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Heredity
Review of Traits
A trait is a characteristic of something
Traits can be both behavioral or physical
Inherited traits are coded in the DNA of the organism
All organisms contain DNA, so all organisms pass on traits
Examples of inherited traits
hitchhiker thumb
Is this a physical trait or a behavioral trait?
Examples of inherited traits
widow’s peak hairline
Is this an inherited trait or an acquired trait?
Examples of inherited traits
attached earlobes
How many people in the class have this inherited trait?
Examples of inherited traits
tongue rolling
Is this a physical trait or a behavioral trait?
Examples of inherited traits
hand clasping
Is this a physical trait or a behavioral trait?
What determines traits? Traits are written
on chromosomes
Chromosomes come in pairs
One chromosome comes from mom
One chromosome comes from dad
What determines traits?Is this a plant or animal cell?
What evidence suggests your inference?
Each particular section of a
chromosome codes for a gene
Humans have about 25,000 genes – we are still discovering!
What determines traits? Each gene codes for a
protein that will help determine a trait
The different versions of a trait are called alleles.
For instance, the same spot on matching chromosomes could contain an allele for straight thumb or an allele for hitchhiker thumb.
What determines traits?
Alleles are kinda like different stitching on the pockets of different brands of jeans
They perform the same function, but are slightly different
Allele for “flying bird”
Allele for “w”
What determines traits?
Your unique alleles determine your many unique traits
No two humans could be identical, because there are almost an infinite number of gene combinations
How do we read the code? The genotype is
the code written on the DNA
The phenotype is the resulting appearance
(pheno is like photo)
How do 2 alleles make 1 trait?
Dominant alleles are like class clowns – you always know if they are in the room.
Recessive alleles are like shy people – you don’t know they are there unless they are alone
How do 2 alleles make 1 trait?
If a dominant allele is present in the genotype, that allele’s phenotype will show outwardly.
Example, Straight Thumb is dominant over hitchhiker’s Thumb
H h
How do 2 alleles make 1 trait?
The only way a hitchhiker’s thumb shows up in the phenotype is if 2 recessive traits are inherited in the genotype.
H + H =
H + h =
h + h =
