1. “Why We Look the Way We Do”
Heredity and Genetics
“Why We Look the Way We Do”

2. What is Heredity?
Heredity = the passing on of traits from one generation to the next.

3. What is a Trait? A trait is a specific characteristic that is unique.
Traits affect the way we look
Traits affect how our bodies function
Traits are inherited
Examples are hair color, eye color, handedness, etc.

4. How Do We Keep Track of Traits?
We use a pedigree chart to keep track of how traits are passed on from generation to generation.

5. What is a Pedigree?
A pedigree is a diagram that shows the history of a trait as it is passed from one generation to the next.
Pedigrees indicate patterns
Pedigrees identify carriers of genetic disorders
Pedigrees are useful for genetic counseling
Example: a pedigree is like a family tree for one trait.

6. Rules For Making A Pedigree
Females are represented by circles
Males are represented by squares
Mother/Father couples are connected by a line
Offspring are shown oldest on the left to youngest on the right
Half-shaded circle represents a female carrier for the trait
Half-shaded square represents a male carrier for the trait
Full-shaded circle represents a female with the trait
Full-shaded square represents a male with the trait

8. A Pedigree
Parents
Offspring
Youngest to Oldest
Trait:

11. What is Mendelian Genetics?
Gregor Mendel was an Augustinian monk who lived in the late 19th century and, through studying peas, developed the basis for the science of Genetics still used today.

14. What Kinds of Traits Are There?
Traits are either Dominant or Recessive.

15. Dominant Trait
A dominant trait is a trait that is always expressed, or shown.
Examples are brown hair, brown eyes, right handed

16. Recessive Trait
A recessive trait is a trait that is covered up or seems to disappear.
Examples are blonde hair, blue eyes, left handed

18. Where Do Traits Come From?
Factors that make up an individual come from both parents.
The trait information is passed on from generation to generation in the form of genes.

19. What are Genes?
A gene is a specific location on a chromosome that controls a certain trait.

20. Where Do Genes Come From?
An individual needs 2 genes for each trait – one gene from each parent.
This gene pair is called an allele.
One gene comes from the sperm cell (from the Father)
One gene comes from the egg cell (from the Mother)

21. How Do Genes Get Their Information?
A chromosome is a structure in the cell that contains the genetic information.
This information is passed on from one generation to the next generation.

23. Gene Representation How Do We Write Our Genetics?
The name of the dominant trait determines what letter is used to represent the gene.
Use a capital of the first letter of the dominant trait to represent the dominant gene.
Use a small version of the first letter of the dominant trait for the recessive gene.
Example: Right-handedness is the dominant trait so use R for the dominant gene and use r for the recessive gene for Left-handedness.
Example 2: Tall is the dominant trait so we use T and we use t for the recessive gene for Short.

24. How Are Genes Expressed?
Traits are how our genes show and since traits are formed from two genes, they are described by the combination of genes that make the pair.
Traits are described as either:
homogeneous, (pure)
heterogeneous, (mixed)

25. Homozygous = Pure (Homogeneous)
Pure Dominant: the. individual only has genes for the dominant trait
Example: TT = a pure tall individual has only tall (T) genes.
Pure Recessive: the individual only has genes for the recessive trait.
Example: tt = a pure short individual has only short (t) genes.

26. Heterozygous = Mixed (Heterogeneous)
A heterozygous individual has one dominant gene and one recessive gene for a trait. The result is the dominant gene is the one expressed, or shown.
Example: Tt = a heterozygote tall individual has both tall (T) and short (t) genes but looks tall.

27. How Do We Predict Offspring?
A Punnett Square is a way to show the possible combinations of genes that offspring of parents could have.

28. Punnett Square

32. What is Phenotype? Phenotype is the way that we look or appear.
Example: brown eyes, blonde hair, tall

34. What is Genotype? Genotype: is the genetic make up for a trait.
Example: Homozygous brown; BB = pure brown: (both genes are the same)

38. Right-handed Parents (RR)x(Rr) Trait: Height Tall Parents (Tt)x(Tt)
Trait: Handedness
Right-handed Parents (RR)x(Rr)
Trait: Height
Tall Parents
(Tt)x(Tt) R T t RR TT Tt r Rr tT tt
Results:
Phenotypes: 100% Right handed 75% Tall
25% Short
Genotypes: 50% RR, homozygous right 25% TT, homozygous tall
50% Rr, heterozygous right 50% Tt, heterozygous tall
0% rr, homozygous left 25% tt, homozygous short

39. Blue-eyed Parents (bb)x(bb) Trait: Handedness
Trait: Eyecolor
Blue-eyed Parents (bb)x(bb)
Trait: Handedness
Pure Right and Pure Left handed Parents (RR)x(rr) b R bb r Rr
Results:
Phenotypes: 100% Blue-eyed 100% Right-handed
Genotypes: 100% bb, homozygous blue 100% Rr, heterozygous
right-handed

40. How Do Genes Control Traits? Deoxyriboneucleic Acid
DNA is the “instruction code” that the genes use to form traits.
DNA is long threads of material found in all cells.
DNA contains the “master code” that instructs all cells in their daily jobs.
Genes are short pieces of DNA that make up our chromosomes.
Each piece of DNA that is related to a gene makes up one trait.

41. Structure of DNA
DNA looks like a twisted “ladder” made of chemical compounds called bases.

42. Models of DNA

43. How Bases Make Up DNA
There are 4 types of bases in DNA: Adenine, Guanine, Cytosine and Thymine.
These bases fit together like puzzle pieces
Adenine with Thymine
Cytosine with Guanine

44. But What ARE Genes? Genes are pieces of DNA that make up a trait
Different genes consist of different arrangements of the Adenine, Thymine, Cytosine, Guanine bases.
These bases can be arranged to form different proteins (chemical messages)
These messages control different traits (some determine how we look, some determine how we feel and function).
There are many millions of possible combinations of these 4 bases – this accounts for the differences, and similarities, between life forms on earth.

45. Traits from Proteins
All characteristics are affected by the DNA in the cells of the individual organism.
These characteristics are called traits. Traits depend on the types of proteins that the 4 bases (A,C,G,T) make up.

46. How Do We Look The Way We Do?
Parents pass on copies of their DNA to their offspring.
The DNA from each parent combines to form the DNA of the offspring.
How the offspring develops depends on the instructions coded in the DNA donated by both parents.
Offspring are similar to parents, but different due to the many possible combinations of the 4 bases.
Every individual is unique.

47. How Can We Use Genetics? To predict looks of offspring
To predict risks of diseases/defects …

48. Genetics Help Predict Diseases
Sickle-cell Anemia is a genetically inherited disease where red blood cells are misshaped.
Red blood cell shape is an inherited trait.
Sickle-cell shape vs Normal cell shape
Sickle-cell anemia is cause by incomplete dominance.

49. Advances in Genetics
We have an increased understanding of certain diseases that are inherited.
We have increased knowledge of many health conditions (treatment, prevention, and cure).
Example: Down Syndrome is caused by an extra chromosome.