Heredity and GeneticsHeredity and Genetics

“Why We Look the Way We Do”

What is Heredity?What is Heredity?

• HeredityHeredity = the passing on of traits from one generation to the next.

What is a What is a TraitTrait??

A trait trait is a specific characteristic that is unique.TraitsTraits affect the way we look

TraitsTraits affect how our bodies function

TraitsTraits are inherited• Examples are hair color, eye color,

handedness, etc.

How Do We Keep Track of How Do We Keep Track of Traits?Traits?

• We use a pedigree chart to keep track of how traits are passed on from generation to generation.

What is a What is a PedigreePedigree??

A pedigreepedigree is a diagram that shows the history of a trait as it is passed from one generation to the next.PedigreesPedigrees indicate patterns

PedigreesPedigrees identify carriers of genetic disorders

PedigreesPedigrees are useful for genetic counseling• Example: a pedigree is like a family tree for one

trait.

Rules For Making A Rules For Making A PedigreePedigree• 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

A PedigreeA Pedigree

Parents

Offspring Youngest to Oldest

Trait:

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.

What Kinds of Traits Are There?What Kinds of Traits Are There?

• Traits are either Dominant or Recessive.

Dominant TraitDominant Trait

A dominant traitdominant trait is a trait that is alwaysalways expressedexpressed, or shown.– Examples are brown hair, brown eyes,

right handed

Recessive TraitRecessive Trait

A recessive traitrecessive trait is a trait that is covered up or seems to disappear.– Examples are blonde hair, blue eyes,

left handed

Where Do Traits Come From?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.

What are Genes?What are Genes?

A gene gene is a specific location on a chromosome that controls a certain trait.

Where Do Genes Come Where Do Genes Come From?From?

• An individual needs 2 genes for each trait – one gene from each parent.

• This gene pair is called an alleleallele.– One gene comes from the sperm cell

(from the Father)– One gene comes from the egg cell

(from the Mother)

How Do Genes Get Their How Do Genes Get Their Information?Information?

A chromosome chromosome is a structure in the cell that contains the genetic information.– This information is passed on from

one generation to the next generation.

Gene RepresentationGene Representation

How Do We Write Our Genetics?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.

How Are Genes Expressed?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)

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.

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.

How Do We Predict Offspring?

A Punnett Square is a way to show the possible combinations of genes that offspring of parents could have.

Punnett Square

What is What is PhenotypePhenotype??

PhenotypePhenotype is the way that we look or appear.– Example: brown eyes, blonde hair, tall

What is What is GenotypeGenotype??

GenotypeGenotype: is the genetic make up for a trait.Example: Homozygous brown; BB = pure

brown: (both genes are the same)

Trait: Handedness Right-handed Parents (RR)x(Rr)

Trait: HeightTall Parents (Tt)x(Tt)

R R T t

R RR RR T TT Tt

r Rr Rr t tT tt

Results:Phenotypes: 100% Right handed 75% Tall

25% ShortGenotypes: 50% RR, homozygous right 25% TT, homozygous tall

50% Rr, heterozygous right 50% Tt, heterozygous tall 0% rr, homozygous left 25% tt, homozygous short

Trait: Eyecolor Blue-eyed Parents (bb)x(bb)

Trait: Handedness Pure Right and Pure Left handed Parents (RR)x(rr)

b b R R

b bb bb r Rr Rr

b bb bb r Rr Rr

Results:Phenotypes: 100% Blue-eyed 100% Right-handedGenotypes: 100% bb, homozygous blue100% Rr, heterozygous

right-handed

What Is Incomplete What Is Incomplete Dominance?Dominance?

• Incomplete dominanceIncomplete dominance is when neither gene that determines a trait dominates, so the recessive trait is not fully hidden.

• The result is a “mixed” genetic trait that is neither dominant nor recessive.– Example: Red (RRRR) x White (WWWW) flowers

yield Pink (RWRW)

How Do Genes Control Traits?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.GenesGenes are short pieces of DNA that make

up our chromosomes.Each piece of DNA that is related to a gene

makes up one trait.

Structure of DNA

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

Models of DNAModels of DNA

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

But What ARE Genes?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.

Traits from Proteins

• AllAll characteristics are affected by the DNA in the cells of the individual organism.

• These characteristics are called traitstraits. TraitsTraits depend on the types of proteins that the 4 bases (A,C,G,T) make up.

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.Every individual is unique.

How Can We Use How Can We Use Genetics?Genetics?

• To predict looks of offspring• To predict risks of diseases/defects• …

Genetics Help Predict Genetics Help Predict DiseasesDiseases

• Sickle-cell AnemiaSickle-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.incomplete dominance.

Advances in Genetics

• We have an increased understanding We have an increased understanding of certain diseases that are inherited.of certain diseases that are inherited.

• We have increased knowledge of We have increased knowledge of many health conditions (treatment, many health conditions (treatment, prevention, and cure).prevention, and cure).– Example: Down Syndrome is caused by Example: Down Syndrome is caused by

an extra chromosome.an extra chromosome.