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

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

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.

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.

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.

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

A Pedigree Parents Offspring Youngest to Oldest Trait:

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

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

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

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

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

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

Where Do Genes Come From? An individual needs 2 genes for each trait – one gene from each parent. alleleThis 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)

How Do Genes Get Their Information? chromosome 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.

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.

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: –h–homogeneous, (pure) –h–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 Phenotype? Phenotype Phenotype is the way that we look or appear. –Example: brown eyes, blonde hair, tall

What is Genotype? Genotype Genotype: 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: Height Tall Parents (Tt)x(Tt) RRTt RRRTTTtTt rRrRrRrRrttTtTt Results: Phenotypes: 100% Right handed75% Tall 25% Short Genotypes: 50% RR, homozygous right25% TT, homozygous tall 50% Rr, heterozygous right50% Tt, heterozygous tall 0% rr, homozygous left25% tt, homozygous short

Trait: Eyecolor Blue-eyed Parents (bb)x(bb) Trait: Handedness Pure Right and Pure Left handed Parents (RR)x(rr) bbRR bbbrRrRrRrRr bbbrRrRrRrRr Results: Phenotypes: 100% Blue-eyed100% Right-handed Genotypes: 100% bb, homozygous blue100% Rr, heterozygous right-handed

Incomplete Dominance? is when neither gene is dominant the recessive trait is not fully hidden. The result is a “mixed” genetic trait that is neither dominant nor recessive. RRWW RW –Example: Red (RR) x White (WW) flowers yield Pink (RW)

Codominance This is when both traits are seen in the phenotype

Codominance

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. Genes 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.

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

Models of DNA

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

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. traitsTraitsThese characteristics are called traits. Traits 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 Genetics? To predict looks of offspring To predict risks of diseases/defects …

Genetics Help Predict Diseases 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 incomplete dominance.Sickle-cell anemia is cause by incomplete dominance.

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