CATALYST Recall and Review:

– 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?

1

Chromosomes, Genes & Alleles

Human Chromosome Magnified

Chromosomes, Genes & Alleles

Human Chromosomes (Karyotype)

4

Chapter 7 DNA Fingerprinting By the end of this chapter 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.

All Rights Reserved South-Western / Cengage Learning © 2009

5

HeredityHeredity

Heredity: the passing of characteristics from parent to offspring

– 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.

HeredityExample

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 results every time?

HeredityExample

One more time…

HeredityExample

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 & TraitsExample

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 Mom IA IB – Dad IA IB Dad IA IB

– Mom IA IA Mom IA i – Dad IB IB Dad i i

Forensic Science: Fundamentals & Investigations, Chapter 7 16

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 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.

Summarize

Summarize what you have learned (or reviewed) today in a 3-5 sentence paragraph.