We briefly talked about the concept of the Punnett square during class today.  Before I start the activity for today's blog post, I would like to review some basic terms that we went over in class.

So what's a Punnett square?  A Punnett square is a graphic representation that shows and predicts all possible gene combinations in a cross of parents whose genes are known.  When the organism is said to be homozygous for that trait, both the alleles of a gene pair are the same.  There are two possible ways for the organism to be homozygous.  The organism can be homozygous dominant (BB) or homozygous recessive (bb).  However, when the two alleles in the gene pair are not the same, we refer the organism as heterozygous (Bb) for that trait.  Finally, we use the term "genotype" to refer the genetic properties of the allele combinations of an organism while the term "phenotype" is used to describe the physical outlook of the trait.

Source: http://1.bp.blogspot.com/_hW5DgGNOtTw/R69n1CJbHCI/AAAAAAAAABk/7HEv1XCSjI4/s320/punnet+square.jpg

Let's look at the picture above to understand how the Punnett square is used to predict the results of a monohybrid cross between the homozygous dominant gray-bodied male bunny with the homozygous recessive brown-bodied female bunny.  First, draw a square and divide it into four parts.  Represent the homozygous dominant gray-bodied male bunny with the genotype "BB" and the homozygous recessive brown-bodied female bunny with the genotype "bb".  These letters represent the alleles donated by the Parent (P) generation. Each square then represents the possible zygote allelic combination. This generation the first (F1) generation.

Fill in each box of the Punnett square by transferring the letter above and in front of each box into each appropriate box. As a general rule, the capital letter goes first and a lowercase letter follows.  Based on the Punnett square above, what will be the genotype for the F1 offspring in this monohybrid cross?  Now predict the phenotypic ratios of the offspring. (Remember that phenotype is the physical appearance of a trait.)

Finally, after you have answered the questions above under the "Comments" section.  I would like for you to find out what seems wrong in the picture above.



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    Ms. Pan is a 7th grade Science teacher at XXX Middle School. 

    Ms. Pan is both a scientist and an educator, but she likes the role of a teacher more than anything else. 

    The purpose of this blog is to provide online learning discussion and stimulate thinking prior classroom activities.
    For students, please check this blog on a daily basis to participate in discussion.
    For parents, please check this blog on a regular basis to see what your children are learning in the classroom.


    April 2009

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