Genetics

Why do offspring look like their parents?

•Parents pass half of their DNA to their offspring

•Heredity (Inheritance) - The passing of traits from one generation to the next

•Inherited Traits – characteristics that are passed from parent to offspring– Examples: Eye color,

Hair type, Face shape, Blood type

Chromosomes and Genes

•Chromosome – A structure found in the nucleus of a cell that contains DNA

•You have 46 chromosomes in every cell! (23 from mom and 23 from dad)

•Gene – A segment of DNA on a chromosome

How many genes are on this chromosome?

9

One Gene

•Our genes determine our traits

•Genes always come in pairs

•One gene from the pair is called an allele.

We talk about genes in 2 different ways:• Genotype – the pair of genes

(the 2 allele letters)• Phenotype – the physical

expression of the genes (what it looks like)

RrGenotype Phenotype

Dominant and Recessive Genes

•Dominant Trait – will be expressed in the phenotype when at least one UPPERCASE letter is present in the genotype– Dominant Genotypes:

RR & Rr

•Recessive Trait – will only be expressed in the phenotype if two lowercase letters are present in the genotype– Recessive Genotype:

rr

• Environmental factors can affect our traits– Nutrients affect: height,

weight, health– Temperature affects: fur

thickness, color of leaves– Injuries cause: scars– Sun Exposure affects: skin

color, hair color