Look Who it Was Random video

Law of probability applied to genetics problems

203 views · Published 6 August 2014 · 8:45 · Indexed 1 November 2026

Channel: Nikolay's Genetics Lessons · 2014 · Education

Watch on YouTube

Punnett Squares are a diagram which biologists use to determine the probability of an offspring having a particular trait. Creating a Punnett Square and using it to determine traits of offspring is called performing a cross. Punnett Square crosses are based on meiosis, a biological process where parents pass on alleles to sex cells, which they later transmit to their offspring. Each parent has two alleles for a trait and passes one along to its offspring. Each offspring ends up with a total of two alleles, one from each parent.
Punnett Squares accomplish two things: They simplify and demonstrate meiosis and also provide scientists with information that they can go on to use in different ways. They use information from the crosses to study and draw conclusions about populations. An example of scientists using information they obtain from a cross is in calculating phenotypic probability. The crosses give predicted outcomes of traits, which can then be translated into numerical statistics about the appearance of those traits in a population.
We are using the Punnett Squares in these instructions to study one trait, but they can also be expanded and used to study more complicated situations in genetics.

These instructions are for anyone, commonly students and scientists, who is predicting the ratios of expected traits in one generation of an organism’s offspring.

Terminology

Allele: one or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.
Dominant Allele: an allele that masks the effect of another allele.
Note- It is represented with an UPPERCASE letter.
Recessive Allele: an allele whose effect is masked by a dominant allele.
Note- It is represented with a lowercase letter.
F#: an uppercase “F” followed by a subscript number denotes a generation of offspring. As the number increases, the number of the generation increases.
F1: the first generation of offspring from a P generation cross
Generation: all of the offspring that are at the same stage of descent from a common ancestor.
Genotype: an organism’s genetic constitution.
Heterozygous: a genotype with two different alleles (one dominant and one recessive).
Homozygous: a genotype with a pair of matching alleles (both dominant or both recessive).
Offspring: the children produced by living organisms who reproduce by sexual reproduction.
P: the parental generation
Phenotype: an individual’s set of observable characteristics that results from the interaction of a genotype with the environment.
Punnett Square: a diagram that is used to predict an outcome of a particular cross.
Each box in the square represents one offspring.
The letters in each box represent the organism's genotype.
Trait: a genetically determined characteristic.

More from this channel