Bellwork: Tues. Jan. 17, 2017 ________ x ________ Cross a female with blonde hair to a male with heterozygous brown hair: 1st, write the cross: Brown Hair (B) Blonde Hair (b) YES!!! Write all of the RED words & punnett square!!!!!! ________ x ________ Genotypic ratio:_____________ Phenotypic ratio:_____________ What % will have blonde hair?______ What % will have brown hair?______ What fraction will have brown hair?___ What fraction will have blonde hair? ___

More on Genetics 2

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Probabilities Predict Averages NOTES: Probabilities predict the average outcome of a large number of events. Probability cannot predict the precise outcome of an individual event! In genetics, the larger the number of offspring, the closer the resulting numbers will get to expected values. 15

Genotype Phenotype (Physical) Genotype (Genetic) Physical characteristics Genotype (Genetic) Genes we inherit from our parents. “Gene” make-up. 16

Phenotype Notice the similarities: Eyes Smile Ears Nose Facial structure Neck 17

"No one ever believes we are twins because I am white and Maria is black," - Lucy  https://www.youtube.com/watch?v=JIUK2KSbvvI

Remember: Mendel's First Law NOTES Remember: Mendel's First Law law of segregation: when gametes are made, each member of allele pair separates from the other member to form the genetic make-up of the gamete (monohybrid cross: )

Independent Assortment: To determine if the segregation of one pair of alleles affects the segregation of another pair of alleles in a two-factor cross. (dihybrid cross)

The Test Cross What if you want to figure out an unknown genotype of an organism with a dominant phenotype? For example, what if you have a rabbit with black hair and want to know if it is homozygous dominant or heterozygous?

Mendel realized that it is possible to find the genotype of an organism simply by crossing. This does not require modern technology.

Test Cross: crossing an organism with an unknown genotype and dominant phenotype with a homozygous recessive organism to determine the unknown genotype.

Is it YY or Yy? (both “appear” yellow) Phenotype To identify the genotype of yellow-seeded pea plants as either homozygous dominant (YY) or heterozygous (Yy), you could do a test cross with plants of genotype _______.

If the unknown genotype is homozygous dominant (YY)… The offspring will ALL have a yellow phenotype.

If the unknown genotype is heterozygous (Yy)… Half of the offspring will be yellow and half will be green.

So if we take our black rabbit (unknown genotype) and cross it with a brown rabbit (homozygous recessive genotype) we get: B? x bb b B Bb ? ?b If the unknown genotype is homozygous dominant, what results would you expect from the offspring?

ALL of the offspring will be black. So if we take our black rabbit (unknown genotype) and cross it with a brown rabbit (homozygous recessive genotype) we get: BB x bb b B Bb ALL of the offspring will be black.

So if we take our black rabbit (unknown genotype) and cross it with a brown rabbit (homozygous recessive genotype) we get: B? x bb b B Bb ? ?b If the unknown genotype is heterozygous, what results would you expect from the offspring?

Example only not in notes 2013 In fruit flies, the allele W for long wings is dominant over the allele w for short wings. Calculate the probability of heterozygous offspring resulting from a cross between two homozygous recessive parents. Cross: ____ x _____ (looking for Ww “baby” flies) Genotypic ratio: Phenotypic ratio: Probability: All ww  4:0 All short-winged: 4:0 P(Ww) = 0 Ww = 0 = 0%

Cross: _____ x ______ Genotypic ratio: Phenotypic ratio: Probability: In fruit flies, the allele W for long wings is dominant over the allele w for short wings. Calculate the probability of long-winged offspring resulting from a cross between a heterozygous parent and a homozygous recessive parent. Cross: _____ x ______ 2 Ww and 2 ww, so 0:2:2 2 long-winged and 2 short-winged, so 2:2 P(WW or Ww)= 2/4 = 0.5 = 50% Genotypic ratio: Phenotypic ratio: Probability:

The Dihybrid Cross: cross involving two sets of traits (alleles) – a monohybrid cross involves one set of traits (alleles)

Genotypic Ratio: Phenotypic Ratio:

Genotypic Ratio: RRYY: RRYy: RRyy: RrYY: RrYy: Rryy: rrYY: rrYy: 1:1:2:2:4:2:2:1:1 Phenotypic Ratio: Round Yellow Round Green Wrinkled Yellow Wrinkle Green 9:3:3:1

A Summary of Mendel's Principles Genes are passed from parents to offspring. There are dominant and recessive alleles. Allele pairs from each parent separate in gamete formation: law of segregation. Genes for different traits (on different chromosomes) can segregate independently during the formation of gametes: independent assortment. Genes that segregate independently do not influence each other's inheritance. alleles for different genes usually segregate independently of one another unless they are on the same chromosome

Mendel didn’t know about Chromosomes or DNA We now know that genes located close together on a chromosome may be inherited together http://www.google.com/imgres?imgurl=http://www.schenectady.k12.ny.us/putman/biology/data/images/inheritance/5vtxrn.gif&imgrefurl=http://www.schenectady.k12.ny.us/putman/biology/data/inheritance/vertical5.html&usg=__AOM-Msycdjh3B4VDEsYOV75bXAs=&h=383&w=374&sz=7&hl=en&start=21&zoom=1&tbnid=RD2sZ4MpKWVDFM:&tbnh=123&tbnw=120&ei=RzIHT4qDF4qEsAK3tpyRCg&prev=/search%3Fq%3DLinked%2BGenes%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26gbv%3D2%26rlz%3D1R2GGLL_en%26tbm%3Disch&um=1&itbs=1

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But… some alleles aren’t completely dominate or recessive

Bellwork: Tues. Jan 13, 2015 Short hair is dominant long hair is recessive Show a cross between two heterozygous guinea pigs. What % of the offspring will have short hair?  ________ What %of the offspring will have long hair?  _______ Two short haired guinea pigs are mated several times. Out of 100 offspring, 25 of them have long hair. What are the probable genotypes of the parents?  ________   x  ___________           

Incomplete & Codominance

Incomplete Dominance: when one allele is not completely dominant over another. The heterozygous phenotype is a “mix of the two homozygous phenotypes. A cross between red (RR) and white (WW) four o’clock plants produces pink-colored flowers (RW).

Incomplete dominance – when one allele is not completely dominant over the other allele WW = White RR = Red WW X RR RW = Pink Genotypic Ratio:__________ Phenotypic Ratio:_________

What happens if you cross the offspring (F1) generation? RW x RW Genotypic ratio Phenotypic Ratio Phenotypic Ratio: Genotyopic Ratio:

Codominance Is a lot like incomplete dominance - A hybrid organism shows a third phenotype --- not the usual dominant versus recessive traits. BUT in codominance both traits show up AT THE SAME TIME!!

Co-dominance: when both alleles contribute to the phenotype. A cross of black chicken (BB) with a white chicken (WW) produces all speckled offspring (BW). BB = black feathers BW = black and white feathers WW = white feathers Genotypic Ratio: Phenotypic Ratio:

Or…. Roan coat color in horses and cows.

Co-dominance: Roan fur. Cattle can be red (RR = all red hairs), white (rr = all white hairs), or roan (Rr = red & white hairs together).  Notice how this cross looks just like the others we have done earlier with dominant and recessive alleles – I would have to tell you this is a co-dominant cross!!!. Cross: ______ X _______ Genotypic Ratio:_____________ Phenotypic Ratio:____________

Now let’s cross two roans: Cross:_____ X______ Genotypic Ratio: Phenotypic Ratio:

roan horses

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Bellwork: Thurs. Jan. 13, 2011 Dihybrid: 2-Factor Cross: First Generation: F1   Mendel crossed true-breeding plants that produced round yellow peas (genotype RRYY) with true-breeding plants that produced wrinkled green peas (genotype rryy): Cross: RRYY x rryy (R) = Round seeds (r) = wrinkled seeds (Y) = Yellow seeds (y) = green seeds Genotypic Ratio: ______________ Phenotypic Ratio: ______________

The Punnett square predicts a Genotypic Ratio: 1:1:2:2:4:2:2:1:1 Phenotypic Ratio: 9:3:3:1 When Mendel crossed plants that were heterozygous dominant for round yellow peas, he found that the alleles segregated independently to produce the F2 generation. F2 Represents: Independent Assortment

Bellwork: Mon???. Jan. 20??, 201? Dihybrid: 2-Factor Cross: First Generation: F1   Mendel crossed true-breeding plants that produced round yellow peas (genotype RRYY) with true-breeding plants that produced wrinkled green peas (genotype rryy): Cross: RRYY x rryy (R) = Round seeds (r) = wrinkled seeds (Y) = Yellow seeds (y) = green seeds Genotypic Ratio: ______________ Phenotypic Ratio: ______________

Bellwork: Mon. Jan. 9, 2012 RRYY x rryy Mendel crossed true-breeding plants that produced round yellow peas (genotype RRYY) with true-breeding plants that produced wrinkled green peas (genotype rryy): Set up the Punnet Square for this cross: RRYY x rryy