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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