1. 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? ___

2. More on Genetics 2

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15. 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

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

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

18. "No one ever believes we are twins because I am white and Maria is black,"
- Lucy 

19. 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: )

20. 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)

21. 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?

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

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

24. 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 _______.

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

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

27. 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?

28. 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.

29. 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?

30. 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%

31. 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:

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

33. Genotypic Ratio:
Phenotypic Ratio:

35. 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

36. 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

37. Mendel didn’t know about Chromosomes or DNA
We now know that genes located close together on a chromosome may be inherited together

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39. https://www. youtube. com/watch

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41. But… some alleles aren’t completely dominate or recessive

42. 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  ___________           

43. Incomplete & Codominance

44. 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).

46. 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:_________

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

48. 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!!

49. 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:

50. Or…. Roan coat color in horses and cows.

51. 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:____________

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

53. roan horses

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56. 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: ______________

57. 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

58. 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: ______________

59. 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