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127 Cards in this Set
- Front
- Back
2 ways to create genetic variability |
Polyploidy Mutation |
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Polyploidy |
Organisms with more than 2 sets of chromosomes in its somatic cells |
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What is the value of having more than two copies of chromosomes? |
Increase the total amount of genetic Variability |
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What is the highest possible number of sets of chromosomes to be found in somatic cells? |
12 most commonly found up to 8 |
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Euploidy |
A complete doubling or quadrupling of chromosomes When every single chromosome is doubled |
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Aneuploidy |
A single chromosome that is doubled Multiple copies of a single chromosome (2n + 1) incomplete sets of chromosomes; one chromosome is either missing or added |
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Describe the variables of a polyploid (X, N, 2n) |
X = basic (original) chromosome number of an organism N= Haploid (Gametic) Chromosome Number; the number of chromosomes that are present within one of the gametes (egg or pollen) 2n = Diploid (Gametic) chromosome number |
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What determines the type of euploid? |
The number of complete sets of chromosomes: Diploid = 2x Triploid = 3x Tetraploid = 4x Pentaploid = 5x Hexaploid = 6x Septaploid = 7x Octaploid = 8x |
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Why are pentaploids rare? |
because uneven amounts of chromosomes create a genetically unstable individual when the cells divide. When an uneven number is divided into two, there is an uneven division of chromosomes between cells. |
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What portion of crops are polyploids? |
1/3 to 1/2 of angiosperms are ployploid |
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How must haploids be reproduced? |
Clonally |
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Two different types of Euploids |
Alloploids and Autoploids |
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Alloploid |
combination of genomes from two or more different species (crossing two unrelated species) |
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Autoploids |
All chromosomes come from within a single species Crossing two related species |
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Chemical used to induce polyploidy? |
Colchocine |
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Colchocine |
water-soluble alkaloid found in the autumn crocus, blocks or suppresses cell division by inhibiting mitosis this causes the spindle fibers to make a failure in connection to each chromosome, causing the chromosome number to be doubled |
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Value of Polyploids |
Increased variation with increasing chromosome number taking a positive gene and doubling it will continue to double the positive effects of the gene may increase plant size as polyploidy number increases (due to larger nuclei in cells to hold more chromosomes, the cells are in turn larger as well) |
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How does colchocine effect spindle fibers? |
it breaks down spindle fibers; thus inhibiting separation of cells |
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How is a triploid created? |
Creating a tetraploid (using colchicine on a diploid) then crossing the tetraploid with a diploid female. (2n=3x) |
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What is the significance of a triploid watermelon? |
Seedless. the seed carries three copies of every chromosome plant is unstable and therefore shuts down the ability to produce seed |
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Microsporogenesis |
a single cell undergoes a process to make 4 haploid pollen grains |
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Megasporogenesis |
a single cell undergoes a process to produce 1 egg |
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True or false: All endosperms are triploids |
True |
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By adding one more chromosome, what happens to the number of phenotypic classes? |
increase the number of phenotypic classes by 1 (from 3 (diploid) to 4 (triploid)) Tetraploid = 5 phenotypic classes |
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What causes Aneuploidy? |
one spindle fiber does not form; one cell has two copies of one of the chromosomes and the other cell ends up with a missing chromosome |
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What are the two potential aneuploids that could be created? |
Monosomic and Trisomic |
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Types of Aneuploidy |
Nullisomic = 2n - 2 Monosomic = 2n - 1 Trisomic = 2n + 1 Tetrasomic = 2n + 2 |
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Why are Nullisomic and tetrasomic individuals very rare? |
because they are very unstable and therefore have a low likelihood for survival |
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Example of chromosomal mutation |
polyploidy |
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Two types of Genetic Mutation |
Recessive mutation Dominant Mutation |
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Recessive mutation |
mutating a recessive trait into its dominant form |
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Dominant mutation |
Mutating a dominant trait into its recessive form |
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Why was there interest in genetic mutation following WWII? |
discovered that plants introduced to levels of radiation would change, altering their phenotypic state this became known as mutation breeding |
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Mutation breeding |
change in state of one gene (goal is to change only one gene) |
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T/F: All mutations have a recognizable phenotype |
False; not all mutations have a recognizable phenotype |
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Two guidelines to mutation breeding |
1) choose a qualitative trait controlled by one gene 2) trait that is chosen must be easily screened (ie. color) |
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Mutation breeding requires methods to |
1) induce radiation 2) screen for advantageous mutations |
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Two methods of inducing mutations |
1) Ionizing radiation: Xray, neutrons, UV radiation, GAmma Rays, Beta Radiation 2) Chemical mutagens (most common): Ethyl methane sulfonate (EMS); ENH, MNH, ENV, DES, EI |
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EMS |
Ethyl methanesulfanate - Mutagen used in mutation breeding |
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Two facilities used for Radiation breeding |
Gamma field Gamma Room |
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Gamma Field |
100m circular field with an 88.8 TBq60Co source at the center |
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Gamma Room |
7m octagonal greenhouse with a 44.4TBq60Co source |
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Mutant variety database |
joint group between FAO and IAEA |
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What departments inspect GMO crop safety? |
USDA, EPA, FDA (only crops that use radiation) |
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T/F: Mutation breeding requires testing and inspection |
False; mutation breeding falls under conventional breeding. Inspection is only necessary when radiation is being used |
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Why don't more people use mutation breeding? |
Expensive and time consuming but a great way for creating genetic variability. |
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V.A.S.T. Labs |
Variation and Abiotic Stress Tolerance Labs
basically G x E experimentation; alters things like water, light, PGR, etc. only evaluates one specific trait |
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Why are chemical mutagen agents preferred over radiation |
simpler to apply produce less damaging and durastic effects fewer chromosomal disruptions |
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Two methods (location) of evaluating breeding material |
Greenhouse or growth chamber Field |
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Goals of line evaluation |
Performance: measure performance of each plant so to compare amongst them (environmental variation) Whole plant evaluation - come up with a way to evaluate all of the genetic variability in order to figure out which plant grows better than everything else (interest in other traits) Comparison - checks |
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Perfect environment |
environment where environmental variation does not change throughout the field |
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Why are replicates so important |
because no environment is different; therefore it is necessary to develop a system that allows a measure of the differences across a single field |
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Which experimental design is preferred? |
randomized block design; want to evaluate each individual plant in a perfect environment |
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Goal of proper experimental design? |
reduce experimental error |
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Experimental error |
error that cannot be defined |
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Considerations of selecting a growing location |
Soils and media heterogeneity growing environment cropping history chemical residues cultural practices |
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Why is a uniform (or perfect) environment so desired? |
in a uniform environment, any change in phenotype is due to genetic variability |
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T/F: The more uniform the environment, the less variation can be explained |
FALSE: the more uniform the environment, the MORE variation can be explained |
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What are some important factors of statistics and experimental design when breeding plants? |
Data collection use of specialized equipment (some crops) Need for proper design |
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How is replication achieved in breeding experiments? |
Grow the same entry in multiple plots Provide sufficient number of replicates |
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Why must breeders provide replicates in multiple plots? |
reduces the effect of random variation by averaging over plots allows for the measurement of random variation |
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How many replicates is sufficient? |
Depends: two, four or more are common |
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What are the possible types of replication |
Within plot Within year Between year |
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As homyzygosity is increased through generations of inbreeding rice, what happens to the number of plants grown? |
As homozygosity is increased, the number of plants grown in each clump is also increased; but reducing the amount of variation (selecting for best clumps) |
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What is the overall goal of the rice evaluation center? |
to evaluate each plant in different environments to determine if any one plant is equal or better than the current commercial standard |
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Why do we try to spread out to multiple environments when experimenting with plant breeding? |
by spreading out to multiple environments, you get more environmental variability and you can therefore determine overall environemntal stability of the plant |
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What must be done before increasing the number of environments in an experiment? |
A certain level of homozygosity must first be reached |
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How long does it take for evaluations of perennials, shrubs, and vines at the Chicago botanic Garden? |
Perennials - 4 years Shrubs and vines - 6 years |
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What did Clematis do that was significant for plant breeding? |
Tested 108 varieites in a uniform environment; but instead of growing in optimal conditions, he chose a screening technique that would select for plants that would be best suited for a home grower environment (poor nutrient and water care) Oranamental qualities, ease of growth, hardiness, disease and pest resistance |
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Criteria for Randomization of an experiment |
1) plots in different orders in different replications 2) Competition between two entries must be "eliminated" 3) Cannot eliminate competition, must account for it 4) Every replication must have different randomization |
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Different types of design plots |
Single-plants multiple plant plots single row plots - (headrows) Multiple row plots |
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What happens to experimental error as interplot competition plays a roll? |
Experimental error increases whenever interplot competition causes performance of a genotype in one plot to be altered by performance of another plot In other words, experimental error increases if one plot has an effect on a different plot |
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What is the point of selection scheme, and how is this achieved? |
Selection schemes are designed to fix genetic variability over time; this is done by fixing genes |
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Oldest method of selection |
mass selection |
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Mass selection |
based on phenotypic selection in a heterogeneous population |
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How mass selection works |
plant a large field with many different varieties, select for a desirable trait and replant all of those seeds. Continue to do this until quantitative trait has been sufficiently reached |
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Problem with mass selection |
1) in some cases, we are Selecting for individuals due to location; environmental variation is not accounted for 2) selecting plants on the edge will effect results due to less competition |
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When does mass selection work best? |
Mass selection works well when heritability for the trait of interest is very high; this is because high heritability means environment doesn't play as much of a role |
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Four techniques that are used for inbreeding while reducing plant number |
1) bulk population 2) pedigree selection 3) single-seed descent (SSD) 4) recurrent selection |
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T/F: Most selection techniques begin with parent plants |
False; most selection techniques begin with plants in the F1 |
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Inbreeding techniques that rapidly increase inbreeding (increased homozygosity) while fixing both qualitative and quantitative characteristics |
Bulk population, pedigree selection, single-seed descent |
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T/F: Recurrent selection is the fastest method of inbreeding |
False; recurrent selection will inbreed at a slower pace, but if done correctly, we will continue to improve quantitative characteristics |
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How long does it take for quantitative characteristics to balance out? |
depends on how many genes effect the trait |
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In annual plants, how long does each step take? |
one year |
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Bulk population |
procedure for inbreeding a segregating population; used mostly in self pollinators procedure continues until an inbreeding level is attained may take advantage of natural selection |
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Methodology of Bulk population |
plant 1000 seeds, select for 100 plants; take 10 seeds from each 100 plants and grow them together this increases the homozygeity of the plants (but back at 1000 plants again) adding a selective pressure each generation of inbreeding and allowing for natural selection to take place in fields and select for plants that survive |
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Who first described bulk population |
Nilsson-Ehle (1908) - Natural selection vs. Competition Winter Hardy Wheat |
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Thermal photography |
decrease of water decreases transpirtaion which increases reflective temperatures. The cooler the plants during drought conditions, the more water that is withheld within the plant Increases the ease of observing a large number of plants |
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Pedigree selection |
Useful in handling segregating generations following initial cross |
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Explain the selection process for pedigree selection |
Selection in F2, F3, or F4 Plants are reselected each generation Pedigree of each selection is maintained by numbering system so that a line can be traced back to an individual F2 plant in any subsequent generation As selfing continues, each generation becomes unique individual; each generation has its own value that can be recreated at any point |
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T/F: The further along in the selfing process you go, the easier it is to recreate it |
True; the further along in the selfing process, the higher percent homozygosity |
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How is environment accounted for in Pedigree selection? |
each generation of pedigree selection requires you to select the plant in the environment in which it will be grown |
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Disadvantage of pedigree selection method |
relatively slow process: one generation per year; 5 years to get to F6 generation |
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When is single-seed descent most commonly used? |
Self fertilized crops |
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Two functions of Single-seed descent |
progress toward homozygosity by selfing selection of superior lines from segregating populations |
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T/F: Single seed descent is faster to reach high % homozygosity than pedigree method |
True |
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How does Single-Seed Descent work? |
During off seasons, selected seeds are sent to a different location with similar environment (ie Brazil, greenhouse) to be grown into the next generation Selection does not take place at the alternate site, but simply increases level of homozygosity quicker |
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T/F: F6 generation can be achieved in 2/3 years in SSD |
True |
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Value of SSD |
speeed; decreases time to go to market |
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Problems with SSD |
loss of ability to look for selection in a large number of environments (cuts the number of environments in half) |
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objective of Recurrent selection |
improve the performance of populations for one or more trait |
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What is Recurrent Selection |
a system of cyclical improvement a systematic selection of desirable individuals from a population recombination of the selected individuals to form a new population used extensively and effectively in cross-fertilized crops taking every selected individual and crossing them with one another |
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T/F: Recurrent selection is best utilized for qualitative traits |
False; recurrent selection is best utilized for selecting quantitative traits only method of increasing quantitative characteristics within a population |
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objective of Early Generation Testing |
eliminate inferior lines or populations that do not merit further evaluation or selection |
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How to: Early generation testing |
Take F2 (and subsequent generations) and evaluate as though it is the most elite line evaluate for everything; yield, disease resistance, etc. |
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what type of crops is early generation testing most commonly used in? |
self and cross pollinated species |
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What is the overall point of early generation testing? |
estimate the genetic potential of an individual or population at an early stage of breeding to get a generalized idea of how well a plant will grow |
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Benefits of early generation testing |
minimize population at an early stage |
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Problems with early generation testing |
Minimizes the number of locations viewed Each location brings value, if not done in enough locations, there may be a miss in an important phenotypic factor--this may be missed and never recreated |
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Selection index |
method of selecting for multiple traits simultaneously Traits are ranked in order of importance; and plants are selected based on this rank Narrows the focus of what is most important in the desired crop (ie. taste, texture, aesthetics, etc.) |
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Backcross Breeding |
essentially a method for improving an established variety that is deficient in only one or a few characteristics |
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What type of reproductive plants is backcross breeding most useful in? |
both self and cross pollinated species |
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What type of traits is backcross breeding most used for? |
Qualitative traits; backcrossing for quantitative traits is out of the question |
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Harlan and Pope |
Bred for the smooth awned : white seeded wheat variety |
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Recurrent parent |
plant that has everything that is desired, besides for one trait |
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Donor Parent |
plant that has nothing that is desired, besides for one trait |
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Basic methodology behind backcrossing |
cross recurrent parent with donor parent to get F1; cross F1 with recurrent parent to get BC1, continue to cross BC generations back to recurrent parent |
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T/F: Harlen and pope found the smooth awned trait in the first generation of backcrossing |
True! 75% of Recurrent parent, 25% of Donor Parent traits |
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Definition of backcrossing |
the repeated crossing of hybrid progeny bak to a single parent |
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At what point is 99% homozygosity reached while backcrossing? |
BC6 |
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Two things to watch while backcrossing |
1) simply inherited (qualitative) traits 2) everything else: trying to reconstitute the original recurring parent while incorporating the desirable trait from the donor plant |
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Mathematical equation for the recovery of the recurrent parent |
1 - (0.5)^m m= number of generations of backcrossing |
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Describe the progression of % recurrent parent through multiple generations (up to BC4) |
F1 - 50% BC1 - 75% BC2 - 87.5% BC3 - 93.75% BC4 - 96.87% |
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How does backcrossing a recessive trait differ from backcrossing a dominant trait? |
It becomes much more difficult because at the BC1, the qualitative trait cannot be selected via natural selection. It requires one of two different methods in order to show the recessive traits |
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What are two methods for determining the BC1 of a backcrossed parent whose desired trait is recessive? |
Testing: Selfing each plant in the BC1 and selecting for those that have the desired trait Blind: Backcrossing every single individual back to the Recurrent parent |
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Which is most efficient, Test or Blind method for determining genetics of a BC1 individual derived from a recessive parent |
Test method takes longer due to the need for a full year to self plants Blind method can be faster, but requires a lot of space and labor, which costs more money |
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Why is selfing a BC generation dangerous? |
Because while selfing a BC1 fixes the desired gene, it can also fix other genes from the donor plant that have not been accounted for (undesirable genes from donor plant) |