Mr. Chapman
DNA & Heredity
Forensics 30
DNA & Heredity
Heredity:
– The study of how characteristics are passed from generation to
generation is
__________________.
– Give three examples of inherited characteristics.
– What characteristics can’t be inherited?
How do humans inherit genetic information?
Remember: Humans receive half of their DNA from their _____________ and half of
their DNA from their ______________.
Where do we get our mitochondrial DNA from? ________________________
So, for each gene that we possess we receive one ____________ from ______ and one
____________ from _______.
Look at the pictures on the right of the slide. Notice that out of the 4 alleles, only one of
them has the affected gene. However, half of the children acquire the affected issue.
In the next example, notice that even some children with the S alleles do not receive the
illness. This is due to the fact that the allele for the illness (sickle cell anemia) is
recessive.
Mr. Chapman
DNA & Heredity
Forensics 30
Alleles and Traits
If an individual has two of the same alleles they are said to be __________________ for
that trait.
If an individual has two different alleles they are said to be _____________________ for
that trait.
One allele will usually be dominant, and the other one will usually be recessive. If a
dominant allele is present, then the person who has it will definitely express that trait.
A genotype is ____________________________________________________, such as
HH, Hh, or hh.
A phenotype is ___________________________________________________, such as
whether a person has Huntington’s disease or does not have Huntington’s disease.
Punnett Squares
If we know the genotypes of both parents for a particular trait, we can use a Punnett
square to predict the genotypes of the offspring.
Example: A blue eyed-man and a heterozygous brown-eyed woman have a child. What
is the change that the child will have blue eyes? Blue is the recessive colour.
Alleles, Traits and Blood Types
Mr. Chapman
DNA & Heredity
Using a Punnett Square, find the probabilities of the following:
Mother AA Father AB
Mother AB Father AB
Mother AA Father BB
Mother AO Father OO
Forensics 30
Mr. Chapman
DNA & Heredity
Forensics 30
Heredity, Genetics & DNA Identification
 Most of the human genome is the same in all humans, but some variation does
exist does exist.
 This variation results in DNA sequences of different length and base pair
sequences.
 These differences are called polymorphisms.
 We can pass these differences onto our offspring.
Paternity
 Within the last two decades we have been able to improve techniques for
identifying a child’s biological parents (in most cases fathers).
Population Genetics and Forensics
 Population genetics is the study of variation in genes among a group of
individuals.
 The proportion of people that have a particular trait is determined by the
proportion of alleles available in the population gene pool.
– Ex: Blue eye are rare in Asian populations, but common in northern
European populations.
 We can compile databases for populations to determine a particular alleles
frequency (percentage).
 We then use this information when investigating forensic DNA samples.
 Calculation are then made to determine the probability that a random person in
the population would have the same alleles as a suspect or potential parent.