1. Fundamentals of Genetics
Ch. 11

2. Gregor Mendel Monk who taught high school science and mathematics
He kept a garden plot at the monastery where he did his science work
Father of genetics for his work on pea plants and heredity.
Heredity: the transmission of characteristics from parents to offspring.

3. Mendel’s Garden Peas He observes 7 characteristics of pea plants
Each characteristic occurred in two contrasting traits
Trait: a category in which alternate characteristics can be observed.
Plant height – long vs. short stems
Flower position – axial vs. terminal
Pod color – green vs. yellow
Pod appearance – inflated vs. constricted
Seed texture – smooth vs. wrinkled
Seed color – yellow vs. green
Flower color – purple vs. white

4. Mendel’s First Observations
He took seeds and noted from which plants they were obtained
Ex: He took purple flower plant seeds and crossed them with some of the same type
He noticed that these plants had purple flowers, but they would also have offspring with white flowers.
He noticed this for each one of the traits.
He wanted to know why this happened

5. Mendel’s Methods
Pollination – occurs when pollen grains produced in the male reproductive parts of a flower, called the anthers, are transferred to the female reproductive part of a flower, called the stigma.
He carefully controlled pollination by removing the anthers after he self pollinated the plants he wanted to cross.
Self pollination occurs when pollen is transferred from the anthers of a flower to the stigma of the same flower or of one on the same plant. (Pea plants usually reproduce this way)
Cross pollination involves flowers of two separate plants.

6. Mendel’s Experiment
Mendel first grew plants that were pure for a trait
Pure: always produce offspring with the desired trait.
Strain: denotes plants that are pure for a specific trait.
He produced strains by only allowing the plants to self-pollinate.
He eventually obtained 14 strains, one for each of the traits he observed.
Each strain was called the parental generation, or P1 generation.
He then cross-pollinated these strains with plants that were pure for the opposite trait to produce the F1 generation.
He collected the seeds from the F1 generation and allowed them to mature and recorded his observations.
He then self pollinated the flowers from the F1 generation to produce the offspring to the F2 generation.
He allowed these plants to mature and recorded once again his observations.
He did this several hundreds of times with each of the traits recording his observations each time.

7. Mendel’s Results and Conclusions
Each time he crossed the P1 generations, the F1 generation always resulted in only one of the two traits being seen physically.
Each time he crossed the F1 generations, the F2 generation always had the ratio of 3:1
He hypothesized that the trait appearing in the F1 generation was controlled by a DOMINANT factor, because it masked, or dominated, the other characteristic.
The trait that did not appear he thought was controlled by a RECESSIVE factor.

8. Chromosomes and Genes
Law of Segregation – a pair of factors is segregated, or separated, during the formation of gametes.
Law of Independent Assortment – factors for different characteristics are distributed to gametes independently. (one factor is inherited separately from another)
Because chromosomes occur in pairs, genes also occur in pairs. Each of several forms of a gene is called an allele.
Mendel’s factors are now called alleles.
The dominant allele for a genes is given a capital letter, whereas the recessive form of an allele is given a lowercase letter.
Ex: Tall is dominant over short, so we use the letter t. T = tall, t = short

9. Genetic Crosses
The genetic makeup of an organism is its genotype. (The allele letter combinations)
The appearance of an organism is called its phenotype.
When both alleles of a pair are alike, the organism is said to be homozygous for that characteristic.
An organism can be homozygous dominant, or homozygous recessive.
Ex: TT or tt
Heterozygous is when the two alleles in the pair are different. Heterozygotes are also referred to as carriers, as they carry the recessive gene, but do not express it.
Ex: Tt

10. Probability
Probability – the likelihood that a specific event will occur.
Expressed as a decimal, a percentage, or a fraction
Probability = # of x’s an event is expected to happen
# of opportunities for an event to happen
In Mendel’s experiments the number of yellow seed color appeared in the F2 generation 6,022 times and the total number of seeds was 8,023
6,022/8,023 = .75 or 75% or 3/4
The green seeds appeared 2,001 times
2,001/8023 = .25 or 25% or ¼

11. Predicting Results of Monohybrid Crosses
A cross between individuals that involves one pair of contrasting traits is called a monohybrid cross.
Punnett squares are used to show the possible outcomes, or probability that a certain trait will be inherited by the offspring.
The following is an example of a cross between a pure/homozygous purple (PP) flowering plant and a pure/homozygous white flowering plant (pp).
Outcome is 100% probability of getting purple flowers
Genotype is Pp and Phenotype is purple

12. Predicting Results of Monohybrid Crosses
A Heterozygous purple flowering plant is X with a Heterozygous purple flowering plant. What will the expected phenotype and genotype ratios be?
Genotype ratio is written as:
1 PP: 2 Pp: 1 pp
Phenotype ratio is written as:
3 purple: 1 white

13. Your Turn
A Homozygous guinea pig for black coat color is crossed with a heterozygous for black coat color.
We can see that black is the dominant trait since heterozygous still results in black color.
What letter shall we use? B (for black), so BB X Bb (bb is brown)
What will the genotype and phenotype ratios be?
Genotype ratio - 2 BB: 2 Bb
Phenotype ratio - 4:4 or 100% black
Unknown dominant genotypes can be determined by crossing it with a homozygous recessive…this is called a testcross.
(Bb) B b BB Bb B
(BB) B

14. Incomplete Dominance
So far we have talked about COMPLETE DOMINANCE alleles, one form of the gene is dominant over the other.
Sometimes F1 offspring will have a phenotype in between that of the parents. This is known as INCOMPLETE DOMINANCE.
Some flowers have alleles where both red and white both influence the color but neither is dominant over the other. The result when a homozygous red and a homozygous white is crossed is all pink flowers.
When two pink flowers are crossed the genotype ratio is: 1 RR: 2Rr: 1 rr
So phenotype ratio is 1 red: 2 pink: 1 white

15. Codominance
Codominance occurs when both alleles for a gene are expressed in a heterozygous offspring.
In codominance neither allele is dominant or recessive over the other.
Nor do they blend in the phenotype.
They are both expressed.

16. Multiple Allele Traits and Polygenic Traits
Multiple allele traits are controlled by three or more alleles of the same gene that code for a single trait.
Ex: blood type
Polygenetic Traits – A trait that is controlled by two or more genes.
Ex: skin color, eye color, height (but height is also environmental controlled)

17. Human Blood Type There are 4 types of human blood – A, B, O, and AB.
AB is a codominant form since both A and B are both dominant.
O is the recessive form of blood.
There is also something called the RH factor. Which means that you can also have a positive or a negative blood type.
Interesting Facts:
Blood types A and B make antibodies against the other dominant type of blood. Neither makes antibodies for O.
AB does not make any antibodies against A nor B since it has both types.
O makes antibodies against blood types A and B.
O is the universal donor (O-more specifically), which means everyone can receive blood from somebody with O blood type or from their own blood type.
O can only receive blood from O.

19. How do Read Blood Type Results

20. Predicting Results of Dihybrid Crosses
A dihybrid is a cross between individuals that involves two pairs of contrasting traits.
In this example we start with a homozygous dominant yellow seed that is round and it is crossed with a homozygous recessive green seed that is wrinkled
All of the F1 generation with be 100% round and yellow and 100% RrYy

21. Heterozygous F1 Cross
When the F1 heterozygous generation is crossed, the results are as follows.
Phenotype ratio is:
9 yellow/round: 3 green/round: yellow/wrinkled: 1 green/wrinkled
The genotype is more complicated ;-)
1 RRYY: 2 RRYy: 2 RrYY: 4 RrYy: 1 RRyy: Rryy: 1 rrYY: 2 rrYy: 1 rryy

22. Sex Determination
Like other chromosomes the sex chromosomes form pairs.
In mammals and most insects, males have one X chromosome and one Y chromosome.
Females have two X chromosomes.
Males determines the sex of the offspring.
Offspring have a 50% chance of either being a boy or a girl.

23. Sex-Linked Traits
More genes are carried on the X gene due to size difference!
Genes carried on the X chromosome are said to be X-linked genes.
Genes found on the Y chromosome are Y-linked.
The presence of genes on the sex chromosomes is called sex linkage.
Examples: Colorblindness, hemophilia, muscular dystrophy
Sex-influenced traits are controlled by hormones, both males and females may have the same genotype but different phenotype.
Ex: male pattern baldness
Males either have the disorder or do not due to size of the Y chromosome (it can not cover up what is on the X chromosome if it does not have a second allele)
Females can have three genotypes two which say they do not have the physical trait and one that does. However, the heterozygous form is called a carrier, cause they can pass on the gene to their sons.

24. Hemophilia Examples Ex: 1 How many children have hemophilia?
What percentage of boys have hemophilia?
Ex: 2
What percentage of children have hemophilia?
What percentage of girls are carriers?