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Alevel Biology > 6.2 > Flashcards

6.2 Flashcards

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1
Q

what is a phenotype

A

the apperance of a living organism

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2
Q

what is a phenotype influenced by

A

both its genotype and its environment

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3
Q

What have mutations contributed to

A

the process of evolution

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4
Q

What is a mutation and what may it involve

A

it is a change to the genetic material, this may involve changes to the strucutre of DNA or changes to the number or gross strucutre of chromosomes

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5
Q

what may lead to genetic variation

A

sexual reproduction and mutations

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6
Q

what is a mutagen

A

a physical or chemical agent that can increase the rate of mutations

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7
Q

What are some examples of mutagens which are physical agents

A

x-rays, gamma rays, UV lights

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8
Q

What are some examples of mutagens which are chemical agents

A

benzopyrene (in tobacco smoke), mustard gas, nitrous acid, reactive oxygen species

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9
Q

What are some examples of mutagens which are biological agents

A

some viruses, transposons (jumping genes, reminents of viral nucelic acid that’s become part of our genome), food contaminants like alcohol or mycotoxins from fungi

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10
Q

What may mutations be

A

harmful, advantageous or neutral

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11
Q

What are mutations that occur during gamete formation

A

persistent:they can be transmmitted through many generations without change and random:they are not directed by a need on the part of the organism in which they occur

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12
Q

when do chromosome mutations occur

A

during meiosis

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13
Q

what are the different types of chromosome mutations

A

deletion, inversion, translocation, duplication, non-disjunction, aneuploidy, polyploidy

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14
Q

What is deletion in chromosome mutations

A

part of a chromosome, containing genes and regulatory sequences is lost.

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15
Q

What is inversion in chromosome mutations

A

a section of a chromosome may break off, turn through 180degress then join again, although all genes still present, some may now be too far away from their regulatory nucelotide sequences to be properly expressed.

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16
Q

What is translocation in chromosome mutations

A

a piece of 1 chromosome breaks of and becomes attached to another chromosome, this may interfere with the regulation of the genes on the translocated chromosome.

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17
Q

What is duplication in chromosome mutations

A

a piece of a chromosome may be duplicated, overexpression of genes can be harmful, as too many of certain proteins or gene-regulating nucleic acids may disrupt metabolism

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18
Q

What is non-disjunction in chromosome mutations

A

1 pair of chromosmes or chromatids fails to separate, leaving 1 gamete with an extra chromosome. When fertilised by a normal haploid gamete, the resulting zygote has 1 extra chromosome. Down-syndrome is caused by non-disjunction.

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19
Q

What is aneuploidy in chromosome mutations

A

the chromosome number is not an exact multiple of the haploid number for that organism. Sometimes chromosomes or chromatids fail to separate during meiosis.

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20
Q

What is polyploidy in chromosome mutations

A

if a diploid gamete is fertilised by a haploid gamete, the resulting zygote will be triploid (have 3 sets of chromosomes). The fusion of 2 diploid gametes can make a tetraploid zygote. Many cultivated plants are polyploid (more than 2 sets of chromosomes)

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21
Q

what has genetic variation from sexual reproduction contributed to

A

evolution

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22
Q

Meiosis produces genetically different gametes, during meiosis what cause this genetic variation

A

allele suffling (swapping of alleles between non-sister chromatids) during crossing over in prophase 1), 9ndependant assortement of chromosomes in metaphase/anaphase 1 and independent assortment of chromatids in metaphase/anaphase 2

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23
Q

are gametes produced by meiosis individually and genetically similar

A

no, they are dissimilar

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24
Q

What are gemetes produced by meiosis

A

individually and geentically dissimilar, they’re haploid, containning 1 of each pair of homologous chromosomes and 1 allele for every gene

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25
Q

what does the random fusion of gametes create

A

more genetic diversity, any male gamete can combine with any female gamete from an organism of the same species

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26
Q

what does random fertilisation of gametes that are already genetically unique produce

A

an extensive genetic diversity amoung the offspring

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27
Q

what are some examples of phenotypic variation caused by the environment and not passed through genes

A

speaking with a regional dialect, a persons offspring doesn’t inherit dialect through their genes, losing a digit or a limb or having a scar following an injury.

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28
Q

what is an example of the environment interacting with genes

A

if plants kept in dim light after germination or soil has insufficient magnesium, leaves don’t develop enough chlorophyll and are yellow. The plant is then chlorotic, or suffering from chlorosis. The plant can’t photosynthesise. Chlorotic plants have the genotype for making chlorophyll but environmental factors prevent the expression of these genes.

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29
Q

what did mendel publish in 1866

A

the results of his investigations that would lay the foundation for a branch of biology known as genetics

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30
Q

what did Mendel study

A

an organism that was easy to grow and, although naturally self-fertilising, was easy to cross-fertilise easily

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31
Q

what did mendel work with

A

7 characteristics of the pea plant, each characteristic having 2 constrasting traits: stem height, seed shape, seed colour, pod shape, pod colour, flower arrangement, flower colour

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32
Q

what did mendel obtain and keep

A

true-breeding strains, where the trait had appeared unchanged generation after generation, from local seed merchants. Mendel also kept accurate and quantative records of data obtained which he analysed

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33
Q

what did Mendels simplest experiment involve

A

only 1 characteristic with 1 pair of contrasting traits, he mated individuals from 2 parent strains, each of which showed a different phenotype. 1 parent was true-breeding for tall stems and the other was true-breeding for short stems. The partents were called P1 (parental generation), all offspring from this cross, the F1 (first filial) generation, were phenotypically identical to 1 parent type. They were all tall

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34
Q

what happened when Mendel allowed members oif the F1 genertaion to self-fertilise

A

the resulting F2 generation contained some short plants, but there were 3 times as many tall as short plants. 3/4 were tall, 1/4 were short

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35
Q

what happened when mdnd crossed true-breeding plants showing the other 6 phenotypic variations

A

he obtained similar resukts to his first experiment

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36
Q

in pea plants what is the characteristic of height

A

it is monogenic, it is governed by 1 gene that has 2 distinc alleles T/t

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37
Q

what happens in pea plants when 1 allele, t, is present in a homozygous individual giving a ohenotype of tt

A

produces phenotypically short plants

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38
Q

what happens in pea plants when the the other allele, T, is present in homozygous (TT) or heterozygous (Tt) indiviuals

A

produces phenotypically tall plants

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39
Q

what is the allele T and t in pea plants described as

A

dominant (it codes for a dominat characteristic) and the t allele is recessive (only visible in phenotype if no dominant allele

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40
Q

What can be visulaised in a punnet square

A

genotypes and phenotypes resulting from the possible combinations of gametes during a monohybrid cross, showing possible outcomes of monogenic inheritence

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41
Q

how do punnett squares work and what do they predict

A

all possible gametes are assigned to a row, with those of the female parents in vertical colums and those of the male in the horizontal row. The genotypes of the next generation are predicted by combining the male and female gamete genotypes (a process that represents all possible random fertilisation events. The phenotype of the genotype can also be predicted.

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42
Q

In medels experiment which did all short pea plants have gennotype tt

A

as hsortness is a recessive characteristic so individuals with that phenotype must have genotype, tt. These are called homozygous recessive

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43
Q

How do we know he tall pea plants in the F1 generation all have the same genotype, Tt

A

they are all heterozygous, this is decuded from the genotypes of thier true breeding parents (TT and tt) and the genotypes of the gametes (T and t) that must have cobined to produce this generation

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44
Q

In the F2 generation some tall plants had genotype TT and some Tt. What does this mean?

A

they both have the same phenotype, tall, and it is impossible to tell thier genotype from their apperence

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45
Q

What is the test cross

A

a simple way to test genotypes devised by mendel

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46
Q

How does the test cross work

A

the organism exhibiting the dominant phenotype (tall) but unknow genotype (TT or Tt) os crossed with an individual showing the recessive phenotype, so being of homozygous recessive genotype (tt). If any of the offspring jave the recessive phenotype then the dominant phenotype organism is heterozygous, Tt

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47
Q

WhT are dihybrid crosses

A

Investigations that examine the simultaneous inheritance of 2 characteristics

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48
Q

What did Mendel examine the inheritance of in 1 of his dihybrid crosses

A

Seed shape and seed colour in pea plants, he crossed true-breeding pea plants with yellow and round seeds with true-breeding pea plants that had green and wrinkled seeds

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49
Q

What we’re all the F1 generations in mebdels dihybrid cross

A

All hybrids, having the phenotype of yellow and round seeds. Each plant in F1 generation is heterozygous for both genes (seed colour and shape), so yellow and round are both dominant traits

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50
Q

From the results of Mendel dihybrid cross what did he deduce

A

The alleles of the 2 genes are inherited independently of each other, so each gamete has 1 allele for each gene loci, and, during fertilisation, any 2 of an allele pair can combine with any one of another allele pair

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51
Q

What can we do if we consider the 2 crosses for seed colour and shape as 2 independent monohybrid crosses with the 2 sets of trait inherited independently

A

We can predict the outcome of allowing the members of the F1 generation to self-fertilise

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52
Q

What are the chances of the seed colour being inherited not influenced by

A

The chances of the trait for seed shape being inherited

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53
Q

If we assume that seed colour and seed shape are 2 separate monogenic characteristics

A

For the characteristic of colour:In the F 2 generation we would predict 3/4 would be yellow and 1/4, a ratio 3:1, for the characteristics of shape:we would predict 3/4 round and 1/4 wrinkled, ratio 3:1

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54
Q

What is the equation when 2 independent events occur simultaneously

A

Product of individual probabilities = combined probability of occurrence

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55
Q

What results did Mendel get from his dihybrid cross

A

9:3:3:1

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56
Q

What did Mendel unknowingly do when investiGting dihybrid inheritance

A

Without knowing the process of genes or meiosis, chose 2 characteristics, the genes for which are on different chromosomes

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57
Q

what is the result of a huge number of changes occuring anywhere within a gene over time

A

many genes have morw than 2 alleles

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58
Q

what does it mean when a gene is said to have multiple alleles

A

when 3 or more alleles at a specific gene locus are known, however, any individual can only posses 2 alleles, one on each gene locus, in a pair of homologous chromosomes

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59
Q

What is a good example of multiple alleles

A

inheritance of human ABO blood groups, it also demonstrates both dominance and codomincace of alleles are involved

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60
Q

what is codominance

A

where both alleles present in genotype of all heterozygous indivdual contribute to indivduals phenotype

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61
Q

What are the 4 blood groups (phenotype - A B AB O) determined by

A

3 alleles of a single gene on chromsome 9, the gene encodes isoagglutinogen, I, on surface of erythrocytes

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62
Q

What is which blood group you get determined by

A

alleles are present in the human gene pool are IA, IB, and IO. IA and IB are both dominant to IO which is recessive. IA and IB are codominant. If both IA and IB are presebnt in genotypethey both contribute to the phenotype. Any individual will have only 2 of 3 alleles in their blood type

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63
Q

What are the other 22 chromosomes not sex chromosomes called

A

Autosomes

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64
Q

WhT is each autosomal pair

A

Fully homologous - they match for length and contain same genes at same loci

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65
Q

What are the sex chromosomes

A

XY in males XX in females, X and Y chromosomes are not fully homologous, a small part of 1 matches a small part of the other, so these chromosomes can pair up before meiosis

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66
Q

What is human X chromosome involved in

A

Has 1000 genes involved in determining many charcateristics or metabolic functions not concerned with sex determination and most have no partner alleles on Y chromosome

67
Q

If a female has 1 abnormal allele on her X chromoskme how will rhe other chromosme be effected

A

She will hace a funtioning allele on same gene on Other X chromosome

68
Q

What hapoens if a male in herits from his mother ab X chromosome woth an abnormal allele for a particular gene

A

He will suffer from a genetic disease as he wont have a functikning allele for that gene

69
Q

What are males for X linked genes

A

Functionslly haploid or hemizygous, they cant be heterozygous or homozygous for X linked genes

70
Q

What ade sex linked characteristics in humans

A

Haemophilia A and colour blindness

71
Q

What is haemophilia A

A

Unable to clot blood fast enough, injuries may cause bleeding or an internal haemorrage

72
Q

How does haemophilia occur

A

1 of the genes on the non-homologous region of the X chromosome codes for a blood-clotting protein called factor 8, mutated form of the allele codes for non functionikg factor 8

73
Q

How are females carriers for haemophilia A

A

If female has 1 abnormal allele and a functioning 1 enough factor 8 is produced for her to clot blood normally when required, female is a carrier

74
Q

What happens when female passes faulty X chromosome to her son

A

He will have no functioning allele for factor 8 on his Y chromosome, he will sufer from haemophila A

75
Q

How is colour blindness a sex linked characteristic

A

1 gene for coding for protein involved in colour vision is on X chromosome but not on Y chromosome, mutated allele of thus gene may reuskt in colour blindness

76
Q

Who will get coliur blindness

A

A women with 1 abnormal allele and one functioning womt ve colourblind but male woth abromal allele on X chromosome does have funxrioning one on his Y so will be colour blond

77
Q

What is colour blindness

A

A recessive sex linked disorder

78
Q

What is sex linkage in cats

A

One of the genes, C, for coat colour in cats is sex linked, its on non homologous region of X chromosome

79
Q

Why do some cats have more than 1 fur colour

A

The alleles are codominant, both colours contribute to phenotype

80
Q

How does cat fur colour work in cats depending on sex

A

Bith orange and black contribute to phenotype, orange allele only expressed in cells where X chromosome bearing black colour coat allele is inactivated and vice versa, male cats may be either black or ginger but not mix as they only have 1 X chromosome

81
Q

Why is 1 X chromosome inactivated in females

A

Females have x2 number of X linked chromosomes expressed as males do, but, a mechansim prevents this disparity, in every female cell nucleus, 1 X chromosome is inactivated. Determination of which chromosome is inacivtaed is random diring embryonic development

82
Q

what are codominant alleles

A

when both alleles of a gene in the genotype of a heterozygous individual contribute to that individuaks phenotype, 2 alleles are responsible for 2 distinct and detectable gene products

83
Q

if phenotype of a heterozygotes different to homozygotes

A

yes

84
Q

what is an example of codominance in cow skin colour

A

a homozygous cattle for red coat, have red coat, a homozygous cattle for white coat, have white coat, heterozygous catlle with genotype for red and white coat will have both a red and white coat

85
Q

what is an example of codominance inheritance in humans with MN blood gorup

A

MN blood group system controlled by 1 gene with 2 alleles, GM, GN, both code for a slightly different protein on erythrocytes surface, and these alleles are codominant. Child of a coupple with one parent having blood group M and other N will have blood group MN

86
Q

how is ABO blood group an example of codominance

A

A and B are dominant to O, but A and B are codomiannt, making 4 blood groups, A,B, AB, O

87
Q

how is sickle cell anaemia an example of codominace but also why may some people disput this

A

in heterozygous person, they will have half normal haemoglobin and half muated haemoglobin (cause sickle cell anaemia), however, in a heterozygous individual can’t have sickle cell anaemia, so muated and normal haemoglobin gene only codomiant if haemogolobin molecule considered to be the phenotype, otherwise its a recessive disorder

88
Q

what is an example of codominant inheritance in plants

A

if some flowers and white and some are red and they are crossed together and have red and white spots then they’re codominant. Both aalleles R and W are expressed in the phenotype of the heterozygous

89
Q

what does the term linked mean

A

when 2 or more gene loci are on the same chromosome

90
Q

why can’t linked genes undergo sexual assortement

A

the chromosome, not the gene, is the unit of transmission during sexual reproduction, so linked genes can’t undergo sexual assortement, they are usually inherited together as a single unit

91
Q

what is autosomal linkage

A

where genes are linked by being on the same autosome

92
Q

what does it mean if linked genes are not affetced by crossing over of non-sister chromatids during phrophase 1 of meiosis

A

then they are always inherited as 1 unit

93
Q

what may produce unexpected results within autosomal linkage

A

recombinant gamete formation when there is crossing over between 2 non-sister chromatids during prophase 1

94
Q

what causes an increased chance of recombinant ganetes forming

A

the further apart 2 gene loci are on a chromosome

95
Q

what is epistasis

A

in some cases different genes, at different loci, on different chromosmes, interact to effect one phenotypic characteristic. When one gene masks or supresses the expression of another gene its called epistasis

96
Q

what are the 2 different ways gene inquest with epistasis may wokr

A

anatgonstically or complementary fashion

97
Q

as the gene loci aren’t linked when epistasis occurs what does this mean

A

they assort independantly during gamete formation, epistasis reduces the number of phenotypes produced in F2 generation of dihybrid crosses and therefore reduces genetic variation

98
Q

what does homozygous presence of recessive allele at first locus prevent (epistasis)

A

the expression of another allele at a second locus, alleles at first locus are epistatic to those at second locus, why are hypostatic to those at first locus

99
Q

What is an example of dominant epistasis

A

feather colour in chicken, there is interaction between 2 gene loci, I/i and C/c. I allele of epistatic gene, I/i, prevents formation of colour, even if 1 C allele is present, individuals carrying at least one dominant allele, I, have white feathers even if they also have 1 dominant allele for coloured feathers

100
Q

in what terms is epistasis often explained in

A

terms of genes working to code for 2 enzymes that work in succession, catalysing sequential steps of a metabolic pathway

101
Q

Whar is discontinuous variation

A

Ehere phenotype clasees are distinct and discrete, each clearly discernible from the others in a qualitative way

102
Q

What is an example of discontious variation

A

Ear lobes, attached or inattacehd

103
Q

What ate characteristics that exhibit discontinuous variation usually dwtetnibed by

A

Alleles of a single gene locus, they are monogenic, sometimes alleles of 2 genes interact to govern a songle charactetostic

104
Q

What 2 things effect discontinous variation

A

Different alleles at a single gene locus hace large effect on phenotype, different gene loci have wuite different effects on characteristic

105
Q

What may genes at different loci interact to influence

A

1 characteristic and produce discontinuous variation, as in epistasis

106
Q

What is continuous variation

A

Where genetic variation between individuals, even if theyre related, wothin a population shiws a range with a smooth gradation between many intermediates

107
Q

What is an example of continous variation

A

Leaf length in plant, birth mass

108
Q

How do genes determine continuous variation characteristics

A

Many genes involved, polygenic

109
Q

Jow is continuous variation determijed

A

Alleles of each gene many contribute a small amount to the phenotyoe, so alleles hace an addictive effect on phenotype, so phebotypic categories vary in quantative way, greater number of loci contributing to determinatikn of characteristic, more continuous cariation (greater range)

110
Q

What is the study of continuous variation called

A

Quantative genetics

111
Q

When does genetic analysis of inheritance of contibuous cariation traits become difficult to analyse

A

As number of gene loci increases above 2 (becomes a trihybrid cross)

112
Q

What does the environment have a greater effect on, polygebic or monogebtic characteristics

A

Polygenic

113
Q

What is example of genes interaction w envuronkejt

A

Person w gebetic potential for height will bot be talk without right nutrients

114
Q

What introduce bew alleles into a population

A

Mutation and migration

115
Q

What does variation in populations mean

A

Some bettwr adapted than others to environment due to genotype and phenotype differences, these are more likely to survive and reprodice passkng on advantageous alleles, over time, allele frequencies within populatjon will change (natural selection), may also lwad to new species or maintain consistency in species

116
Q

What are the 3 tyoes of selection

A

Stabilising, directional and disruptive selection

117
Q

What is stablilisong selection

A

Notnally occurs when organisms environment remains unchanged, favours intermediate phenotypes

118
Q

Example of stablilisong selection

A

Babies w birth mass near 3.5kg more likely to sirvive, offspring inherit alleles grom them and wlso have mean birth mass

119
Q

What is directional selection

A

If environment chnages, like got colder, larger size would be advantage and ideal for selection, larger individuals survive and reproduce and pass on their alleles for large size, over generatoks gradual shift in optimum value for the trait

120
Q

What happens if populatoon descends from small number of parents

A

Gene pool woll lack genetic variation, some alleles resulting from mutation bring no advantage or disadvantage on individual, so no selection pressure acting upon them, but, chance events may drastically influence the allele frequecy

121
Q

What is example of genetic drift

A

If small popualtion descend from 2 parents and onlt alleles A and a in it, if earthwuake occured 1 of alleles may disappear from pooualtion, populatipn size will recover but genetic diversity will be low. Allele in questikb didnt disapear due to selection pressure but due to genetic drift

122
Q

When can genetic drift arise

A

After genetic bottleneck or due to founder effect

123
Q

What is a genetic bottleneck

A

When a popualtipn shrinks and then increases again

124
Q

What happens as result of genetic bottleneck

A

Genetic diveristy within popultoon will be reduced, loss of some advantageous alleles of disproportionate frequency of deleterious (harmful) alleles, resucing chance og populatiom LT survival

125
Q

How could a genetic bottleneck be a good thing

A

If the ones that survive are those that have a particular advantage, then it could improve gene pool whilst shrinking genetic diversity

126
Q

What is the founder effect

A

If a new population is established by a very small numver of individuals who originate form a larger parent popualtion, new popualtion will exhibit loss of genetic variation

127
Q

What is example of founder effect

A

Some groups of migrating humans, not fully genetically representative of the parent population, have set up populations in new areas, if they remian isolated from other humans then newer popualtion will have smaller gene pool

128
Q

When is chi squared usef

A

If we get results that are not as we expected, we need to know if difference is due to chance or if difference between what we expect and observed is significant, if significant may be inheritance pattern is different to what we thiught

129
Q

When can we use chi squared

A

When data is in categories and not continuous, we have strong biological theory to use to predict expected values, sample size is large, data is raw (no percebtage or ratio), have strong biolgical theiry to use to predict expected values

130
Q

What is the null hypothesis

A

Statistical tests dont directly test hypothesis the test null hypothesis, if null not supported we accept orignal hypothesis, null states, there is no statistically songicicant difference between observed and expected vakues

131
Q

Explain chi squared equation

A

Difference between may be positive or negative so it is swuared, dividng by E takes into account size of numvers, sum of sign takes into account number of conarisons being made

132
Q

What are the 4 steps of chi squared

A

1.calculate value of x*2 2.determine degrees of freedom (no categories-1), 3.determine value of P from distribution table, w 0.005 probability 4. Decide if difference is significant at 0.005 probability

133
Q

what does population genetics attempt to study

A

changes in allele frequencies within a population, overtime

134
Q

what mmust happem for a species to succeed and not become extinct

A

it needs genetic variation between the individuals in its populations, individuals inherit their genomes from their parents and pass some of their genetic material to their offpspring

135
Q

what does population genetics study

A

the variation in alleles and genotypes within the gene pool and how their frequency varies overtime

136
Q

what are factors that affect allele frequencies within populations and genetic diversity within the gene pool

A

population size, mutation rate, migration, natural selection (stabilising, directional, disruptive), changes in environment, isolation of population from other populations of same species (founder effect), non-random mating, genetic drift, gene flow

137
Q

when does one species become 2

A

when 2 populations have become so genetically different that they can no longer interbreed to produce fertile offspring, undergone specification and formed 2 new alleles

138
Q

what is Hardy-Weinberg principle

A

a fundamental concept in population genetics, describes and predicts a balanced equilibrium in frequencies of alleles and genotype within a breeding population, also used to determine frequencies of those determining a recessive allele (heterozygotes) for a genetic disorder with recessive inheritance pattern, if we know incidence of effected babies born each year in that population

139
Q

what does Hardy-Weinberg principle assume (4)

A

population size is large enough to make samoling error negilgible, mating within population occurs at random, no selective advanatge for any genotype and hence no selection, there is no mutation, migration or genetic drift

140
Q

what must happen for a species to split into 2 separate ones

A

it must split into an isolated population, as when this happens any mutations that occur in one population are not transmitted by interbreeding to other population. In each location there’s a different selection pressure and each population will accumulte different allele frequencies, so each population evolves differently

141
Q

what are sub-species

A

during the evolutionary process when 2 populations are different but can still successfully interbreed

142
Q

when do 2 populations become separate species

A

when sufficient genetic, behavioural and physiological changes in 2 populations that they can no longer interbreed

143
Q

what is specification

A

the process by which new species are formed

144
Q

what are 2 main isolating mechanisms

A

geograophical and reproductive

145
Q

what is geographical isolation

A

if populations separated and isolated from each other by geographical features like lakes, rivers, oceans, these act as barrier to gene flow between populations

146
Q

what is allopatric specification in geographical isolation

A

isolated populations subject to different selection pressures in 2 different environments, then undergo independant changes to allele frequencies and/or chromosome arrangements in their gene pool, these changes will result in mutation, selection and genetic drift and as a result each becomes adapted to their environment (allopatric selection)

147
Q

what is reproductive isolation

A

biological and behavioural changes within a species may cause reproductive isolation

148
Q

example of reproductive isolation

A

if mutation leads to some organisms in population changing foraging behaviour and becoming active at dawn, dusk or night rather than day, enabling to exploit new things, members of diurnal population won’t mate with members from crepuscular (active dawn and dusk) or nocturnal population

149
Q

how may genetic chnages cause reproductive isolation

A

change in chromosome number may prevent gamete fusion, make zygote less viable so fail to develop, lead to infertile hybrid offspring with an odd number of chromosomes so no chromosome pairing in meiosis

150
Q

how may mating between members of reproductively isolated population be prevented

A

by mutations leading to changes in courtship behavour (time of years it occurs or courtship rituals),, antimal genitalia or plant structure

151
Q

what is sympatric specification

A

specification resulting from reproductive isolation

152
Q

difference between artifical and natural selection

A

natural is having the environment as selection agent, artifical is huamns as agents of selection, breeders select individuals with desired triats and interbreed them and prevent those without desired traits from breeding

153
Q

what are desirable characteristics in plants

A

increased yield, pest and disease resistance

154
Q

what are desirable characteristics in livestock

A

docility, placidity, ability to be trained (e.g. to accept human as leader)

155
Q

what are some examples of artifical selection and how there used by humans

A

cattle (milk, meat), horses (transport), dogs (companionship, hunting), sheep (wool), ceral (improved flavour + dough, pest, flood, wind resistance)

156
Q

how may new breeds be produced by selective breeding programmes

A

breeders may grow plant of certain type under conditions they wosh this plant to survive (like low temp), they then select individuals who grow best under these conditions and cross polinate them, collect and sow the seeds and repeat for many generations (up to 20years)

157
Q

what is interbreeding depression

A

at each stage of selective breeding ones with most desirable characterostics are chosen and causes reduction in gene pool/genetic diversity. Interbreeding depression is when 2 related individuals aare crossed which results in increased chance of inheriting 2 copies of a harmful recessive allele

158
Q

what is hybrid vigour

A

breeders sometinmes outcross individuaks belonging to 2 different varieties to obtain individuals that are heterozygous at many gene loci

159
Q

why does hybrid vigour need to be increased in commercial plants

A

as they are all geentically similar and if a pathogen is introduced it could kill them all, some may need to be outcrossed with wild ancestors, often kept in gene bank, in order to retain their genetic diversity

160
Q

what is purpose of gene banks, give example

A

purpose is to store genomes, in their organisms. E.g. if a wheat yeild decrease over 30degrees but global warming makes this temp more common may use a gene bank to cross this wheat to create a crop to withstand higher temps

161
Q

what are examples of gene banks (8)

A

rare breed farms, wild populations of organisms, crops in cultivations, botanic gardens and zoos, seed banks, sperm banks, cells in tissue culture, frozen embryos

162
Q

what are ethical consideratioins to artifical selection

A

domesticated animals retain docile traits making them easy pray/can’t defend themseleves, livestock need less fat and more meet but they may become cold in low temp if not housed, dogs domesticated meaning at disadvantage if they went into the wild, interbreeding caused suseptibiltiy to disease in some dogs, soem coat colours selcted would fail to camoflage animal

163
Q

give an example of a condition a boxer and german shepard suceptible to

A

heart diease and cancer

Alevel Biology (25 decks)

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