Bell Ringer: (5 min.)
Section 11-3: Exploring
Mendelian Genetics
Independent Assortment
• Mendel wanted to know:
– Does the segregation of one pair of alleles affect
that of another?
• For example: Does the allele for seed color effect the
shape of the seed?
• 1. To find this Mendel created a two factor
cross and followed two different genes as they
passed from one generation to the next.
The Two Factor Cross: F1
• Crossed true breeding plants for round (RR)
yellow (YY)peas
– 2. Genotype (RRYY)
• With true breeding plants for wrinkled (rr)
green (yy) peas
– 2. Genotype (rryy)
• And proceeded to observe the offspring
The Two Factor Cross: F1
ry
ry
ry
ry
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
The F1 Results:
• 3. This shows that the dominant alleles are
present:
– Phenotype:
• Heterozygous
• Round Yellow Seeds
– Genotype:
• RrYy
• 4. Does this result show if genes segregate
independently?
– Nope
The Two Factor Cross: F2
• 5. Mendel took the F1 generation
(heterozygous) and crossed them.
• He wanted to see if the two traits would
separate independently of one another or if
dominant would stick with dominant and
recessive stay with recessive.
• Was very curious of the possible outcomes.
10. The Two Factor Cross: F2
RY
RY
Ry
rY
ry
Ry
rY
ry
The F2 Results:
• 6. & 8. There was a total of 556 seeds produced:
–
–
–
–
–
Round Yellow: 315
Round Green: 105
Wrinkled Yellow: 104
Wrinkled Green: 32
7. There were seeds that displayed combinations not
found in the parents (RRYY and rryy)
• Did Independent assortment occur?
– YES!
Let’s Look at the Numbers Again:
• 9. Count up the Phenotypes, what is the ratio?
– 9:3:3:1
• Round Yellow: 9
– RRYY, RrYy
• Round Green: 3
– RRyy, Rryy
• Wrinkled Yellow: 3
– rrYY, rrYy
• Wrinkled Green: 1
– rryy
11. Independent Assortment
• The alleles for a given trait segregate
independently of one another and do not
influence each other’s inheritance.
12. A Summary of Mendel’s Principles
• The inheritance of biological characteristics is
determined by genes that are passed down
from parents to their offspring
• 13. Two or more forms of a trait may exist (ex:
Dominant and Recessive)
• The copies of genes are segregated from each
other when gametes are formed
• The alleles for different genes usually
segregate independently from one another
Beyond Dominant and Recessive
• 14. There are some alleles that are neither
dominant or recessive, and many traits:
• Genetics tends to be a bit more complicated
than that:
– The majority of genes have more than two alleles,
and important traits are controlled by many
different genes.
15. Incomplete Dominance
• Cases in which one allele is not dominant over
the other
– The heterozygous phenotype is somewhere
between the two homozygous phenotypes
– Ex:
• Strawberry Blonde
• 4 ‘o Clock Plants
15. Codominance
• Both alleles contribute to the phenotype
– Both alleles will be shown in the offspring
• Ex:
– Erminette Animals
• Black feathers is
codominant with white
• Offspring show both colors
– Humans
• Proteins synthesis
15. Multipe Alleles
• Genes that have more than two possible
alleles
• This does not mean that an individual can
have more than two alleles for a gene
– It means that there could be more than two
possibilities in a population
– Ex:
• Rabbit fur color
• Blood Types in humans
Multiple Alleles
15. Polygenic Traits
• Traits that are controlled by two or more
genes
– Many traits are produced by the interaction of
several genes
– Ex:
• Human Skin Color
• 4 genes control skin color
• Human Eye Color
Applying Mendel’s Principles
• Thomas Morgan- Geneticist that worked with
Fruit Flies to test Mendel’s Principles of
Segregation
– 16. Chose Fruit Flies because:
• Small in size
• Easy to take care of in a lab setting
• Capable of producing large numbers of offspring very quickly
• 17. The conclusion:
– Mendel’s Principles apply to not just pea plants, but
other organisms as well
Genetics and the Environment
• 18. Genes are not the only factor for
determining characteristics of an organism
• The Environment plays a role as well
– Ex: Sunflower Height is determined by the genes,
but this will change depending on factors such as
climate, water availability, and soil composition
Exit Slip
Katy Perry
Wolverine
X
bbCc
Hair Color: Claws:
-B: Black -C: No Claws
-b: Blue
-c: Claws
Bbcc
Solve the Cross:
Bbcc
bbCc