Transcript Incomplete dominance

Make Observations
Standard
S7L3
UNDERSTAND THE IMPORTANCE OF AND HOW
BIOLOIGICAL TRAITS ARE PASSED ON FROM
GENERATION TO GENERATION
Learning Target
I can understand how heredity
does not always follow Mendelian
rules.
GENETICS SINCE
MENDEL
Gregor Mendel--A Reminder
• Austrian Monk who is considered the
“Father of Genetics.”
• Mendel’s Rules:
• Traits are controlled by 2 (or more)
alleles.
• One allele may be dominant. The other
may be recessive
• Alleles separate in gametes during
meiosis.
If Gregor Mendel were given a black
mouse & a white mouse,
• What would he have said about the
offspring?
• He would have said that the
phenotype of the offspring resembled
one of the parents, black or white.
• If so, how did the mouse get gray fur?
Genetics Today----Not
Always Following the Rules
Incomplete Dominance
Incomplete dominance is a heterozygous
condition in which both alleles are
PARTIALLY expressed.
The offspring will be a blended form. This
will be different than the homozygous forms
of either parent.
Incomplete dominance
This is a form of intermediate
inheritance in which one
allele for a specific trait is not
completely dominant over the
other.
Offspring of Incomplete Dominance
1. In incomplete dominance three
phenotypes are involved: One for EACH
parent and a third SEPARTE phenotype
for the offspring.
2. The trait in the offspring is a BLEND (or
mixing) of the parental traits.
Broken down, this means …
Incomplete Dominance
• Neither allele for a trait is dominant.
• The heterozygous phenotype is
intermediate or is between the homozygous
parent forms.
For Example
Chestnut Horse + Cremello Horse = Palomino
Chestnut Horse: Dominant color is chestnut.
Cremello Horse: Dominant color is creme/white.
Say it Again?
• A palomino horse will result when a
chestnut horse and cremello colored horse
are crossed.
• This is because the heterozygous palomino
gets a single allele of a cream colored gene
crossed with a red (chestnut) gene.
Incomplete Dominance
RR
WW
RW
RR RW
WW
Try This:
• Complete a Punnett square for the following
cross.
Red (Four O’Clocks) X White
All of the offspring were pink.
This is intermediate between red and white.
Answer the Following:
In humans hair textured is controlled by incomplete
dominance. A curly haired individual and an
straight haired individual have all wavy haired
children. If two wavy haired people have children,
what will the phenotypic ratio be?
CoDominance
–Neither phenotype is dominant.
Instead, the individual expresses both phenotypes.
 Codominance
Co – both are dominant enough to be expressed!!
Dominique Chickens
Co-Dominance
• “CO” is together. “Cooperate; Co-Captain”
• As with incomplete dominance, a hybrid offspring
will show a THIRD PHENOTYPE.
• With incomplete dominance, there is a blending.
With CO-DOMINANCE, BOTH TRAITS appear
TOGETHER in the offspring.
Answer the Following:
A cross between a black cat and a tan cat
produces a tabby pattern (black and tan fur
together). What percent of kittens would
have tan fur if a tabby cat is crossed with a
black cat?
For Example
• With incomplete dominance, a red and white flower will
produce a pink flower.
• In CO-DOMINANCE, a red and white flower will produce
a red and white flower.
Multiple Alleles
• Within the population, there may be multiple
forms for alleles.
• Many traits are controlled by more than two
alleles. These are said to be controlled by
multiple alleles. Two of these alleles are
CODOMINANT.
• Blood type is an example of multiple alleles.
Blood Type/Multiple Alleles
• The alleles for blood type are A, B, and O.
• Both A and B are dominant. These are co-
dominant.
• O is recessive.
• If someone had the A and B alleles, the blood
type would be AB. (Both are exhibited/codominant.)
• If someone exhibits blood type A, do both alleles
have to be A?
• For someone to have the blood type O, both
parents would have to carry the allele.
Answer the Following:
A man with blood type B marries a woman with
blood type A. Their first child is blood type O.
Predict what other blood types are possible for
any children they may have in the future.
To answer this, complete a Punnett square.
Or the Y
chromosome
Environmental Role
• The environment plays a role in how some of your genes
are expressed.
• These influences may be internal or external.
• Example: Some people may be at risk for skin cancer.
These people need to limit their exposure to the Sun.
Sex Determination
• Chromosomes that determine the sex of an organism are
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XX in females and XY in males.
Females produce eggs with an X chromosome only.
Males produce sperm with either an X or a Y
chromosome.
The diagram is of a karyotype.
Karyotypes are pictures of homologous chromosomes.
(Note the last pair indicates gender.)
Homologous chromosomes are identified by size,
bands/banding, and centromere placement.
Female Karyotype
Male Karyotype
Mutations
• A mutation may be harmful, beneficial, or have not effect.
• Mutations occur when a gene is altered or copied
incorrectly.
• Chromosome disorders are caused by more or fewer
chromosomes than normal. These can occur because of
mistakes made during the process of ______________.
Pedigree
• A pedigree follows a trait through generations of a family.
• Circles indicates a female. Square indicates a male.
• Partial coloring indicates a carrier. (Carrier = has the
allele and passes this to offspring.)
• Completely colored in indicates the trait is present.
Selective Breeding
• Selecting qualities within
individuals of a breed that are
desired to be passed on to the
next generation.
Selective Breeding
• Inbreeding - produces individuals with similar
characteristics.
• Hybridization – involves crossing individuals with
different traits. (This is done with the hope of
producing offspring with the best traits
of both organisms.)
What is genetic engineering?
• Today scientists can use biology or chemistry to
change the arrangement of DNA that makes up a
gene.
• This is used today for many reasons. One of
those reasons is to produce larger volumes of
medicine.
• Cloning is a type of genetic engineering.
• In cloning, the genetic information from a single
cell of an organism is used to produce another
organism with the same genetic information.
What other ways can genes be used?
• Genes can be changed by scientist to
make plants more resistant to disease.
• Genes from one type of plant may be
inserted into another type of plant to help
fight crop diseases!