Module 6.2 Flashcards
1
Q
genotype
A
genetic makeup of an organisms .
2
Q
phenotype
A
visible characteristics of an organisms
3
Q
genetic factors that have contributed to evolution
A
-mutations have contributed to the process of evolution .
-A mutation is a change to the genetic material . This may involve changes to the structure of DNA AS DESCRIBED in topic 6.1.1 or changes to the number or gross structure of the chromosomes .
4
Q
Physical agents that are mutagens
A
x-rays
-gamma rays
-uv light.
5
Q
Chemical agents that are mutagens
A
-benzopyrene found in tobacco smoke
-mustard has
-nitrous acid
-aromatic amines -insome synthetic .
-
6
Q
Biological agents - Mutagen
A
Some viruses
Transposon
Food Contaminants
7
Q
mutations can be three things , what are they ?
A
harmful , advantageous , or neutral .
8
Q
mutations are PERSISTENT
A
They can be transmitted through many generations without changr .
9
Q
Mutations are RANDOM
A
they are not directed by a need on the part of the organism in which they occur .
10
Q
first type of chromosome mutation - DELETION
A
Part of a chromosome containing, genes and regulatroy sequences is lost
11
Q
second type of chromosome mutation -INVERSION
A
inversion -a section of a chromosome may break off , turn through 180 degrees and then join again although all genes arestill present
12
Q
third type of chromosome mutation - TRANSLOCATION
A
a piece of one chromosome breaks off and then becomes attached to another chromosome . This may also interfere with the regulation of the genes on th translocated chromosome .
13
Q
fourth type of chromosome mutation =- DUPLICATION
A
A piece of a chromosome , may be duplicated . Over expression of genes can be harmful , because too many of certain proteins or gene-regulting nucleic acids may disrupt metabolism .
14
Q
fifth type of chromosome muttion - nondisjunction
A
one pair of chromosomes or chromtids fails , to separate , leaving one gamete with an extra chromsoome , when feritislied by a norml halpoid gamete ,t he resuling zygote has one extra chromosome . DOwn syndrome , or trisomy 21 , is cause dby non-disunciton . FIgure 1 shows anothe rexample of the consequences of non-disjunction .
15
Q
what is aneuploidy
A
the chromosome nmber is not an exact multiple of the haploid number for that organism . Sometimes , chromosomes or chroamtids fail to separate during meiosis (e.g trisomy ).
16
Q
what is polyploidy
A
if the diploid gamete is fertilised bby a haploid gamete , the resultign zygote will be triploid (it has three sets of chromosomes ) . The fusion of two diploid gaametes can make a tetraploid zygote . Many cultivated plants are polyploid (they have more than two sets of chromosomes ) .
17
Q
sexual reproduction 0 genetic variation resulting from sexual reproduction has contirbuted to evolution .
-Meiosis produces gentically different gametes . During meisosis , we can see that egentic variation may result from what things
A
-Allele shuffling (swapping alleles between non-sister chromatids ) , during crossing over in rpophase 1 .
-Independant assortment f chromosomes during metaphase/ anapahse 1 .
-Independent assortment of chromatids during metaphase / anaphase 2 .
18
Q
what are the characteristics of gametes produced by meisosis
A
gametes porduced by meisoissi are individually and egentically dissimialr .
-THey are also haploid , containing only one of each pair of hoomolgous chrosomes and one allele for every gene .
19
Q
what does the random fusion of gametes create in meisosis
A
the random fusion of gametes creates more genetic diversiy . Any male , gamete can be potentitally combined with any female gamete from an organism , of the same species .
-The random fertilisation of gametes , tht are alrady genetically unqiue , produces extenive geentic dieveristy among the resulting offspirng .
20
Q
example of variation caused solely by the environment part one
A
speaking with a particualr regional dialect . A person’s offpsirng , would not inherit the dialect thorugh their genes , although they might learnt to speak in this way by listening to other people .
21
Q
example of variation caused solely by the environment part two
A
losing a digit or limb or having a scar followign an injury .
22
Q
example of variation caused by the enviornment interacting with genes
A
if plants are kept in dim light after germination , or if the sooil in which they are grown contains insufficent magnesium , then the leaves do not develop enough chlorhyll and are yellow , yelllow-white .
-The plant is descirbed as chlorotic , or suffering from chlorosis . The plant cannot photosynthesisie , Chlorotic plants have the genotype fo rmaking chlorphyll , but ENVIRONEMNTAL FACTORS ARE PREVENTING THE EXPRESSION OF THESE GENES .
23
Q
Meaning of allele
A
a version of genes
24
Q
meaning of heterozygous
A
not ture - breeding , having different alleles at a particular gene locus on a pair of homogous chromosomes .
25
meaning of homozyguous
true-breeding having identical alelels at a particular gene locus on a pair of homoglous chromosomes .
26
meaning of monogenic
determined by a single gene
27
the foundation for genetics
-in 1866 , Gregor Mendel , published the results of his investigations that would lay the foundtions for the branch in biology known as geneitc which is now at the forefron of modern bioog .
28
what did mendel study
mendel studied an organsm that was easy to grow and although naturally self-feritlising , was easy to cross-feritlise rtifically . He worked with seven characrtersitcs of the pea plant , each chracterisitc haivng two disticntl contrasting trists ; stem height ,s eed shape , seed colour , pod shape , pod colour , flower rrangement and flower colour .
29
mendel obtained TRUE BREEDING STRAINS - explain
wehre the trait had appeared unchanged geenration after generation from local seed merchants . Mendel also kept accurate and wuantitiatie records of data obtained which he analaysed .
30
Monohybrid cross - EXPLAINED
Mendel;s simplex experiemnts invovled onlyo ne characterisitcs with one pair of contrasting traits .
-He mated , individuals from two aprent strains ,e ach of which showed a different phenotype .
31
monohybrid cross (part two )
one parent , was true0breeding of rtall stems , and the other was true breeding for short steams ,
--Parnet are called P1 GENERATION .
-all offspirng are F1 genertion , they were all phenotupicall idneitcal ot one parent type , they were all TALL .
32
what happened when mendel allowed members of the f1 generation to self fertilise
this resyllted , in f2 containg SOME short palnts but there were three times as man talls as short palnts 3./4 were tall and a wuarter were short . check page 181 for simialr result .
33
In pea plants , the chracterisitcs of height is wht
it is monogenic , it is governed by one allele that has two disinct lleels T and t .
-one allele t when present in hozomygous invidual givign the tt producs phenotypicall short plants . what
34
what charactersitc is presented with allel T
when presented in homozygous or heteorzygous , indivudals produ ce phenotipically tall plants . tHE ALELE t IS DESCIRBED AS DOMINANT (IT OCDES FOR A DOMINANT CHRACTERISITC ) , AN THE ALLELE T IS RECESSIVE - CODING FOR A RECESSIVE CHRACTERSITC , that will only be visible int he phenotype if there is NO DOMINANT ALLEEL .
35
punnett squares type 1
the genotypes and pehnotypes resulting fromt he possinle combinations of gametes during a monohbrid cross , showing the possible outcomes of monogenic inheritance , can be visualised in a punnet sqaure named after its invenot .
36
what odes a punnet square show
-In a punnet swuare , all possible gametes are assigned to a row , with those of the female parent , in the vertical column ,a nd those of the male parent in the horizontl row .
-The genotpes of the next genertion are predicted by combining the male and female gmete genotypes - a prpocess that represents all possible randomf ertilsiaiton events . check figure 4
37
the test cross - outcome 1
genotypes mendels pea plants = all short pea plants have the genotype tt , because shortness is a recessivee characterisitc , so individuals with that phenotype must hve the genotype tt . THey are homozyhous recessicve .
38
the test cross - outcome 2
the tall pea plant in the f1 genertion all have the same genotype , Tt . THEY are all heterozygou , We can deduce this fromt he genotypes of their true-breeding parents (TT and tt ) and the enotypes of the gametes (T and t ) tht must hve combined to produce this generation .
39
the test cross - outcome 3
in the f2 , egenration , some of the tall plants have the genotype TT and some hve the genotype Tt . tHEY BOTH HAVE THE SAME PHENOTPE , TLL AND IT IS IMPOSSIBLE TO TELL THEIR GNOETYPE fromt heir appearnace .
-Mendel devised a simple way to test the phenotypes ,c alled the test cross this methos is still used tody .
40
what is dihbyrid
involving two gene locio
41
one dhybrid cross - mendel examined what
the inheritancce of seed shape and seed colour in pea plants . He crossed ture-breeding pea palnts with yellow and round seeds , with ture - breeding pe plants that had green and wrinkled seeds .
42
one - dihbyrid cross - result
all tge f1 egenrationw ere hdybirds , having hte phenotyp of yellow and orund seeds .. Each plant in the f1 geenration is heterozygous , for both genes (seed colour and shape ). THerefore yellow and round are both dominant tits .
-checlk figure 1 - 183
43
what were the results of the dihbyrid cross that mendel deuduced
-the alleles of the two genes are inherited independently of ech other , so ech gamete has one allele for each gene locus .
-During fertilisation , an one of an allele pair can combine with any one of other allele pair .
44
prediciting rations of traits in the f2 geenration
-if we consider the two crosses for seed colour and seed shape , as two indpeendnet monhybrid crosses , with the two sets of traits being inherited idepndently , swe can rpedict the outcome of llwoing the members of hte f1 generation to self fertilise .
-The chances , of the raits of rseedc olour being inherited are not influenced hby the chances of the traits for seed shape being inherited .
45
assuming that seed colour and seed shape are two seaparate monogenic charactersitics ;
-For the characterisitcs of colour in the f2 , egenration we could predict 3/4 , would be yellow and 1/4 green a ratio of 3;1.
-For the characterisitc of shape ; we would predict that 3/4 , would be round and 1/4 wrinked a ratio of 3;1 .
46
what happens when two independent events occur simulatenosuly
product of individual probailtiies = combine probability of occurence . We can use this equation to calcualte the prop . eortie of all the other phenotypes in this generation , checkk page
47
when mendel counted his pea plants in the f2 generation of the dihybrid cross what was the ratio that he had obtained
9:3:3:1
48
what is codominancee
where both alelels present int he genotype of a heteoryzyous incivudal contribute to the individual's phenotype .
49
multiple allees
characteristics for which there are three or more alleles in the population;s gene pool .
50
overtime a huge number of chnages can occur anyhwere within a gene , as a result what happens
many genes have more than two alleles .
-When three or more alleles at a specific gene locus are known , then the gene is said to have multiple alleels . HOwever , any individul can only posses two alelles , one on each gene locus in a pair of homoglous chrosomes .
51
example of codominance
the inheritanceo f human ABO , blood groups is a good example of multiple alleles .. It also demosntrates both dominance and codminance of the alleles involed .
52
explain the four blood groups phenotpes
A B AB and O are determined bby THREEE alleles of a single gene on chromosmose 9 . The gene encoded an isoagglutinogen , ont he surace of the erythorcytes
-The alleles present in theu human gene pool are IA , IB, IO . IA + IB ARE BOTH DOMINANT TO I0 which is recessive .
- IA + IB are codominant , hte wll both be presen tint he genotype and contibute to the phenotype . Any idnidual will have onlyt wo of the three alleles within their genotype . check figure 1 on page 185
53
coat colour in rabbits - agouti
each hair has a grey babse and a yellow band and a black tip .
54
coat colour in rabbits albino
the condition where no pigments develops and the fur is white .
55
coat colour in rabbits - chinchila
hairs are silvery gey because they lack the yellow band .
56
coat colour in rabbits - himalayan
white but with black feet , ears nose and tail .
57
what is the dominance hierachy in coat colour in rabbits
agouti C , is dominant to all other alleles .
-Chinchill , C ch , is dominnt to himalayan , C h .
-Albino , c , is recessive to all other alleles .
CHECK PAGE 186 OFR EXAMPLES .
58
WHAT IS sex - linked
gene present on one of the sex chromosome
59
what is sex determined by in humans
one of the 23 pairs of chromosomes called the sex chrosoomes .
59
what are the other 22 pairs called
autosomes , each of the autosomal pairs in fully homologus - they match for length and contian the same genes at the same loci .
60
what are he sex chromsomes in mal and female
XY in males and XX in females .
-the X and Y chromosomes are not fully homolgous . A small part of one other matches a small part of the other ,s o that these chromosomes can pair up before miesosis
61
women are genetically more stable then men aka superior Explain
the human X , chromosome contains over 1000 genes that are inovvled in determining many charcterisitcs or metlloic funcitons . Not conenred with sex detminiaiton and most of these hve no aprtner alleles on the y chormomose .
-If a female has one abonromal , allele on of o her x chrosomes ,s he will proabl have a fucnitonign allele ont he same gene on her other x chroomosme .
62
women are genetically more stable then men aka superior Explain - what happen sif a male inheirst s from his mother an x chromosme with an abonromal allele for a particiualr gene
he will suffer froma genetic disease , as he will not have funcitonign alele for that gee.
-Males are fucnitonally haploid or hemizygous for X-linked egens , they cnnot be heteroxyous oro homoxyous for x - linked genes .
63
exampples of sex - linked characterisitcs include
haemophilia A and colour blindness .
64
what happens to a perosn with haemophilia A
is unable to clot blood fast enough . Injuries mah cause bleeding or an internal haemorrhage .
-One of the genes of the non-homogous region of X chromosome codes for a blood - clotting , protein called factor 8 . A mutated form of the allele codes for the non-fucntioning factor 8 .
65
what happens with a female with one abnormal allele and one functioning allele for Haemophilia A
they produce enough factor 8 , to enable her blood to clot norally when reqruied . However , this female is a carrier for the diseases . Id sucha feamle passes the X chromosome containing the fault allele to her son , he will have no funcitong alele ofr factor 8 on his y chromosome , As a result he will suffer from ahemophillia A .
66
check figure 3 on page 187 for inheritiance o ahemophilia A .
p,g 187
67
colour blindness - one of the genes invovled in coding for a portein invovled in colour vision is on the x chromosome but not on the y chromosome , so what oes this eman .
- a mutated allele of this gene may result in colour blidness cannot see difference between red and green .
-a female with one abornmal alleles and one funcitonign allele will not suffer from colour blindness but a male wiht an abnormal allele on his X chromosome will not hve a fucnitoning alele on his y chromosome and will therefore suffer from red green colour bllindenss .
68
inactivation of x chromosomes in female mammals (1)
-It may appear that females have twice the number of x-linked genes being expressed as do males . HOwveer , a mechanisms prevents this disaprity .
-in every female cell nuclues one x chromosome is inactivated .
69
inactiviation of x chromosome in female mammals (2)
determination of which memebr of the pair of x chromosomes become inactivated is random and happens duing ealry embryonic development .
70
meaning of codminant
where both alleles present in the genotype of a heterozygous inidivudal contribute to the individual's; phenotype .
71
codminant allele explained
when both alelles of a gene in the genotype of a heterozygous indiviudal contirbute to that individual's phenotype , the aleles are dscribed as codminant . thE TWO ALLEELS ARE RESPOISBLE FOR TWO DISTINCT AND DECTABLE GENE PRODUCTS .
tHE PHENOTUPE OF heteroygotes is DIFFERENT FROMT HE PHENOTPE OF THE HOMOZYGTOES .
72
Codominant inheritance in animals - coat colour in shorthorn cattle - the one gene for coat colour has two alles CR ( RED ) AND CW (WHITE )
-Cattle that are homozygous , for the red-coat allele , CR , HAVE A RED (CHESTNUT) coat .
-Cattle homozygous for the white coat allele CW - have a white coat .
-Heterozygous cattle genotype CRCW have both red and white hairs a roan coat .
73
if red and white shorthorn cattle are interbred :
all the offspirng are roan
74
if roan cattle are amted
then the offspring will show all three pehnotyes in the ratio 1 white ; 2roan ; 1red
75
ABO blood groups - codimannce recap
6.2.4- describes the inheritance of the ABO blood groups .
-You will notice that fromt he information that the allels IA and Ib , are codonimant to echother .
-An inidivudal of genotype IAIB , expresses both and has both types of isoagglutinogen protein on their erythrocytes . THe inheritnce of these blood groups also show DOMINANCE AS both IA and IB are dominnt to the llele IO .
76
WHAT is sickle cell anaemia
sickle cell anaemia is caused by a mutation in the gene that codes for the beta globin chain of the haemogloin .
-The mutuant alele is given the smbol HbS , annd the nromal allele is given the symbol HbN .
77
sickle cell anaemia in relation to heteorygous people
in heterozygous people , at least half the haemoglobin in their red blood cells is normal and half is abnormal . HOwever , heterozygous people od not usfer from sickle cell anaemia .
78
Haemglobin as the phenotype ...
these alleles , are considiered as codominant .
-HOWEVER , if we take sickle cell anaemia to be the phenotype , the HbS alelle is considered to be recessive as this diosorder has a recessive inheritance pattern .
79
autosomal linkage
gene loci present on the same autoosme ( non - sex chromosome that are often inherited togehter .
80
linkage - mendel
when mendel invesitgated the simulatenous inheritance , of two chractersiitcs he chose seven chraracterisitcs for which the gene were on differen chromosomes . Hence the genes assorted independetly .
81
is the chromosome or the gene the unit of tranmission during sexual reproduciton , and what does this mean
The chromosome is , therefore linked genes are not free to undergo independent assortmenet , they re usually inherited together as a single unit . Describes sx linkage . This topic is cocenrned with autosmal linkage where genes are linked bybeing ont he same autosome .
82
inheritance of autosomally linked genes with no crossing over
if linked genes are not affected by crossing over of non-sister chromatids during prophase 1 of meioisis , they they are always inherited as one unit .
-F1 - shows the formation of gametes under these circumstances .
83
84
Example - in sweet pea plants , the genes for flower colour and pollen grain are ont he same chroomomse , what are the two alleles for each gene .
-the gene for flower colour has two alles ; P for puple flowers and p for red floweres .
the gene for pollen grain shape has two alelles L for long grains the l for short grains .
85
check page 191 F-2
shows the phenotype ratios of the F1 , offspirng porduces when ture-breeding purple flowered , long-grain plants l homozygous t both gene loci are crossed with ture - breeding red-flwred short-grained plants , homozygous both at the gene loci . All the f1 , plants are heteroxygyous and pehnotypiclly the same exhibitign the domiannt chracterisitcs .
86
f-2 of page 191
it also shows the predicted phenotype ratios of the F2 , generation offspirng resulting from interbreeding memebrs of the f1 genrtion , As there is no independnet assortment , we expect onl two types of gaete .
87
figure 2 explained
-the phenonotype ratio in the f2 generatio is 3 purple flowered long-grined .
-1 red - floweed short-grined plants . The genotype ratio is 1 homozygous dominant , 2 hetroiyxygous ; 1 homozygous recessive .
88
f02 explained aprt two
-These ratios ,a re the same as the Mendelian monhybrd inheritance ratios , with onl two phenotypes in the F2 generation . If the genes were not linked we would expect ofur ditinct phenotypes int he f2 genertion in the 9;3;3;1
89
innhertiance of autosomll linked genes with crossing over example on 192 explained
-The expected , phenotypic ratio is 3 purple flowered long grained plants ; 1 red flowered short grianed plants .
-From this sample of 1283 , F2 plnts , we expect to see 962 purple - flowered long-grained plants and 321 red-flowered short grained plants .
90
phenotpes in the f2 generation explained
from this sample of 1283 F2 , plants we expect to see 962 purple flwoered long-grained plants and 31 red flowered short-grained plants we would not expect nhy f the recombinant phenotype , those with pruple flowers and short pollen grins or with red flowers and short pollen grians .
91
what has happened to these recombinant gametes
;they have been produced by crossing over during meiosis 1 , as explained in figure 3 , figure 3 shows how recominant gamete fusion may produce the unecpected phenotpe in f2 egenration .
-Herre there are four phenotypes in the f2 genertion but they are not in the 9;3;3;1 ratio we would expect if the genes were not linked . THE FURTHER APART the gene loci are on chromosome , the greater is the chance of recominant gamete forming .
92
epistasis
interction of non-linked gene loci where one mask the expresion of the other from the greek ephistanai meing stoppage .
93
what affect does different genes at different loci on different chromosomes interact to affect one phenotypic chraceristic
when one gene masks or suppresses the expression of another gene this is called epistasis .
-he gene in question may wor together antagonisticll 9agaisnt each other ) or in a complementary fashion .
94
how do genes assort during gamete formation
as the gene loci are not linked , they assort independentl , during gamete formtion . Epistasis , reduces the number of phenotypes produced int he F2 egenrtion of dihbyrid crosses and herefore reduces genetic variaiton .
95
genes working antagonistiically - how does recessive epistasis
the homozygous presence of a recessive allele at the first locus prevents the expression of another allele at a second locu . The alleles at the first locus are episati to those at the second locus , which are hypostatic to those at the first locus .
96
an example of recessive epistasis
is the inheritance of flower colour in saliva , two gene loci A/a and B/b on two different chrosomes are invovled .
97
what is the genotype of offspirng og a pure breeding pink-flowered variety of slvia AAbb is crossed wiha puorebreed whie flowered varity aaBB
All the offspring of the f1 generation have purple flowers is AaBb
98
what is the ratio of inerbeed salvia flowers
interbreeding memebrs of the f1 generaiton results in plants that bear purple , pink and white flowers in the ratio 0:3:4 . Thisi s a modieified version of the dihbrid 9:3:(3:1) ratio .
99
the homzocyous aa is epistaitc to both allels of the B/b gene , what does this me
Neither ,t he allele B for puple nor the allee b for pink , hwen int he homozygou sstate , can be expressed i no dominant A allele is presen .
100
Dominant epistasis
The inheritanceof feather colour , in chickens is an expale of dominant epistasis . There is an interaction between two gene locio I/i , and C/c . The hpostaitc gnee , C/c codes for cloured featehrs . The Ii allele of the epistaitc gene I/i , precvens the foration of colour even if one C allee is present .
101
individuals carrying at least one dominant allee I have white feathers ... even
if they hae one dominant alele for coloured feathers .
102
birds , that are homozygou for the recessie alele , c are also white ...
as this mutated allele does not cuse pigment to be made
103
what is the pure-breeding white leghorn chicken genotype
IICC - purebreeding white wyandotte chickens have the genotpe iicc .
104
if white leghorn hcicken is crossed wih white wyandote hickens what do you get
IICC x iixx
All offspring will have the genotype IiCc .
105
If the progeny is interbeed what do you produce in the F2 generation
if the progeny interbreed they produce in the f2 geenration , white-fethered chikcens and coloured-fethered chicens in the ratio of 13;3 , CHECK F4 ON 194 FOR THIS explanation .
106
genes working in a complemenary fashion
as scienitsits are discovering more about how genes work nd interact with echother . E[istasis , is more often explained int erms of the genes working to coe for two enzymes that work in succession , catalsing sequential steps of metabolic pathway
107
cot colour in mice
-gene locus C/c demines coat colour
CC or Cc produced coloured fur .
however in the recessive homozyous sae genotype cc , no pigment , develops and mice are albino
A/ a determined what that colour is by determining the distribution of pigment . The dominant allele , A , produces agouti colour - each hair has black pigemn and a yelllow band producing grey colour .
--recessive allela when homozygous porduce balck fur as the yellow frome ch hair is LACKING .
but teo c alelles noc olour will develop as their is no pigment to be disributed . CHECK TABLE 1 ON 194
108
109
Figure 5 - page 194 - recessive epistasis - in the presence of a c alelle
the black pigment can be made from a colourless substance ,
110
110
Figure 5 - page 194 - recessive epistasis 0 ub tge oresence of an a allele
this black pigment is deposited during the evelopment of hair in a pattenr combined witha tellow band on each hair , tht produces the agouti colourtion .
111
wht does the ratio 9:3:3: mean
Mendelian ratio from a dihbyrid inheritance where the two genes are unlinked epistasis also involved two unliked gene loki .
111
skim over 195-196
...l
112
what does a 9:3:4 ratio mean
kay suggest recessive epistasis .
113
12:3:1 and a 13:1 ratio mean
they both suggest dominant episasis , hwoever , epistasis may occur by complementary gene action .
114
a 0:7 ratio or a 9:3:4 ratio may suggest what
ma suggest epistasis b complemntary gene action . Complementary gene action may also produce 9:3:3:1 ratio.
115
what is a chi squared test
statistical test designed to find out if the difference between observed and expected data is significant or due to chance .
116
what happens if we obtain results that are not quite as expected
we need to know whether the differnece is just due to chnce or whether the difference between what we observe and wht we expect is significnt . If it is significant , it maybe that hte inheritance pattern is different to what we thoought and we need to rethink how to explain our obervations .
117
what is the predicted outcome of a dihybrid cross
we expect 9:3:3:1 ratio .
118
what may prevent us from getting 9:3:3:1 ratio
-if the sample collected is alrge we SHOULD otain results that are close to tha we expect to see . however if the sample is not so large , we many not ge an exct 9:3:3:1 ratio .
-Also , some ovules may not become fertilised and some seeds may not develop in pod . There is also the influence of the genetic lottery as to which gamete fuse at fertilisation .
119
Wehn can
119
we use he chi-squared test when : (1)
-the data are in categories (e.g different phenotypes or discrete variables ) , and are not continuous .
-we have a strong biological theor to use to predict expected values .
120
we use the chi squared rest whe (2)
the sample size is large /
-the data are onl rw counts (percentages or ratios cannot be used )
-there are no zero scores in the rae count data .
121
what is a null hypothesis
-statisical test cannot be used to directly test a hypotheiss instead they test a null hypothesis . If the null hypotheiss is not supported , then we accep the original hypotheissi .
-The null hypotheisis states - there is no statisitically significant difference between the observed and expected data - any difference is due to chance .
122
out of 288 individuals assuming 9:3:31 ratio , what is the expected numbers in each phenotpe category wuold be ;
9/16-288 = 162 would be yellow and round .
3/16 of 288 - 5
would be green and round .
-3/16 of 288 - 54 would be yellow and wrinkled
-1/16 of 288 18 would be green and wrinkled .
123
check page 198 - check the formula for calculating the value of chi-squared x2 is
x2 = the sum of (each observed number (o) - each expected number (e)2/ each expected number e
124
explannation of chi squared test equation
-in this equation - differences maybe positive or negative , so they are squared . tHIS PREVENTS NY NEGATIVE VALUES CANceling out an positive valules .
-dividing e takes into account the size of the numbers .
-the sum of sign takes into the number o comparisions eing made .
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procedure of chi squared test (1)
-calculting the valu eof x2
2.deterined the number of degrees of freedom (= number of categories -1 )/
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procedure of chi squared test (2)
determine the value of p from a distribution table . THe probability valu eof 0.05 identifies the level that could occur by chance just 5 times in 100 (5%) , or 1 time in . We neeed ot know the probability of our deviation being the result of the chance is greater than 5% /
4. decide whether the difference is significant at the p =0.05 level of probabilit .
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do chi squared test porcedure on page 198
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128
what is continous varation
variation that produces phenotpic variaion where the quantiative trais vary nync ery small amounts btween one group and the next .
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what is discontinous variation
genetic varaiaiton producing discrete phenotpes - two or more nonoverlapping catgeires .
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for discontinous variation - there are no or very few intermedites between the different phenotpes - give an exampel
for example , you are either male or feamle and hve only one of the four possible abo groups .
ear loves ar attached or free hanging .
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what are the characteristics that exhibit discontinous variation are usually determined by what
By the alleles of single gene locus .
-They are mongenic . Sometimes the alleles of two genes interact to govern a single chraccharacteristicterisitc in either case .
-different alleles at a single gene locus have large effects on the phenotype .
-different gene loci have quite diferent effects on the chracteristic .
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snother way disconitnous variation can be produced
genes at different loci may interact to infleunce one charcterisitc nd produce discontinous variation as in epistasis .
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continous variation has a smooth gradation between the many intermedites
...
134
examples of continous varation
-birth mass , foot size
-cob length
lef length
-Mnay genes are inovled in determining such characterisitcs . Therefore such chracteristics are descirbed as polygenic .
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how may the allels of a gene contirbute a small amount to the phenotype .
-the amy contoibute a small amount ot the penotype therogre the alelels hav an dditive effect on hte phenotype . As a result the phenotypic categories vry in quntitiive wy .
-The greter the number of gene loci contirbuting to the determination of the characterisitcs , the more continous variation .
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interaction between genes and enviornenvironmentemnt - which has the greater effect on expression of genes
the ENVIRONMENT , has a greater efect on the expression of polygenes / polygenic chracteristics , than it does on monogenic characterisics .
-For example , ech peron has a genetic potentil for height and intellligence , but without proper nutirtion and also for intelligence , mental stimulaiton , these potential iwll not be reached .
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what is directional selection
- a type of natural selection that occurs when an enviornemntal change favours a new phenotype and so as a results in a change in the populaiton mean .
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what is the founder effect
when a small sample of an original population establishes in a new area its gene pool as it is as diverse as that of the parent population .
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genetic bottleneck
a sharp reduciton in size of a population due o environemtnal catastrophes such as earthquake , floods , disease or human activties such as habitat desturction , overhuntng or genocide which reduces genetic diversity . As he popultion expands it is less geneticall diverse than befor .
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stablisilng selection
natural selection leading to a costancyw ithin a populaiton . Intermediate phenotpes are favoured and extreme phenotpes selected agisnt allees for exxrrme phenotpes mabe rmeoved from the populaiton . STBILISING SELECTION REDUCES GENETIC VSRATION Within the opulation .
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what do mutations and migration do to a population
they introduce new alleles into a population . some individuals ,within a population will be better adapred than other to the environemnt . due to differences in their genotypes and phenotypes .
--Tehse individuals re more likely to survive and reproduce , passing on the advantagoues alleles .
-OVERTIME , allele frequences within the population will chanve , thisis natrual selection . Nnatural selection may also maintian contancy of a species as well as leading to a new species .
142
what are the three main types of selection
stabilising , directional , and disruptive selection
143
explain stablising sleectiono - check graph on page 201
stabilising selection normall occurs when the organisms's enviornemnt remains unchaged it favours intermediate phenotypes .
--In humans , babies of birth close to 3.5g are more likle to survive , their offspirng inheirt alleles form them also leading to this mean bith mass .
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what is directional selection
if the enviornemtn changes fo eexample by becoming colder , there may now be an advanatge to being larger , so a new larger becomes the ideal and will be selected for . If more larger individuals surivive nd reproduce , thew ill be more likley to pass genes and alleles for larger size to their offspring .
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consequences of directional selection
Overall several generations , there is a gradual shift in the optimum value for the trait . F-2 , shows the impact of directional selection on the mean value for a trait within a population
directional selection i sused by plant and animal breeders to produce desirable traits . In anture , withina popularion periods of directional selection may alternte with epriods of stbilising sleection .
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what is genetic drift part one
if a population descends from a small nnumber of parents the gene pool ill lack genetic variation . Some alleles resulting from mutation confer neither an advantagr nor disadvaaage ont he individual so there iwll be no selection pressure acting up on them .
- however , chnce events may drasticllya lter the allele frequency . Imagine , a small popultion descended from one set of heterozygou paretns .tEHRE ARE ONLYTWO ALLELS a AND A IN THE POPULATION .
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WHAT IS THE GENETIC DRIFT PART TWO
If a catastrophic events occurs such as an earthquake flood outrbeak of a disease or a severe shortage of food , which lead o the death of many of the already small population one of the alleles may dispper from this population .
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what happens when population recovers after a genetic dirft
-when the populaiton recovers and increases in size , it will have less genetic diversity thn before and may lack particualr alleles . The alleles in quesiton did not disapper due to selction pressure but due to geentic drift .
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what is genetic bottleneck
when a population size shrinks and then increases again it is said to have gone through a genetic ottleneck .
150
what happens after a genetic bottleneck
after this event , the genetic diversity within that populaiton will be reduced . There may be loss of some advanagtegous alleles or a disporportionate frequency of a deleterious (harmful) alleles , putting that population;s chances of a lt surivial at risk .
-Sometimes , after genetic bottleneck a population shirnks to such small size that its fertilit is affected leding to the species becoming endangered and then extinct .
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what happens to those who survive egentic bottle neck have a particular advanatge
for example resitance to a particualr pathogen , then a bottleneck could improve the gene pool whilst lso shrinking generic diversity .
-species that have been selectively bred for certain traits have also veen through a geneitc bottleneck .
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what is the founder effect
if a new population is established , by a very small number of individuals who orgiinate from a larger parent populaiton , the new population is likley to ehibit loss of genetic variation .
-some groups of migrating humans not full egenticlly represnetative of the parent population , have set up population in new areas . IF THEY HAVE REMAINED ISOALTED FROM OTHER HUMAN POPULATIONS OF REXAMPLE , BECAUSE OF RELGIOUS AND CULTURAL DIFFERENCES OR DUE TO GEOGRPAHIC isolation , then the new populaiton will have a small gene polol.
