I dont know how you would explain monohybrid crosses which can also be represented as punnett squares(basically the same thing) without a video so:
https://www.youtube.com/watch?v=i-0rSv6oxSY pretty dope video by amoeba sisters. Try to understand the video.
Explanation(IK not trying to freak you out, its actually really simple once you get it. just trying to practice my expression, teaching is the best learning after all
looks like an essay dont read it all unless you still can't get it ):
An Allele as you should recall is an alternative form of a gene. Organisms get one allele for each trait from each parent. This means they have two alleles, which may or may not be identical, for the same trait.
The two alleles that an organism has for a trait(for example height) has can be represented with letters. For example TT means two tall alleles(It is
homozygous for tall). Tt means one allele is for tall and the other allele is for short(It is
heterozygous for tall). tt means the organism has two short alleles and it will be short(homozygous for short). The letters can vary depending on what is dominant e.g. SS if short was the dominant trait. Or Rr or Zz or whatever letter you want depending on what trait you are talking about.
A punnett square (which give the same result as a monohybrid cross) is when you write the two genotypes(that is tt or TT for example) on the sides of the box. Write down what you get when you cross the two letters together. These are the possible combinations for the offspring. (each box has a 25% chance of occurring) (see attached, really hard to explain with words.)
When you cross one purebreed tall TT and one purebreed tt(which Mendel did), you should get Tt, Tt, Tt, Tt (100% chance of Tt which means heterozygous for tall). This means the F1 generation only has the phenotype for Tall(the dominant trait.) (See attached for an example or watch the video)
When Mendel crosses Tt with another Tt plant, he got this:
TT, Tt, Tt and tt.(see attached) Remember Tt means it is heterzygous for tall which means it will be tall since tall is dominant. tt means it will be short. So there are 3 three Tall plants for every 1 short plant offspring (on average). hence the ratio 3:1. This means the F2 generation has a ratio of 3:1. This ratio represents dominant:recessive phenotypes.
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Mendel's law of dominance is:
The two different alleles for the trait have to have one that one is dominant over the other. (only the dominant actually matters and the recessive is ignored in terms of expressing the trait(that is only the dominant allele affects the
phenotype. Phenotype means the physical characteristic of the plant-not its genetics)). If there are two recessive alleles, for example, two short alleles, the plant would express the short gene. that is it will be short.
For example, suppose there is only one gene that controls whether a plant is tall or short. Assume that tall is dominant. If the plant has one tall allele then it will be tall. It does not matter if the other allele is the short allele or if it is another tall allele in terms of the phenotype. There needs to be two short alleles for the plant to be short as the trait for shortness is
recessive.
The law of segregation is:
Basically, Each trait(for example height) has only has one pair of alleles(Factors) that controls it(for example: either a short allele or a tall allele).
Factors of the same characteristic occur in pairs in an individual.
These pairs separate at gamete formation. see attached.
Law of independent assortment:
Going back to my previous example, The plant can only have two alleles(both can be either tall or short) that influences that trait. There are no other alleles that influence the trait. For example, just imagine there are alleles for the colour of the leaves (either green or yellow). This does not affect how tall the plant is. This is because all genes have a different locus(location) on the chromosome.
You can inherit one trait without inheriting another. You can have a tall plant with a yellow leaves . The plant could also have green leaves.In fact, no other alleles affect how tall the plant is.
I would try to revise some monohybrid crosses to help you understand this better. It is much easier to learn with videos or pictures.
Everything I said is just Mendelian laws and it may not always apply for example a plant could blend the characteristics. e.g. Another species of plant with a tall allele and a short allele can be a medium height plant.
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