1. Mendel’s Contribution to Genetics

2. Gregor Mendel (1822 – 1884) Work with Pea plants
simple genetic make up.
Cross-pollinate – have two different parents. or
Self-pollinate – have only one parent.
Mendel is called “the father of genetics” for his studies on plant inheritance.
Formed through discovery the 3 basic principles of genetics.

3. Principle of Dominance
Mendel’s principle of dominance states that some forms of a gene or trait are dominant over other traits, which are called recessive.
A dominant trait will mask or hide the presence of a recessive trait.

4. Principle of Segregation
This principle states that when forming sex cells, the paired alleles separate so that each egg and sperm carries one copy of the paired alleles.
The two forms of the allele come together again during fertilization.

5. Principle of Independent Assortment
This principle states that each pair of alleles segregate independently (crossing over)during the formation of the egg or sperm.

6. Genetic Expression

7. Genes
Genes are portions of DNA that determine hereditary characteristics.
Each person has a pair of alleles for each trait.
Alleles are different molecular forms of a gene.

8. Dominant and Recessive Genes
The dominant gene are the expressed genes.
BB (Both alleles are dominant= dominant trait expressed)
Bb (One dominant and one recessive = dominant trait expressed)
In order for expression of the recessive gene to occur, both alleles must be the recessive ones.
bb (both recessive = recessive trait expressed)

9. Genotype and Phenotype
Genotype is the term used for the combination of alleles inherited from the parents.
What the genes look like: ex. Bb, BB, bb
Phenotype is the physical expression of the traits. The phenotype does not necessarily reveal the combination of alleles.
What you look like: ex. Brown eyes, dark hair

10. When studying the expressions of traits:
Geneticists use letters as symbols for the different traits.
Capital letters are used for dominant alleles.
Lowercase letters for recessive alleles.

11. Looking at Alleles
If an individual inherits two of the same alleles (either dominant or recessive) for a particular characteristic, the individual is homozygous (Homo – same). Ex. BB, bb also called purebred
If the offspring inherits one dominant allele and one recessive allele, the individual is heterozygous (Hetero – different).Ex. Bb also called hybrids

12. Punnett Squares
A Punnett Square is used to express the possible combinations for a certain trait an offspring may inherit from the parents
The Punnett Square shows possible genotype and phenotypes of one offspring.
Monohybrid cross – is a cross involving one trait.

13. Completing a Punnett Square Cont.:

14. Modes of Inheritance

16. Sex-Linked Traits:
Sex chromosomes are the 23rd pair of chromosomes and are sometimes called X or Y chromosomes.
Females have the genotype XX
In females, one X comes from their mother and one X comes from their father.
Males have the genotype XY
In males, the X chromosomes comes from their mother and the Y chromosome comes from their father.

18. Sex-Linked Traits Continued:
Sex linked traits are carried on the X chromosome.
Color blindness and hemophilia are two examples.
In sex-linked traits – it is more likely that males will have the condition since they only have one X Chromosome.
Males do not have another X chromosome or a duplicate copy of the gene.
A female that has a recessive gene on one X chromosome is a carrier for that trait.

19. Incomplete Dominance:
A situation when one trait is not completely dominant over the other.
Think of it as a blending of the two traits.

20. Incomplete Dominance Continued:
A cross between a red four o’clock and a white four o’clock demonstrate this point.
The offspring in this cross will be pink

21. Incomplete Dominance Continued:
Palomino horses are the blend of white and chestnut (brown) coats.
Two Palomino horses will produce: 25% white coats, 25% chestnut coats and 50% palomino coats.

22. Co-Dominance
Both alleles are dominate, so both traits appear in the offspring and contribute to the phenotype.

23. Roan Horse

24. Genetic Pedigrees

25. What is a Pedigree?
A pedigree is a graphical chart used to identify the lineage of individuals.
They are used when the genotype of individuals is unknown.
Pedigrees also help to show inheritance of genetic disorders within families.

26. Pedigrees:
Pedigrees represent males with a square and females with a circle
People born or diagnosed with a disorder are often shaded or colored
Horizontal lines indicate matings
Vertical lines indicate offspring arranged from left to right in order of their birth
Each pedigree has a key to help you determine the best way to understand the information displayed.

27. Example of Pedigree:

28. Genetic Disorders and Diseases

29. Hemophilia

30. Hemophilia: “The Royal Disease”

31. Down’s Syndrome

32. A person with Down’s Syndrome inherited an extra copy of chromosome 21, and therefore, has 47 total chromosomes instead of the usual 46 found in humans.
Nondisjunction has occurred in this situtation – the failure of one pair of homologous chromosomes to separate during Anaphase I of Meiosis.

33. Other Genetic Disorders and Diseases
Sickle-cell anemia
Phenylketonuria (PKU)
Cystic Fibrosis

34. Tay-Sachs
Found on chromosome 15 – blindness, deafness, difficulty swallowing and eventually death. Children don’t live past the age of 3.