1. Genetics the scientific study of heredity.

2. Traits
Many of your physical traits resemble those of your parents. These are physical or behavioral characteristics that vary from one individual to another.
Heredity can be defined as the passing of genetic traits from parents to offspring.
Before DNA and chromosome structure were discovered, genetics was one of the biggest mysteries of science.
Question: Which one of the president’s daughters looks more like their mother?

3. These experiments led to the understanding of heredity.
Gregor Mendel
Gregor Mendel was an Austrian monk and a scientist who performed experiments with garden peas.
Mendel studied seven pea plant traits, each with two contrasting characters.
He crossed plants with each of the seven contrasting characters and studied their offspring.
These experiments led to the understanding of heredity.
Genetics is the branch of biology that focuses on heredity.

4. Gregor Mendel’s Methods
Mendel knew that the male part of each flower produces pollen (containing sperm).
He also knew the female part of the flower produces egg cells.
Pea flowers are self-pollinating.
Sperm cells in pollen fertilize the egg cells in the same flower.
The seeds that are produced by self- pollination inherit all of their characteristics from the single plant that bore them.
Gregor Mendel’s Methods

5. Mendel wanted to produce seeds by joining male and female reproductive cells from two different plants.
He cut away the pollen-bearing male parts of the plant and dusted the plant’s flower with pollen from another plant.
This process is called cross- pollination. Crosspollination produces seeds that have two different parents. These plants are called hybrids.
Experiments of Mendel

6. Mendel’s Crosses
Each original pair of plants is the P (parental) generation.
The offspring are called the F1, or “first filial,” generation.
The F1 hybrid plants all had the character of only one of the parents.

7. Mendel’s Seven Traits
Mendel's first conclusion was that biological inheritance is determined by factors that are passed from one generation to the next.
He called these factors genes.
Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characters for each trait.

8. Principle of Dominance
The different forms of a gene are called alleles.
Mendel’s second conclusion is called the “Principle of Dominance.” which states that some alleles are dominant and others are recessive.

9. Next, Mendel crossed the new generation of plants, and he found the white flowers reappeared in the next generation.
True Breeding plants are allowed to self-fertilize (pollinate) and produce the P generation (parental).
F1 Generation results from the cross-fertilization (pollination) of the P generation. The dominant allele masks the recessive allele.
F2 Generation results from the self- fertilization of the F1 generation. The recessive allele shows up again in some of the plants. This showed the alleles had been separated, or segregated from the dominant trait.
Segregation

10. Mendel suggested that the alleles segregate from each other during the formation of the sex cells, or gametes.
When each F1 plant flowers and produces gametes, the two alleles segregate from each other so that each gamete carries only a single copy of each gene.
Therefore, each F1 plant produces two types of gametes—those with the allele for purple flowers, and those with the allele for white.
Gamete Formation

11. More Key Words
Phenotype: the physical characteristics of an organism (what it looks like, i.e.: tall or short)
Genotype: The genetic makeup of an organism (TT or Tt) due to the alleles it has for a trait
Homozygous: Two alleles of a particular gene that code for the same trait are the same. Ex PP (dominant purple color) or pp (recessive white flower color).
Heterozygous: Two alleles of a particular gene are different for a trait. ex Pp or Yy

13. Mendel’s Principles Genes are passed from parents to their offspring.
If two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive.
In most sexually reproducing organisms, each adult has two copies of each gene. These genes are segregated from each other when gametes are formed.
The alleles for different genes usually segregate independently of one another.

14. Ratio Results Which plant height was dominant in Mendel’s experiment?
Which plant height was recessive?
Mendel found the same results in his experiments, time and time again.
The ratio of plants showing the dominant phenotype (TT or Tt genotype) to those showing the recessive phenotype(tt genotype) plants is 3:1.
The predicted ratio showed up in Mendel’s experiments, indicating that segregation did occur.

15. Probability, Ratios and Punnett Squares
The likelihood that a particular event will occur is called probability.
Probability can be used to predict the outcomes of genetic crosses.
Punnett squares are diagrams used to predict and compare the genetic variations that will result from a cross.

16. Punnett Square Practice
To determine the phenotype of an offspring you must first recognize its genotype.
We have discussed two types of alleles, Dominant (B) and Recessive (b)
We have also discussed Heterozygous (Bb) and Homozygous (BB) or (bb) alleles
Punnett squares provide a means for determining the phenotypic outcome resulting from the combination of gametes
The basic construction of a simple punnet square is to the left of this explanation.
Punnett Square Practice

17. List the phenotype and genotype outcomes for each cross below using the Punnett Square.
Practice Problems
Heterozygous dominant x Homozygous recessive
Hh x hh ( H = white, h = green )
homozygous recessive x homozygous recessive
bb x bb ( B = Black, b = brown)
Heterozygous dominant x homozygous dominant
Tt x TT ( T = tall, t = short )

18. Probability and Predicted Averages
• 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.

19. Independent Assortment
•To determine if the segregation of one pair of alleles affects the segregation of another pair of alleles, Mendel performed a two-factor cross. •Mendel crossed true-breeding plants that produced round yellow peas (genotype RRYY) with true-breeding plants that produced wrinkled green peas (genotype rryy). •All of the F1 offspring produced round yellow peas (genotype RrYy).

20. Two Factor Hybrid Cross
For a two-factor F1 hybrid cross, the Punnett square predicts a : 3 : 3 : 1 ratio in the F2 generation.

21. Beyond Dominant and Recessive Alleles
Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

22. When one allele is not completely dominant over another it is called incomplete dominance.
In incomplete dominance, the heterozygous phenotype is between the two homozygous phenotypes.
A cross between red (RR) and white (WW) four o’clock plants produces pink colored flowers (RW).
Incomplete
Dominance

23. Codominance In codominance, both alleles contribute to the phenotype
(like spots!).
• In certain varieties of chicken, the allele for black feathers is codominant with the allele for white feathers.
•Heterozygous chickens are speckled with both black and white feathers. The black and white colors do not blend to form a new color, but appear separately.

24. Multiple
Alleles
Genes that are controlled by more than two alleles are said to have multiple alleles.
•An individual can’t have more than two alleles. However, more than two possible alleles can exist in a population.
•A rabbit's coat color is determined by a single gene that has at least four different alleles.

25. Polygenic Traits
Traits controlled by two or more genes are said to be polygenic traits.
•Skin color in humans is a polygenic trait controlled by more than four different genes. Scientists do not believe they have identified all the genes responsible for eye color.

26. REVIEW
The name of the scientist responsible for forming the foundations of genetics is __________.
Why did this scientist chose garden peas to perform his experiments?
Heredity can be defined as ________
Genetics can be defined as _______
What is difference between dominant and recessive traits?
Explain the difference between the P, F1 and F2 generations. What type of genetic characteristics can be observed in each one?
The difference between a gene and an allele is?
Homozygous is?
What is codominance?
What is incomplete dominance?