Gregor Mendel

Gregor Mendel & the Discovery of Genetics Images

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     A.   Gregor Mendel was an Austrian monk who for a time studied at a university.
            Although he failed to achieve his desired goal -- that of a natural science teacher
            -- he did apply some of the math lessons he learned to his growing of garden
            peas.

            Mendel noticed that many traits occurred in pairs. Pea seeds were either round
            (smooth) or wrinkled and either yellow or green. Examine the diagram below for
            the seven pairs of traits that Mendel published in the 1860's.   In each of the
            seven pairs of images, the dominant is pictured first (on the left) and the recessive
            gene is pictured second (on the right).

Figure 1 -- Mendel's Seven Published Pea Traits

#1 In pea plants, which color allele is the dominant?

#2 In pea plants, which stem length (long or short) is dominant?

    B. We'll now feature two of the seven pairs of alleles (genes) that Gregor (Mendel)
            studied. They are the traits for pea (seed) color (yellow or green) and pea
            texture (round or wrinkled)

green : yellow wrinkled : round (smooth)
Figure 2 (color) Figure 3 (texture)

    The order of these photos is not mine. I have to use what I find
    of the web unless I sneak my digital in here and photo some
    sleepy pea seeds in the lab.

#3 The dominant pea seed color is __________
#4 The dominant pea texture is __________

C. Mendel's First Crosses
You should refer to the first cross in the diagram below which ENDS with
the formation of the F1 generation. We'll cover the second cross later.

Figure 4

Let's talk generations. On the right are three symbols representing three pea generations.
#5 P is the starting generation and stands for P _ _ _ _ _ _ L generation.
#6 F1 (subscripts not available here) is the second generation and this stands
for the FIRST F _ _ _ _ L generation. (The F _ _ _ _ L is a Latin term!)
#7 F2 (same comment) is the third or grandchildren generation and the F2
stands for the SECOND F _ _ _ _ _ generation.

Press here for the answers to 5,6,7!

Both of the starting parents had been grown in separate fields and each was
the progeny of plants that bred true generation after generation. We can thus
safely assume that each is true breeding. The technical term for such true
breeders is #8a _______ ZYGOUS.

#8b In the Parental generation above, the two genes of the dominant are __ __.
#9 In the Parental generation, the two genes of the recessive parent are __ __.

#10 In the first parents, these two identical alleles (_ _ & _ _) now must
S _ _ A _ _ T _ from each other.
#11 This event occurs during the biological process known as _ _ _ O S I S.
#12 Mendel knew about the "parting of the two genes" and this is
known as his Law of S E _ _ _ G _ _ I _ N (also a civil rights term!).

Press here for answers to Questions 10, 11, 12.

D. Yes, this is more about that first cross.

Figure 4 (repeated)

        #13 Let's talk F1 offspring. Yah! Each F1 offspring has ____ alleles. One must
              have been received from the G _ _ E _ _ from the mother and one must
              have been received from the gamete from the _ A _ _ _ R.

#14 In the above diagram, these two F1 genes are _ _. The two GENes that an
organism has for a trait are known as its _ _ _ O T Y P E.

                Press here for the answers to Questions 13,14.

      #15 In the above diagram, the PHysical appearance of these F1 offspring are all
              _________.   That means that the allele for the trait _________ must be the
             expressed or __________ gene and the allele for the trait __________ must
             be the hidden (for now at least) ____________ gene.

#16 The PHysical appearance that a trait shows (in this case round or wrinkled)
is known as the _ _ ENOTYPE of that organism.

Press here for the answers to Questions 15,16.

      #17 These lovely F1's were created when ____ allele(s) from Mom joined with
              ____ allele(s) from Dad. This joining is the biological process of
             ______________.

      #18 All this fuss over the F1's is amazing. But they too are amazing. Their
             _____ alleles for pea texture are (the same/ different) __________.
             An organism in which the two alleles are not the same is ______ZYGOUS
             for that trait.

                Press here for the answers to Questions 17,18.

E. Mendel's Next (second I hope) Cross.

This time refer to the second cross in this same diagram.

Figure 4 (for the third time)

        Let's start with the F1's this time n Mendel's next cross. Wowski! Mendel
      decided to find out what happened if an F1 mates with another F1. Relax there
      students, these are pea plants, so this is really not incestuous immoral behavior.

    #19 Each F1 has two alleles (_ _). Once again during the process of _ _ _OSIS,
            these alleles must undergo S__________ with ____ (a number) allele(s) out of
            the pair then heading for each F2 offspring.
    #20 That means that the first F1 produces alleles (_ + _) which have separated
            (you show this by the + sign between them) and the second F1 produces alleles
            (_ + _).

Press here for the answers to Questions 19,20.

F. Let's look at the F2 (grandchildren) generation!
Yes, this is the same diagram again.

Figure 4 (for the fourth = last time)

#21 We were left with a bit of a dilemma. Both F1's had the same
        _____TYPES (_ _) But which of the two alleles is passed on to the
        next (F2) generation? Is it the first allele (__) or the second allele (__)?
        The answer is __________________________________________.

#22 We must allow the possibility for either allele to be passed on. That's
       why after SEGREGATION, we wrote the alleles for both parents as
       ( _ + _).   That now means that in this second mating, we have ...
       ( _ + _) (2 options for one F1) times ( _ + _) (2 options for the other F1).

        Press here for the answers to Questions 21,22!

#23 If it looks like a B _ _ O M _ _ L from math, then treat it like one.
       The entire equation for the second cross (mating) follows:
        ( _ + _) x ( _ + _) yields _ _ + _ _ + _ _ + _ _   (4 F2 genotypes)
        These are the results we should get (Expected data) when any two
        H _ _ _ I _ S   are crossed.
        The F1 genotype ratio (count them up) is __ RR: __ Rr : __ rr (3 parts)
        The F1 phenotype ratio is __ Round: __ wrinkled

Press here for the answer to Questions 23!

G. Mendels Next Set of Crosses (P Generation)

Figure 5 (first time)

           #24 Look carefully at the pea seeds. This time Mendel decided to simultaneously
                (and also at the same time too) study two different traits. As with the prior
                cross, these peas were from separated fields that only produced plants of the
                same characteristics. In other words all the parents are assumed to be
                _______ZYGOUS

#25 The first pictured P(arent) is both _________ (texture) and ______ (color)
The second P(parent) is both ___________ (texture) and ______ (color).

#26 The first parent must be genotype _ _ for texture and _ _ for color.
The second parent must be genotype _ _ for texture and _ _ for color.

Press here for the answers to Questions 24, 25,26!

Figure 5

    H. Mendels Next Set of Crosses (F1 Generation)
        (Of course based on the same prior picture repeated below!)

         This time we'll focus on the F1 generation. Surprise!

#27 After segregation, each F1 gets one gene for each trait from each parent.
Each F1 is (_ _) for texture and is (_ _) for color.

      #28 That's right folks, with two traits to study, this is more complex.
              The genotype of the first F1 is (combine all four alleles) _ _ _ _
              The genotype of the second F1 is also _ _ _ _

Press here for the answers to Questions 27,28!

      #29 Since each F1 is Heterozygous (_ _ _ _ _ ) for two traits. it is referred to
             as being a _ _ (prefix for two) _ _ _ _ _ _ (heterozygous).   The results of the
             F1 x F1 mating is known in biology as the D _ _ Y _ _ _ _   CROSS. It is
             tricky to analyze, but we now have the visible graphic to help us.

Press here for the answer to Question 29.

I. Mendels Next Set of Crosses (F2 Generation)

Does this graphic look familiar?

      #30 Let's look at the lovely F2's. They each look different and indeed do represent
             many different gene combinations (______TYPES) and ___ (a number)
             different physical appearances (_______TYPES). But these different types of
             F2 offspring (grandchildren) are not found in equal numbers. Nor were they in
             the F2 generation of the monohybrid cross way back in #23.

But these different types of F2 offspring (grandchildren) are not found in
equal numbers. Nor were they in the F2 generation way back in #23.

#31 Look at either (or both) of the above diagrams. They represent the
F2 progeny when both the F1's were _ I _ _ B _ _ _ S.

      #32 The number of F2's which show the double dominant (round & yellow)
              is (count them up)    __/16
             The number of F2's which show round (dominant) with green (recessive)
             is (count them up)     __/16
             The number of F2's which show wrinkled (recessive) with yellow
             (dominant) is             __/16
              The number of F2's which show double recessive (wrinkled & green)
             (count them up) is     __/16

      #33 Congratulations, this is major (not captain!)   When both parents are
            ____________, and if there are a heck of a lot of progeny (reliable data)
            the next generation should be found in an approximate   __: __: __: __
            ratio.   (Did you count the numerators in #32?)

Press here for the answers to Questions 30, 31, 32, 33!

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