Probability is the term used to describe the likelihood that some event will occur. In relation to genetics, the principle of probability allows us to predict the possible combinations of phenotypes in a genetic cross by using a diagram called Punnett squares
Punnett square
The Punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach. The diagram is used by biologists to determine the probability of an offspring having a particular genotype. The …
What does probability have to do with genetics?
• Probability calculations are used in genetic problems to predict the outcome of crosses • To compute probability, we can use three mathematical operations – Product rule –Sum ruel – Binomial expansion equation PROBABILITY Product rule • The probability that two or more independent events will occur is equal to the product of
What can geneticists use the principles of probability for?
Principles of Probability- They can be used to predict the outcomes of genetic crosses. Principle of Independent Assortment- Genes for different traits can segregate independently during the formation of gametes. Independent Assortment helps account for the many genetic variations observed in plants, animals, and other organisms.
What does probility have to do with genetics?
What does probability have to do with genetics? In a genetic cross, the allele that each parent will pass on to its offspring is based on probability. What is a genotype? An organism's genetic makeup or allele combinations. What is a phenotype? An organism's physical appearance or visible traits.
How can you use probability to predict traits?
How can we use probability to predict traits? In genetics, theoretical probability can be used to calculate the likelihood that offspring will be a certain sex, or that offspring will inherit a certain trait or disease if all outcomes are equally possible. It can also be used to calculate probabilities of traits in larger populations.
What is probability in math?
Probabilities are mathematical measures of likelihood. In other words, they’re a way of quantifying (giving a specific, numerical value to) how likely something is to happen. A probability of for an event means that it is guaranteed to happen, while a probability of for an event means that it is guaranteed not to happen. A simple example of probability is having a chance of getting heads when you flip a coin, as Sal explains in this intro to probability video.
How to find the probability of the outcome?
You can think of the sum rule as the “or” rule: if an outcome requires that either event X or event Y occur, and if X and Y are mutually exclusive (if only one or the other can occur in a given case), then the probability of the outcome can be calculated by adding the probabilities of X and Y.
How to find the probability of getting a Bb genotype?
To calculate the probability of getting a Bb genotype, we can draw a -square Punnett square using the parents' alleles for the coat color gene only, as shown above. Using the Punnett square, you can see that the probability of the Bb genotype is . (Alternatively, we could have calculated the probability of Bb using the product rule for gamete contributions from the two parents and the sum rule for the two gamete combinations that give Bb .) Using a similar Punnett square for the parents' fur texture alleles, the probability of getting an Cc genotype is also . To get the overall probability of the BbCc genotype, we can simply multiply the two probabilities, giving an overall probability of .
What is the dominant homozygote in a Punnett square?
Once again, this is the same result we’d get with a Punnett square. One out of the four boxes of the Punnett square holds the dominant homozygote, AA. Two more boxes represent heterozygotes, one with a maternal A and a paternal a, the other with the opposite combination. Each box is out of the boxes in the whole Punnett square, and since the boxes don't overlap (they’re mutually exclusive), we can add them up () to get the probability of offspring with the dominant phenotype.
How many chances do you get an a allele from a male parent?
There's a 1/2 chance of getting an a allele from the male parent, corresponding to the rightmost column of the Punnett square. Similarly, there's a 1/2 chance of getting an a allele from the maternal parent, corresponding to the bottommost row of the Punnett square. The intersect of these the row and column, corresponding to the bottom right box of the table, represents the probability of getting an a allele from the maternal parent and the paternal parent (1 out of 4 boxes in the Punnett square, or a 1/4 chance ).
How to find probability of offspring with a dominant phenotype?
So, the probability of offspring with a dominant phenotype is: (probability of A from Mom and A from Dad) + (probability of A from Mom and a from Dad) + (probability of a from Mom and A from Dad) = .
How to use the product rule?
In general, you can think of the product rule as the “and” rule: if both event X and event Y must happen in order for a certain outcome to occur, and if X and Y are independent of each other (don’t affect each other’s likelihood), then you can use the product rule to calculate the probability of the outcome by multiplying the probabilities of X and Y.
What are the applications of statistics and probability?
Statistics and probability have many applications to science. One such connection between another discipline is in the field of genetics. Many aspects of genetics are really just applied probability. We will see how a table known as a Punnett square can be used to calculate the probabilities of offspring having particular genetic traits.
What is the probability that all offspring of homozygous parents will have the same dominant trait?
In other words, there is a 100% probability that an offspring of such a pairing will exhibit the dominant phenotype.
What happens if both parents are heterozygous for the trait in question?
If both parents are heterozygous for the trait in question, then they both have the same genotype consisting of one dominant and one recessive allele.
How many alleles does a homozygous parent have?
We could also consider the possibility that the homozygous parent possesses two recessive alleles. Here if the homozygous parent has two recessive alleles, then half of the offspring will exhibit the recessive trait with genotype bb. The other half will exhibit the dominant trait but with heterozygous genotype Bb.
How many ways does an offspring exhibit a dominant trait?
The Punnett square from this configuration is below. Here we see that there are three ways for an offspring to exhibit a dominant trait and one way for recessive. This means that there is a 75% probability that an offspring will have the dominant trait and a 25% probability that an offspring will have a recessive trait.
How many genotypes are there for brown eyes?
The trait that is displayed is called the phenotype. So for the phenotype of brown eyes, there are two genotypes. For the phenotype of blue eyes, there is a single genotype. The remaining terms to discuss pertain to the compositions of the genotypes. A genotype such as either BB or bb the alleles are identical.
What happens if both parents are homozygous?
If both parents are homozygous, then all of the offspring will have an identical genotype. We see this with the Punnett square below for a cross between BB and bb. In all that follows the parents are denoted with bold.
