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More Patterns of
Inheritance
Incomplete Dominance
• A cross where neither allele is dominant over the other.
• The traits appear to be blended together.
• Ex. Snapdragon flowers• RR=Red• WW=white• RW=pink
The Cream Dilution GeneIs white when homozygous.
What will it do to horses?
Bay is brown with black.
CREAM and BROWN
produce New color: BUCKSKIN
brown with black.
What Pattern of Color Inheritance Does this show?
Cream dilutes red-brownTo make….
PALOMINO, a golden color.
IncompleteIncompleteDominanceDominance
Codominance• A cross where both alleles are equally expressed.
• Ex. Horse Coats– CBCB=Brown coat– CWCW=White coat– CBCW=Roan coat: has both brown and white hairs.
Co-dominance
Andalusian Chickens
• Black feathers and white feathers are co-dominant. • Cross FB FB and FW FW and what will be produced?
Andalusian Chickens
Q: Cross FB FB and FW FW and what will be produced?A: A Steel Blue Chicken FB FW
Do this:
1.Cross a heterozygous red
rose with a homozygous
recessive yellow rose. Red
is the dominant allele.
What are the possible
colors of offspring?
X
What will the offspring look like?
2. A farmer is planning to
mate a bull and cow. The
male has a roan coat (brown
and white hairs) and the
female has a white coat
(white hairs). What might
their calves look like?
X
What will the offspring look like?
3. Your parents have decided to plant some snapdragons and want to know why there are three colors – red, pink and white. You volunteer to explain it to them by showing them the cross of 2 hybrid pink snap dragons – what are the possible offspring?
4. You and your partner carry sickle cell trait.What are your chances of having a baby with
sickle cell anemia? Use RR for normal blood. RS for carriers and SS
for sickle cell anemia.
Normal
Carrier
Sickle Cell Anemia
5. Two heterozygous parents with free earlobes have 4 children predict the genotypes and phenotypes for the children’s ears.
F = free ear lobesff = attached ear lobes
XHybrid
Hybrid
XHybrid
Hybrid
Warm-Up• No blurting – give everyone a chance
• Decide if the pictures are examples of:– Simple dominance– Incomplete dominance– Codominance
Andalusian Chickens
Warm-Up• Complete this problem in your journal:–If a man an a woman are having a baby, what are the chances the baby will be a boy? Use a Punnett Square to justify your answer. Hint: Think about which chromosomes a male has and which ones a female has
Blood Types are an example of co-dominance
Human Blood Types
Phenotype:The protein
Genotype:The genes
A IAIA or IAi
B IBIB or IBi
AB IAIB
O ii
Blood type rules
• A is dominant over O• B is dominat over O• O is recessive to A and B• A and B are co-dominant to each other.
• Genes that are located on the X sex chromosomes.
• Males will have one copy of the gene. Normal male- XB YAffected Male- Xb Y• Females Will have 2 copies of the gene:
Normal Female – XB XB
“Carrier” Female – XB Xb Affected Female – Xb Xb
X-Linked Genes
Gender Determination• (Very few genes are found on the Y Chromosome)
• Only females can be carriers for sex-linked disorders on the X.
XY
Carrier – a person who transports the recessive allele but does not show the recessive trait. *Are they heterozygous or homozygous?*
X Chromosome
• Recessive genes found there:– Colorblindness Xc
– Baldness Xb
– Hemophilia - bleeding disorder where blood won’t clot. Xh
A male with the XbY will have the recessive trait for baldness.
Polygenic• A trait that is produced (controlled) by two or more genes
Eye Color Example
• Controlled by at least three genes.• Act together to produce your eye color
Lethal Genes
• Any genetic trait that causes death.Examples:Hemophilia- bleed to deathHuntington’s disease- brain shrinks
Lethal Genes
Hemophilia (lethal and sex-linked) bleed to deathXhY
Lethal Genes
Huntington’s disease- brain shrinks