BIOL - Interpreting Genetic Diagrams
Biology, genetic diagram, genetic inheritance - IGCSE | IBDP | DSE | GCE | IAL | AP Biology
In this article, we are going learn about genetic inheritance
Terminology You Should Know for Genetic Inheritance
You must be confused with so many new words that does not make much sense to you. Let's take a look at a simple example so that you can better understand these new terminology.
There are two alleles for the gene that determines the seed color of peas. The yellow allele is dominant, so let's express the allele as Y. The green allele is recessive, so let's express the allele as y.
The 3 different genotypes that an individual can have are:
Now, we will learn how we can predict the phenotype and genotype of offspring of a cross using genetic diagrams.
In the following examples, there are two alleles for a gene that determines the height of pea plants: tall allele (dominant, T) and dwarf allele (recessive, t).
I. Crossing TT x tt
This can also be done using the Punnett square:
II. Crossing Tt x Tt
Punnett square for this looks like this:
When neither allele is recessive and both alleles contribute to the phenotype of a heterozygote.
For example, there are two alleles for the color of petals of a flower: R (red) and r (white).
There are three possible genotypes: RR, Rr, and rr.
There are also three possible phenotypes: red, pink, and white.
A typical example of codominance in humans is the ABO blood type.
A family pedigree can be used to see how a genetic disorder is inherited in a family.
Let's take a look at an example of a pedigree that shows the pattern of inheritance of a familial hypercholesterolemia (FH) within a family. Familial hypercholesterolemia (FH) is an inherited condition caused by a dominant allele. People with the condition have high levels of cholesterol in their blood. This increases the risk of dying from blocked arteries.
If Person A is heterozygous for FH, what is the probability of G and H having three children who all have FH?
To answer the question, we need to find out the genotype of G and H.
👇 Punnett square of a cross between heterozygous and homozygous recessive 👇
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