Monday, October 18, 2010

Karyotypes!! Say what!

Karyotype practice and vocabulary

The link above will take you to the second website we visited in class today.  There you can find practice terms and revisit how to make and read a karyotype.

The karyotype above is a normal male.  A technician preparing a karyotype would first arrange the chromosomes by length from longest to shortest.  Then they would match up pairs using banding patterns and centromere placement.

Just think of the way you would match up your socks when folding laundry.  You wouldn't pair the ankle sock with a tube sock.  Nor would you match a pink ankle sock with a white one.  Socks are matched by length and pattern just like chromosomes are matched by length and banding patterns.

Once the karyotype is arranged, then we make sure all the chromosome are normal:
   1. Correct length
   2. Correct banding pattern
   3. Correct # of chromosomes in each pair (none missing and no extra)
If any of these characteristics aren't met, then they seek to diagnose the disorder.

For example, above is a karyotype from a human breast cancer cell.  In a normal cell, there are 46 total chromosomes.  As you can see, the cell division process has been altered and the chromosomes are duplicating without any checks and balances.

In the above karyotype, this female is missing a whole piece of her chromosome.  So even though there are 46 chromosomes present, there is still a disorder because information is missing.

This patient has monosomy 7 because there is only 1 chromosome at pair 7.

Basically it boils down to Goldilocks again!  Too much information = problem.  Too little information = problem.

When meiosis goes wrong, the zygote's chromosomal make-up will suffer!

Sex-Linked Traits

In addition to determining the sex of a child, our sex chromosomes have traits on them that code for a variety of characteristics.  If there are recessive alleles at some of these traits, then the offspring can express those phenotypes.

Because females and males differ in their sex chromosomes, they also differ in the type of genes found on these chromosomes and the frequency at which they are expressed.

First things first, females have 2 X chromosomes (called X because during meiosis and mitosis they look like x's)  and males have XY (the Y gets its name from its shortened appearance in comparison to the X during cell division).

Every time a sperm and egg combine to form a zygote, there are the same 50/50 chance of having a boy or a girl.

To notate that a trait is found on a chromosome, we place our trusty upper and lowercase letters as superscripts to the right of the X or Y (it depends on whether the trait is X or Y linked as to where the letter will be placed).

Some other common sex-linked traits: color blindness and male pattern baldness.

Multiple Alleles

When there are more than 2 choices of allele at one gene locus, there are more phenotypes possible.  This pattern of inheritance is known as multiple alleles because where we have only seen 2 options of alleles (dominant and recessive or 2 different dominants), now we have more!

Human blood type is the classic example of multiple alleles that we studied in class.  There are 2 dominant alleles and 1 recessive making for 6 possible genotypes and 4 possible phenotypes.

Codominance - Roan Cows and Erminette Chickens

In some traits, there are dominant alleles that fight for expression.  Because they are both dominant, neither one wants to give up expression -- there will be NO blending of phenotype here.

Here are some classic examples!


These cows have possibilites of several colors of hairs that aren't a blend of the dominant and recessive phenotypes because the traits for each phenotype are dominant.
RR = red cow hairs
RW = red and white cow hairs
WW = white cow hairs

These chickens have feathers that are both white and black, but not grey.

BB = black feathers
BW = black and white feathers
WW = white feathers

The alleles for A and B are codominant so that if both are in the genetic code then they are expressed as blood type AB.

Wednesday, October 13, 2010


Be sure to check out the following link to practice pedigrees.

Make sure you open it in Internet Explorer (Mozilla Firefox doesn't work)!

Drag and Drop Pedigree Practice

Monday, October 11, 2010

Incomplete Dominance

So far according to Mendel's rules.....

Genes have two options (aka alleles): dominant and recessive.

Dominant traits always outweigh or mask the recessive traits.

Phenotype (outward appearance) is only dominant or recessive.


As we have pursued genetics as a science further, we quickly realized that not all traits are inherited in such a simple pattern.

Patterns that follow a similar pattern as the one Mendel put in place, but have some special circumstances are known as Non-mendelian patterns of inheritance.

This blog entry will focus on the pattern known as incomplete dominance.
In the picture above you should see 3 different colored snapdragon flowers: red, pink, and white.  The color of this flower is determined by a similar set of alleles as simple dominance, but the way in which those genes expressed differs.

In Punnett squares before we saw fewer phenotypes than genotypes because Aa and AA would reflect the same dominant phenotype.

In snapdragons, inheritance is expressed with a slight twist.  Homozygous dominant flowers are red (RR) and homozygous recessive flowers are white (rr), but the heterozygote (Rr) is a blend of dominant and recessive or in this case pink.

Wednesday, October 6, 2010

Probability by Punnett

Sir Reginald Punnett was born at the turn of the 20th century in England.  While in medical school at Cambridge University he became interested in research and starting working on reproducing Mendel's experiments with Bateson a professor at the college.

He noted the need for a mathematical tool to predict phenotype and turned to his mathematician cricket partner to help devise a tool.  Thus the Punnett square was born!
The picture above shows Reginald Punnett (left) with his professor and then colleague William Bateson.  As their experiments progressed, they soon realized the vast body of research that lay before them and the rest of the scientific community.  The started the first genetics department at Cambridge University.

Oh Punnett squares!  How we love thee!

Punnett squares allow scientists to predict how traits will be passed along in generations of the same species.
As you can see above, in a monohybrid cross (only focusing on 1 trait) you place the possible alleles (form of gene; like for height: tall and short) on each side being sure to keep the alleles for each parent on separate sides.

Then you simulate all the possible combinations of gametes by writing the allele donated from each parent in the box.  Use the arrows above to review how to place each allele in the appropriate box.

The resulting genotypes are the probable genetic combinations for the offspring of the parents.  Punnett squares more so prove what is not possible.

In the square above, all genotypes are possible because each parent has a copy of both dominant and recessive alleles making all combinations doable.

In addition to using your flashcards we made today, visit the link below to experiment with the Punnett square calculator.  It not only shows a square for monohybrid crosses, but also allows you to view dihybrid and trihybrid crosses!

Punnett Square Calculator

As we learn more types of inheritance, you will find that while phenotype possibilities expand, Punnett square set up really only comes down to the 6 scenarios you translated into flashcards.

Get to practicing your Punnett squares my lovelies!

Mendel and His Peas

Pictured above is the father of modern genetics: Gregor Johann Mendel.  He was born in 1822 in what is today the Czech Republic.  He was the son of a farmer that due to financial issues joined a monastery so that his pursuit of math and science would be paid for in full.

Interestingly enough he wanted to be a teacher but after several failed attempts to pass his teaching certification exam, he resorted to a life a research and eventually became head of the monastery.

Over a 7 year course of time (1860s), he bred around 30,000 pea plants keeping detailed observations of their lineage while he tracked traits such as flower color and plant height. 

Unfortunately, his attempts to publish his works were not received well and it wasn't until he died that his experiments were recognized for their attention to detail and proof of genetic inheritance.

Review Mendel's pea plant experiments by following the hyperlink and go through the animation.

His laws are the basis for current genetic theory and research:

1. Law of segregation
    Think back to meiosis.  Remember that of each pair of chromosomes (DNA) separates in anaphase II so  
    each gamete only has 1/2 of alleles.  For example, if your normal body cells have a dominant and  
    recessive allele for a particular trait, then each of your gametes will have either a dominant or a recessive 
    allele for that trait because the pairs separate in the final stages of meiosis.

     Click this link for a review of meiosis and be sure to follow the chromatids on their journey to see how 
     the pair of gametes are split from their homolog in the final stages.

2. Law of Independent Assortment  (Click the title for a review animation)
     Genes located on separate chromosomes are inherited without relying on one another.  Much like 2 cars 
     driving down the highway are able to make turns without prompting the other vehicle to follow suit.

Mendel put into works what may have taken scientists far longer to have discovered in present day.  Read the next blog to hear about Sir Reginald Punnett and his miraculous tool to predict how offspring will inherit their traits.

Cell Division Test Images


Thursday, September 30, 2010

Sex cells......Meiosis!

SO....once in a while an organism needs to reproduce.

Some organisms can make copies of their own cells that will become separate organisms that live separate from their parent.  Reproduction without any other contribution is asexual.

However some organisms create special cells known as gametes that only have 1/2 the normal amount of chromosomes as other body cells in that organism's structure.  Sexual reproduction is a process that requires these gametes and there is a specialized process to create these particular cells known as meiosis.

Meiosis is cellular division that creates gametes aka sex cells aka reproductive cells aka in humans called sperm and eggs.

A cell going through meiosis only takes place in the gonads of a human.  Each cell that will form gametes goes through the following stages:

1. Interphase: before meiosis begins, the chromatin (DNA) must replicate just like in interphase prior to mitosis.

2. Meiosis I begins!

a. prophase 1

Chromosomes appear as they do in mitosis, except a very special event is taking place.  Homologous chromosomes (chromosomes that have similar gene loci  ex. both contain different versions of the same blood type gene) pair up in a tetrad.  The pairing is known as a tetrad because there are 4 individual chromatids in the grouping and "tetra" means 4.   Tetrads form so that they can exchange little pieces of DNA.

Imagine that you are back in elementary school and it's lunchtime.  You pull out your sandwich and sigh because you have turkey. AGAIN!  You peer into your friend's bag and become jealous because they have a peanut butter and grape jelly sandwich that sounds SO much better than yours.  After some quick negotiation, you trade your sandwich for theirs and everyone is happy.

This exchange of sandwiches is much like the exchange of DNA during crossing over.  The section of DNA that is exchanged between nonsister chromatids is from the same gene (i.e. eye color isn't exchanged for blood type).

Once crossing over has occurred, the chromosome head towards the center still in their tetrads.

b. metaphase 1

Each tetrad lines up on the center plate between the centrioles instead of lining up in a straight line as the chromosomes do in mitosis.

Each set of homologous pair remains together like holding hands with a buddy and standing in line.

c. anaphase 1

Because each homologous chromosome is pulled to an opposing side, each cell is on its way to being haploid.  Remember diploid means having both members of each set of homologous chromosomes.

d. telophase 1

Each resulting cell now has 1/2 the chromosomes (n) as the original cell (sometimes called the parent cell).
3. Meiosis II begins and proceeds pretty much just like mitosis.

a. prophase II

In each cell the single homolog prepares to separate into gametes

b. metaphase II

Each homolog lines up in a straight line along the metaphase plate and centrioles attach spindle fibers to the centromere in order to now separate each chromatid from their sister.

c. anaphase II

Each chromosome in each of the two cells is split from its sister chromatid and head toward opposing poles.

d. telophase II

The nucleus reforms around the 1/2 set of DNA and the cell prepares for cytokinesis.

At the end of this process, we have 4 gametes that each have 1/2 the set of chromosomes that were in the original cell as opposed to the 2 clone cells that mitosis produces.

To review, click on the link below to watch an animation that should make this process clear.

Meiosis YouTube Review Video

Be sure that you look at the differences and similarities between mitosis and meiosis.  Below I have posted some diagrams and other helpful tools to guide you in your review.
Nova has a great comparison website that is interactive and puts each phase side by side.  Click on the link below and enjoy!

Nova comparison website

Below is a link to a great comparison chart.  Click away my pretties!

Comparison chart

Watch this cute old man biology teacher as he helps you hash out the differences between the two processes!

Video comparison

I hope all this information is wrinkling into your brains!  See you in the a.m.!


Tuesday, September 28, 2010

The Cell that Divides

Have you ever wondered how your cuts and bruises heal, how sperm and eggs are formed, or how cancerous cells go out of control????


There are 2 types of cell division: mitosis and meiosis.  They are each a part of a larger process called the cell cycle.

The cell cycle has 3 stages or steps:

1. Interphase - during this step the cell is growing, organelles are replicating, and the DNA is copying its code.  It takes the majority of cell cycle's time.

2. Mitosis or Meiosis - during this stage the cell's nuclear material (DNA) is divided equally among resulting cells.

3. Cytokinesis - during this quick stage, the cell's cytoplasm divides and the cell membrane pinches or cleaves to finally form 2 separate cells.

Now lets get more detailed information about mitosis.  There are 4 stages of mitosis: prophase, metaphase, anaphase, and telophase.

Once a cell has entered mitosis, it already has a duplicate copy of each strand of DNA that was created during interphase.

1. Prophase
a. chromosomes become visible as sister chromosomes that look like a series of Xs
b. nuclear envelope disintegrates
c. nucleolus also disintegrates
d. centrioles begin to migrate towards opposite poles and to form spindle fibers.
 2. Metaphase
a. each pair of sister chromatids (1 chromosome at this point) lines up in a straight line down the equator (i.e. center of the cell) much like we line up in a line for a movie or to get a meal at a fast food joint.

b. Centrioles that are now at opposing poles attach their spindle fibers to each centromere to prepare to pull each sister chromatid to their respective poles.
3. Anaphase
a. centrioles pull each sister chromatid away from its partner and toward opposing poles
4. Telophase
a.Cell boundaries start to reform
b.2 new nuclei from around their new DNA package in separate areas.
c. Cell begins to look pinched as it prepares for cytokinesis
After mitosis, the cell splits its cytoplasm, closes up its cell membrane, and presto we have 2 cells.

Below is a summary of the cell cycle using a special kind of microscope that relies on fluorescence

Finally, as a total review of mitosis click on the link below to watch a WONDERFUL mitosis video.

Mitosis YouTube Review Video

Tomorrow we will review meiosis which is the process by which an organism forms gametes or sex cells each having half the set of chromosomes as the original cell.

Until then....may your cells divide with a quickness that heals all your worries and woes and makes you appreciate each day we are given to study biology!

Love ya! Mean it!

Friday, September 24, 2010

So to Recap.......a Little Review From Me to You

Below are some review tools to help prepare for the assessment on Monday/Tuesday.

1. Illuminating photosynthesis!

The images below are a guided webquest to help break down what happens in this website.  Combined poems and helpful animation should shine some light on any last minute confusion about photosynthesis.

2. Review Packet for Energy
If you can answer the questions below, then you are well prepared for our test of energetic reactions in living organisms.

Thursday, September 23, 2010

Just Breathe --- Or You Can't Break Down Your Food -- at Least Not All the Way

So..we discussed respiration yesterday.  I wanted to expand further on the differences between aerobic and anaerobic respiration.

Anaerobic respiration takes place solely in the cytoplasm and requires no oxygen to process the glucose molecule.  Anaerobic respiration only provides 2 ATP per 1 glucose molecule, but those organisms that rely only on this method of energy production are single celled organisms that don't need much energy to maintain homeostasis.

Eukaryotic organisms take this process further by shuffling the now broken sugar molecule into the mitochondria.  Inside the mitochondria, the sugar is further broken down to release more energy.  As a result of 1 glucose molecule being processed in the presence of oxygen, the cell receives 36 to 38 ATP as compared to only 2 ATP in anaerobic respiration.

As far as anaerobic respiration (aka fermentation) goes, there are 2 outcomes for sugar.

1. Alcohol fermentation - When an organism processes sugar in this manner, it produces alcohol and ethyl alcohol and of course ATP.

Follow the link below to watch a video about fermentation.....maybe you can even try to make the ginger soda they demonstrate.

Alcoholic fermentation

2. Lactic acid fermentation - When an organism processes sugar in this manner, it only produces lactic acid and of course ATP.

So no matter what the nucleus situation a cell has they are able to release the energy in their food by cellular respiration.

Wednesday, September 22, 2010

Now Break it Down!

That's right.....we talked about making the food, now we focus on breaking that food down to release the energy that was stored.

Cellular respiration is the process by which food molecules are broken down (i.e. their bonds are snapped) to release energy.

All cells need energy; therefore all cells have to process food to release that energy.  We tend to assume that this process happens solely in the mitochondria, but that isn't the case.  Otherwise organisms that lack mitochondria wouldn't be able to process food and release energy.  The first step happens in the cytoplasm without the presence of oxygen.  The first step (glycolysis) happening outside the mitochondria doesn't make a lot of ATP, but it does allow bacteria to process their food.  

The next 2 steps (citric acid cycle and the electron transport chain)  happen in the presence of oxygen within the double membrane of the mitochondria.

In comparison with photosynthesis, the input of cellular respiration is the output of photosynthesis.  What this means is instead of taking in carbon dioxide and water, cellular respiration minimally needs a carbon compound (namely sugars and lipids) to start the process of releasing energy.

The first time sugar is split in the cytoplasm no oxygen is required.  The lack of oxygen is known as anaerobic respiration.

Aerobic respiration occurs when an organism further breaks down the split sugar within a mitochondria.

Aerobic respiration only releases 2 ATP while aerobic respiration can release 36-38 ATP per the same glucose molecule.

Here is a picture to review the structure of the mitochondria!  Enjoy!

May the ATP with you!

Tuesday, September 21, 2010

The Anacharis and the Light

To understand better the ingredients and environment necessary for photosynthesis, we started an experimental setup using an aquatic plant called Anacharis.  We added water and carbon dioxide bubble to a snippet of the aquatic plant.  Then we put one set of flasks in the light and other in a drawer.

We will see what happens tomorrow as our plants sit in their flasks.

Bromothymol blue is an indicator that lets us know the approximate pH (how acidic) of a solution.  When we bubble carbon dioxide through the water, the pH is lowered because we are creating carbonic acid. 

As you can see, we lowered the pH of our flasks from around 8-10 down to around a 6.

Let's see what happens tomorrow!!


Monday, September 20, 2010

Who Needs Energy??? I Do! I Do!

All cells guessed it!!!   ENERGY!

This week we venture into the processes of photosynthesis and cellular respiration.

We will first speak about how inorganic molecules (carbon dioxide and water) are combined using the energy gathered from the sun to create organic molecules for that organisms and others to break down later for energy.

This fancy process is known as photosynthesis because light (photo) is used to combine (syn) the inorganic molecules to make organic molecules.

There is a similar process called chemosynthesis that uses the energy from chemicals as the combining factor, but we will focus on the process involving light.

Photosynthesis depends on chlorophyll whether it is housed in the chloroplast like in a plant or free floating in the cytoplasm of a bacterial cell.

We will focus on the process that involves the chloroplast.  This green pigment traps light energy and converts it into ATP (chemical energy) that cells can use to combine the carbon dioxide and water to make simple sugars like glucose.

Just to review the structure of the cholorplast:

1. Inside there are stacked membranes.  Each "tire" is a thylakoid filled with chlorophyll.  Each "stack of tires" is known as a grana.  The area around these stacks is known as the stroma.
2. Own set of DNA that allows the choroplast to self replicate when needed.
3. Double membrane.

Just to review the function of the cholorplast:

1. Each thylakoid filled with chlorophyll collects sunlight and converts it to ATP.
2. The area around the thylakoids (stroma) is where the food is made.
We will continue our discussion of cellular energy tomorrow as we look at the importance of light in the process of photosynthesis by denying some aquatic plants light while exposing others.

Finally below is a link for a review exam for both cell anatomy and plasma membrane structure and function.

Until we meet again!!!  Bode