What’s the difference between a phenotype and a genotype? Agenda for Friday Jan 30 th 1.Go over HW (Dihybrid) 2.Incomplete and codominance.
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What’s the difference between a phenotype and a genotype?
Agenda for Friday Jan 30th 1. Go over HW (Dihybrid)2. Incomplete and codominance
Complete Dominance
Purebred red snapdragons were crossed with purebred white snapdragons all offspring were pink
Incomplete Dominance• one allele for a trait is not completely dominant
over the other allele
• Combined (blended) phenotype
R = allele for red flowers W = allele for white flowers red x white ---> pink RR x WW ---> 100% RW
Co-dominance• In COdominance, both traits appear together in
the phenotype of hybrid (heterozygous)
WHITE RED
ROAN
PracticeSet up genotypes for the phenotypes listed in each
set. Remember that the "medium" trait is always heterozygous.
a) Birds can be blue, white, or white with blue-tipped feathers.
b) Flowers can be white, pink, or red.c) A Hoo can have curly hair, spiked hair, or a mix of
both curly and spiked.
1. Write the genotypes for the pictured phenotypes
2. Show the cross between a star-eyed and a circle eyed. What are the phenotypes of the offspring? What are the genotypes?
3. Show the cross between a circle-star eyed, and a circle eyed.How many of the offspring are circle-eyed? How many of the offspring are circle-star eyed?Write the genotypic and phenotypic ratios.
4. Show the cross between two circle-star eyed. How many of the offspring are circle-eyed? How many of the offspring are circle-star eyed? How many are star eyed?
Agenda for Monday Feb 2nd 1. Go over Incomplete/codominance wkst2. Sex linked traits
In humans, straight hair and curly hair are incompletely dominant traits that result in hybrids that have wavy hair. Cross a straight hair with a wavy hair.
What are the chances of having a curly haired child?What are the chances of having a straight hair child?
Sex Determination
• Thomas Hunt Morgan – studied fruit flies in the early 1900’s
Sex Determination
• Observed that one pair of chromosomes was different between males and females
– Large one named “X” chromosome
– Smaller one named “Y” chromosome
– XX = female; XY = male
Sex Linkage
• Sex Linkage: the presence of a gene on a sex chromosome (X or Y)
• X-linked genes: genes found on the X chromosome– X chromosome carries more genes
• Y-linked genes: genes found on the Y chromosome
Fruit Fly Eye Color
• Fruit flies normally have red eyes– Red is dominant; white is recessive
• A few males have white eyes
Morgan’s Fruit Fly Experiments
• Red-eyed female (XRXR) x White-eyed male (XrY)
XR XR
Xr
Y
XRXr XRXr
XRY XRY
RESULTS:
F1 generation – all red-eyed
Morgan’s Fruit Fly Experiments
• Red-eyed female (XRXr) x Red-eyed male (XRY)
XR Xr
XR
Y
XRXR XRXr
XRY XrY
RESULTS:
F2 generation – 3 red-eyed and 1 white-eyed
** all white-eyed where males…why?
Morgan’s Conclusions
• Gene for eye color is carried on the X chromosome = eye color is an X-linked trait
• Y chromosome does not carry a gene for eye color
• Red-eyed = XRXR, XRXr , XRY• White-eyed = XrXr, XrY
In humans colorblindness (b) is an example of a sex-linked recessive trait. A male without colorblindness marries a female who isn’t colorblind but carries the allele.
1. How many females will be colorblind?2. What sex will any colorblind children be?3. What percent will be male and colorblind?
In fruit flies red eye color (R) is dominant to white eyes (r) and is a sex linked trait.
A heterozygous red eye female mates with a red eye male.
1. How many will have red eyes?2. What percent will have white eyes?3. How many will be female and red eyed?
In fruit flies red eye color (R) is dominant to white eyes (r) and is a sex linked trait.
A homozygous red eye female mates with a white eye male.
How many males will have white eyes?
In humans colorblindness (b) is an example of a sex-linked recessive trait. A male with colorblindness marries a female who isn’t colorblind and does not carry the allele.
What is the chance they will have a child that is colorblind?
In humans colorblindness is an example of a sex-linked recessive trait. A male with colorblindness marries a female who is a carrier. What is the chance they will have a child that is colorblind?
Agenda for Wednesday Feb 4th 1. Disorder project
What is meant by a sex-linked trait?
Agenda for Thursday Feb 5th 1. Go over HW2. Multiple alleles
Quiz tomorrow
Projects due Monday
Multiple Alleles• Multiple alleles – traits
determined by more than 2 alleles– Increases possible number of
genotypes & phenotypes– Blood groups
Blood Types• A,B,O blood types• A and B are dominant over O
– Co-dominant to each other• O blood type is recessive
GENOTYPEIAIA IAi
RESULTING PHENOTYPES Type A Type A
IBIB IBi
Type B Type B
IAIB Type AB ii Type O
• More alleles means more combinations• 6 different genotypes & 4 different phenotypes
• 2 genotypes for both "A" & "B" blood --- either homozygous (IAIA or IBIB) or heterozygous with one recessive allele for "O" (IAi or IBi).
• The only genotype for "O" blood is homozygous recessive (ii).
• And lastly, what's the deal with "AB" blood? The "A" trait & the "B" trait appear together in the phenotype. What is this an example of?
Problems• A woman with Type O blood and a man who is Type
AB have are expecting a child. What are the possible blood types of the kid?
• What are the possible blood types of a child who's parents are both heterozygous for "B" blood type?
One More
• What are the chances of a woman with Type AB and a man with Type A having a child with Type O?
Complete dominance - 2 traitsBB Bb bb**Homozygous dominant same as heterozygousIncomplete Dominance – 2 different lettersRR WW RW ** heterozygous is a blend of other 2 traitsCo-dominance - 2 different letters GG TT GT **heterozygous see both of the other 2 traitsSex Linked Traits – use X’s and Y’s **no gene on YMultiple alleles – blood type, use I’s
What are the chances of a woman with Type AB and a man with Type O having a child with Type O?
Agenda for Friday Feb 6th 1. Quiz2. Finish notes3. Disorders
Epistasis• Epistasis – one allele hides/suppresses another allele
Polygenic• Phenotype depends on alleles in multiple
genes– Skin color, height, eye color– Continuous progression in expression of traits
Another example of a polygenic trait:
• Hair Color– Hair color is controlled by alleles on chromosomes 3,
6, 10, and 18. – The more dominant alleles that appear in the
genotype, the darker the hair!
Eye Color
• Has to do with the amount of melanin– More melanin = darker eyes
• Multiple genes determine how much melanin– More dominant genes = more melanin
• Heterochromia = different color eyes– uneven distribution of melanin
Environmental Influences
• Inherit tendency of getting heart diseases– Diet/exercise can also
influence
• Water/ temperature/ sunlight effect plants
Agenda for Tuesday April 29th 1. Sex Linked traits (go over HW)2. Multiple alleles3. Epistasis/polygenic4. Talk about disorder project
In fruit flies red eye color (R) is dominant to white eyes (r) and is a sex linked trait. Cross a heterozygous female with a white eye male.
How many will be red eye and male?
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