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How do you write genotypic and phenotypic ratios?

How do you write genotypic and phenotypic ratios?


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If two homozygous recessive parents are crossed, I know that all of the offspring will be homozygous recessive as well. Would you write the genotypic ratio as 0:0:4 then and the phenotypic as 0:4? (Does order matter? i.e. compared to 4:0) Also, if the results are 2 homozygous dominant and 2 heterozygous, is it necessary to put the zero for recessive (2:2:0) or would 2:2 be fine?


I don't think there is formal notation for those ratios.

One would note that perfect dominance and recessivity, perfectly discrete phenotypes without pleiotropy and without environmental variance is extremely rare and these examples are pretty much only encountered in intro classes but never in the real life. There is hence, for the phenotypes at least, really no need for any formal notation here.

That being said, out of clarity, I would definitely prefer 0:0:4 (genotypes) and 0:4 (phenotypes) over 4 (for either genotype or phenotype) and I would definitely prefer 2:2:0 over 2:2


Difference Between Phenotype and Genotype Ratio

The key difference between phenotype and genotype ratio is that the phenotype ratio is the relative number of or the pattern of the offspring manifesting the visible expression of a particular trait while the genotype ratio is the pattern of offspring distribution according to the genetic constitution.

Phenotype and genotype are two terms that use to describe the characteristics of an organism in genetics. These terms help to explain how traits inherit and how they subject to evolution. If consider a particular trait or a characteristic, the phenotype refers to the physical expression or the visible characteristic while the genotype refers to the genetic composition or the set of genes responsible for the characteristic. Both terms immensely contribute to the study of the inheritance of traits. Genotype collectively with the environmental factors influences the phenotype of a trait. In simple words, genes are responsible for the observable expression of a characteristic with a little influence of the environment. When you perform a cross between two individuals, the resulting progeny population can be analyzed for the phenotype ratio and genotype ratio.

CONTENTS


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Non-Mendelian Inheritance

In this tutorial, find out more about certain types of inheritance that does not follow the Mendelian inheritance patterns. Examples are incomplete dominance and complete dominance.

Dominance

This tutorial presents Gregor Mendel's law of dominance. Learn more about this form of inheritance and how it can be predicted using a Punnett square.


Monohybrid Cross and the Punnett Square

When fertilization occurs between two true-breeding parents that differ by only the characteristic being studied, the process is called a monohybrid cross, and the resulting offspring are called monohybrids. Mendel performed seven types of monohybrid crosses, each involving contrasting traits for different characteristics. Out of these crosses, all of the F1 offspring had the phenotype of one parent, and the F2 offspring had a 3:1 phenotypic ratio. On the basis of these results, Mendel postulated that each parent in the monohybrid cross contributed one of two paired unit factors to each offspring, and every possible combination of unit factors was equally likely.

The results of Mendel&rsquos research can be explained in terms of probabilities, which are mathematical measures of likelihood. The probability of an event is calculated by the number of times the event occurs divided by the total number of opportunities for the event to occur. A probability of one (100 percent) for some event indicates that it is guaranteed to occur, whereas a probability of zero (0 percent) indicates that it is guaranteed to not occur, and a probability of 0.5 (50 percent) means it has an equal chance of occurring or not occurring.

To demonstrate this with a monohybrid cross, consider the case of true-breeding pea plants with yellow versus green seeds. The dominant seed color is yellow therefore, the parental genotypes were YY for the plants with yellow seeds and yy for the plants with green seeds. A Punnett square, devised by the British geneticist Reginald Punnett, is useful for determining probabilities because it is drawn to predict all possible outcomes of all possible random fertilization events and their expected frequencies. Figure 8.2.5 shows a Punnett square for a cross between a plant with yellow peas and one with green peas. To prepare a Punnett square, all possible combinations of the parental alleles (the genotypes of the gametes) are listed along the top (for one parent) and side (for the other parent) of a grid. The combinations of egg and sperm gametes are then made in the boxes in the table on the basis of which alleles are combining. Each box then represents the diploid genotype of a zygote, or fertilized egg. Because each possibility is equally likely, genotypic ratios can be determined from a Punnett square. If the pattern of inheritance (dominant and recessive) is known, the phenotypic ratios can be inferred as well. For a monohybrid cross of two true-breeding parents, each parent contributes one type of allele. In this case, only one genotype is possible in the F1 offspring. All offspring are Yy and have yellow seeds.

When the F1 offspring are crossed with each other, each has an equal probability of contributing either a Y or a y to the F2 offspring. The result is a 1 in 4 (25 percent) probability of both parents contributing a Y, resulting in an offspring with a yellow phenotype a 25 percent probability of parent A contributing a Y and parent B a y, resulting in offspring with a yellow phenotype a 25 percent probability of parent A contributing a y and parent B a Y, also resulting in a yellow phenotype and a (25 percent) probability of both parents contributing a y, resulting in a green phenotype. When counting all four possible outcomes, there is a 3 in 4 probability of offspring having the yellow phenotype and a 1 in 4 probability of offspring having the green phenotype. This explains why the results of Mendel&rsquos F2 generation occurred in a 3:1 phenotypic ratio. Using large numbers of crosses, Mendel was able to calculate probabilities, found that they fit the model of inheritance, and use these to predict the outcomes of other crosses.


Forked-Line Method

When more than two genes are being considered, the Punnett-square method becomes unwieldy. For instance, examining a cross involving four genes would require a 16 × 16 grid containing 256 boxes. It would be extremely cumbersome to manually enter each genotype. For more complex crosses, the forked-line and probability methods are preferred.

To prepare a forked-line diagram for a cross between F1 heterozygotes resulting from a cross between AABBCC and aabbcc parents, we first create rows equal to the number of genes being considered, and then segregate the alleles in each row on forked lines according to the probabilities for individual monohybrid crosses ([link]). We then multiply the values along each forked path to obtain the F2 offspring probabilities. Note that this process is a diagrammatic version of the product rule. The values along each forked pathway can be multiplied because each gene assorts independently. For a trihybrid cross, the F2 phenotypic ratio is 27:9:9:9:3:3:3:1.



3:1 Ratio

For a more complicated version of the same theme, see 9:3:3:1 ratio and Mendelian ratio. Note the use of a Punnett square in the following figure:

Figure legend: B and W are alleles, indeed, as contained within sperm and eggs. BB , BW , and WW are all genotypes, created by the fertilization of egg by sperm. The associated phenotypes, 'black' and 'white' are as indicated with both BB and BW black and WW white. Note the ratio of three black progeny from this mating to one white. The mating itself was BW × BW , which themselves were both black rather than white in phenotype, that is, black/B is dominant phenotypically to white/W in this hypothetical mating by an unspecific species.

3:1 ratios are what is most commonly taught when learning Mendelian genetics and therefore what we might feel is the simplest of all possible cases. The truth, though, is that 3:1 ratios seem simple only because of familiarity (assuming, of course, that you are familiar with 3:1 ratios ☺).

The simplest of crosses instead is between two homozygotes of the same type. Furthermore, codominance and incomplete dominance actually are much simpler to follow since their phenotypic ratios and genotypic ratios are identical.

In fact, there is an emphasis on 3:1 ratios when learning genetics not because they represent the simplest of cases but instead because they represent a relatively hard while at the same time hugely important case, illustrating the impact of dominant-recessive relationships between alleles on mating outcomes.


Monohybrid Crosses

Download the following questions.

After completing the assignment, submit your work to the dropbox Monohybrid Crosses.

You may also use your assignment to complete the assignment check on Heredity Problems and Monohybrid Crosses.

For each problem:

  • Write and identify the two letters, which will represent the alleles (letters) for the dominant and recessive traits.
  • Write the cross (Male X Female)
  • Draw your Punnett Square. (You will do this on your own-not to be turned in)
  • Answer the questions in the order they are asked.

Abbreviations:

HD: Homozygous Dominant

HR: Homozygous Recessive

Hetero: Heterozygous

GT: Genotype

PT: Phenotype

1. The ovule (egg) of a white flower is fertilized by the pollen (sperm) of a heterozygous purple flower.

a) What is the dominant color?

b) Predict the probable F1 genotypic and phenotypic ratios (HD: Hetero: HR)

2. In humans, normal vision is dominant and myopia (nearsightedness) is recessive. If a homozygous normal female marries a myopic male:

a) What would be the possible GTs and Pts of the F1?

3. Albinism (the total lack of pigmentation) is recessive (and really rare!) in humans. If an albino female marries a normal but heterozygous male:

a) What are the chances they will have an albino child? (Looking for a % here)

b) What are the predicted GTs and PTs of their children?

4. The ability to curl the tongue in dominant to the inability to do so. If Eric (heterozygous tongue curler) marries Brandy (also heterozygous) what are the predicted GTs and PTs of the offspring?

5. If blond hair is recessive to brown hair:

a) How many of Tim (heterozygous--Brown) and Wendy's (Blond) 12 children would probably have blond hair?

b) What are the chances that their 13th will be blond?

c) How many of their beloved kids will carry at least one gene for blond hair?

6. In cocker spaniels, black coats are dominant to red. In a cross between two cockers, the litter showed 2 black and 2 red.

a) What must be the GTs of the parents?

7. A heterozygous male black guinea pig is mated to a white female.

a) Predict the possible GTs and PTs of the F1 generation.

8. Short hair is due to a dominant allele in rabbits and long hair to its recessive allele. A cross between a shorthaired female and a longhaired male produced a litter of one long and seven short-haired bunnies.

a) What are the Gts of the parents?

b) What PT ratio was to be expected from the cross?

9. A female with blue eyes has brown eyed parents. (Brown is dominant over blue)

b) What are the parents GTs? Explain

10. Dwarfism is a rare DOMINANT trait in humans. However, homozygous dominance is lethal (the fertilized egg will be miscarried).

a) What are the chances of dwarfism in F1 if two dwarfs marry?

b) If a female dwarf marries a male of normal height, what will be the chances of dwarfism?

When you have completed this assignment, follow your teacher's directions for submitting your work.


Alleles – T tall, t short

  • When 2 hybrids were crossed, 75% (3/4) of the offspring showed the dominant trait & 25% (1/4) showed the recessive trait always a 3:1 ratio
  • The offspring of this cross were called the F2 generation
  • Mendel then crossed a pure & a hybrid from his F2 generation known as an F2 or test cross
  • 50% (1/2) of the offspring in a test cross showed the same genotype of one parent & the other 50% showed the genotype of the other parent always a 1:1 ratio

Problems: Work the P1, F1, and both F2 crosses for all of the other pea plant traits & be sure to include genotypes, phenotypes, genotypic & phenotypic ratios.

  • Mendel also crossed plants that differed in two characteristics (Dihybrid Crosses)
    such as seed shape & seed color
  • In the P1 cross, RRYY x rryy, all of the F1 offspring showed only the dominant form for both traits all hybrids, RrYy

Traits: Seed Shape & Seed Color

Alleles: R round Y yellow
r wrinkled y green

Traits: Seed Shape & Seed Color

Alleles: R round Y yellow
r wrinkled y green

Genotypes Genotypic Ratios Phenotypes Phenotypic Ratios
RRYY 1 Round yellow seed
9
RRYy 2
RrYY 2
RrYy 4
RRyy 1 Round green seed
3
Rryy 2
r rYY 1 Wrinkled yellow seed
3
r rYy 2
r ryy 1 Wrinkled green seed
1

Problems: Choose two other pea plant traits and work the P1 and F1 dihybrid crosses. Be sure to show the trait, alleles, genotypes, phenotypes, and all ratios.


Ratio by Observation

Make a frequency chart by labeling the desired traits in columns and placing a tally mark to count the number of subjects with that trait. Count the individuals in the group only once.

Rank the frequencies from smallest to largest by writing a number next to each of the categories.

Divide each frequency by the smallest one, and note the answer in the margins of the table. For example, if there are 10 in category one and 30 in category two, 10 divided by 10 equals 1 and 30 divided by 10 equals 3.

Write the phenotypic ratio using rounding when appropriate. So a ratio of 8.7, 3.1 and 1 would be written as 9:3:1.


Genetics?

i dont know about every spore. but yes. genetics are handed down from the parent to the spore produced mushrooms of that parent just like with any other species. there is still usually room for variance seeing as your dealing with thousands and thousands of sproes from any single mushroom.

eventually i'm sure you could accomplish the same thing that inbreeding does to humans and end up with disastrous effects, but i dont see it being worth the time.

i have received prints in trades from certain members here that were 'experiments' with cloned mutants. such as a malaysian that would more than occaisonally throw off upside down fruits and caps that would open as pins and still mature out into some weird shapes. the spores of a product like this would carry some of these traits along (as did the print i first received) and if you only printed mutants you would end up with some serious issues. i always tell people i give these prints where it came from, and i never print the mutants for trades as i worry about the undesirable but fun to watch mutant strain could flood the market. especially for a strain thats not as common as others around here.

please be ethical and make sure people know what your trading them is if you have prints from something like this.

#3 Phidell

Genetic variation is kind of a 'goal' for a species. Hence genetics are often mixed together (sexual reproduction, crossing over of chromosomes in mitosis/meiosis) to create varied offspring.

The more varied a species, the more likely it is able to survive change in it's environment, so they tend to make their gametes (e.g. sperm, egg) different.

But I'm really not too sure about fungi genetics.

#4 warriorsoul

Many of the random parents from single strain multi-spore inoculations may be undesirable for breeding since they may pass on tendencies such as slow growth, weak activity or retarded maturation.

With some care the breeder can avoid the hidden dangers of unconscious selection. Definite goals are vital to progress in breeding Psilocybe mushrooms. What qualities are desired in a strain that it does not already exhibit? What characteristics does a strain exhibit that are unfavorable and should be bred out?
Answers to these questions suggest goals for breeding. In addition to a basic knowledge of mushroom botany, propagation, and genetics, the successful breeder also becomes aware of the most minute differences and similarities in phenotype. A sensitive rapport is established between breeder and mushrooms and at the same time strict guidelines are followed. Selection is the first and most important step in the breeding of any mushroom.

One must get clearly in mind the kind of mushroom he wants, then breed and select to that end, always choosing through a series of generations the mushrooms which are approaching nearest the ideal, and rejecting all others.
Proper selection of prospective parents is only possible if the breeder is familiar with the variable characteristics of Psilocybe mushrooms that may be genetically controlled, has a way to accurately measure these variations, and has established goals for improving these characteristics by selective breeding. By selecting against unfavorable traits while selecting for favorable ones, the unconscious breeding of poor strains is avoided.

Essential Points of Mushroom Breeding

1.The genotypes of mushrooms are controlled by genes which are passed on unchanged from generation to generation.
2.Genes occur in pairs, one from each parent spore.
3.When the members of a gene pair differ in their effect upon phenotype, the mushroom is termed hybrid or heterozygous.
4.When the members of a pair of genes are equal in their effect upon phenotype, then they are termed truebreeding or homozygous.
5.Pairs of genes controlling different phenotypic traits are (usually) inherited independently.
6.Dominance relations and gene interaction can alter the phenotypic ratios of the F1, F2, and subsequent generations.

Genotype and Phenotype Ratios

Phenotype and genotype ratios are probabilistic. If recessive genes are desired for three traits it is not effective to raise only 64 offspring and count on getting one homozygous recessive individual. To increase the probability of success it is better to raise hundreds of offspring, choosing only the best homozygous recessive individuals as future parents. All laws of inheritance are based on chance and offspring may not approach predicted ratios until many more have been phenotypically characterized and grouped than the theoretical minimums.

The genotype of each individual is expressed by a mosaic of thousands of subtle overlapping traits. It is the sum total of these traits that determines the general pheno- type of an individual. It is often difficult to determine if the characteristic being selected is one trait or the blending of several traits and whether these traits are controlled by one or several pairs of genes. It often makes little difference that a breeder does not have mushrooms that are proven to breed true. Breeding goals can still be established. The selfing of F1 hybrids will often give rise to the variation needed in the F2 generation for selecting parents for subsequent generations, even if the characteristics of the original parents of the F1 hybrid are not known. It is in the following generations that fixed characteristics appear and the breeding of pure strains can begin. By selecting and crossing individuals that most nearly approach the ideal described by the breeding goals, the variety can be continuously improved even if the exact patterns of inheritance are never determined. Complementary traits are eventually combined into one line whose seeds reproduce the favorable parental traits. Inbreeding strains also allows weak recessive traits to express themselves and these abnormalities must be diligently removed from the breeding population. After five or six generations, strains become amazingly uniform. Vigor is occasionally restored by crossing with other lines or by backcrossing.
Parental mushrooms are selected which most nearly approach the ideal. If a desirable trait is not expressed by the parent, it is much less likely to appear in the offspring. It is imperative that desirable characteristics be hereditary and not primarily the result of environment and cultivation. Acquired traits are not hereditary and cannot be made hereditary. Breeding for as few traits as possible at one time greatly increases the chance of success. In addition to the specific traits chosen as the aims of breeding, parents are selected which possess other generally desirable traits such as vigor and size. Determinations of dominance and recessiveness can only be made by observing the outcome of many crosses, although wild traits often tend to be dominant. This is one of the keys to adaptive survival. However, all the possible combinations will appear in the F2 generation if it is large enough, regardless of dominance.

Now, after further simplifying this wonderful system of inheritance, there are additional exceptions to the rules which must be explored. In some cases, a pair of genes may control a trait but a second or third pair of genes is needed to express this trait. This is known as gene interaction. No particular genetic attribute in which we may be interested is totally isolated from other genes and the effects of environment. Genes are occasionally transferred in groups instead of assorting independently. This is known as gene linkage, These genes are spaced along the same chromosome and may or may not control
the same trait. The result of linkage might be that one trait cannot be inherited without another. At times, traits may be associated with the sex chromosomes and they may be limited to expression in only one sex (sex linkage). Crossing over also interferes with the analysis of crosses. Crossing over is the exchanging of entire pieces of genetic material between two chromosomes. This can result in two genes that are normally linked appearing on separate chromosomes where they will be independently inherited. All of these processes can cause crosses to deviate from the expected Mendelian outcome.
Chance is a major factor in breeding mushrooms, and the more crosses a breeder attempts the higher are the chances of success.
Variate, isolate, intermate, evaluate, multiplicate, and disseminate are the key words in mushroom improvement. A mushroom breeder begins by producing or collecting various prospective parents from which the most desirable ones are selected and isolated. Intermating of the select parents results in offspring which must be evaluated for favorable characteristics. If evaluation indicates that the offspring are not improved, then the process is repeated. Improved offspring are multiplied and disseminated. Further evaluation in the field is necessary to check for uniformity and to choose parents for further intermating. This cyclic approach provides a balanced system of mushroom improvement.
The basic nature of mushrooms make them challenging to breed. Developing a knowledge and feel for the mushroom is more important than memorizing Mendelian ratios. The words of the great Luther Burbank say it well, "Heredity is indelibly fixed by repetition."

List of Favorable Traits of Mushrooms in Which Variation Occurs
1. General Traits
a) Size and Yield
b) Vigor
c) Adaptability
d) Hardiness
e) Disease and Pest Resistance
f) Maturation
g) Mycelium Production
h) Pin Set

2. Specific Traits
a) Shape
b) Form
c) Color
d) Psilocybin/Psilocin Level
e) Taste and Aroma
f) Drying Rate
g) Ease of Harvest
h) Spore Characteristics
i) Maturation


Watch the video: Learn Biology: How to Draw a Punnett Square (July 2022).


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