Transcript Mendelian Genetics 3

Mendelian Genetics 3
AIM: How do complex heredity patterns
determine phenotype?
DO NOW: Complete Do Now assignment on
today’s handout
HOMEWORK: Handout on Mendel’s Laws
I. Incomplete Dominance
Sometimes it’s not a matter of who “wins” like it is in
dominant and recessive genes. Sometimes it’s more
cooperative.
What are we doing when we do cooperative learning?
A. Incomplete dominance – neither allele is dominant,
so there is a blending of traits, resulting in an
intermediate phenotype
White (WW)
PINK (??)
RED (RR)
B. Snapdragon Flowers
If you cross a
white ______
WW flower with a red ______
RR flower,
you get a pink ______
RW flower.
Is the pink flower purebred or hybrid?
W
R
RW
W
RW
R
RW
RW
*REMEMBER* Since neither one is dominant over the other,
both are written with CAPITAL letters!
II. Codominance
What happened here?
Does it look like dominance?
Does it look like incomplete dominance?
A. Codominance – neither allele is dominant, so
both alleles show up at the same time in the
organism’s phenotype
B. This horse’s color is called roan, which is a
codominant phenotype resulting from a cross
WW and purebred red
between purebred white _____
WR
____.
RR The genotype for roan is _____.
C.Codominance example: Ms. Wolf’s pet mice
I had one black pet mouse, named Inky.
I had one white pet mouse, named Blinky.
Pretty soon, I had a 3rd pet mouse, named Moo-Cow.
________
BB
Inky
________
WW
Blinky
________
BW
Moo-Cow
B
B
W
BW
BW
W
BW
BW
D. Codominance example: Sickle Cell Disease
1. Sickle Cell Disease results in
crescent-shaped red blood cells.
That means cells can get stuck in
the bloodstream and make it very
difficult to transport oxygen.
2. People that have two alleles for this
disease usually die, so those that
have it are usually heterozygous.
Normal cell allele = N
Sickle cell allele = S
What genotype would
a person living with
sickle cell disease
have?
III. Multiple Alleles
So far, we’ve learned that genotypes can be either Y or y, A or
a, E or e…
…but in reality, most genotypes are not formed from only 2
alleles – they are formed from multiple allele possibilities
A. Multiple Alleles – traits that are controlled by
more than 2 allele types
B. Multiple allele example: Blood Types
1. Blood types have 3 forms of alleles. They are
sometimes called AB Markers.
IA = Type A
IB = Type B
i = Type O (absence of AB markers)
Type O is recessive to type A and B,
but A and B are codominant
You can see that Type O
can be used by every
blood type.
Why do you think that is?
C. Multiple allele example: Rabbit fur color
1. Rabbit coat color depends on
five genes! Some turn off
color expression, some turn
them on. The final result
makes some rabbits very
common and some very rare.
Which would you be more likely to find?
SUMMARY
How do complex heredity patterns determine
phenotype?
Complete the summary worksheet
IV. Sex-Linked Traits
What genotype makes an organism male?
What genotype makes an organism female?
XY
XX
A. Men only get one X chromosome. If there happens
to be a recessive gene on the X, men don’t have a
dominant gene that can cancel it out. They are
going to express it.
B. Females have a far greater chance of having a
dominant gene to hide the recessive one.
C. Sex-linked traits – traits carried by either the X or
the Y chromosome
D. Sex-linked trait example: Color Blindness
Color blindness is a gene located on the
X-chromosome.
Who would be more likely to be affected by this gene?
Men or women?
E. Sex-linked trait example: Hemophilia
1. Hemophilia – characterized by really slow
clotting of the blood
V. Polygenic Traits
A. Most traits are the result of the action of many genes (One
trait = many genes).
ex. Skin color and height depend upon the interaction of
many independent genes.
B. Polygenic traits are controlled by two or more genes.
1. They show a wide range of phenotypes
VI. Environmental Influences on Heredity
Your genes are not the final answer!
There is so much that can be influenced by the environment,
including nutrition, exercise, and where you live.
Genes + Environment = Phenotype
Analyze the phrase,
“Heredity loads the
gun, but environment
pulls the trigger”
Ex. Diseases like
diabetes or ulcers may be
in a genetic code, but may
never be seen in the
phenotype if the person
leads a healthy lifestyle.
SUMMARY
How do complex heredity patterns determine
phenotype?
Complete the summary worksheet