1. Do you have space with a sink? Pigs are a lot more involved than frogs and the preservatives will need to be drained and pigs rinsed. This is not a good dissection for classrooms that do not have sinks.
2. Have your students completed the frog dissection? The pig is more advanced, students should have a basic understanding of dissection protocols.
3. Pigs will need to be ordered from a biological supply company. If they are not injected, the circulartory system is very difficult to view. Generally, 1 pig for two students is a good match, but you could get away with 3-4 students per pig.
4. Safety: Goggles are required for all dissections. Latex gloves are optional, though generally preferred. Students should always wash hands even if they wore gloves. Many chemicals will seep through the latex. I have switched to nitrile gloves because it provides more of a barrier from harsh chemicals, but they are slightly more expensive.
5. Assessment. I take a grade on the completion of this lab guide. But as worksheets go, you do want the students to work out the answers together and ask for help when needed. Generally I use a quick and easy method to grade it. Each section is worth 5 pts. If its completed and looks mostly right, then they get the full 5 pts. Reduce pts if there are blanks or incorrect answers.
The biggest part of their grade comes from the LAB PRACTICAL. This is where pigs are set up at stations with numbered or colored tags in the structures. Students have 1 minute at each station to identify the structure and write it on their answer sheet. This is done in complete silence with no working together. Depending on the class, I may or may not allow them a word bank. Honors classes do not get a word bank usually unless I have an IEP or student that needs differentiation. The sheets below can be printed for the practical, they are numbered 1-50, though you don’t need to use all of the blanks. Just make sure your practical contains enough stations to keep students busy. If you have 30 students, you can have 25 stations with questions, and 5 “rest stations” interspersed.
Lab Practical Blanks | .doc file
Also print out the fetal pig lab guide – this just lists all of the structures they need to find with a checkbox. It makes for a good reference and study guide.
Fetal Pig Dissection: External Anatomy
1. Determine the sex of your pig by looking for the urogenital opening. On females, this opening is located near the anus. On males, the opening is located near the umbilical cord. Check the bags and packaging, they are often labeled with the pig’s sex. Make sure you mix them up within the classroom.
If your pig is female, you should also note that urogenital papilla is present near the genital opening. Males do not have urogenital papilla.
Both males and females have rows of nipples, and the umbilical cord will be present in both.
What sex is your pig? _________
2. Make sure you are familiar with terms of reference: anterior, posterior, dorsal, ventral. In addition, you’ll need to know the following terms
Medial: toward the midline or middle of the body
Lateral: toward the outside of the body
Proximal: close to a point of reference
Distal: farther from a point of reference
*label the sides on the pig picture above. On the pig picture, they should just labe the anterior, posterior, dorsal, ventral.
3. Open the pig’s mouth and locate the hard and soft palate on the roof of the mouth. Can you feel your own hard and soft palates with your tongue?
Note the taste buds (also known as sensory papillae) on the side of the tongue. Locate the esophagus at the back of the mouth. Feel the edge of the mouth for teeth. Does the fetal pig have teeth? _yes
Are humans born with teeth? ___ no _
Locate the epiglottis, a cone-shaped structure at the back of the mouth, a flap of skin helps to close this opening when a pig swallows. The pharynx is the cavity in the back of the mouth – it is the junction for food (esophagus) and air (trachea). To find the epiglottis, you will need to make deep cuts at the edges of the mouth, I also place a lot of pressure on the jaw to break it and to get the mouth to fully open. Students will often be too gentle opening the mouth.
4. Gestation for the fetal pig is 112-115 days. The length of the fetal pig can give you a rough estimate of its age.
11mm – 21 days | 17 mm – 35 days | 2.8 cm – 49 days
4 cm – 56 days | 22 cm – 100 days | 30 cm — birth
5. Observe the toes of the pig. How many toes are on the feet? _________________
Do they have an odd or even number of toes? ______odd toed – artiodactyls_________________
6. Observe the eyes of the pig, carefully remove the eyelid so that you can view the eye underneath. Does it seem well developed? Do you think pigs are born with their eyes open or shut? _____________eyes developed, they usually open their eyes within first day__________________
7. Carefully lay the pig on one side in your dissecting pan and cut away the skin from the side of the face and upper neck to expose the masseter muscle that works the jaw, lymph nodes, and salivary glands. The salivary glands kind of look like chewing gum, and are often lost if you cut too deeply. Salivary glands are usually in the same spot, near the cheek and jaw. Lymph nodes can be in different spots and be difficult to locate.
**Make sure you know the locations of all the bold words on this handout**
The Anatomy of the Fetal Pig (internal)
pig diagramIdentify the structures on the diagram.
3. _____gall bladder_________
4. ____bile duct___________
8. ____small intestine_______
11. ___large intestine__________
13. ___umbilical arteries__________
Identify the organ (or structure)
14. _____pyloric sphincter valve____ Opening (valve) between stomach and small intestine.
15. _____gall bladder_____________ Stores bile, lies underneath the liver.
16. ___________cecum___________ A branch of the large intestine, a dead end.
17. ___________diaphragm________ Separates the thoracic and abdominal cavity; aids breathing.
18. ________mesentery___________ Membrane that holds the coils of the small intestine.
19. ________duodenum___________ The straight part of the small intestine just after the stomach.
20. _______bile duct______________ Empties bile into the duodenum from the gall bladder.
21. _______rectum_______________ The last stretch of the large intestine before it exits at the anus.
22. _______pancreas_____________ Bumpy structure under the stomach; makes insulin
23. _______bladder_______________ Lies between the two umbilical vessels.
Urinary and Reproductive Systems
1. Locate the kidneys; the tubes leading from the kidneys that carry urine are the ureters. The ureters carry urine to the urinary bladder – located between the umbilical vessels. To find the ureters, expose the kidney and wiggle it, the ureter is attached and you’ll see it move.
2. Lift the bladder to locate the urethra, the tube that carries urine out of the body. checkbox
3. Note the vessels that attach to the kidney – these are the renal vessels checkbox
1. Find the scrotal sacs at the posterior end of the pig (between the legs), testis are located in each sac. Open the scrotal sac to locate the testis. checkbox
2. On each teste, find the coiled epididymis. Sperm cells produces in the teste pass through the epididymis and into a tube called the vas deferens (in humans, a vasectomy involves cutting this tube).checkbox
3. The penis can be located by cutting away the skin on the flap near the umbilical cord. This tube-like structure eventually exits out the urogenital opening, also known as the urethra. checkbox The penis of the fetal pig is actually pretty difficult to find because it is internal (this can lead for much hilarity in the lab as students try to locate the structure. A simple technique I use to find it is to find the area just behind the urethral opening and roll this area (its also where the umbilical arteries are attached) between the thumb and forefinger. You should feel a solid tube like structure just under the skin – this is the penis.
4. In the female pig, locate two bean shaped ovaries located just posterior to the kidneys and connected to the curly oviducts. checkbox
5. Trace the oviducts toward the posterior to find that they merge at the uterus. Trace the uterus to the vagina. The vagina will actually will appear as a continuation of the uterus. checkbox
LABEL THE DIAGRAMS
urinary system femalemale
Dissection of the Thoracic Cavity
Identify by number:
Aorta __2__ Dorsal Aorta _9__Pulmonary Trunk _1_
Common carotid _4__ Left & Right Carotid _7,8__
Coronary vessels _6__ Left Subclavian__5__
Right Subclavian __10__ Right Brachiocephalic _3___
Right Atrium __12__ Left Atrium _13__
Intercostal __11___ Ventricle __14_
Identify the structure.
1. _______pericardium________ Membrane over the heart.
2. _____trachea________ Airway from mouth to lungs
3. ____carotids_______ Blood supply to head
4. ____ventricles_________ Lower heart chambers
5. ____dorsal aorta_______ Blood supply to lower body
6. ____diaphragm_______ Muscle to aid breathing
7. ____vena cava_______ Returns blood to heart
8. ____aorta (or pulmonary)____ Large vessel at top of heart
9. ____larynx______ Used to make noises
10. ___coronary______ Arteries on heart surface.
Fetal Pig – Dissection of the Lower Arteries
I often do this part as an “optional section”. Some students will work very fast and will need something to do while others catch up. I have also offered extra credit to students who can expose these arteries to view (cleanly), which gives them extra incentive to work on it. The problem is, if you are spending time with groups that are farther behind, then you don’t have a lot of time to help students with the arteries. Giving them extra credit encourages them to try, but also requires them to work on their own.
1. Trace the abominal aorta (also called the dorsal aorta) to the lower part of the body, careful tweezing of the tissue will reveal several places where it branches, though some of the arteries may have been cut when you removed organs of the digestive system. checkbox
2. The hepatic artery leads to the liver. (may not be visible) checkbox
3. The splenic artery leads to the spleen (may not be visible) checkbox
4. The renal arteries lead to the kidney. checkbox
5. The mesenteric artery leads to the mesentery and branches into many smaller vessels. Look in the small intestine to find this artery. checkbox
6. Trace the abominal aorta and note where it joins the umbilical arteries. You will need to cut the muscle in the leg to trace the next vessels. Use a pin to carefully tease away the surrounding muscle and tissue. checkbox
7. The abominal aorta splits into two large vessels that lead to each leg – the external iliac arteries will turn into the femoral arteries as they enter the leg checkbox
8. Follow the umbilical artery toward the pig, you’ll find that it branches and a small artery stretches toward the posterior of the pig – this is the ilio-lumbar artery. checkbox
9. Follow the external iliac into the leg (carefully tease away muscle),it will branch into two arteries: the femoral (toward the outside of the leg) and the deep femoral (toward the back of the leg) checkbox
Creative Commons LicenseThis work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License.
Ch 17 HW(Click for answers)
Activity: DNA and RNA Structure
In the accompanying image, a nucleotide is indicated by the letter _____.
Which of these is a difference between a DNA and an RNA molecule?
This is an image of a(n) _____.
The letter A indicates a _____.
A nitrogenous base is indicated by the letter _____.
You can tell that this is an image of a DNA nucleotide and not an RNA nucleotide because you see a _____.
Which of these nitrogenous bases is found in DNA but not in RNA?
Which of these is(are) pyrimidines?
In a nucleotide, the nitrogenous base is attached to the sugar’s _____ carbon and the phosphate group is attached to the sugar’s _____ carbon.
Nucleic acids are assembled in the _____ direction.
In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.
Activity: The Hershey-Chase Experiment
This is an image of a _____.
Who demonstrated that DNA is the genetic material of the T2 phage?
The radioactive isotope 32P labels the T2 phage’s _____.
Hershey and Chase used _____ to radioactively label the T2 phage’s proteins.
After allowing phages grown with bacteria in a medium that contained 32P and 35S, Hershey and Chase used a centrifuge to separate the phage ghosts from the infected cell. They then examined the infected cells and found that they contained _____, which demonstrated that _____ is the phage’s genetic material.
DNA Replication (1 of 2): DNA Structure and Replication Machinery (BioFlix tutorial)
Part A – The chemical structure of DNA and its nucleotides
Part B – The role of DNA polymerase III
Part C – The replication bubble and antiparallel elongation
DNA replication always begins at an origin of replication. In bacteria, there is a single origin of replication on the circular chromosome, as shown in the image here. Beginning at the origin of replication, the two parental strands (dark blue) separate, forming a replication bubble. At each end of the replication bubble is a replication fork where the parental strands are unwound and new daughter strands (light blue) are synthesized. Movement of the replication forks away from the origin expands the replication bubble until two identical chromosomes are ultimately produced.
In this activity, you will demonstrate your understanding of antiparallel elongation at the replication forks. Keep in mind that the two strands in a double helix are oriented in opposite directions, that is, they are antiparallel.
Part D – Unwinding the DNA
DNA Replication (2 of 2): Synthesis of the Leading and Lagging Strands (BioFlix tutorial)
Part A – Comparing the leading and lagging strands
As the two parental (template) DNA strands separate at a replication fork, each of the strands is separately copied by a DNA polymerase III (orange), producing two new daughter strands (light blue), each complementary to its respective parental strand. Because the two parental strands are antiparallel, the two new strands (the leading and lagging strands) cannot be synthesized in the same way.
Part B – RNA primers on the leading and lagging strands
The diagram below shows a replication bubble with synthesis of the leading and lagging strands on both sides of the bubble. The parental DNA is shown in dark blue, the newly synthesized DNA is light blue, and the RNA primers associated with each strand are red. The origin of replication is indicated by the black dots on the parental strands.
Part C – Synthesis of the lagging strand
In contrast to the leading strand, the lagging strand is synthesized as a series of segments called Okazaki fragments. The diagram below illustrates a lagging strand with the replication fork off-screen to the right. Fragment A is the most recently synthesized Okazaki fragment. Fragment B will be synthesized next in the space between primers A and B.
Activity: DNA Packing
The letter A indicates _____.
Where would RNA polymerase attach?
The letter C indicates _____.
What is this an image of?
What is this an image of?
Scientific Skills Exercise: Working With Data in a Table
Even before the structure of DNA was elucidated, Erwin Chargaff and his coworkers noticed a pattern in the base composition of nucleotides from different organisms: the number of adenine (A) bases roughly equaled the number of thymine (T) bases, and the number of cytosine (C) bases roughly equaled the number of guanine (G) bases. Further, each species they studied had a different balance of A/T and C/G bases. We now know that these consistent ratios are due to complementary base pairing between A and T and between C and G in the DNA double helix, and interspecies differences are due to the unique sequences of bases along a DNA strand. In this exercise, you will apply Chargaff’s rules to predict the composition of nucleotide bases in a genome.
In Chargaff’s experiments, DNA was extracted from the given organism, denatured, and hydrolyzed to break apart the individual nucleotides before analyzing them chemically. These experiments provided approximate values for each type of nucleotide. Today, the availability of whole-genome sequencing has allowed base composition analysis to be done more precisely directly from the sequence data.
Part A – Analyzing the data
Tables like the one shown here are useful for organizing sets of data representing a common set of values (in this case, percentages of A, G, C, and T) for a number of different samples (in this case, species).
|Data from several papers by Chargaff: for example, E. Chargaff et al., Composition
of the desoxypentose nucleic acids of four genera of sea-urchin, Journal of Biological
Chemistry 195: 155-160 (1952).
Part B – Calculating missing data
You can use Chargaff’s rules to predict the percentage of one or more bases in the DNA of a species if at least one value is known.
|Data from several papers by Chargaff: for example, E. Chargaff et al., Composition
of the desoxypentose nucleic acids of four genera of sea-urchin, Journal of Biological
Chemistry 195: 155-160 (1952).
Part D – Evaluating a hypothesis
Misconception Question 79
Misconception Question 78
Misconception Question 80
Misconception Question 77
Misconception Question 76
AP Exam Prep Question 30
In E. coli replication the enzyme primase is used to attach a 5 to 10 base ribonucleotide strand complementary to the parental DNA strand. The RNA strand serves as a starting point for the DNA polymerase that replicates the DNA. If a mutation occurred in the primase gene, which of the following would you expect?
AP Exam Prep Question 31
AP Exam Prep Question 32
Chapter 16 Question 1
Chapter 16 Question 2
Chapter 16 Question 3
Chapter 16 Question 4
Chapter 16 Question 5
Chapter 16 Question 6
Chapter 16 Question 7
Chapter 16 Question 8
Activity: DNA Double Helix
Chapter 16 Pre-Test Question 3
Chapter 16 Pre-Test Question 2
Chapter 16 Pre-Test Question 1
Activity: DNA Replication: A Review
Which of these is responsible for catalyzing the formation of an RNA primer?
Activity: DNA Replication: A Closer Look
Activity: DNA Replication: An Overview
Activity: DNA Synthesis
DNA Replication: Mechanism and Proteins
Part A – The mechanism of DNA replication
Part B – Processes occurring at a bacterial replication fork
Chapter 16 Pre-Test Question 9
Chapter 16 Pre-Test Question 10
Chapter 15 Pre-Test Question 9
How are human mitochondria inherited?
Chapter 15 Pre-Test Question 2
Chapter 15 Pre-Test Question 3
Chapter 15 Question 1
When Thomas Hunt Morgan crossed his red-eyed F1 generation flies to each other, the F2 generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?
Chapter 15 Pre-Test Question 4
Chapter 15 Pre-Test Question 10
Chapter 15 Question 3
Chapter 15 Question 25
What does a frequency of recombination of 50% indicate?
Chapter 15 Question 26
Chapter 15 Pre-Test Question 5
In general, the frequency with which crossing over occurs between two linked genes depends on what?
Chapter 15 Pre-Test Question 7
Chapter 15 Question 40
If cell X enters meiosis, and nondisjunction of one chromosome occurs in one of its daughter cells during meiosis II, what will be the result at the completion of meiosis?
Chapter 15 Pre-Test Question 8
What phenomenon occurs when a particular allele will either be expressed or silenced, depending on whether it is inherited from a male or a female?
AP Exam Prep Question 29
Misconception Question 72
Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel’s law of independent assortment?
Chapter 15 Question 43
Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?
Chapter 15 Question 23
Which of the following statements is true of linkage?
Chapter 15 Pre-Test Question 6
Which of the following results in a situation in which the chromosome number is either 2n+1 or 2n-1 ?
Chapter 15 Question 41
One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this alteration called?
Chapter 15 Question 42
A nonreciprocal crossover causes which of the following products?
Chapter 15 Question 27
Recombination between linked genes comes about for what reason?
Chapter 15 Question 24
How would one explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?
Chapter 15 Question 31
In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure above. What is the order of these genes on a chromosome map?
Chapter 15 Question 32
Use the following information to answer the question(s) below.
A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine as follows:
A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type):
Which of the following are the phenotypes of the parents in this cross?
The inheritance of a skin condition in humans
Consider the following family history:
- Bob has a genetic condition that affects his skin.
- Bob’s wife, Eleanor, has normal skin. No one in Eleanor’s family has ever had the skin condition.
- Bob and Eleanor have a large family. Of their eleven children, all six of their sons have normal skin, but all five of their daughters have the same skin condition as Bob.
Based on Bob and Eleanor’s family history, what inheritance pattern does the skin condition most likely follow?
Part B – A sex-linked gene for eye color in Drosophila
|A homozygous wild-type female fly is mated with a vermilion male fly.|
Predict the eye colors of F1 and F2 generations. (Assume that the F1 flies are allowed to interbreed to produce the F2 generation.)
Part C – The inheritance of both a sex-linked trait and an autosomal trait in humans
- A man with a widow’s peak and normal color vision marries a color-blind woman with a straight hairline.
- The man’s father had a straight hairline, as did both of the woman’s parents.
Use the family history to make predictions about the couple’s children.
AP Exam Prep Question 28
Experimental Inquiry: What Is the Inheritance Pattern of Sex-Linked Traits?
Part A – Experimental technique: Reciprocal crosses
- Drag blue labels onto the blue targets to indicate the genotypes of the parents and offspring.
- Drag pink labels onto the pink targets to indicate the genetic makeup of the gametes (sperm and egg).
Labels can be used once, more than once, or not at all.
Part B – Experimental results: The F2 generation
Next, Morgan crossed the red-eyed F1 males with the red-eyed F1 females to produce an F2 generation. The Punnett square below shows Morgan’s cross of the F1 males with the F1 females.
- Drag pink labels onto the pink targets to indicate the alleles carried by the gametes (sperm and egg).
- Drag blue labels onto the blue targets to indicate the possible genotypes of the offspring.
Labels can be used once, more than once, or not at all.
Part C – Experimental prediction: Comparing autosomal and sex-linked inheritance
Suppose that a geneticist crossed a large number of white-eyed females with red-eyed males.
Consider two separate cases:
- Case 1: Eye color exhibits sex-linked inheritance.
- Case 2: Eye color exhibits autosomal (non-sex-linked) inheritance. (Note: In this case, assume that the red-eyed males are homozygous.)
Linked Genes and Linkage Mapping
In this tutorial, you will compare the inheritance patterns of unlinked and linked genes.
Part A – Independent assortment of three genes
In a cross between these two plants (MMDDPP x mmddpp), all offspring in the F1 generation are wild type and heterozygous for all three traits (MmDdPp).
Now suppose you perform a testcross on one of the F1 plants (MmDdPp x mmddpp). The F2 generation can include plants with these eight possible phenotypes:
Part B – Gene linkage and phenotypic ratios
Part C – Building a linkage map
Use the data to complete the linkage map below.
Scientific Skills Exercise: Using the Chi-Square Test
Genes that are in close proximity on the same chromosome will result in the linked alleles being inherited together more often than not. But how can you tell if certain alleles are inherited together due to linkage or due to chance?
If genes are unlinked and therefore assort independently, the phenotypic ratio of offspring from an F1 testcross is expected to be 1:1:1:1. If the two genes are linked, however, the observed phenotypic ratio of the offspring will not match the expected ratio.
Given random fluctuations in the data, how much must the observed numbers deviate from the expected numbers for us to conclude that the genes are not assorting independently but may instead be linked? To answer this question, scientists use a statistical test called a chi-square (χ2) test. This test compares an observed data set to an expected data set predicted by a hypothesis (here, that the genes are unlinked) and measures the discrepancy between the two, thus determining the “goodness of fit.”
If the difference between the observed and expected data sets is so large that it is unlikely to have occurred by random fluctuation, we say there is statistically significant evidence against the hypothesis (or, more specifically, evidence for the genes being linked). If the difference is small, then our observations are well explained by random variation alone. In this case, we say the observed data are consistent with our hypothesis, or that the difference is statistically insignificant. Note, however, that consistency with our hypothesis is not the same as proof of our hypothesis.
Part A – Calculating the expected number of each phenotype
In cosmos plants, purple stem (A) is dominant to green stem (a), and short petals (B) is dominant to long petals (b). In a simulated cross, AABB plants were crossed with aabb plants to generate F1 dihybrids (AaBb), which were then test crossed (AaBb X aabb). 900 offspring plants were scored for stem color and flower petal length. The hypothesis that the two genes are unlinked predicts the offspring phenotypic ratio will be 1:1:1:1.
Part B – Calculating the χ2 statistic
The goodness of fit is measured by χ2. This statistic measures the amounts by which the observed values differ from their respective predictions to indicate how closely the two sets of values match.
The formula for calculating this value is
where o = observed and e = expected.
Part C – Interpreting the data
A standard cut-off point biologists use is a probability of 0.05 (5%). If the probability corresponding to the χ2 value is 0.05 or less, the differences between observed and expected values are considered statistically significant and the hypothesis should be rejected. If the probability is above 0.05, the results are not statistically significant; the observed data is consistent with the hypothesis.
To find the probability, locate your χ2 value (2.14) in the χ2 distribution table below. The “degrees of freedom” (df) of your data set is the number of categories (here, 4 phenotypes) minus 1, so df = 3.
Chromosomal mutations are changes in the normal structure or number of chromosomes.
- Changes in chromosome structure can result from errors in meiosis or from exposure to radiation or other damaging agents.
- Certain changes in chromosome number can result from nondisjunction during either meiosis or mitosis.
Both structural mutations and nondisjunction can play a role in trisomy 21, commonly known as Down syndrome.
Part A – Changes in chromosome structure
The following table illustrates some structural mutations that involve one or both of these chromosomes. Identify the type of mutation that has led to each result shown.
Part B – Nondisjunction
Suppose a diploid cell with three pairs of homologous chromosomes (2n = 6) enters meiosis.
How many chromosomes will the resulting gametes have in each of the following cases?
Part C – Trisomy 21
Suppose that a carrier of familial Down syndrome mated with a person with a normal karyotype. Which gamete from the carrier parent could fuse with a gamete from the normal parent to produce a trisomy-21 zygote?
Make Connections: Chromosomal Inheritance and Independent Assortment of Alleles
Part A – Reviewing independent assortment of alleles
- Under the hypothesis of dependent assortment, the alleles inherited from the parental generation should always be transmitted to the next generation in the same combinations.
- Under the hypothesis of independent assortment, alleles for different characters should segregate independently of each other, meaning that alleles should be packaged into gametes in all possible combinations, as long as each gamete has one allele for each gene.
The figure below shows the experiment that Mendel used to distinguish between these two hypotheses. The results of the experiment confirmed that the alleles for these characters undergo independent assortment.
Part B – Chromosomal inheritance during meiosis
- The number at the top of each column corresponds to the same number in the image above. Each column describes what happens at that numbered stage.
- Use only white labels for white targets, blue labels for blue targets, and pink labels for pink targets.
Part C – Do the alleles for different characters always sort independently?
- Flower color, which can be blue (BB) or purple (bb)
- Petal shape, which can be pointy (PP) or rounded (pp)
You use the following procedure.
- In the parental generation, you breed a plant that you know to be homozygous for blue-pointy flowers (BBPP) with a plant that you know to be homozygous for purple-rounded flowers (bbpp).
- In the F1 generation, all your plants have blue-pointy flowers (BbPp).
- You then allow the F1 plants to self-pollinate to produce F2 offspring. In the F2 generation, you obtain 80 plants with the following phenotypes. Note that an underscore “_” in the genotype indicates that the second allele for that gene could be either dominant or recessive:
|Phenotype||Number of individuals|
|Blue flower/pointy petal (B_P_)||59|
|Blue flower/rounded petal (B_pp)||1|
|Purple flower/pointy petal (bbP_)||0|
|Purple flower/rounded petal (bbpp)||20|
To try to explain this unusual data, you come up with two alternate hypotheses in addition to your original hypothesis of independent assortment.
Hypothesis 1: The alleles for flower color and petal shape are found on different chromosomes. (This is independent assortment as observed by Mendel with the characters of seed color and shape.)
Hypothesis 2: The alleles for flower color and petal shape are found on different chromosomes, but the blue-rounded (B_pp) and purple-pointy (bbP_) phenotypes typically do not survive, for a reason that has yet to be determined.
Hypothesis 3: The alleles for flower color and petal shape are found close to each other on the same chromosome.
Activity: Mistakes in Meiosis
Activity: Polyploid Plants
Misconception Question 71
Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel’s law of segregation?
Misconception Question 73
Misconception Question 74
Imagine a human disorder that is inherited as a dominant, X-linked trait. How would the frequency of this disorder vary between males and females?
Here is a PDF with the answers to the packet for chapter 15.
Here is a PDF for the answers for the packet for this chapter.