Nothing flashy, but a quick review of inheritance followed by a silent tutorial on how to use/read a pedigree. Remember a few vocabulary that we discussed:

Autosomal chromosome– this is referring to your body chromosomes
Sex chromosome – this is referring to your sex chromosomes (X & Y for humans)
Dominant – this is referring to an allele for a trait that can mask a recessive trait (typically shows in every generation)
Recessive – this is referring to an allele for a trait that is masked by a dominant trait (typically skips a generation)

Gregor Mendel & Punnett Squares

The following video clip reviews how to create and fill out Punnett squares. Now we like to use letters that represent what we are looking at and they should always be the same for dominant and recessive. When we write heterozygous allele pairs, they should always have the dominant allele written first.

If you want to go a little furthur and review some of the concepts from today (before we make it more complicated next class) watch the following lesson.


The following video shows the stages of meiosis. Remember that meiosis is the process of producing haploid gametes.

The only thing missing from this video is crossing over where genetic material is swapped between homologous chromosomes.

This second video includes crossing over and shows the same process in a little different way. Remember that Meiosis and Mitosis are similar processes, but the end result is different because Meiosis has a second division and produces haploid gametes instead of diploid body cells.

Mitosis Meiosis
Goal Identical Cells Sex Cells
(egg & sperm)
Divisions Divides Once Divides Twice
Outcomes 2 Identical Cells 4 Sex Cells
Chromosomes All 46 chromosomes are present
Only 23 chromosomes are present

Genetics Practice Problems

The following websites have some practice problems covering all types of genetics.

The second half of the second page we have not covered all of and some of it we will not cover, so keep that in mind.

Meiosis and Non-disjunction

The following clip looks at the stages of meiosis and does a good job explaining it.

The next clip identifies the differences between male and female gamete formation.

The following clip looks at the process of non-disjunction in meiosis II which can lead to the development of monosomies or trisomies.

The second clip looks at the process of a non-disjunction in meiosis I which can lead to the development of monosomies or trisomies.

Notice the number of chromosomes in each gamete. Notice the difference in what is occuring with the spindle. How does non-disjunction in meiosis I differ from non-disjunction in meiosis II?

EXTRA CREDIT: Why Pedigrees & Family Trees Matter…

You know I do not provide many opportunities in the way of extra credit, but I thought this would be a good one. If you ever questioned the value of studying and learning about pedigrees, genetics, inheritance, etc. This webquest will help you to learn that family medical histories can inform you about your risk of developing a chronic disease. You will also discover that lifestyle modifications can help to reduce your risk. Below is a worksheet taken from Teach.Genetics at the University of Utah that will lead you on a WebQuest dealing with Using Family History to Improve Your Health. Complete this worksheet for extra credit.

If you would like to take this one step further and look at your own family health history, there is a link to materials for your own family health history search (includes both English & Spanish forms).’s%20Your%20Story.pdf