Mendelian Genetics
What is
Inherited?
 _____________ – sequence of DNA that codes for a protein, that
determines a trait
 Genes are located on ___________________________________
 Humans have 46, or 23 “_________________” pairs
Genetics
 Genetics is the study of how ___________ (specific characteristics) are
passed on from generation to generation
Gregor
Mendel




Alleles
 There are different possible forms of the same gene called alleles.
o Example: pea plants can have a purple allele or a white allele for
flower color.
 _______________ – forms of a gene
 _______________ – an allele that always shows (B); needs only 1 copy
to show
 ________________ – an allele that only shows when no dominant
allele is present (b); needs 2 copies to show
“Father of Genetics”
Monastery pea garden
Application of Mathematics
____________ are determined by specific sequences of DNA called
___________.
o Example: pea plants have a gene for flower color, pea plants
have a gene for plant height, pea plants have a gene for seed
shape.
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Plants
 Flowers reproduce ____________________. One flower contains
sperm cells in its pollen and egg cells in its ovaries. Male and female
sex cells must join in______________________________.
 Found ________________________________________ – selfpollination produced offspring with _____________ identical to
parents.
 ___________________________ – produced seeds with 2 different
parents
 ______________________ -produced offspring with 2 different
parents
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Genotype
and
Phenotype




____________________ – actual copies of a gene (letters)
____________________ – the visible characteristic
____________________– shows gene combinations
____________________ – possess 2 identical alleles
o Ex. GG or gg
 ____________________ – possess 2 different alleles
o Ex. Gg
Genotype vs.  Difference between how an organism “looks” & its genetics
 description of an ___________________________________________
Phenotype
 description of an ___________________________________________
 2 organisms can have the same phenotype but have different
genotypes
3 Generation
of Traits
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Mendel’s
Law of
Heredity #1
 _____________________________________
o when gametes (eggs & sperm) are produced during meiosis,
homologous chromosomes separate from each other
o each allele for a trait segregates (is packaged) into a separate
gamete
Simple
Dominance
 One allele is _________________ dominant over the other.
 Offspring will express the ___________________________
Completing a 1. Write the parent
genotypes
Monohybrid
(Single Trait) 2. Separate alleles
into gametes
Cross
3. Fill in the offspring
genotypes (down
AND across)
4. Check your work
o All offspring
have the same
number of
alleles
o Dominant
alleles are
written first
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Examples
1. A man with brown eyes (Bb) and a woman with blue eyes (bb) want to
know what color eyes their children might have.
Possible Offspring
Genotype
_________
_________
_________
Phenotype
_________________
________________
________________
What is the probability an offspring will show the DOMINANT TRAIT ?
What is the probability an offspring will show the RECESSIVE TRAIT ?
2. A man with brown hair (BB) and a woman with blonde hair (bb) want
to know what color hair their children might have.
Possible Offspring
Genotype
_________
_________
_________
Phenotype
_________________
________________
________________
What is the probability an offspring will show the DOMINANT TRAIT ?
What is the probability an offspring will show the RECESSIVE TRAIT ?
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3. Mendel crosses a HYBRID purple plant (Pp) with a PURE white flower
plant (pp). What are the possible offsprings?
Possible Offspring
Genotype
_________
_________
_________
Phenotype
_________________
________________
________________
What is the probability an offspring will show the DOMINANT TRAIT ?
What is the probability an offspring will show the RECESSIVE TRAIT ?
Mendel’s
Laws of
Heredity #2
 ___________________________________________________
o States each pair of alleles — for each trait —segregates into
gametes independently = independent assortment
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 Independent assortment helps account for the many
________________________________observed in plants, animals and
other organisms.
Dihybrid
(Two Factor)
Crosses
 Determining possible gametes:
o A gamete contains ONE allele for EACH gene
o Include ALL possible combinations
 Check your work:
o 4 alleles for each offspring
o Alleles for the same gene stay together
o Dominant allele first
Examples
IN PEAS:
R = round
r = wrinkled
T = tall
t = short
Y = yellow peas
y = green peas
P = purple flowers
p = white flowers
MAKING HOMOZYGOUS TWO GENE CROSSES: (X = crossed with)
Use colors to circle the offspring with the same phenotype.
HOMOZYGOUS
TALL & ROUND
Parent genotype
__________________
Possible gametes
____ ____ ____ ____
X
PURE
SHORT & WRINKLED
______________________
____ ____ ____ ____
How many out of 16 will be
_______ TALL & ROUND
_______ TALL & WRINKLED
_______ SHORT & ROUND
_______ SHORT & WRINKLED
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MAKING HETEROZYGOUS TWO GENE CROSSES: (X = crossed with)
Use colors to circle the offspring with the same phenotype.
HETEROZYGOUS
TALL & ROUND
Parent genotype
__________________
Possible gametes
____ ____ ____ ____
X
HYBRID
TALL & ROUND
______________________
____ ____ ____ ____
How many out of 16 will be
_______ TALL & ROUND
_______ TALL & WRINKLED
_______ SHORT & ROUND
_______ SHORT & WRINKLED
Other
Patterns of
Inheritance
1. ________________________________ – one allele is not dominant
over the other
o Heterozygote is blended
o Ex. four o’clocks
 RR – Red
 WW – White
 RW - Pink
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 If the dragons in Harry Potter have fire‐power alleles F (strong fire)
and F’ (no fire) that follow incomplete dominance, what are the
phenotypes for the following dragon‐fire genotypes?
o FF
o F’F
o F’F’
2. ______________________ – both alleles contribute to the phenotype
 Heterozygote shows both
If merpeople have tail color alleles B (blue) and G (green) that follow the
codominance inheritance rule, what are possible genotypes and
phenotypes?
Genotypes
Sample
Problems
Phenotypes
1. In horses, alleles for red (R) and white (W) hairs are codominant,
and the heterozygous condition is called roan. Show a cross and
ratios between two roan horses.
2. In Four O’Clock plants red flowers (R) are incompletely dominant
over white (r) flowers. Heterozygous plants show a blended
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phenotype of pink flowers. Make a cross with a red Four O’Clock
plant and a white Four O’Clock plant.
3. The Four O'clock plant has two alleles for flower color: Red (R) and
white (r). These show incomplete dominance. Show the expected
offspring of a cross between two pink-flowered plants. Include
genotypes, phenotypes and ratios.
4. In cats, black fur (B) and tan fur (T) are co-dominant. Hybrid cats
show a tabby pattern that includes black and tan hairs. Cross a
TABBY female cat and a TAN male cat.
5. IF the red allele in Four-o’clocks was completely DOMINANT over
the white allele, what would the phenotype be for a plant with a Rr
genotype?
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Blood Typing  Ex. Human Blood Groups
o A, B are codominant
o O is recessive
 2 alleles affect the phenotype in separate, distinguishable ways
o ABO blood groups
o Both the IA, IB, are dominant to the i allele
o IA & IB alleles are codominant to each other
 Determines presence of oligosaccharides on the surface of red blood
cells
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Blood Typing
Problems
1. A man has type A blood and his wife has type B blood. A physician
types the blood of their four children and is surprised to find one of
each of the four blood types among them. He is not familiar with
genetics and asks how such a thing could happen. How would you
explain this to him? (include a diagram).
2. A couple preparing for marriage have their blood types
determined, along with their required blood test for syphilis. Both
individuals are type AB. They ask what types of blood their
children may have. What would you tell them and how would you
explain your answer? (include a diagram in your explanation).
3. A wealthy, elderly couple die together in an accident. Soon
afterwards a man shows up to claim their fortune contending that
he is their only son who ran away from home as a boy. Other
relatives dispute this claim. Hospital records show that the
deceased couple are blood type O and AB. The claimant (son?) to
the fortune was type O. Do you think that the claimant was an
imposter, or not? Explain, with use of diagram.
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4. Veronica has a baby, and accuses Frank as being the father. Frank
says "No, I'm not the father. I think her friend Hank is the father of
her baby." The court orders blood types of all four of these people:
Veronica's blood type is B, her baby's type is A, Frank is type AB,
and Hank is type O. From this evidence alone, what would the
court's conclusion be about each man (as to being the father of the
child)? Explain the conclusion using diagrams.
Other Things 1. __________________________
2. __________________________
Affecting
3. __________________________
Phenotype
4. __________________________
5. __________________________
Sex-Linked
Genes
3. ______________________________ – special inheritance pattern for
genes on the X or Y chromosome.
 Males only have 1 X chromosome, so ALL alleles from it are
expressed, even if they are recessive.
 Ex. Colorblindness – 1/10 US males have red/green
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Sample
Problems
1. In humans colorblindness (b) is an example of a sex-linked recessive
trait. In this problem, a male withcolorblindness marries a female who
is not colorblind but carries the (b) allele.Using a Punnett square,
describe the phenotypes of their potential offspring.
2. In fruit flies red eye color (R) is dominant to white eyes (r). In a cross
between two flies, 50% of the male and50% of the female offspring
had red eyes. The other half of the males and females had white eyes.
What are the phenotype, and all possible genotypes, of the offspring?
3. Hemophilia is a rare heredity human disease of the blood. The blood
of individuals with this condition does not clot properly. Without the
capacity for blood clotting, even a small cut can be lethal. In a
marriage of two nonhemophiliac parents, a bleeder son is born. What
are the probabilities of these parents giving birth to sons being
bleeders, and to daughters being bleeders?
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