Transcript Chapter 3 Mendel Power Point

MENDEL & GENETICS
Peas, Peas, Peas, Peas
Studying Mendel’s Peas
(Sing to tune of “Eating Goober Peas”)
Gregor Mendel
• 1822-1884
• Austrian monk
• High school
science teacher
• Discovered laws of
inheritance
Gregor Mendel
• Studied pea plants
• Easy to study
• Many traits only have
2 forms
• 7 different traits
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Stem height
Seed shape
Seed color
Seed coat color
Pod shape
Pod color
Flower position
A Closer Look at Pea Traits
• Stem Height
• 2 forms
• Tall stems
• Short stems
• All traits have 2
forms, a dominant
& a recessive
2 types of Alleles
(forms of a trait)
• Dominant allele
• Always shows up if
present
• Recessive allele
• May be present
but masked if
paired with a
dominant allele
• Only shows up if
paired with
another recessive
alleles
Examples of common traits
• Tongue rolling
• Can roll tongue - dominant
• Can’t roll tongue - recessive
• You have 2 alleles for this trait
Where do your
alleles come from?
• One from mom
• One from dad
What does this mean?
• If you can roll your tongue, you
have either
• 2 dominant alleles
Or
• 1 dominant and 1 recessive
What does this mean?
• If you can’t roll your tongue, you
have
• 2 recessive alleles
MENDEL & GENETICS
PART 2
CHROMOSOMES & YOUR
CELLS
Where do they come from?
Chromosomes & Body cells
• All cells have chromosomes
• Number of chromosomes for an
organism is unique
• Humans - 46 chromosomes
• Dogs - 78 chromosomes
• Silkworms - 56 chromosomes
How do they get there?
• By mitosis, of course!
• Remember - mitosis creates new cells
that are identical to the original cell
• So that means a cell with 46
chromosomes will create a new cell
with 46 chromosomes!
But what about our sex cells?
• Sex cells are created through a
process called meiosis
• New cells have half the number of
chromosomes
• New cells are not identical to original
cells
Why is this important?
• Remember, all organisms have a
unique number of chromosomes
• On offspring may not survive if the
number of chromosomes is
incorrect
Why is this important? (con’t)
• Think about how you were created,
a sperm fertilized an egg.
• The sperm donated half the
chromosomes (23)
• The egg donated the other half of
the chromosomes (23)
So why is it important that
sex cells have half the
number of chromosomes?
Your turn to write an answer