Transcript 11-3 Exploring Mendelian Genetics

11-3 Exploring Mendelian
Genetics
Page 270
Think about it….
• Mendel wondered if alleles sorted
independently…
• ….for example…
• “…is the gene for green/yellow peas linked to
the gene for round/wrinkled peas…..
• …..like….are green peas always round….or…..
• …hmmmm…”
A. Independent Assortment
• 1. Mendel performed an experiment, to follow
two genes going from one generation to the
next, called a two-factor (dihybrid) cross.
A. Independent Assortment
• 2. First, Mendel crossed true-breeding
(Homozygous) plants. Two-Factor Cross: F1
• 3. Genotypes: RRYY and rryy
• Phenotypes: Round/Yellow & Wrinkled/Green.
A. Independent Assortment
• 4. All the F1 offspring had the genotype RrYy
(heterozygous) and phenotype round/yellow.
A. Independent Assortment
• 5. Two-Factor Cross: F2 Mendel found that some
of the offspring looked NOTHING like the parents!!
A. Independent Assortment
• 6. In conclusion ALL of
a gamete’s alleles
segregate
independently; known
as independent
assortment.
A. Independent Assortment
• 7. Mendel’s results closely matched the
expected ratio of 9:3:3:1.
9: Round and Yellow
3: Round and Green
3: Wrinkled and Yellow
1: Wrinkled and Green
• In mice the ability to run normally is a
dominant trait. Mice with this trait are called
running mice ( R ). The recessive trait causes
mice to run in circles. Mice with this trait are
called waltzing mice ( r ). Hair color is also an
inherited trait in mice. Black hair ( B ) is
dominant over brown hair ( b ).
running mice (R), waltzing mice (r),
Black hair (B), brown hair (b).
• 1. Cross a heterozygous running heterozygous
black mouse with a homozygous running,
homozygous black mouse.
• running mice (R), waltzing mice (r), Black hair
(B), brown hair (b).
• 2. Cross a homozygous running, homozygous
black mouse with a heterozygous running,
brown mouse.
• running mice (R), waltzing mice (r), Black hair
(B), brown hair (b).
• 3. Cross a homozygous waltzing brown mouse
with a homozygous waltzing brown mouse.
• running mice (R), waltzing mice (r), Black hair
(B), brown hair (b).
• 4. Cross a homozygous running, heterozygous
black mouse with a homozygous waltzing
brown mouse.
• running mice (R), waltzing mice (r), Black hair
(B), brown hair (b).
• 5. Cross a homozygous running, brown mouse
with a heterozygous running, homozygous
black mouse.
• running mice (R), waltzing mice (r), Black hair
(B), brown hair (b).
• 6. Cross a heterozygous running, heterozygous
black mouse with a heterozygous running,
heterozygous black mouse.
B. A Summary of Mendel’s Principles
• 1. Genes are passed from parents to offspring.
• 2. When there are 2 alleles (form of a gene), 1
is dominant and 1 is recessive.
B. A Summary of Mendel’s Principles
• 3. Most organisms have two copies of a gene,
one from each parent, that are segregated
when gametes are formed (meiosis).
B. A Summary of Mendel’s Principles
• 4. Alleles segregate independently from each
other (independent assortment).
How do you think this happens??
C. Beyond Dominant and Recessive
Alleles
• 1. Some alleles
are neither
dominant or
recessive, many
traits are
controlled by
multiple genes
or alleles.
C. Beyond Dominant and Recessive
Alleles Ex: Flower color.
• 2. Incomplete
dominance occurs when
one allele is not
completely dominant
over another. (The
heterozygous phenotype
is between the
homozygous dominant
and homozygous
recessive phenotypes.)
Red=AA, White= aa,
Pink= Aa
C. Beyond Dominant and Recessive
Alleles
• 3. Codominance occurs when both alleles
contribute to the phenotype.
• Ex:
Blood
Types
C. Beyond Dominant and Recessive
Alleles
• 4. Some genes have multiple alleles to create
a phenotype.
– Ex: Fur Color in Rabbits
C. Beyond Dominant and Recessive
Alleles
• 5. Polygenic Traits are traits controlled by 2 or
more genes.
– Ex: Skin tone is
controlled by 4
genes.
C. Beyond Dominant and Recessive
Alleles
• 6. Sex-Linked Traits
express their
phenotype based on
the sex chromosomes.
– EX: Colorblindness
Matching
• 1. Incomplete
Dominance
• 2. Codominance
• 3. Multiple Alleles
• 4. Polygenic Traits
• 5. Sex-Linked Traits
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A. Colorblindness
B. Skin Tone
C. Blood Type
D. Rabbits Fur
E. Flower color
D. Applying Mendel’s Principles
E. Genetics and the Environment