Download Genetics, Part I - stephen fleenor

Warm-Up January 25, 2017
When a trait or characteristic
occurs in several or more
members of a family, it is
said to “run in the family”.
What do you think is meant
by this expression? What
are some traits that run in
your family?
Genetics part 1
■ Genetics is the study of heredity or how
characteristics are passed from parents to offspring
Genetics part 1
■ Gregor Mendel, the father of genetics, used pea plants to
study heredity.
Genetics part 1
Genetics part 1
■ Mendel found that each trait is controlled by a gene on homologous
chromosomes.
■ Genes come in pairs:
– Each gene has two copies
– Each copy is called an allele
Genetics part 1
allele – one copy of a gene.
■ Genes are represented by letters, like “A”
 each allele is either “A” or “a.”
Homozygous – both alleles are the same (AA
or aa).
Heterozygous – the two alleles are different
(Aa).
Turn-n-Talk
■ What is the difference between an allele and a gene?
– Sentence stem: The difference between an allele and a
gene is that an allele is ________________, while a gene
is ______________________.
■ How do you get one allele from each parent?
– Sentence stem: You get one allele from each parent
by……..
Genetics part 1
Homozygous or Heterozygous?
Heterozygous
■ Aa _____________
Homozygous
■ RR _____________
Heterozygous
■ Tt ______________
Heterozygous
■ Pp ______________
Homozygous
■ YY ______________
Genetics part 1
During sex, dad gives one
allele and mom gives the
other.
Punnet Square –
shows all the possible
allele combinations.
Genetics part 1
A
Punnet Square
A
a
A
a
A
a
AA
Aa
Aa
aa
a
Genetics part 1 – How to set up a Punnett square
Step 1: draw a 4-square grid
Genetics part 1 – How to set up a Punnett square
Step 2: Put the alleles of one parent across the top and
those of the other parent down the left side
Example: if mom is RR and dad is rr , the setup would be:
r
R
R
r
Genetics part 1 – How to solve a Punnett square
Step 3: fill in the boxes by copying the row and column-head letters across
or down into the empty squares.
Genetics part 1 – How to analyze a Punnett square
■ The probability that the offspring will be Rr is 100% (4/4).
■ The probability that the offspring will be rr or RR is 0% (0/4).
R
R
r
r
Rr
Rr
Rr
Rr
Now, try by yourself 
■ Set up and solve a punnet square if one parent is Bb
and the other parent is bb.
b
B
b
Bb
Bb
b
bb
bb
The probability that the
offspring will be Bb is
50% or 2/4.
The probability that the
offspring will be bb is 50%
or 2/4.
Carousel Activity
10 points per question
(You can get up to 120 points!)
Closure
Complete a punnet square for parents who
are both heterozygous for the “B” gene.