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Genetics: Heredity and Traits
What is heredity?
Heredity - the passing of characteristics from
parents to offspring
characteristics that are inherited are called traits.
Genetics - the branch of biology that studies
heredity
Can you think of some
traits that are inherited?
Genes are the ‘blue prints’
for protein products
•
Genes are found on
chromosomes.
•
Genes makes products,
like proteins.
•
•
Proteins are the “building
blocks” of all living
organisms.
Our proteins make us look
like humans, not a
mushroom.
How many nucleotides (bases)
are in the Human Genome?
ANSWER:
~ 3.3 billion bases
~ 21,000 genes
Who discovered genes?
Gregor Mendel: a friar (monk) living
in a monastery in Brno, Czech
republic (1822-1884; work 1850s1860s)
His work involved studying variation
in pea plants (testing ~29,000
plants)
Pea Plant Traits
(Dominant versus Recessive)
How did Mendel determine
which trait was dominant?
Pea Plant Crosses (Example)
• Mendel always investigated
only a single trait
(2 forms of the trait)
• 1st – Cross two ‘Pure
Breeding’ parents
• 2nd – the F1 generation
would result in all being
identical (All Dominant)
• 3rd – the F2 generation
would result in a 3:1 ratio
(3 Dominant: 1 Recessive)
But why?
•Why are all the F1 plants
‘Tall’ (not short, or a mixture
of both)?
•How are some of the F2
plants ‘Short’? They
disappeared in the F1, and
are back again.
•The way an organism looks is
referred to as a ‘Phenotype’.
Let’s look at this a little
differently…
•Instead of “phenotype” (Large versus Short), lets
compare “genotypes” (number and versions of a
gene).
•First, how many copies of a gene do most
organism have (including peas)?
(HINT – It is equal to the number of parents).
Yes – 2 copies!
Let’s look at this a little
differently…
•CHECK – We have 2 copies of all genes!
•Second, how many different versions of a gene
(also called “alleles”) do we have?
(HINT – It is equal to the number of different
phenotypes).
Yes – 2 Versions (Alleles)!
Let’s redo our previous analysis of
Mendel’s cross using genotypes
What do we know?
1.Parents were purebreds.
2.We have two copies of all genes.
3.There are two versions of all genes.
4.Mendel was following one trait at a time.
What would Tt
look like
(phenotype)?
T = Tall and t = Short
HINT: Dominant
F1 Generation: All Tall Plants
Yes - All F1 Plants are
‘Tall’
Is it possible to have
‘Short’ F1 plants?
What are all the genotypes possible for
the F2 generation? Phenotypes?
DRAW A PUNNETT SQUARE BEFORE
YOU MOVE TO THE NEXT SLIDE…
F2 Generation: 3 Tall to 1 Short
All F1 Plants are ‘Tall’
F2 Plants are both
‘Tall’ and ‘Short’ (3:1
ratio)
Quickly - Let’s look at how
gender is determined in
Humans
Male
Female
How many different copies of
a gene do humans have?
How many different
chromosomes
do males contribute?
Females?
What is the ratio of males versus females?
Quiz (no worries; not graded!)
dominant
dominant
dominant
?
recessive
dominant
dominant
?
recessive
recessive
recessive
?
Quiz (no worries; not graded!)
What offspring do you get from
a ‘Back-Cross’ (LL x Ll)?
L = long stems
l = short stems
All Phenotypes?
All Genotypes?
Final question…
•
Use Teammates Consult to discuss with your
group what you have learned about heredity.
Summarize your thoughts on your paper. Use as
many vocabulary words as you can to support
evidence of your learning.