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.

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

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: 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