1. Introduction to Genetics
Chapter 10
Introduction to Genetics

2. Theories emerged…. Including:
A Brief History
In the past, people did not understand how traits were inherited, but there were many guesses based on things that could be observed.
Theories emerged…. Including:
Blending Theory - offspring are a straight mix
Golden Doodle

3. Who was Gregor Mendel? GENETICS – study of heredity
He was known as the “FATHER OF GENETICS”
He discovered how traits were inherited
GENETICS – study of heredity
HEREDITY – the passing of traits from parents to offspring

4. Mendel’s Peas Mendel did his study on pea plants
which have many traits
tall/short
purple /white flowers
round/wrinkled seed

5. Traits in Pea Plants

6. Pea plants can be self-fertilized or cross-fertilized

7. True-Breeding Plants -always create plants that look like themselves (self breeding plants)
Hybrids – offspring of true-breeding plants (cross breeding plants)
HYBRIDS

8. Some traits are dominant over others.
Tall x Short = all tall offspring (hybrids)
*Tall is the dominant trait T
* Short is recessive t

9. Mendel discovered that each trait is controlled by two factors (alleles)
Genes – factors that determine your traits
Genes are located on chromosomes

10. Genes Genes- 1. Composed of DNA
2. Located at permanent locations on chromosome
3. Each chromosome may
contain 100’s of genes.

11. Essential Question: What is an allele?
Allele- pair of genes that carry the same trait and are found at the same location on pairs of homologous chromosomes

12. Alleles

13. Explaining the Cross
When a parent makes sperm or eggs, their genes separate         (PRINCIPLE OF SEGREGATION)
The GAMETES (egg or sperm) contain either a T allele (tall) or a t allele (short)

14. Crossed tall pea plants with short pea plants (parental generation).
ESSENTIAL QUESTIONS: What are dominant and recessive alleles? How does the allele affect the phenotype of an individual?
Gregor Mendel
Crossed tall pea plants with short pea plants (parental generation).
All the offspring (first filial generation-F1) were tall.
Later crossed F1 generation and discovered ¾ tall and ¼ short 9 produced over 1000 plants).
Used 7 contrasting traits.

15. Pea Characteristitics

16. Based on Mendel’s work, scientists have come up with the Law of Dominance.
Law of Dominance- The allele that appears or shows up in an individual with two different alleles.

17. ESSENTIAL QUESTIONS: What are dominant and recessive alleles
ESSENTIAL QUESTIONS: What are dominant and recessive alleles? How does the allele affect the phenotype of an individual?
Basics of Genetics:
Dominate Allele-
a. The allele that is expressed (shown) in an allele pair
b. Expressed by a capital letter.
Recessive Allele-
a. The gene that is present but not expressed
in an allele pair. Ex. Tt
b. Expressed by a lower case letter.

18. Essential Question: What is a genotype and a phenotype?
Genotype-genetic makeup
Phenotype-physical appearance
Homozygous (pure)-two alleles for the same trait are the same. Exs. TT, tt
Heterozygous (hybrid)-two alleles for the same trait are different. Ex. Tt

21. GENOTYPE - what genes, letters, the organism has (TT, Tt, tt)
PHENOTYPE  - what it looks like (tall or short)
TT x tt
Tt x Tt
TT Tt Tt tt

22. What does this letter actually represent?
11. What is the diagram shown below called?
What does this letter actually represent?

23. Check for understanding
1.  A one-eyed purple people eater is crossed with a two eyed purple people eater.  All of their offspring have two eyes.   Which trait is dominant?

24. 2. If you use the letter E for this gene
2.  If you use the letter E for this gene.   What is the genotype of the offspring if the parents were EE x ee
    
3.  If you crossed the offspring with each other?  How many of the new offspring would you expect to have two eyes?
EE = two eyes
Ee = two eyes
ee = one eye

25. DIHYBRID CROSSES - involve 2 traits - RrYy x RrYy
- rabbits - guinea pigs
Set up a square to show this cross:
Rryy x rrYy

26. Neither allele is completely dominant over the other allele.
Incomplete Dominance
Neither allele is completely dominant over the other allele.
A heterozygous phenotype
A mixture of the two

27. Four-o’ clock flowers Incomplete dominance Neither Red (R)
or White (W) is dominant
When a homozygous red flower (CR CR)
Mix with a homozygous white flower (CW CW ), the alleles blend in the hybrid (CR CW) to produce pink flowers

28. Andalusian Chickens Incomplete dominance Neither Black (B) or
White (W) are dominant
The offspring of a black feathered chicken (CB CB ) and a white feathered chicken (CW CW ) are blue (CB CW ) – BLUE Chickens!

29. Codominance - alleles are both expressed
Incomplete Dominance - neither is expressed
Ex: Red flower x White flower = Pink
Codominance - alleles are both expressed
Ex: Red cow x White Cow = Roan

30. Multiple alleles and CODOMINANCE
Heterozygote express the distinct traits of both alleles
Example: Human blood system
A, B, AB, or o
The letters are antigens found on the surface of red blood cells
Red blood cells may be coated with one protein (A), the other (B), both (AB), or neither (O)
There are six possible genotype combinations

31. Multiple Allele Traits - more than two alleles control the trait
Example: Blood Type
Blood Type
Genotype A
IA IA, IA i B
IB IB, IB i AB
IA IB (codominant) O
ii (recessive)

32. Phenotype
Genotype
Protein on RBC (antigen)
Antibodies in the blood plasma
Type A
IA IA and
IA i A b
Type B
IB IB and
IB i B a
Type AB
IA IB
A and B
Type O ii
a and b

33. ABO Blood System
Antibodies (proteins) also found in the blood serum that attacks foreign antigens
Blood A has antibody Anti-B
Blood B has antibody Anti-A
Blood AB has no antibody
Blood O has Antibody Anti A and B
Blood O is the universal donor
Blood AB can receive any blood type

34. Rh Factor Rh positive (Rh +) has protein in blood
Rh negative (Rh -) has no protein in blood
Rh+ is dominant

35. Some of us have it, some of us don't
Some of us have it, some of us don't. If it is present, the blood is Rh positive, if not it's Rh negative. So, for example, some people in group A will have it, and will therefore be classed as A+ (or A positive). While the ones that don't, are A- (or A negative). And so it goes for groups B, AB and O.
85% of the population is Rh positive, the other 15% of the population is running around with Rh negative blood.

36. Do you know which blood group you belong to?
According to above blood grouping systems, you can belong to either of following 8 blood groups:
Do you know which blood group you belong to?

37.                                                                            
A person with Rh- blood can develop Rh antibodies in the blood plasma if he or she receives blood from a person with Rh+ blood, whose Rh antigens can trigger the production of Rh antibodies.
A person with Rh+ blood can receive blood from a person with Rh- blood without any problems.

38. Each pair of alleles adds something to the resulting phenotype.
Definition
Some traits are determined by the combined effect of two or more pairs of alleles. These traits are called polygenic traits.
Each pair of alleles adds something to the resulting phenotype.

39. Polygenic traits are continuous
Because so many alleles contribute to the final phenotype, a variety of phenotypes can occur!
For example, height is a polygenic trait.

40. POLYGENIC TRAITS - when many genes control one trait, usually resulting a wide RANGE of phenotypes
Examples: Skin color, height, eye color (human)

41. Sex-linked genes
The eggs contain a single X chromosome and sperm contain either an X or a Y
Sex of the offspring depends on whether the sperm that fertilizes the egg has an X or a Y
Any gene located on a sex chromosome (X) is called a sex-linked gene
Most are found on the X (2,000) and few on the Y (24)

42. Written as a XRXr for heterozygous.
Sex-linked traits
Written as a XRXr for heterozygous.
Y chromosome carries no allele and the phenotype is dependant upon the woman’s allele
Therefore, males carry one allele for a sex-linked trait.

43. Red-green blindness Hemophilia (inability of blood to clot)
Sex-linked disorders
Red-green blindness
Hemophilia
(inability of blood to clot)