Transcript DNA heredity

CATALYST

Recall and Review:
–
–
–


1
What are chromosomes?
What are genes?
What are alleles?
How do these terms relate to DNA?
How do these terms relate to the
characteristics that you and I possess?
Chromosomes,
Genes & Alleles
Human Chromosome
Magnified
Chromosomes,
Genes & Alleles
Human Chromosomes
(Karyotype)
DNA Fingerprinting
you will be able to:
 explain how traits are passed on from parent to
child.
 Predict the probability for traits to be passed on to
offspring.
 Understand how paternity tests are performed.
4
Heredity

Heredity: the passing of characteristics from
parent to offspring
–
–
–

5
The study of how characteristics are passed from
generation to generation is genetics.
Give three examples of inherited characteristics.
What characteristics can’t be inherited?
How do humans inherit genetic information?
Heredity

Remember: Humans receive half of their
nuclear DNA from their mother and half from
their father.
–

Think: Where do we get our Mitochondrial DNA
from?
So, for each gene that we posses we receive
one allele (form) from mom and one allele
(form) from dad.
Heredity
Example


For the trait pictured,
Mom has two of the
same alleles and Dad
has two different alleles.
Only one allele from
each parent will be
passed to their children.
Would these be the
result every time?
Heredity
Example

One more time…
Heredity
Example

What is occurring in
the image to the right?
Alleles & Traits

Alleles can be expressed in different ways.
–
Some alleles are dominant. We represent these
with a capital letter (i.e. A, B, T).

–
What does dominant mean?
Some alleles are recessive. We represent those
with a lower case letter (i.e. a, b, t).

What does recessive mean?
Alleles & Traits

If an individual has two of the same alleles
they are said to be homozygous for that
trait.
–

Can you think of two examples for eye color using
the letter “Bb”.
If an individual has two different alleles they
are said to be heterozygous for that trait.
–
Can you think of an example for eye color?

Describe the genetic
makeup for each
individual pictured, use
the letter “Aa” for the
trait.
Alleles & Traits
Example
Here is an example of how the dominant
allele for Huntington’s
disease (a rare
neurological
condition) is inherited.
 A genotype is an
individual allele
combination
 A phenotype is how
the gene is expressed

Alleles & Traits:
The Punnett Square

If we know an
individual’s genotype
we can use punnett
squares to predict the
probability for offspring
genotypes.
Alleles & Traits:
The Punnett Square

Humans have 3 alleles for blood type:
IA - Type A blood allele
– IB – Type B blood allele
– i – Type O blood allele
**Both A and B are dominant (how we get AB blood
type)
–

What are the possible genotypes for each blood
type? (there are 6)
Alleles & Traits:
The Punnett Square

Using a Punnett Square, find the probabilities
for the following:
–
Mom IA IA
– Dad IA IB
Mom IA IB
Dad IA IB
Mom IA IA
– Dad IB IB
Mom IA i
Dad i i
–
16
Forensic Science: Fundamentals & Investigations, Chapter 7
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).
How is this possible? How would we go
about doing this?
Population Genetics & 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.
Population Genetics & Forensics



We can compile databases for populations to
determine a particular alleles frequency
(percentage).
We then use this information we 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.
Summarize

Summarize what you have learned (or
reviewed) today in a 3-5 sentence
paragraph.