1. Mendelian Genetics Notes

2. Genetics
HEREDITY is the transmission of traits from parents to their offspring
GENETICS is the study of heredity
GREGORY MENDEL is the father of genetics

3. Gregory Mendel An Austrian monk (during the 1820’s)
Given the task of tending the garden
Studied the hereditary patterns of pea plants

4. Mendel’s Experiments Studied the 7 characteristics of pea plants
Round vs. wrinkled peas, yellow vs. green peas, white vs. grey seed coats, inflated vs constricted pods, yellow vs. green pod color, tall vs. short plants, flowers on sides vs. flowers on the ends

5. Mendel’s Experiments
He let the plants pollinate themselves to produce pure strains
Called TRUE BREEDING (made clones)
Then he cross pollinated plants to see what would happen
Called HYBRIDS (since parents had different traits)
Results: patterns emerged in the offspring of the pea plants

7. Concepts from Mendel’s Work
P GENERATION is the Parental Generation
This is the original pure strain parents
F1 GENERATION is the First Filial Generation
This is the offspring from parents in the P generation (children)
F2 GENERATION is the Second Filial Generation
This is the offspring from two parents from the F1 generation (grandchildren)

9. Concepts from Mendel’s Work
CHROMOSOMES are the rod shaped form DNA takes during meiosis that contains genes
Offspring get one chromosome of each homologous pair from each parent at fertilization

10. Concepts from Mendel’s Work
GENE is the segment of DNA that controls a particular hereditary trait

11. Concepts from Mendel’s Work
ALLELES are the alternate forms of genes
Dominant allele – Capital letter (T or tall)
Recessive allele – small letter (t or not tall, or short)
A pair of alleles would be TT, Tt, or tt
Each allele is on a different homologous chromosome
Meaning you get one allele from MOM and the other allele from DAD

12. Concepts from Mendel’s Work
GENOTYPE is the genetic makeup of an organism; what genes it has (TT, Tt, or tt)
PHENOTYPE is the physical appearance of an organism; how the genes are expressed (tall or short)

13. Concepts from Mendel’s Work
HOMOZYGOUS is an organism with two of the same kind of alleles
Homozygous dominant: TT
Homozygous recessive: tt
HETEROZYGOUS is an organism with different alleles for a trait
Heterozygous: Tt

14. Mendel’s Three Principles
PRINCIPLE OF DOMINANCE traits are controlled by pairs of genes
One allele is DOMINANT meaning it masks or dominates the other trait
One allele is RECESSIVE meaning it is masked in the presence of the dominant trait
Ex. T is the dominant allele
A plant with the genotype TT or Tt = DOMINANT
A plant with the phenotype tt = RECESSIVE

18. HOW DID A TRAIT DISAPPEAR AND THEN REAPPEAR?

19. Mendel’s Three Principles
PRINCIPLE OF SEGREGATION the two genes for a pair of traits segregate during meiosis so each sperm and egg only gets one gene from a pair

21. Mendel’s Three Principles
PRINCIPLE OF INDEPENDENT ASSORTMENT genes for some characteristics are not connected to each other, so they are assorted into sex cells independently from each other
This is why all tall people do not have brown eyes and all short people have blue eyes, etc.

23. Genetic Crosses
PROBABILITY is the likelihood that a specific event will occur
= number of one kind of event
number of all events
Ex. Flipping a coin and the probability of getting heads? ½
Probability of getting tails? ½
What is the probability if I flip a coin 3 times in a row that it will land heads up every time?
If I flip a coin once and get heads, does that mean with 100% certainty that on the next flip I will get tails?

24. Probability
What is the probability if I flip a coin 3 times in a row that it will land heads up every time?
½ X ½ X ½ = 1/8
If I flip a coin once and get heads, does that mean with 100% certainty that on the next flip I will get tails?
NO!!!!!!!!!!!!!!!!!!!!!!!
This means PAST OUTCOMES DO NOT AFFECT FUTURE OUTCOMES

25. Genetics uses Probability
Used to predict the genotypic and phenotypic ratios of offspring produced by genetic crosses
If two organisms produce offspring, what is the expected result of genotypes and phenotypes in their offspring?

26. Punnett Square
PUNNETT SQUARE is a diagram used to aid (help) biologists in predicting probabilities in offspring

27. PARENT’S ALLELES IN GAMETES
Punnett Square
PARENT’S ALLELES IN GAMETES
Note this DOES NOT SHOW ACTUAL results, just PREDICTIONS
POSSIBLE OFFSPRING

32. Monohybrid Crosses
MONOHYBRID CROSS is a cross between individuals that involves one pair of contrasting traits

33. Homozygous Dominant X Homozygous Dominant
Key: T= Tall
t = Short
Cross: TT x TT If 100 plants
100 tall
T T T TT TT TT TT

34. Homozygous Dominant X Homozygous Dominant
Predicted genotypes of offspring: TT
Genotypic ratio: 4 TT / 4 Total
Predicted phenotypes of offspring: TALL
Phenotypic ratio: 4 Tall / 4 Total
4 / 4 or 100% Probability of tall offspring

35. Homozygous Recessive X Homozygous Recessive
Key: T= Tall
t = Short
Cross: tt x tt If 100 plants
100 short
t t t tt tt tt tt

36. Homozygous Recessive X Homozygous Recessive
Predicted genotypes of offspring: tt
Genotypic ratio: 4 tt / 4 Total
Predicted phenotypes of offspring: SHORT
Phenotypic ratio: 4 Short / 4 Total
4 / 4 or 100% Probability of short offspring

37. Heterozygous X Heterozygous
Key: T= Tall
t = Short
Cross: Tt x Tt If 100 plants
75 tall
25 short
T t T t TT Tt Tt tt

38. Heterozygous X Heterozygous
Predicted genotypes of offspring: TT, Tt, and tt
Genotypic ratio: 1 TT/ 2 Tt / 1 tt
Predicted phenotypes of offspring: TALL, SHORT
Phenotypic ratio: 3 TALL / 1 SHORT
3 / 4 or 75% Probability of tall offspring
1 / 4 or 25% Probability of short offspring

39. Mendel’s Crosses T T t P  2 pure strains Key: T= Tall t = Short
Tall x short
Cross: TT x tt
- F1 GENERATION = ALL Tt (Tall)
Genotypic ratio:
4 Tt / 4 Total
- Phenotypic ratio: Tall / 4 Total
T T t Tt Tt Tt Tt

40. Mendel’s Crosses T t T t Two F1 individuals crossed Key: T= Tall
t = Short
Tall x Tall
Cross: Tt x Tt
- F2 GENERATION = 75% Tall and 25% Short
Genotypic ratio:
1 TT / 2 Tt / 1 tt
Phenotypic ratio: 3 Tall / 1 Short
If you have 100 offspring, you would expect 75 to be tall and 25 to be short
T t T t TT Tt Tt tt

42. How can the Environment affect our phenotypes?

43. Incomplete Dominance
INCOMPLETE DOMINANCE is the intermediate phenotype that results when one allele is not always totally dominant over the other

44. Incomplete Dominance R R I RI RI RI RI Ex. Snapdragons (flowers)
Key: RR = Red
II = Ivory
RI = Pink
What would we get if we crossed a pure Red flower with a pure Ivory flower?
Red x Ivory Cross: RR x II
Genotypic ratio: 4RI / 4
Phenotypic ratio: 4 Pink / 4
R R I RI RI RI RI

45. Incomplete Dominance R I R I RR RI RI II
What would we get if we now allowed the F1 generation to self pollinate?
Pink x Pink Cross: RI x RI
Genotypic ratio: 1RR / 2RI/ II
Phenotypic ratio: 1 RED / PINK / 1 IVORY
Therefore, the genotypic and phenotypic ratios for incomplete dominance are the EXACT SAME
R I R I RR RI RI II

46. Codominance
CODOMINANCE is when both alleles from a gene are expressed in the heterozygous individual, at the SAME TIME

47. Codominance W W Y YW YW YW YW Ex. Flowers Key: YY = Yellow WW = White
YW = Roan (Yellow with White Spots)
What would we get if we crossed a pure Yellow flower with a pure White flower?
Yellow x White Cross: YY x WW
Genotypic ratio: 4YW / 4
Phenotypic ratio: 4 Roan / 4
W W Y YW YW YW YW

48. Multiple Allele Traits
MULTIPLE ALLELE TRAITS occur when three or more contrasting alleles control a trait
Example: Blood types ABO
Gene for type A blood: IA
Gene for type B blood: IB
Gene for type O blood: i
Both A and B are dominant, O is recessive
A blood cells carry the A antigen (causes the body to make antibodies  clotting)
B blood cells carry the B antigen
O blood cells carry no antigen

49. Multiple Allele Traits
Type A blood: IAIA or IAi
Type B blood: IBIB or IBi
Type AB blood: IAIB
Type O blood: ii AB A B O

51. Polygenic Traits
POLYGENIC TRAITS are traits controlled by more than one pair of genes
Example: skin color, eye color, and height
There are at least 4-7 pairs of genes that control each one of these traits
These genes can be on the same chromosomes or different chromosomes
There is a wide variety of phenotypes shown
There is no necessary dominant/recessive, instead genes are turned on/off (if on will add some affect on trait)

53. Dihybrid Crosses
DIHYBRID CROSS is a cross between individuals that involves the pairing of two contrasting traits
There are more possible combinations of alleles
There are 16 squares in the Punnett square used
There are four combinations of alleles possible in gametes from each parent

55. FOIL Method Suppose: Parent: TtGg First TG Outside Tg Inside tG
T = tall t = short
G = green g = yellow
Use the FOIL method to determine the possible gametes from each parent
Parent: TtGg
First TG
Outside Tg
Inside tG
Last tg T t G g

56. Homozygous Dominant x Homozygous Recessive
TTGG x ttgg
Genotypic ratio: 16 TtGg / 16 Total
Phenotypic ratio: 16 Tall, Green / Total
All Plants = Tall and Green tg tg tg tg
TtGg TG TG TG TG

57. Heterozygous x Heterozygous
TtGg x TtGg TG Tg tG tg
TTGG
TTGg
TtGG
TtGg
TTgg
Ttgg
ttGG
ttGg
ttgg TG Tg tG tg

58. Heterozygous x Heterozygous
Genotypic ratio: TTGG 1 TTGg 2 TTgg 1 TtGG 2 TtGg 4 Ttgg 2 ttGG 1 ttGg 2 ttgg 1 Phenotypic ratio: Tall, green 9 Tall, yellow 3 Short, green 3 Short yellow 1

59. Summary of heterozygous vs. heterozygous cross
Monohybrid
Genotypic ratio: 1 : 2 : 1
Phenotypic ratio: 3 : 1
Dihybrid
Genotypic ratio:1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1
Phenotypic ratio: 9 : 3 : 3 : 1