1. Mendelian Genetics Chapter 11 Part 1 pp. 189-197, 202-204

2. Genetic Theories 1. Blending Theory -
traits were like paints and mixed evenly from both parents.
2. Incubation Theory -
only one parent controlled the traits of the children.
Ex: Spermists and Ovists

3. 3. Particulate Model -
parents pass on traits as discrete units that retain their identities in the offspring.

4. INTRODUCTION TO GENETICS2

5. Fruit and Flower of the Garden Pea
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Flower Structure
anther
stamen
filament
stigma
style
carpel
ovules in
ovary a. 5

6. Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation
White 1
Removed stamens from purple flower
Stamens
Carpel 2
Transferred pollen from stamens of white flower to carpel of purple flower
PARENTS (P)
Purple 3
Pollinated carpel matured into pod
This illustration shows his technique for cross- fertilization that results in hybrid offspring 4
Planted seeds from pod
OFF-SPRING (F1)
Figure 9.2C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

7. Self-pollination
One flower as both parents.
Natural event in peas.
Results in pure-bred offspring where the offspring are identical to the parents.

9. Results - Summary
In all crosses, the F1 generation showed only one of the traits regardless of which was male or female.
The other trait reappeared in the F2 at ~25% (3:1 ratio).

10. Mendel’s 4 Conclusions: 1. Various forms of genes exist6

11. Mendel’s 4 Conclusions:
2. For each characteristic, we inherit 2 alleles (one from each parent)
3. If alleles are different, in complete dominance, there is a dominant and recessive allele
GENE LOCI
DOMINANT
allele P a B P a b
RECESSIVE
allele
GENOTYPE: PP aa Bb
HOMOZYGOUS for the dominant allele
HOMOZYGOUS for the recessive allele
HETEROZYGOUS
Figure 9.4
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

12. Mendel’s 4 Conclusions:
4. Law of Segregation: alleles separate during meiosis and rejoin during fertilization of sperm and egg. Remember Anaphase I (separation of tetrads)
GENETIC MAKEUP (ALLELES)
P PLANTS PP pp
Gametes
All P
All p
F1 PLANTS (hybrids)
All Pp
Gametes
1/2 P
1/2 p P P
Eggs
Sperm PP
F2 PLANTS p p Pp Pp
Phenotypic ratio 3 purple : 1 white pp
Genotypic ratio 1 PP : 2 Pp : 1 pp
Figure 9.3B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

13. MENDEL’S LAW OF SEGREGATION
During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.  Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. Rr R r

14. We can show Mendel’s idea in the form of punnet squares:
What is the probability that a couple will have a boy? 10 10

15. Modern Genetics View
Each trait in a pea plant is controlled by two alleles (alternate forms of a gene)
Dominant allele (capital letter) masks the expression of the recessive allele (lower-case)
Alleles occur on a homologous pair of chromosomes at a particular gene locus
Homozygous = identical alleles
Heterozygous = different alleles 15

16. Genotype versus Phenotype
Refers to the two alleles an individual has for a specific trait
If identical, genotype is homozygous
If different, genotype is heterozygous
Phenotype
Refers to the physical appearance of the individual 16

17. Patterns of Inheritance
Complete dominance (Mendel’s focus)
Incomplete dominance
Codominance
Multiple Alleles
Pleiotropy
Epistasis
Polygenic Traits 11 11

18. Heterozygous phenotype same as that of homo- zygous dominant PP Pp
Fig. 14-UN2
Degree of dominance
Description
Example
Complete dominance
of one allele
Heterozygous phenotype
same as that of homo-
zygous dominant PP Pp
Incomplete dominance
of either allele
Heterozygous phenotype
intermediate between
the two homozygous
phenotypes
CRCR
CRCW
CWCW
Codominance
Heterozygotes: Both
phenotypes expressed
IAIB
Multiple alleles
In the whole population,
some genes have more
than two alleles
ABO blood group alleles
IA , IB , i
Pleiotropy
One gene is able to
affect multiple
phenotypic characters
Sickle-cell disease

19. Examples of COMPLETE DOMINANCE
Class Example: Brown eyes are dominant over blue.What is the probability that Mr. and Mrs. Brooks will have a child with brown eyes if both are hybrids?
Class Example:The ability to roll the tongue is dominant to the lack of this ability. Mr. Brooks is recessive and Mrs. Brooks is heterozygous.
Class Example: Right handedness is dominant to left. Tommy is right-handed but not a hybrid and his brother is left handed.
What is the phenotypic ratio?
If Tommy has a child in the future, what handedness will this child be?
What was the probability that Tommy would have the genotype he has?
What was the probability that Tommy would have the phenotype he has? 10 10

20. Punnett Square Showing Earlobe Inheritance Patterns
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents Ee Ee
eggs E e E EE Ee
spem
Punnett square e Ee e e
Offspring
Allele key
Phenotypic Ratio
E = unattached earlobes
e = attached earlobes 3
unattached earlobes 1
attached earlobes 20

21. Mendel’s Law of Probability Multiplication
Allows us to easily calculate probability, of genotypes and phenotypes among the offspring
Punnett square in next slide shows a 50% (or ½) chance
The chance of E = ½
The chance of e = ½
An offspring will inherit:
The chance of EE =½x½=¼
The chance of Ee =½x½=¼
The chance of eE =½x½=¼
The chance of ee =½x½=¼

22. Mendel’s Law of Probability: Addition
Rule of Addition is that the probability of an event that can occur in two or more independent ways is the sum of the separate probabilities of the different ways….applies to heterozygous being produced (Ee)
An offspring will inherit:
The chance of EE =½x½=¼
The chance of Ee =½x½=¼
The chance of eE =½x½=¼
The chance of ee =½x½=¼
The probability that a heterozygous offspring will be produced is 1/4 + 1/4 = 1/2. 14

23. EXAMPLES Monohybrid using Rules of multiplication and addition
AA x Aa……Probability of Aa offspring?
Aa x Aa…..Probability of Aa offspring? 15

24. What if you don’t know each parent’s genotype
What if you don’t know each parent’s genotype? TEST CROSS – designed to reveal the genotype of an organism when you do not know

25. Example using a TEST CROSS
The ability to roll the tongue is dominant to the lack of this ability. Mr. Smith is a tongue roller while Mrs. Smith is not. What are the possible probabilities of the next generation? 17 15

26. Mendel’s Law: The LAW of INDEPENDENT ASSORTMENT is revealed by tracking 2 traits
By looking at two characteristics at once, Mendel found that the alleles of a pair segregate independently of other allele pairs during gamete formation
This is known as the law of independent assortment
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

27. DIHYBRIDS Analysis of two traits simultaneously
Trait: Handedness (right vs. left) and Eye Color (brown vs. blue)
Use ‘H’ for handedness and ‘E’ is for eye color. Right handedness is dominant to left and brown eyes are dominant to blue. Mom is heterozygous for both traits and dad is a hybrid for both traits.
WHAT IS THE PHENOTYPIC RATIO?

28. Rules of Probability Applies to Dihybrid Crosses too
For a dihybrid cross, HhEe x HhEe, what is the probability of an F2 having the genotype
HHEE?
HhEe?
hhee?

29. Let’s Try a Trihybrid
Determine the probability that the offspring would produce recessive phenotypes for at least 2 of the 3 characters.
Heterozygous purple flowers and yellow seeds and round seeds crossed with heterozygous purple and recessive green and wrinkled. 21

30. Fig. 14-UN1

31. Incomplete Dominance
Class Example: A cross between a red four o clock and a white four o clock produces a pink one. Cross a red four o clock with a pink four o clock.

32. Codominance
Two alleles affect the phenotype in separate and distinguishable ways.
Neither allele can mask the other and both are expressed in the offspring and not in an “intermediate” form.
In a study conducted by the University of Michigan, pitch black feathered birds crossed with gray feathered birds produced a spotted (black and gray), bird. Show a cross between 2 speckled birds.

33. 1) In cattle, roan coat color (mixed red and white hairs) occurs in the heterozygous (RW) offspring of red (RR) and white (WW) homozygotes. When two roan cattle are crossed, the phenotypes of the progeny are found to be in the ratio of 1 red:2 roan:1 white. Which of the following crosses could produce the highest percentage of roan cattle?
A) roan x roan
B) red x white
C) white x roan
D) red x roan
E) All of the above crosses would give the same percentage of roan.

34. Multiple Alleles
ABO Blood System

35. Multiple Allelic Traits

36. Rh Factor associated with Blood Types demonstrates Complete Dominance29 29

37. Pleiotropy
Most genes have multiple phenotypic effects. The ability of a gene to affect an organism in many ways is called pleiotropy.

38. Epistasis
Epistasis occurs when a gene at one locus alters or influences the expression of a gene at a second loci. In this example, C is for color and the dominate allele must be present for pigment (color) to be expressed.
 In a certain breed of plants, B produces blue flowers and is dominant over b which produces green flowers.  Another gene determines in which cells the pigment will be synthesized.  Allele M allows complete synthesis of the pigment throughout the flowers but the mutant allele m prevents pigment production. 
You cross two plants that are BbMm.

39. Polygenetic Inheritance
Qualitative variation usually indicates polygenic inheritance. This occurs when there is an additive effect from two or more genes. Pigmentation in humans is controlled by at least three (3) separately inherited genes.

40. 18

41. Heterozygous phenotype same as that of homo- zygous dominant PP Pp
Fig. 14-UN2
Degree of dominance
Description
Example
Complete dominance
of one allele
Heterozygous phenotype
same as that of homo-
zygous dominant PP Pp
Incomplete dominance
of either allele
Heterozygous phenotype
intermediate between
the two homozygous
phenotypes
CRCR
CRCW
CWCW
Codominance
Heterozygotes: Both
phenotypes expressed
IAIB
Multiple alleles
In the whole population,
some genes have more
than two alleles
ABO blood group alleles
IA , IB , i
Pleiotropy
One gene is able to
affect multiple
phenotypic characters
Sickle-cell disease

42. Relationship among genes Description Example Epistasis
Fig. 14-UN3
Relationship among
genes
Description
Example
Epistasis
One gene affects
the expression of
another
BbCc
BbCc BC bC Bc bc BC bC Bc bc 9
: 3
: 4
Polygenic
inheritance
A single phenotypic
character is
affected by
two or more genes
AaBbCc
AaBbCc