Mitosis, Meiosis, and Genetics

• Mitosis/Meiosis Photos
• Coin Toss Data
• Genetics Practice Problems

Background

Dr. Fankhauser on the wall of Mendel’s greenhouse In his studies on inheritance in peas, Gregor Mendel showed that an offspring formed by the fertilization of an egg by a sperm gets half its alleles from each parent. Exactly which alleles for each trait the offspring receives from the parents follows the laws of probability. This can be illustrated by coin tosses. If a single coin is tossed, it will land heads or tails with a 50:50 chance of each. If two coins are tossed, each has a 50:50 chance of being heads or tails. Thus, the probability of obtaining, for example, two heads should be ½ × ½ = ¼.

The genotype of an organism is its actual genetic make-up; which two alleles for a trait (gene) it actually has. Its phenotype (pheno = show, seem, appear) is how those genes are expressed; what it “looks like”. For example, a person with one allele for brown eyes and one for blue will have the genotype Bb, but that person’s phenotype will be brown eyes because brown is dominant over blue (like getting one head plus one tail when two coins are tossed together).

The processes of mitosis and meiosis were discovered in the 1870s and 1890s, respectively. It was later concluded that the movement of the chromosomes in meiosis was responsible for the behavior of the alleles during reproduction, as Mendel noted. Mitosis (mito = a thread) is the process of replication and division of the chromosomes as a cell divides to make two cells. Meiosis (meio = less) is a special type of division in which the chromosome number is reduced by half, resulting in gametes (sex cells: eggs and sperm) with only one chromosome from each of the pairs that are present in our somatic cells (general body cells - soma = body).

Materials Needed

Part A — Mitosis and Meiosis

• microscope
• slide of onion (Allium cepa) root tip mitosis (# B-552)
• slide of whitefish (Coregonus clupeiformis) blastula mitosis (# E-1025)
• slide(s) of Ascaris megalocephala (a roundworm) uterine section showing meiosis or mitosis in eggs, zygotes, or embryos (# E-325, E-335, E-354, E-355)
• slides of lily (Lilium sp.) anthers showing meiosis to form pollen (# B-680, B-682, B-682b, B-683, B-684, B-685)
• slide of grasshopper testis showing spermatogenesis (including meiosis) (# G-145)

Part B — Probability and Genetics

• mono- and dihybrid cross genetic corn ears
• plain, PTC, thiourea, and sodium benzoate taste test papers
• coins (total of 4 of 2 kinds)

Procedure

Part A — Mitosis and Meiosis

Working individually, obtain and examine under the microscope each of the slides discussed below. Try to find cells in each of the stages of mitosis (mito = a thread; -sis = the act of) or meiosis (meio = less): interphase (inter = between, among), prophase (pro = before, in front of), metaphase (meta = between, with, after), anaphase (ana = up, throughout, again), and telophase (telo = end, complete). Draw what each of these cells you observe looks like. Label such things as nucleus, nucleoli, nuclear envelope, chromosomes (chromo = color; soma = body), spindle fibers, asters (aster = star), etc. if/when present. For further information, you may also wish to refer to the chapters on mitosis and meiosis in your lecture text.

A set of photos from a prepared slide of onion (Allium cepa) root tip

Interphase	Prophase	Metaphase
Anaphase	Telophase

1. Plant Mitosis: An onion root tip is a rapidly-growing (meristematic) portion of the onion, thus many cells in various stages of mitosis may be seen. In interphase, note that the chromosomes are long and entangled and are not individually visible, thus the nucleus of such a cell would be fairly-evenly colored and may also contain one or more nucleoli. During prophase, the chromosomes contract and become distinct, thus the nucleus of a cell in prophase frequently has a “grainy” appearance. By metaphase, the chromosomes are contracted, distinct, and lined up on the metaphase plate. Try to find and draw a cell that clearly shows chromosomes with sister chromatids and centromere (this doubled structure should be visible by late prophase or metaphase). Try to find a cell in which the chromosomes are fairly well spaced and count them. What is the diploid chromosome number of onion? Are there asters present in any stage(s)? In anaphase, note the disjunction of the sister chromatids. In telophase, note the formation of the new cell plate. How many chromosomes should be included in each of the daughter nuclei?

A set of photos from a prepared slide of whitefish (Coregonus clupeiformis) blastulas

Interphase	Prophase
Metaphase	Anaphase
Telophase

2. Animal Mitosis: In whitefish, as in humans, the blastula (blasto = bud, sprout; -ula = little) is the hollow ball stage in embryonic development, and thus is characterized by rapid growth. In prophase, note the chromatin within the nucleus (the nuclear envelope is intact in early prophase, although not visible). Are there any asters at this stage? In metaphase, note that the chromosomes are lined up alone the equator of the cell. Asters are readily visible and polar fibers are attached to the centromeres of each chromosome. In anaphase, note the disjunction of the chromosomes. In telophase, note the constriction type of cytokinesis.
3. Plant Meiosis: A lily plant is 2n, like humans. However, plants do things a bit differently than we do. The 2n plant generation is called the sporophyte because it produces haploid spores (via meiosis). Then, those spores grow (via mitosis) into a totally different 1n plant generation called the gametophyte (the plant generation which produces gametes). Male gametophytes make sperm and female gametophytes make eggs. In gymnosperms and angiosperms, the male gametophytes are called pollen. Notice, “pollen” and “sperm” are not the same thing! In the angiosperms, meiosis happens in two different places within their flowers. In the anthers, meiosis results in microspores which grow into male gametophytes which produce sperm, and in the ovary, meiosis results in megaspores which grow into female gametophytes which produce eggs.
   We will be examining the process of meiosis as it occurs in the anthers to produce microspores, then male gametophytes (pollen). Because of the timing of this process, it cannot all be viewed on one slide. Thus, to understand this process, you will need to view a series of slides made at different points during meiosis.
   1. # B-680: Lily Anther, general structure — These anthers just have the precursor 2n germ cells in them.
   2. # B-682: Lily Anther, early prophase I — The chromosomes have paired and have begun meiosis.
   3. # B-682b: Lily Anther, late prophase I — Chromosome tetrads/bivalents should be visible.
   4. # B-683: Lily Anther, first meiotic division — The chromosomes separate, resulting in 2 daughter cells that are 1n.
   5. # B-684: Lily Anther, second meiotic division — The sister chromatids are separated, resulting in a total of 4 daughter cells that are 1n.
   6. # B-685: Lily Anther, pollen tetrads — Because of the way plants reproduce, these would be the precursors to the microspores which will subsequently germinate and grow into the male gametophytes, also known as pollen. Within the pollen, two sperm nuclei will be produced. Again, pollen and sperm are not the same thing, but rather, pollen is a plant generation that makes sperm.
   7. # B-686: Lily Anther, mature pollen grains — These are the mature, multicellular, male gametophytes (pollen), including two special nuclei referred to as the sperm nuclei visible in each.
   Note that the end result of meiosis is four daughter cells. Remember that in prophase I and metaphase I of meiosis, the homologous chromosomes are paired (synapsis) into bivalents or tetrads. How many of these bivalents do you see? What is the diploid chromosome number of lily?

A set of photos from prepared slide of a grasshopper testis

Various Stages and Structures as Noted
Primary and Secondary Spermatocytes
Spermiogenesis

4. Animal Meiosis: In male grasshoppers’ testes (note: “testis” is singular, “testes” is plural), sperm are formed by meiosis (females’ ovaries make eggs). The testes themselves are 2n, while the sperm formed within them are 1n. Each testis is organized into a series of side-by-side testicular lobes, all of which open at their proximal (basal, closest) end into the vas deferens. Within each lobe are a number of testicular cysts, each surrounded by a septum made of connective tissue. In each cyst are a number of cells that are undergoing meiosis, and typically, all the cells in a given cyst are in the same stage of meiosis. Typically, the cysts in the distal (apical, farthest from the vas deferens) region contain 2n, primary germ cells (cells which give rise to sperm) called spermatogonia or cells in very early prophase I. As the cells within the cysts undergo meiosis, the cysts travel from the distal to the proximal end of the lobe, so that cysts near the proximal end contain “finished,” 1n spermatozoa.
   The slide to be examined is a longitudinal section (l.s.) of a grasshopper testis, and should contain one or more oblong lobes, sliced “lengthwise” so a number of cysts and a variety of stages in meiosis should visible in each lobe. At the rounded, distal end, notice the 2n spermatogonia (goni = seed). These cells undergo the process of spermatogenesis (genesis = origin, birth), which includes meiosis and spermiogenesis, the maturation of the 1n spermatids into motile spermatozoa. As the cells undergo meiosis I, they are first called primary spermatocytes (cyto = cell), then during meiosis II, secondary spermatocytes, then (when meiosis is complete) spermatids. The rounded spermatids are transformed, via the maturation process called spermiogenesis, into mature spermatozoa (zoa = animal) as they develop flagella and become motile.
   While many of the primary spermatocytes are in prophase I (in various of the stages just mentioned), try to find primary spermatocytes in other stages of meiosis I. In metaphase I, the tetrads move to the center of the cell, line up there, and are attached by their centromeres to the spindle fibers. with each of the homologous chromosomes in a pair attaching to a spindle fiber from the “opposite” centriole/pole. In anaphase I, the whole chromosomes (not just the chromatids as in mitosis) are pulled to the poles, with one homologous chromosome from each pair being pulled to each pole. This is the reduction division that is characteristic of and central to the process of meiosis. Meiosis I ends with telophase I, in which the secondary spermatocytes are formed. The secondary spermatocytes may be distinguished from the primary spermatocytes by their smaller size. They undergo meiosis II, a process that’s similar to mitosis in that the sister chromatids are separated (and thus, become chromosomes). The resulting 1n cells are the spermatids. The spermatids undergo a maturation process called spermiogenesis which involves changing from a rounded to a pointed shape and the growth of flagella to enable them to swim.
   Reportedly, 2n = 8 for this organism. Remembering that grasshoppers are an example of XO inheritance, technically the 2n number should be 7 (because there is no Y to pair with the X chromosome), and thus, in anaphase I of spermatogenesis, one daughter nucleus should get 3 autosomes and an X chromosome while the other should get only the 3 autosomes. (Female grasshoppers would have two X chromosomes, thus, in oogenesis, all daughter cells would be expected to receive 4 chromosomes.)

A set of photos from a prepared slide of an Ascaris megalocephala uterus

Prophase (side) or Metaphase (top)?	Metaphase (note polar body, lower left)
Anaphase	Telophase

5. Animal Meiosis/Mitosis: Ascaris megalocephala is a type of large roundworm that parasitizes horses. This slide is a cross-section (x.s.) of a female, and at the point in her body from where these slides were cut, most of what’s visible is the uterus. The process of egg development in Ascaris is similar to humans: before the “egg” has completed meiosis, first the sperm nucleus enters. That triggers completion of meiosis in the “egg,” including formation of polar bodies, then the sperm and egg nuclei unite to form a zygote, then the zygote begins to divide, forming a 2-celled, then a 4-celled, etc., embryo. This whole process is usually not visible all on one slide, so depending on which slide you are viewing, you will see portions of this process. Depending on which slide you are viewing, the uterus contains numbers of either “eggs” in the process of being fertilized and undergoing meiosis, or newly-fertilized and rapidly dividing zygotes or very young embryos. Note that if you are viewing a slide with zygotes/embryos on it, you may see a mixture of 1-celled zygones and both 2-celled and 4-celled embryos, in various stages of mitosis. Observe cells in each stage of mitosis. When are asters present? Find a cell in which the chromosomes are well spread and try to count them — what is the chromosome number of this organism?

Part B — Probability and Genetics

1. As a class, examine various human traits which are each thought to be controlled by only one gene. Note: many of these, previously thought to be one-gene traits, are turning out to be controlled by several genes. Traits which may be examined include:
   • Sex: We all have at least one X chromosome. Usually, a person with two X chromosomes (genotype XX) is female, and a person with a Y chromosome (genotype XY) is male. However, it is important to remember that sex is a phenotype, not a genotype. Sex is not about how many X or Y chromosomes a person has, but rather, how the genes on those (and other) chromosomes are actually expressed.
     In humans, sex is a phenotype which is determined by the influence or lack of influence of the genes located on the Y chromosome, whereas in fruit flies, sex is determined by the effects of the ratio of the number of X and Y chromosomes (if an abnormal number). Thus in humans, XO and XXX would typically also be female while XXY would typically be male. In humans, a combination such as XXXY would produce a male phenotype because of the effects of the genes on the Y chromosome, but in fruit flies would produce a female phenotype because of the relatively larger number of X chromosomes. However, to “complicate” the situation, in humans, there is an X-linked recessive mutation for androgen insensitivity syndrome (AIS) which causes all cells in the person’s body to be insensitive to the effects of testosterone. Thus, even if such a person has a Y chromosome, most of its alleles have no effect and that person is be female. There is more detailed information on AIS, on the Genetics Practice Problems Web page.
   • Eye color: We typically talk about this in terms of B– coding for brown eyes, and bb coding for blue eyes. Again this is an over-simplification. According to the OMIM Web site, there are at least two genes which contribute to eye color. One of these genes has an allele that codes for “make brown pigment” and another allele for “we don’t know how to make brown” = default blue color. The other gene has an allele for “make green pigment” and an allele for “we don’t know how to make green”. While, starting out, it may be easier to understand how genetics works if we only look at the brown-blue gene, in reality, eye color phenotype is a combination of the effects of the alleles for both of these genes.
   • PTC-Taster: PTC (phenylthiocarbamide) is a chemical that tastes bitter to some people while others cannot taste it at all. Here, too, while we tend to talk about this in terms of tasters (T–) and non-tasters (tt), the reality is a slightly more complicated situation. This gene, located on chromosome 7, actually has multiple alleles, one for “tasting” and at least two different forms of “non-tasting.” The penetrance of the gene can vary, and people who are TT often find the test paper extremely bitter, while people who are Tt may find it bitter, but not extremely so. There is also considerable variability (controlled by other genes) in the threshold concentration needed to trigger a taste reaction, so some people might not notice a bitter taste at a lower concentration, but would react negatively to a higher concentration. One researcher found that a 0.02% solution of PTC was tasteless to 75% of the people on whom he tested it, but a 0.64% solution was tasted by 85% of his subjects. Interestingly, PTC must be dissolved in a person’s own saliva to be tasted. If it is dissolved in someone else’s saliva or in plain water, and placed on a “dry” tongue, the person cannot taste it.
     It is reported that, in the “average” US population, about 70% of people are tasters and 30% non-tasters. Thus, this gene is often used to introduce the concept of population genetics, the “rules” of which were developed by two people named Hardy and Weinberg, hence referred to as the “Hardy-Weinberg Law.” If “p” is the probability of the allele “T” and “q” is the probability of the allele “t,” then the probability of “TT” would be p², the probability of “tt” would be q², and the probability of “Tt” (= Tt + tT, remember?) is 2pq. Since everyone in the population has to be either TT, Tt, or tt, the probabilities of those have to add up to 1 (100%), so p² + 2pq + q² = 1. Recall from algebra that p² + 2pq + q² = (p + q)². Thus, if (p + q)² = 1 and we take the square root of both sides, that means p + q = 1, too. If 30% (0.30) of the population are non-tasters, that means q² = 0.30. From that, we can calculate q = 0.55, and if that’s the case, then p = 1.00 – 0.55 = 0.45. From those, in turn, we can calculate p² (the probability or frequency of TT) as being 0.45² = 20%, and of 2pq (the probability of Tt) as being 2 × 0.45 × 0.55 = 50%. To check our math, notice that 20% + 50% do, indeed, equal the observed value of 70%. Note that these percentages are different for other areas of the world, other ethnic groups.
     The PTC molecule contains a N–C=S group that is thought to be related to its bitter taste. This group is also found in several other bitter-tasting chemicals, including those found in cabbage varieties, including broccoli, brussels sprouts, and cauliflower, and it has been noticed that often, people who are TT dislike the taste of those (and other strongly-flavored) foods, while, in general, non-tasters tend to be more willing to eat a more varied diet, including more dark-green, leafy vegetables. It has been suggested that, evolutionarily, this gene might have been advantageous because many plant toxins taste bitter, so being able to taste, and therefore avoid, those toxins might have been beneficial in a hunter-gatherer society.
     Thiourea is another chemical that tastes very bitter to some people (dominant trait) and is tasteless to others (recessive allele).
     A third chemical that tastes different to different people is sodium benzoate, a controversial food preservative. Typically, a solution of 0.1% is used for food preservation, and researchers have shown that a 0.1% solution was tasted by about 25% of the people on whom it was tested. Interestingly, however, for people who are tasters, the taste varies. Some people think it tastes sweet, some salty, some sour, and some bitter.
     Taste differences occur for other substances including the barium sulfate “milkshakes” fed to people prior to GI X-rays. For most people this is tasteless, but to some, it is bitter.
   • Tongue Rolling: People who can roll their tongues into a tube have at least one R allele (R–) and those who can’t are rr.
   • Widow’s Peak: If your hairline forms a “V” on your forehead, you are W– and if your hairline is straight, you are ww.
   • Ear Lobes: If your earlobes are detached, you have at least one E (genotype E–), but if they are attached, you are ee.
   • Little Finger: Hold your hand out with fingers together. If the end joint of your little finger bends in, you are F–. If it is straight, you are ff.
   • Hitchhiker’s Thumb: Hold out your hand like you’re hitchhiking. If your thumb bends back at quite an angle, you are H–. If your thumb is fairly/nearly/almost straight, you are hh.
   • Mid-digital Hair: Look closely at the middle segments (not knuckles or joints) of all of your fingers to see if any of them have hair growing on them (If it’s a finger you use a lot, the hairs may be worn down to stubble, so look closely.). If there is any hair on any of them, you are D’. If all your middle segments are totally bald, you are dd.
   Considering just these 9 traits, and assuming all are simple one-gene-with-two-alleles situations would give 2⁹ or 512 different possibilities, and the lab room will only hold 20 students. Note that, in humans with 23 pairs of chromosomes, a gamete would have 2²³ = 8,388,604 possible combinations of chromosomes (each bearing numerous genes) from that parent. Any couple could have 2²³ × 2²³ = 70,368,744,177,644 (70 trillion) different possible children, based just on the number of chromosomes, not actual genes. Thus, based on the number of chromosomes, the chance of 2 siblings (other than identical twins) being exactly identical is 1/70 trillion. To make things even more complex, crossingover, or exchange of segments between homologous chromosomes during synapsis, can add further variation.
2. Work individually on the coin tosses, as described below, recording your data on the charts provided along with your protocol. Since the probabilities involved in genetics exactly parallel the probabilities of coin tosses, this is an excellent way to grasp the theory behind genetic probabilities. Once you have all your data, please submit your coin toss data online. When everyone has had a chance to enter their data, you may view and print the class data
   1. Most organisms have two sets of chromosomes, and only one from each pair is passed on, at random, to the offspring through the process of meiosis by which eggs and sperm are formed. Thus, since the chromosomes contain or are made up of genes, the eggs and sperm get only one allele (alternate forms for genes; allelo = one another, parallel) for each gene. Obtain a coin. Let us assume that heads represents, say, brown eyes and tails represents blue eyes, and that this “parent” has one allele for brown eyes and one for blue (a heterozygote — hetero = other, different, zygo =a yoke). To illustrate the chances of having one or the other of these alleles in any particular gamete (egg or sperm - gamet = a wife or husband), toss the coin on the tabletop 100 times. Using “chicken scratches” record the number of heads and the number of tails on the chart for Step A.
   2. To illustrate what happens when the possible alleles from two heterozygous parents unite in an offspring, obtain two coins of the same type (say, two pennies). Toss these, together, onto the tabletop 100 times. Tally and record in the chart for Step B the numbers of a) two heads, b) one head and one tail, and c) two tails. As in the previous part, let us assume that these represent eye color in humans. It is known that in human eye color, brown eyes is dominant over blue: that is, if an individual has one allele for brown and one for blue, that individual will have brown eyes. Thus, in your coin tosses, HH or HT would be brown-eyed, while TT would be blue-eyed. What ratio of brown to blue eyes did you get (i. e. what ratio of HH and HT combined versus TT)?
   3. In a dihybrid (di = two) cross, geneticists look at two traits (such as eye color and tongue-rolling ability) passed on from parents to offspring. Assuming that the two genes involved are not on the same chromosome, they are inherited independently of each other. To show the possible gametes (eggs/sperm) produced by a parent heterozygous for both traits, obtain two different coins (penny and nickel) and toss them together 100 times. Record how many of each of the combinations H1+H2, H1+T2, T1+H2, and/or T1+T2 are obtained. What ratio/percentage of each were obtained? Record your numbers in the chart for Step C.
   4. To simulate possible offspring of a dihybrid cross produced by random union of an egg and sperm from two parents each heterozygous for two traits obtain four coins of two types (2 pennies + 2 nickels, etc.) and place together in a container. Shake thoroughly and toss out onto the tabletop. Tally the results for 96 such tosses on the chart for Step D. Rather than figuring out percentages, divide all your numbers by 6 to obtain how many out of 16 were of that type (96 ÷ 6 = 16).
      Why 16? The probability of getting, for example, H for penny #1 is ½, and the probability of getting H for penny #2 is also ½. Thus, the probability of getting HH is ½ × ½ = ¼. The same is true for your nickles (or dimes, or whatever), so the probability of getting HH + HH would be ¼ × ¼ = ⅟₁₆, the probability of getting HH + HT would be ¼ × ²⁄₄ = ²⁄₁₆, etc. Thus it will be much easier to express and understand your final numbers in terms of how many out of 16, rather than as a percentage.

H T H HH HT T HT TT

B b B BB Bb b Bb bb

3. Geneticists use Punnett squares like these to show what can be expected from a cross between two parent organisms.
   First, the possible gametes from each parent are determined (like Steps A or C above). The possible gametes from the male parent are usually written across the top of the Punnett square and those from the female parent are usually written down the left side of the square. From this, the possible genotypes of the offspring are calculated by filling in the small boxes. These Punnett squares illustrate Steps A and B above. “B” represents the brown-eyed allele, “b” represents the blue-eyed allele, and HH, HT, and TT have been converted to the appropriate genotypes. The Punnett square thus obtained is 2 × 2 or 4 boxes in size. One of the gametes (technically, which allele ended up in that sperm) from the father has been written above each column and one of the gametes (technically, which allele ended up in that egg) from the mother has been written in front of each row. Geneticists list the dominant allele first. The male gametes have been copied into the boxes under each and the female gametes into the boxes next to each, placing the dominant allele first. This gives four possible genotypes for the offspring, which correspond to the results of Step B above. From this, figure out the expected frequency/percentage of each genotype and phenotype of offspring.
4. From Steps C and D above, let coin 1 represent some gene, A, where H=A and T=a. Let coin 2 represent some gene, B, where H=B and T=b.
   Draw a Punnett square that is 4 boxes on a side (total of 16 boxes). “Translate” the gametes from Step C into A, a, B, and/or b and write in along the sides of the square (you should have four gametes with one of each gene for each parent – AB, Ab, aB, ab). Remember: gametes should have ONE ALLELE FOR EACH GENE! Fill in the boxes and the results should match with what you got in Step D. Note that when doing a dihybrid cross, the “A” alleles should be written next to each other and the “B” alleles should be kept together. Determine the genotype and phenotype ratios that you would expect from this cross.
5. Individually, examine the monohybrid (mono = one) and dihybrid crosses illustrated by corn. Count at least three rows of kernels, but please do not mark on the corn. Ears of corn representing other genetic combinations may also be available.
   What genes are illustrated by these crosses and what are the two alleles for each of these genes? Which is dominant and which is recessive — how can you tell? Draw Punnett squares for the first filial (F₁) and second (F₂) crosses (fili = son or daughter). For each Punnett square, what genotype and phenotype ratios would be predicted? Count the kernels of corn. How closely to the predicted phenotype ratios do these samples come?
6. Do the genetics problems listed in the protocol. The Genetics Practice Problems Web page gives a more thorough explanation of how to do these. These are intended to illustrate various principles of genetics (if you run out of time in lab, these may/should be done on your own). If you work on these while viewing the Web page, do not neglect to take notes in your lab notebook.
7. Using squares to represent males and circles to represent females and using a white circle/square to represent blue eyes and a black circle/square to represent brown eyes, draw a pedigree for as much of your family as you are able (grandparents, parents, aunts, uncles, siblings, cousins, etc.). Notice in this example, the way a line is drawn between two people to show a marriage, and notice how the lines are extended below that to indicate their children. From your family pedigree, can you tell which of the brown-eyed people are heterozygous? What is your genotype? Can you predict what color eyes your children might be likely to have? Note: gray eyes are considered to be a variation on blue, while green, to further complicate things, is a totally separate gene. Apparently, a person can be dominant or recessive for the blue/green gene separate from the blue/brown gene, and eye color is actually influenced by both.
   After constructing and contemplating this sample pedigree, it becomes obvious that the people marked with an asterisk (*) are heterozygous. Can you figure out why/how? Hopefully, your family pedigree will provide you with similar information about your family members. An alternate, more official way to indicate a heterozygote is by using a box or circle that’s half filled in, like this one to the left.

Things to Include in Your Notebook

Make sure you have all of the following in your lab notebook:

• all handout pages (in separate protocol book)
• all notes you take during the introductory mini-lecture
• drawings (yours!) of mitotic stages in onion (Allium) root tip
• drawings (yours!) of mitotic stages in whitefish blastula
• drawings (yours!) of stages in Ascaris
• drawings (yours!) of spermatogenesis in grasshopper
• drawings (yours!) of meiosis to form pollen in lily
• if done, notes on taste-testing (PTC, etc.)
• coin toss data, calculations, and any other related notes
• corn kernel data & calculations
• drawing of ears of genetic corn
• completed genetics practice problems
• family pedigree for eye color
• any other notes and data you gather as you perform the experiment
• print-out of class data (available online)
• answers to all discussion questions, a summary/conclusion in your own words, and any suggestions you may have
• any returned, graded pop quiz