1. Patterns of Inheritance
Chapters 11.1/2/3, 14.1/2, 17.1

2. Gregor Mendel All Things Inheritance Begin with Him! Austrian Monk
During his childhood, Mendel worked as a gardener.
Studied practical and theoretical philosophy as well as physics.
Also bred bees in a bee house in hives that he designed.
He also studied astronomy and meteorology.

3. Gregor Mendel

4. The Hypothesis of Inheritance
Trait – A variation of a particular character
The color of flowers

5. Mendel’s Experiments
19th Century – Mendel was one of the first to apply and experimental approach to the question of inheritance.
His work led to:
Genetics – The study of heredity
Mendel bred pea plants for 7 years
He recorded inheritance patterns in offspring
Particulate Hypothesis – this hypothesis states that
parents pass on to their
offspring separate and
distinct factors (AKA
Genes) that are responsible for
inherited traits.

6. Mendel’s Experiments
Mendel stressed that these heritable factors retain their identity generation after generation.
Genes are like marbles; They do not blend like paint.
Starry Night by Vincent van Gogh

7. How Mendel did it… 1st – Identify true breeding pea-plants
True – Breeding plants produce offspring identical generation after generation
Purple flowering pea plants (when self fertilized) always produced purple flowers
To make sure there was no cross fertilization he put bags over the flowers

8. How Mendel did it… + 2nd – Tested his “particulate hypothesis”
Mendel crossed true breeding plants +
Parents
Cross Fertilization – Sperm from the pollen of one
flower fertilizes the eggs in the
flower of a different plant.
Fertilized eggs produced seeds; Mendel planted seeds
Seeds grew produced flowers

9. Inheritance and Rules of chance:
Mendel experimented with pea plant’s flower color and seed shape.
Principle of Segregation
Hybrids – The offspring of two different true
breeding varieties
Parent Plants are designated the:
P generation (P for Parent)
F₁ generation (F for Filial; Latin for son)
F₁ self fertilize or fertilize each other their offspring is designated F₂

10. Inheritance and Rules of chance:
One experiment – Mendel crossed purple-flowered pea plants with white-flowered pea-plants
Monohybrid Cross – a pairing in which the parent
plants differ in only one
character
Results: The F₁ hybrids were not a “blend” of purple and white
All flowers were purple
Then: F₁ plants self-fertilized
Results: ¼ the of F₂ plants had white flowers!
So purple + white did not make white flower disappear.

11. Inheritance and Rules of chance:
Mendel reasoned that F₁ plants carried two factors 1 for purple and 1 for white
These factors are called gene.
To confirm his results Mendel investigated 6 other pea plants characteristics
Each cross produced the same pattern
Results were all the same; 1 of 2 parent traits disappeared in the F₁ generation, then reappeared in about ¼ of the F₂ offspring.

12. The Results Produced 4 Hypothesis
Alleles – Alternate form of a gene
The gene for flower color in pea plants exist in one form for purple; one form for white
For each inherited character, an organism has 2 alleles for the gene controlling character
One from each parent
Homozygous – When two alleles are the same form
that character.
Heterozygous – Two alleles are different.

13. The Results Produced 4 Hypothesis
Dominant Allele – when only one of two
different alleles in a
heterozygous
individual appears to
affect the trait.
Represented by the capital letter P
Recessive Allele – the trait in a heterozygous
that does not appear
Represented by the lower case letter p

14. Mendel’s Principle of Segregation
Mendel’s Hypothesis
Two alleles for a characteristic segregate (separate) during the formation of gametes (sex cells)
So each gamete carries only one allele for each character
Mendel’s Principle of Segregation
The union of gametes during fertilization reforms allele pairs in the offspring

15. Probability and Punnett Squares
In a monohybrid cross of true-breeding (homozygous) purple-flowered and white flowered plants
He hypothesized that each: F₁ (Plant) will get the dominant purple – flower allele (P) from one parent.
One recessive white flour allele (p) from the other parent
Each F₁ plant will be heterozygous: Pp
These plants make gametes on P; one p
If 2 F₁ plants fertilize each other the F₂ generation will individual pair

16. Probability and Punnett Squares
PP – ¼ Pp – ½ Pp – ¼ PP Pp pp
PP, pp Each with probability of ¼ each
Punnett Square – A type of diagram that shows
all possible outcomes of
genetic cross

17. Genotype and Phenotype
Phenotype – An observable trait
Ph for physical
Genotype – the genetic make-up or combination
of alleles
GEN for genetics
So the phenotype for purple vs. white flowers is 3 purple : 1 white
Genotypic Ratio: 1 PP: 2 Pp: 1 pp

18. Testcross
Used to determine whether a plant is homozygous or heterozygous
A testcross breeds an individual of unknown genotype, but dominant phenotype with a homozygous recessive individual
The appearance of the offspring resulting from the testcross will reveal the genotype of mystery plant.
Why: a recessive parent can only contribute a recessive allele to offspring
Phenotype will tell you the allele contributed by the mystery plant

19. Testcross Purple – Flowered Homozygous
Expect all offspring to be purple because mystery plant can only contribute a P allele.
So all offspring will be Pp
But: if purple flowered plant is heterozygous (Pp) expect both purple-flowered (Pp) and white flowered (pp)
When you cross Pp x pp the predicted outcome 1 : 1 (1 purple to 1 white) of phenotype.

20. Mendel’s Principle of Independent Assortment
Dihybrid Cross – Crossing organisms
different in two characters.
When crossing true-breeding with true breeding
Dominant Round Yellow with a dominant wrinkled green:
P generation – RRYY x rryy
Gamete – RY x ry
F₁ generation: RrYy
F₂ generation: 4 different pea phenotypes
result: 9 (Round yellow):3 (wrinkled yellow):3 (round green):1 (wrinkled green )

21. Mendel’s Principle of Independent Assortment
Based on these results Mendel proposed:
The Principle of Independent Assortment
States that gamete formation in an F₂ cross, a particular allele for 1 character can be paired with either allele of another character

22. The Principle of Independent Assortment
Example:
In the Round-Yellow x Wrinkled Green (Pea)
R (round) can end up with Y(yellow) or y (green)
and
r can end up with Y or y
Like everything else there are exceptions!

23. Variations of Inheritance Patterns
Intermediate Inheritance
In Mendel’s pea crosses the F₁ offspring always looked like the dominant homozygous parent.
Because one dominant allele produced one dominant phenotype
A recessive phenotype required inheriting two recessive alleles
If neither allele is dominant – the heterozygotes have a phenotype that is intermediate between the phenotypes of the two homozygotes

24. Variations of Inheritance Patterns
Intermediate Inheritance
Inheritance in which heterozygotes have a phenotype intermediate between the phenotypes of the two homozygotes
NOT A MIX
Not a Blend/Mix because the parent phenotypes can reappear in in F₂ generation
F₂ Generation is 1 : 2 : 1 ratio

25. Multiple Alleles
This is what happens when many alleles exist in the genes
This expands the number of genotypes and phenotypes
Example: Blood Types
Letters represent a carbohydrate (antigen) that exists on the surface of the red blood cell
There are 6 possible genotypes

26. Multiple Alleles Codominance – the heterozygote expresses both traits
Shows separate traits of both alleles.

27. Polygenic Inheritance
When two or more genes affect a single character
Example: Height and Skin Color
Height = A, B, C (Tall)
X, Y, Z (Short)
AABBCC = Very Tall
AXBBCC = Less Tall
Now imagine the different combinations

28. Environmental Effects
A leaf on a tree will vary through-out the year depending on varying sunlight.

29. Environmental Effects
Siamese Cat – are covered with creamy white fur, except for the ears, face, feet, and tail.
An enzyme responsible for black fur is only active at the cooler temperatures found at the extremities

30. Environmental Effects
In Humans Phenotype is not rigid it can be influenced by the environment:
Nutrition influences height, exercise build, sunlight (darkness of skin)
Even twins have the same genotypes have differences in phenotypes as the results of their exposure to the environment.
In humans genes determine phenotypes like blood type with no environmental influence
But blood count (Red vs. White) is sensitive to the environment.
Like altitude, physical activity, and infection (white blood cell count)

31. Meiosis and Mendel’s Principles
Chromosomes Theory of Inheritance
States that genes are located on chromosomes and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns
Biologist worked out mitosis and meiosis in the 1800’s
1900’s Biologist noticed similarities between Mendel’s principles and inheritance patterns
European Biologist: Hugo de Vries, Karl Correns, and Erich von Tschermak independently made the connection.

32. Meiosis and Mendel’s Principles
Remember:
Every diploid individual has two sets of homologous chromosomes
1 from the male
1 from the female
Gene Locus – a specific location of a gene on
a chromosome.
The alleles of a gene reside at the same location

33. Meiosis and Mendel’s Principles
Gene Locus

34. Meiosis and Mendel’s Principles
Genetic Linkage – the tendency for the alleles on
one chromosome to be
inherited together.
When genes are on separate chromosomes they sort independently of each other during meiosis.
During genetic linkage: the closer two genes are on a chromosome the greater the genetic linkage
The farther apart the genes are, the more likely it is that a cross-over event will separate them.

35. Sex-Linked Traits Sex-Linked Gene – Is any gene located on a sex
chromosome
In humans most sex-linked genes are found on the X chromosome
They are obviously larger than the Y chromosome

36. Discovered by Thomas Hunt Morgan
Sex-Linked Traits
Discovered by Thomas Hunt Morgan
Studied the inheritance of white eye color in fruit flies
White eyes are rare; normal fruit fly eye color is red.

37. Sex-Linked Traits
Morgan mated white eyed male fruit fly with red-eyed females
All F₁ (offspring) had red eyes
When Morgan bred the F₁: offspring had the 3 : 1 ratio in the F₂ generation
3 red : 1 White
After MANY trials Morgan realized all white eyed fly’s were male
Morgan deduced that this trait was located on the X chromosome.

38. Female: Other X chromosome “blocks” the recessive trait
Sex-Linked Traits
Explanation: White eye color is recessive so a female can only have white eyes if she has this chromosome on both X chromosomes
A male only needs one.
Male: Missing part of chromosome allows the trait to show
Female: Other X chromosome “blocks” the recessive trait

39. Red – Green Color Blindness
Sex-Linked Disorders
Red – Green Color Blindness

40. Sex-Linked Disorders Hemophilia (a blood clotting disorder)
Queen Victoria Queen of England at the age of 18
Appeared in her children