1. The science of heredity Frank Gregorio
Genetics
The science of heredity
Frank Gregorio

2. GREGOR MENDEL – Father of Genetics
He experimented with pea plants.
They worked well because they reproduce quickly and create a large number of offspring in one generation.

3. Heredity- The passing on of characteristics from parents to offspring.
Traits- Characteristics that are inherited.
Ex: Brown or
Blue Eyes

4. DOMINANT GENE –Stronger gene – This trait will show up if it is present in an organism. (CAPITAL LETTER)
RECESSIVE GENE – Weaker gene. This trait will be hidden in the organism. (LOWER CASE LETTER)
Each organism receives 2 genes (alleles) from each parent.

5. HOMOZYGOUS DOMINANT OR PUREBRED HOMO = The same 2 Recessive Genes
The Rules:
2 Dominant Genes
ex) B B (capital letters)
HOMOZYGOUS DOMINANT OR PUREBRED
HOMO = The same
2 Recessive Genes
ex) b b
HOMOZYGOUS RECESSIVE OR PUREBRED RECESSIVE

6. 1 Dominant gene and 1 Recessive gene
ex) B b = HETEROZYGOUS OR HYBRID.
HETERO = Different
CAPITAL LETTER ALWAYS GOES FIRST

7. PHENOTYPE – The trait expressed (observed) in an organism
PHENOTYPE – The trait expressed (observed) in an organism. The physical trait.
GENOTYPE – The two genes that determine a specific inherited trait.

8. STRAIGHT: HAIR TEXTURE
Example
STRAIGHT: HAIR TEXTURE
DOMINANT
TRAIT
RECESSIVE
SYMBOL
CURLY x C
STRAIGHT X c
WHAT ARE POSSIBLE COMBINATIONS OF GENOTYPES AND PHENOTYPES FOR HAIR TEXTURE (CURLY/STRAIGHT)?

9. ANSWER
GENOTYPE PHENOTYPE
CC  CURLY  HOMOZYGOUS DOMINANT
Cc  CURLY  HETEROZYGOUS
cc  STRAIGHT--  HOMOZYGOUS
RECESSIVE

10. Review Genotype – Genetic makeup
Ex. Bb, Gg, Tt
Phenotype – physical appearance as the result of the genotype.
Ex: Brown vs. blue, Green vs. yellow, Tall vs. short.
Dominant – Traits that are expressed
Recessive – Traits that are hidden.
Hybrid/Heterozygote – The offspring resulting from a cross with parents with contrasting traits.
Ex: Brown and Blue eyed parents (BB vs bb = Bb)

11. P GenerationF1 Generation
Mendel selected a 6 ft tall pea plant and a 2 ft tall pea plant for the parent generation.
All of the offspring (F1 generation) were tall.

12. F1 Generation
Mendel let the tall F1 pea plants (offspring of P generation) pollinate with themselves.
Ex: F1 x F1
The offspring (F2 generation) were ¾ tall and ¼ short.
This makes a 3:1 ratio of Dominant:Recessive

15. Test Cross – Crossing a homozygous recessive allele with an unknown dominant genotype.
TT x tt = 100 % Tall
Tt x tt = 50 % Tall, 50 % short 

16. Monohybrid cross – hybrid cross, because only one pair of contrasting traits is being studied.
Dihybrid cross – crossing two different traits.

17. Punnett Squares

18. Example 1
BB x bb

19. Example 2
Black hair x White hair Rabbit Bb x bb

20. Example 3
Widow’s Peak x Widow’s Peak WW x Ww

21. Mendel’s Laws
Law of Dominance- When an organism is hybrid for a pair of traits, only the dominant trait can be seen in the hybrid.
Ex. Brown Eyes (BB) x Blue Eyes (bb) = Brown Eyed offspring (Bb)

22. Mendel’s Laws
2. Law of Segregation- Every gene has 2 alleles and when gametes are produced, each gamete receives one of these alleles.
A a A a

23. Mendel’s Laws
3. Law of Independent Assortment-Different traits are not inherited together. -Ex: No connection between Pea color, Pea shape, Pod Shape, Flower Color. All are inherited separately. One does not affect the other being inherited.

25. Pedigree - a table or chart recording a line of ancestors.

28. Incomplete Dominance – Heterozygotes have an intermediate phenotype.
Ex. Crossing white and red flowers.

29. Codominance – Two dominant alleles are expressed equally at the same time.

30. Co-Dominance

31. Multiple alleles – Traits with more than two alleles.
Ex. ABO blood type.

33. Linked Genes- Genes that are typically inherited together.
Example: Red hair and freckles

34. Sex-linked Trait- Traits controlled by genes located on sex chromosomes (X and Y).
Ex: Red-Green Color Blindness, Hemophilia

35. Sex-Linked Inheritance:
Men are likely to be affected (only 1 X chromosome)
Woman are likely to be carriers (2 X chromosomes)

36. Polygenic Inheritance- The inheritance of a trait that is controlled by two or more genes.
Ex: Skin color, Hair Color, Height

37. The Environment Influences Gene Expression, too!
External Environment Influences:
Temperature
Nutrition
Light
Chemicals
Infectious Agents (Viruses, Bacteria, Parasites)

38. Internal Environment Influences: Ex: Hormones, Body Differences
Female or Male
Ex: Hormones, Body Differences