Welcome to Class
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Transcript of Welcome to Class
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Welcome to Class
Cross a homozygous dominant green plant with a heterozygous green plant. What are the genotypic and phenotypic
ratios.
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Agenda
• Complex patterns of inheritance– Incomplete and Co-dominance
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Incomplete Dominance• Organism is heterozygous its phenotype will
show the dominant trait
• When red snapdragons (RR) were crossed with white snapdragons (rr) offspring were pink (Rr)
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Incomplete Dominance• one allele for a trait is not completely dominant
over the other allele
• Combined phenotype (blended)
R = allele for red flowers W = allele for white flowers red x white ---> pink RR x WW ---> 100% RW
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Co-dominance• In COdominance, the "recessive" & "dominant"
traits appear together in the phenotype of hybrid (heterozygous) organisms
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PracticeSet up genotypes for the phenotypes listed in each
set. Remember that the "medium" trait is always be 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.D) A Sneech can be tall, medium, or short.
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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?
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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?
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Welcome
In humans, straight hair (ss) and curly hair (cc) are co-dominant traits that result in hybrids that have wavy hair (sc). Cross a Straight hair female with a wavy haired male.
• What are the chances of having a curly haired child?• What are the chances of having a straight hair child?• What are the chances of having a wavy hair child?
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Agenda
• Quiz• Sex Linked Traits
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Sex Determination
• Thomas Hunt Morgan – studied fruit flies in the early 1900’s
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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
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XY XX
X Y X X
X X
X
Y
XX
Female
XX
Female
XY
Male
XY
Male
50% Female; 50% Male
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Sex Linkage
• Sex Linkage: the presence of a gene on a sex chromosome (X or Y)
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Sex Linkage
• X-linked genes: genes found on the X chromosome– X chromosome carries more genes
• Y-linked genes: genes found on the Y chromosome
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Fruit Fly Eye Color
• Fruit flies normally have red eyes
• A few males have white eyes
• Red is dominant; white is recessive
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Welcome to Class
What is sex linkage?
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Agenda
• Finish sex linked traits notes– worksheet
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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
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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?
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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
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In humans colorblindness (b) is an example of a sex-linked recessive trait. A male with colorblindness marries a female who is not colorblind but carries the (b) allele.
Using a Punnett square, determine the genotypic and phenotypic probabilities for their potential offspring.
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In fruit flies red eye color (R) is dominant to white eyes (r). In a cross between two flies, 50% of the male and 50% of the female offspring had red eyes. The other half of the males and females had white eyes.
What are the phenotype, and all possible genotypes, of the offspring?
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Welcome to Class
In fruit flies red eye color (R) is dominant to white eyes (r). Cross a heterozygous female with a white eye male. What are the phenotypic and
genotypic ratios?
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Agenda
• Review Sex linked traits
• Multiple Alleles
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Epistasis• Epistasis – when one allele hides another
• Labrador Coat Color– 2 alleles– Dominant allele E determines pigment
• ee will have no pigment
– Dominant allele B determines how dark the pigment• EEbb or Eebb = chocolate brown• eebb, eeBb, or eeBB will be yellow because e masks effects
of dominant B allele
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Multiple Alleles• Multiple alleles – traits that are determined by
more than 2 alleles– We have only 2 alleles (1 from mom, 1 from dad)– Blood groups (ABO)– O is recessive (i allele)
ALLELE IA IB i
CODES FOR Type "A" Blood Type "B" Blood Type "O" Blood
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GENOTYPES IAIA IAi
RESULTING PHENOTYPES Type A Type A
IBIB IBi
Type B Type B
IAIB Type AB
ii Type O
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• More alleles means more combinations• there are 6 different genotypes & 4 different phenotypes
for blood type
• Note: 2 genotypes for both "A" & "B" blood --- either homozygous (IAIA or IBIB) or heterozygous with one recessive allele for "O" (IAi or IBi).
• Note too that the only genotype for "O" blood is homozygous recessive (ii).
• And lastly, what's the deal with "AB" blood? What is this an example of? The "A" trait & the "B" trait appear together in the phenotype.
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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?
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One More
• What are the chances of a woman with Type AB and a man with Type A having a child with Type O?