This is the physical traits of an individual.

This is normally just a description like 'Dog with yellow fur.'

Phenotype

This is the exact alleles (Letters) and individual has.

Either shown as letters like Aa
Or
Described with words like 'Homozygous Recessive.

Genotype

Some more big terms...

Here's a sample problem. We're going to do it in 5 steps

The Problem:

Yellow fur is dominant to Black fur in domestic dogs. If a Heterozygous Yellow dog is crossed with a Black dog, what are the chances that the offspring will end up being black dogs?

1st, find information about inheritance and parents.

I've bolded the dominance and underlined parents.

Yellow fur is dominant to Black fur in domestic dogs. If a Heterozygous Yellow dog is crossed with a Black dog, what are the chances that the offspring will end up being black dogs?

2nd, Make a key.

My key is going to have all possible combos of alleles.

Yellow fur is dominant to Black fur in domestic dogs. If a Heterozygous Yellow dog is crossed with a Black dog, what are the chances that the offspring will end up being black dogs?

F = Yellow
f = black

FF = Yellow (Homozygous)
Ff = Yellow (Heterozygous)
ff = black (homozygous)

4th, Set up and fill in your square.

I'm keeping my key handy!

Crossing Ff x ff

F = Yellow
f = black

FF = Yellow (Homozygous)
Ff = Yellow (Heterozygous)
ff = black (homozygous)

F f

f Ff




f

Finally, use your square for ratios and answer the question!

I'm keeping my key handy!

Crossing Ff x ff

F = Yellow
f = black

FF = Yellow (Homozygous)
Ff = Yellow (Heterozygous)
ff = black (homozygous)

F f

f Ff ff


f Ff ff

Phenotype:
There are 2 Yellow and 2 Black
That's a 2:2 ratio, or
50%:50% percent ratio.

Genotype:
There are two Ff and two ff
That's also 2:2 or 50%:50%