but don't suffer from SCA
- Cecilia plants- if red and white flower genotype crossed, end up with red and white spotted flowers
55
Co-dominance example cross
56
Describe multiple alleles
- characteristics for which there are three or more alleles in the population gene pools
- when three or more alleles at a specific gene locus are known
- occur as a result go many changes occurring anywhere within a gene over time
- however an individual can only possess 2 alleles- one on each gene locus- in a pair of homologous chromosomes
57
Describe human blood groups
- exhibits dominance, codominance, and multiple alleles
- Groups include A, B, AB, and O
- determined by 3 alleles of a single gene on chromosome 9- gene codes for an isoagglutinogen (I) on the surface of erythrocytes
- Ia and Ib are dominant (also codominant- if both present, will both contribute to phenotype)
- Io is recessive
58
Define allele
a version of a gene
59
Blood group genetic cross example
60
Describe a different example of multiple alleles (not human blood groups)
- rabbit coat colours- 4 alleles in allele hierarchy- Agouti, Chinchilla, Himalayan, albino
61
Describe sex linkage
- a gene present on one of the sex chromosomes
62
Describe the sex chromosomes in humans
- sex determined by last of the 23 pairs of chromosomes
- other 22 pairs are autosomes-each member of pair is fully homologous- match for length and contain same genes at same loci
- sex chromosomes- X and Y not fully homologous- small part of one matches a small part of the other- so that these chromosomes can pair up before meiosis
- XX in females, XY in males
63
Describe sex linkage in humans
- the human X chromosome contains over 1000 genes that are involved in determining many characteristics or metabolic factions not concerned with sex determination
- most of these have no partner alleles on the Y chromosome
- if a female has one abnormal allele on one of her X chromosomes she will probably have a functioning allele of the same gene on her other X chromosome
- however, if a Male inherits an X chromosome form his mother with an abnormal allele or a particular gene, he will suffer from a genetic disease, as he will not have a functioning allele for that here
- males are functionally haploid (or homozygous) for X-Linked genes- cannot be heterozygous or homozygous
64
Name examples of sex linked characteristics in humans
- haemophilia A
- colour blindness
65
Describe the genetic basis of haemophilia A
- person with Haemophilia A us unable to clot blood fast enough- injuries may cause bleeding or an internal haemorrhage
- one of the genes on the non-homologous region of the X chromosome codes for blood clotting protein- factor 8
- a mutated form of the allele codes for non-functioning factor 8
- a female with one normal allele and one functioning allele produces enough factor 8 to enable blood to clot normally, however, this female is a carrier of the disease
- if such a female passes the X chromosome containing the faulty allele to her son, he will have no functioning allele for factor 8 on whY chromosome- will ahem haemophilia A
- means females less likely to have haemophilia A as would need 2 faulty alleles- usually fatal
66
haemophilia example genetic cross
67
Describe the genetic basis of colour blindness
- one of genes involved in coding protein involved in colour vision is on X chromosome, but not on Y chromosome
- mutated allele may result in colour blindness- inability to distinguish between red/green
- female with one abnormal allele and one functioning allele will not be colour blind, but male with one abnormal allele on X chromosome will not have functioning allele on Y chromosome- will be red/green colourblind
- recessive sex-linked dissorders are as haemophilia A
68
Describe another example of sex-linkage
Coat colour in cats:
- Gene for coat colour in cays is on non-homologous region of X chromosome (gene C)
- Allele Co produces orange fur, allele Cb produces black fur
- these alleles are codominant- cats with genotype XCo XCb are tortishell (patches of black and ginger fur)
- male cats may be either black or ginger but can't be tortishell, as only have one X chromosome
69
Cat fur colour genetic cross example
70
Describe inactivation of X chromosomes in female mammals
- in every female cell nucleus, one X chromosome is inactivated
- determination of which member of the pair of X chromosomes become inactivated is random and happens during early embryonic development
71
What mechanism stops females from having twice the number of X-linked genes being expressed
inactiavation of X chromosomes in female mammals
72
What are dihybrid crosses
Investigations that examine the simultaneous inheritance of 2 characteristics
73
Diagram of the diffident possible gametes on 2 pairs of homologous chromosomes
Independent assortments leads to 4 possible gametes when both characteristics are heterozygous:
74
Describe the mechanisms of dihybrid inheritance
- the alleles of the 2 genes are inherited independently of each other, so each gamete has one allele for each gene locus
- during fertilisation, any one pair of allele can combine with any one of anther allele pair
75
Dihybrid cross example
76
What is the ratio always for breeding the F1 generation pf a dihybrid cross
9:3:3:1
77
What is the combined probability of occurrence when 2 independent events occur simultaneously
The product of individual probabilities (NB- different when genes are on the same chromosome)
78
Define autosomal linkage
Gene loci present in the same autosome (non-sex chromosome) that are often inherited together
79
Why is autosomal linkage different to normal dihybrid inheritance
- when the genes are on different chromosomes, they are independently assorted
- however, when two or more gene loci are on the came chromosome, they are linked
- the chromosome, not the gene, is the unit of transmission during sexual reproduction, and therefore linked genes are not free to undergo independent assortment- they are usually inherited together as a single unit
80
What can result in unexpected results from autosomal linkage
Crossing over
81
describe how crossing over affects autosomal linkage
- if crossing over occurs during meiosis 1, the linked genes are no longer on the same autosome
- produces recombinant gametes
- the further apart the 2 gene loci are on a chromosome, the greater the change of recombinant gametes forming
82
Autosomal linkage example
83
How do you set up an autosomal linkage cross
Place the genes on the same autosome above each other, with the second autosome next to it with the same letter next to eachother
84
What letter is usually sued for co-dominance as well as the allele
C
85
What is important to remember while doing monohybrid inheritance crosses (not codIomionant)
Use the same letters with capital and lowercase not different
86
Define epistasis
- the interaction of non-linked gene loci where one masks the expression of another
- different genes ay different loci on different
- chromosomes interact to affect one phenotypic characteristic
- the gene loci are not linked so tehy assort independently during hamete formation
- reduces genetic variation as it redices teh number of phenotypes produced in the F2 generation of dyhybrid crosses
87
Name different elements of epistasis
- recessive epistasis
- dominant epistasis
- complimentary action
EITHER ANTAGONISTIC OR COMPLIMENTARY
88
Outline recessive epistasis
- if the first locus is homozygous reccessive, the allele at the second locus wont be expressed
- the alleles at the first locus are epistatic to the second locus, and the alleles at the second locus are hypostatic to the first locus
89
What is the ratip for reccessive epistatis if both are heterozygous
9:3:4
90
Recessive epistasis example cross
91
Describe dominant epistasis
- if the epistatic gene has a dominant allele, the hypostatic allele is not expressed
- a mutation may mean that genotypes with 2 recessiveq alleles (i) are not expressed as colour as the hypostatic alleles ate homozygous
92
Dominant epistasis example cross
93
Describe complementary action in genes
- e.g. one gene locus determines whether the coat will have colour, and the next determines the type of colour
- if both c's are recessive (homozygous), the coat will be alibono
- if there is a dominant C but no dominant A, the coat will remain black
- if there is both a dominant C and a dominant A, the coat will be agouti- the black pigment is deposited and then develops a yellow band
94
Example of complementary gene action cross
95
What ratios are seen in dominant epistasis
12:3:1
13:3 (if mutation)
96
What ratios are seen in complementary gene action
9:7
9:3:4
9:3:3:1
97
Difference between epistasis and other dihybrid crosses
Epistasis involves 1 phenotype
98
What test is used in genetics
Chi-squared
99
Describe what Ch-squared results tell us genetics
- determines wether the difference tween observed and expected results are significant
- of it is significant, suggests the inheritance pattern is different to what was expected- may need to rethink explanation
100
When can the chi-squared test be used
- when the data is in categories and are not continuous
- when there is a strong biological theory to use to predict expected values
- when the sam epee size is large
- when the data are only raw counts (percentages/ratios can't be used)
- when there are no zero scores in the raw count data
101
What is done first when doing the chi squared
Write a null hypothesis- stating "there is no statistically significant difference between the observed and expected data. Any difference is due to chance"
102
Steps of doing chi squared
1) Work out he expected number of individuals in each category by multiplying the expected fraction by the total number of individuals
2) subtract the expected value from the observed value
3) square all of these numbers
4) Divide these numbers by the expected number
5) Add all of these numbers to find X squared
6) work out degrees of freedom by subtracting 1 from the number of categories
7) Find critical value at this degree of freedom and at 95% certainty
8) if the calculated value is SMALLER than the critical value, ACCEPT the null hypothesis. if LARGER, REJECT the null hypothesis
9) Write ' the calculated value of chi-squared is (smaller/larger) than the critical value of chi-squared at p.05, there for the difference (is/isn't) significant and we (accept/reject) the null hypothesis
103
Chi-squared example
104
Why may observed results be significantly different to expected results
- a small sample may have been used
- some ovules may not become fertilised and some seeds may not develop in the pod
- 'genetic lottery' as to which gametes fuse ay fertilisation
- some allele combinations (such as 2 dominant alleles) may be fatal
105
Outline discontinuous variation
- phenotype classes are distinct and discrete
- phenotypes are clearly discernible from the others in a qualitative way
- no/very few intermediates between different phenotypes
- usually monogenic- if not, they are an example of epistasis- genes at different loci interact t produce one characteristic that is discontinuous
- usually determined by alleles of a single gene locus
- either different alleles at a single gene locus have large effects on the phenotype, or different gene loci have quite different effects on the characteristic
- examples- flower colour, seed shape
106
Outline continuous variation
- polygenic- many genes involved
- alleles may have additive effect on the phenotype- each contributes a small amount
- often quantitative variation between phenotypic categories
- the greater the number of gene loci contributing to the determination of the characteristic, the more continuous variation (greater range)
- study of such inherited genetic characteristics is qualitative genetics
- examples- birth mass, leaf length, tail length
107
Describe the interaction of genes and environment in relation to continuous/discontinuous variation
- environment has greater effect on the expression of polygenic characteristics (continuous) than out does on ontogenetic characteristics (discontinuous)
- e.g. each person has genetic potential for height and intelligence, but without proper nutrition/mental stimulation, these potentials will not be reached
108
Name 2 factors that can change allele frequencies over time
- natural selection
- genetic drift
109
Name 3 types of natural selection
- stabilising selection
- directional selection
- disruptive selection.
110
Outline stabilising selection
- favours intermediate phenotypes
- normally occurs when organisms environment remains unchanged
- e.g. robin eggs- larger clutches lead to malnourishment, whereas smaller clutches may result in no viable offspring
111
Outline disruptive selection
- favours both extreme phenotypes, intermediate phenotype is selected against
- e.g. rabbits with black, white and brown fur- if move to area of black/white rocks, brown rabbits would be eaten before reproduction
112
Describe directional selection
- if an environment changes, e.g. by becoming colder, there may now be advantage for become larger- larger mass will be the ideal and will be selected for
- more will survive and reproduces- ore likely to pass genes/alleles for larger size onto offspring
- over several generations, there is gradual shift in the optimum value for that trait
113
Nam 2 types of genetic drift
- genetic bottleneck
- founder effect
114
What is genetic drift
- A change in the allele frequency within a population by chance over time
- don't cause mutations or the emergence of harmful alleles, however, they contribute to the increase of mutations and harmful allels within the resulting population
115
Describe genetic bottleneck
- when a population size shrinks and then increases again, it is said to have gone through a genetic bottleneck
- after an event the genetic diversity within that population will be reduced
- there may be loss of some advantageous alleles or a disproportionate frequency of harmful alleles (deleterious)
- puts populations' chances of long-term survival at risk
- sometimes, population shrinks to such a small size that its fertility is affected- leading its species becoming endangered then extinct
- however, if the ones that survive are those that have a particular advantage, e.g. resistance to a pathogen, then a bottleneck could improve the chances of the gene pool while also shrinking genetic diversity
- species that have been selectively bred for certain traits have also been through a genetic bottleneck
116
Compare genetic drift and natural selection
Both affect the number of alleles, however natural selection is caused by changes in the environment, whereas genetic drift is caused by a short, catastrophic event
117
Describe the founder effect
- if a new population is established by a very small number of individuals who originate from a larger parent population, the new population is likely to exhibit loss of genetic variation
- some groups of migrating humans, not fully representative of the parent population, have set up populations in new areas
- if they have remained isolated from other human populations because of religious/cultural differences due to geographic isolation- means the new population will have a small gene pool
- happened in iceland, the Faroe island, Pitcairn Island, Easter island and among the Amish people of North America
118
What are population genetics
- studies the changes in allele frequencies within a population over time
119
Name factors that affecvt allele frequencies wothim populations (and hence the genetic diversity within a gene pool)
- population size
* mutation rate
* migration
* natural selection (whether stabilising, disruptive or directional) changes to the environment - e.g. adverse environments can lead to a genetic bottleneck
* isolation of a population from other populations of the same species (founder effect)
* non-random mating
*genetic drift
* gene flow
120
What is the key principle in population genetcis called
the Hardy-Weinberg principle
121
Describe the basis of the Hardy-Weinberg principle
- descibes and predicts a balanced equilibrium in the frequencies of alleles and genotypes within a breding population
- can also be used to determine the frequencies of those carrying a recessive allele (heterozygotes) for a genetic disorder with a. reccessive inheritance pattern, if we know the incidence of affected babies born each year in that population
122
Assumtions of the Hardy-Weinberg principe
- the population is large enough ti make sampling error negligible
- mating within the population occurs at random (no selective breeding)
- there is no selective advantage for any genotype and hence no selection
- there is no mutation, migration, or genetic drift
123
equation of the Hardy-Weinberg principle
124
Hardy-Weinberg example- reccessive trait
125
Hardy-Weinberg example- dominant trait
126
What is the term for the process by which new species are formed
Speciation
127
What causes a species to elviolve into 2 species
- must be split into 2 isolated populations
- means mutations that occur in 1 arent transmitted by interbreeding to the other population
- different selection pressures in each population- accumulate different allele frequencies- each population evolves along its own lines
- when there have been sufficient genetic, behavioural, and physiological changes in the 2 populations so that they can no longer interbreed, they are separate species
128
Describe an intermediate step of speciation
- 2 populations will be different, but still able to interpreted
- called sub-species
129
Nam ethe 2 types of isolating mechanisms
- geographical
- reproductive
130
Describe geographical isolating mechanisms
- populations separated by geographical features e.g. lakes, rivers, mountains, oceans
- act as barriers to gene flow between the populations
- the isolated populations are subject to different selection pressures in the 2 different environments- undergo independent changes to the allele frequencies and/or chromosome arrangements within their gene pools
- genetic changes may be the result of mutation, selection, and genetic drift
- as a result of natural selection, each population becomes adapted to its environment
- called allopatric speciation
131
Describe reproductive isolating mechanisms
- biological and behavioural changes within a species may lead to the reproductive isolation of one population from another
- if a mutation leads to some organisms in a population changing their foraging behaviour and becoming active at dawn, dusk or at night rather than during the day, enabling them to exploit a new niche, the members of the diurnal population will be unlikely to mate with members of either the crepuscular or nocturnal populations
- genetic changes can also lead to reproductive isolation- change in chromosome number may prevent gamete fusion, make the zygotes less viable so they fail to develop, or lead to infertile hybrid offspring with an off number of chromosomes, so that chromosome pairing during meiosis cannot occur
- mating between reproductively isolated populations may also be prevented by mutations leading to changes in courtship behaviour e.g. time of year for mating or courtship rituals that precede mating, or by animal genitalia or flower structure in plants
- speciation resulting from reproductive isolation is called sympatric speciation
132
What is the name of speciation occurring from geographical vs reproductive isolating mechanisms
- geographical- allopatric
- reproductive- sympatric
