Module 6.2 Flashcards
genotype
genetic makeup of an organisms .
phenotype
visible characteristics of an organisms
genetic factors that have contributed to evolution
-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 .
Physical agents that are mutagens
x-rays
-gamma rays
-uv light.
Chemical agents that are mutagens
-benzopyrene found in tobacco smoke
-mustard has
-nitrous acid
-aromatic amines -insome synthetic .
-
Biological agents - Mutagen
Some viruses
Transposon
Food Contaminants
mutations can be three things , what are they ?
harmful , advantageous , or neutral .
mutations are PERSISTENT
They can be transmitted through many generations without changr .
Mutations are RANDOM
they are not directed by a need on the part of the organism in which they occur .
first type of chromosome mutation - DELETION
Part of a chromosome containing, genes and regulatroy sequences is lost
second type of chromosome mutation -INVERSION
inversion -a section of a chromosome may break off , turn through 180 degrees and then join again although all genes arestill present
third type of chromosome mutation - TRANSLOCATION
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 .
fourth type of chromosome mutation =- DUPLICATION
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 .
fifth type of chromosome muttion - nondisjunction
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 .
what is aneuploidy
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 ).
what is polyploidy
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 ) .
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
-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 .
what are the characteristics of gametes produced by meisosis
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 .
what does the random fusion of gametes create in meisosis
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 .
example of variation caused solely by the environment part one
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 .
example of variation caused solely by the environment part two
losing a digit or limb or having a scar followign an injury .
example of variation caused by the enviornment interacting with genes
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 .
Meaning of allele
a version of genes
meaning of heterozygous
not ture - breeding , having different alleles at a particular gene locus on a pair of homogous chromosomes .
meaning of homozyguous
true-breeding having identical alelels at a particular gene locus on a pair of homoglous chromosomes .
meaning of monogenic
determined by a single gene
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 .
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 .
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 .
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 .
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 .
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 .
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
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 .
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 .
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
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 .
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 .
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 .
what is dihbyrid
involving two gene locio
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 .
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
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 .
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 .
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 .
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
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
what is codominancee
where both alelels present int he genotype of a heteoryzyous incivudal contribute to the individual’s phenotype .
multiple allees
characteristics for which there are three or more alleles in the population;s gene pool .
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 .
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 .
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
coat colour in rabbits - agouti
each hair has a grey babse and a yellow band and a black tip .
coat colour in rabbits albino
the condition where no pigments develops and the fur is white .
coat colour in rabbits - chinchila
hairs are silvery gey because they lack the yellow band .
coat colour in rabbits - himalayan
white but with black feet , ears nose and tail .
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 .
WHAT IS sex - linked
gene present on one of the sex chromosome
what is sex determined by in humans
one of the 23 pairs of chromosomes called the sex chrosoomes .
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 .
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
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 .
