Connect!
 Where do you get your traits from?
 What does dominance mean?
 What controls your traits?
Foundations of Genetics
Gregor Mendel, an Austrian monk and
biologist, is considered the founder of
genetics
He used math to develop some basic principles
of genetics
He used pea plants to develop these principles;
now fruit flies (Drosophila) are generally used
1. DOMINANCE
 is when only one of the
genes in a pair is
expressed
 The other gene which is
not expressed is called
recessive.
 An upper case letter is
used to symbolize a
dominant gene while a
lower case letter
symbolizes a recessive
gene.
 For example, in certain
pea plants, the gene for
tallness (T) is dominant
and the gene for shortness
(t) is recessive.
2. GENETIC CROSSES
are used to show matings of individuals
 The first step in predicting the possible
outcomes of a genetic cross is to determine the
genes of the parent generation, if possible.
For example, we can show a cross between a
tall (TT alleles) and a short (tt alleles) pea plant
TT x tt
 The second step in solving a genetics problem
is to make a Punnett square.
The parents alleles go on the outside, while the
possibilities of the offspring get filled in on the
inside.
What if two of the tall (Tt) offspring were crossed?
Tt x Tt
Chunk Time!
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Who is the founder of genetics?
What did he study?
Why are fruit flies used now, instead?
Explain Mendel’s principle of dominance.
What is the gene that is not expressed called?
What do upper and lower case symbolize?
What do heterozygous and homozygous mean, in terms
of letters?
 Make a Punnett square showing a cross between 2
heterozygous purple flower pea plants. HINT: Purple is
dominant over white flower.
Does your Punnett Square
look like this?
Good job, Bob!
JFF