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Genetics
• Have you
looked in the
mirror
recently?
• Who do you
think you look
the most like,
your mother or
father? Your
grandma or
grandpa?
Heredity
• These traits are inherited!
• Heredity is the passing of physical
characteristics from parents to offspring
Gregor Mendel
• Mid 1800’s priest
• Tended a garden in a
monastery
• His experiments with
heredity would
influence how we
study heredity today
Mendel’s Questions
• Why do different pea plants have different
characteristics?
– Some grow tall, while others short
– Some green, some yellow
• Each of these characteristics are known as
traits
Mendel’s Studies
• He studied traits of peas
Trait
Delving into Mendel!
• http://www.youtube.com/watch?v=aoVeSncK
FAY
• Who is 100% one nationality?
• If you are, you are what’s called a PUREBRED
• Mendel started with purebreds, which are
organisms that have had the same trait for
many generations
• Example: purebred short pea plants always
come from short parents plants
His experiments
• Started with parents, or P generation
• Crossed purebred TALL plants with purebred
SHORT plants
• First generation from P generation is called
the F1 generation (filial)
• Gene: a section of
DNA that codes for
a trait
• A chromosome is a
chunk of DNA and
genes are parts of
chromosomes
GENE
ALLELE
• Allele: the different
options for a gene
• Example: attached
or unattached
earlobes are the
alleles for the gene
for earlobe shape
• Two alleles together
make a gene or trait
DOMINANT
• Dominant: an allele that blocks or hides a
recessive allele
Recessive
• Recessive: an allele that is blocked by or
hidden by a dominant allele
• Question: Using purebred crosses, how did
Mendel figure out that genes are either
dominant or recessive?
GENOTYPE Tt
• Genotype: A person’s set of alleles (gene options
or code for what someone will look like)
• Genotype is written in letters
• It is usually the first letter of the dominant allele
to make it easier
• Choose a letter for each of these traits. Write
both the dominant and the recessive genotype
allele letters
–
–
–
–
Attached Earlobes
Freckles
Dimples
Tongue-roller
GENOTYPE
• Now, using your letters from before write
a genotype for a person without freckles
(Freckles are dominant)
• Write a genotype for a person with
freckles
GENOTYPE-HETEROZYGOUS AND
HOMOZYGOUS
• A Heterozygous genotype means an organism has both
the dominant and the recessive allele (e.g. Aa)
• Homozygous recessive means an organism has 2
recessive alleles (e.g. aa)
• Homozygous dominant means an organism has 2
dominant alleles (e.g. AA)
PHENOTYPE
• Phenotype: A person’s physical features
because of their genotype (appearance!)
• What you look like (your phenotype) is based
on what your genotype is (your genes)
• What will the phenotype of these genotypes
be:
• WW, Ww, ww (Widow’s Peak dominant over straight
hair line)
• HH, Hh, hh (Hitch hiker’s thumb is dominant over a
straight thumb)
• CC, Cc, cc (Curly hair is dominant over straight hair)
HOMOZYGOUS/HETEROZYGOUS
• Homozygous: When a person’s two alleles
for a gene are the same
• Heterozygous: When a person’s two alleles
for a gene are different
• You get one allele from your mom and one
from your dad.
• If you get the same alleles from your mom
and dad, you are homozygous for that trait.
• If your mom gave you a different allele than
your dad, you are heterozygous for that trait
BUT, not all of genetics follow this simple “Mendelian Genetics”...
Sometimes there’s no clear
cut dominant and recessive,
so therefore scientists came
up with “Non-Mendelian
Genetics.”
Examples:
Blood type
“Mixed” appearances (like
red and white flowers
making pink flowers)
“Both allele” appearances
(such as roan cows!)
Codominance
• Codominance = when both alleles are
expressed (think of co-captains)
– Example: Roan cow
Codominance Continued
• Blood type controlled by 3 alleles: A, B and O
– O is recessive, two O alleles must be present for
the person to have type O blood
– A and B are codominant. If a person receives an A
allele and a B allele, their blood type is type AB
Incomplete Dominance
• Incomplete dominance = both traits are
expressed, but are “blended” to make a NEW
trait
Incomplete Dominance and
Codominance
• When are they expressed?
• What do their genotypes look like?
Genotypes of Incomplete and Codominance
• The letters of their genotypes will be
different, unlike complete dominance where
we have a capitalized and lower case letter
(Tt)
– Example: For roan cows (co-dominance)➔R and
W for red and white alleles, roan is RW
– For pink flowers➔ R and W for red and white
alleles, pink is RW
How can you tell if it is NOT the
normal, complete dominance, like Tt?
Either will show it is NOT complete dominance:
1) Notice that the offspring is showing a 3rd
phenotype. The parents each have one, and the
offspring are different from the parents.
--What is this called?
2) Notice that the trait in the offspring is
a blend (mixing) of the parental traits.
--What is this called?
Create A Baby Activity
•Use a coin or a coin app on your phone (as long as you
use the app, nothing else on the phone!) to flip heads or
tails
•Heads = dominant allele (capital letter in Mendelian
genetics OR first letter in Non-Mendelian genetics)
•Tails = recessive allele (lowercase letter in Mendelian
genetics OR second letter in Non-Mendelian genetics
–Example: I am looking at hair curliness (NonMendelian). I flip heads and my partner flips tails. I
get C1 and my partner gets C2.
•My baby’s genotype is C1C2 (heterozygous)
•My baby’s phenotype is wavy hair
Create A Baby Activity (Continued)
•When figuring out the sex of the child:
–XX = girl
–XY = boy
–Flip heads for X and tails for Y. Remember one flip per person
•When getting to multiple alleles, flip for one of each letter.
–Example: hair color has 2 different alleles
•One partner flips for A AND B and the other partner flips A
AND B.
•Result should have two A’s and two B’s
**ULTIMATE GOAL = DRAW WHAT YOUR BABY LOOKS LIKE!**
***This is based upon probability or chance of getting either allele***
SO, how did Mendel predict what each
generation would look like?
• He used Punnett squares
– Grid that looks at genotypes
– Predicts offspring, or can work backwards to find
parents
Which kind of dominance does this
Punnett Square show?