MS-LS3-2: Modeling Asexual and Sexual Reproduction and Genetic Variation
In plain English: MS-LS3-2 is the NGSS middle school performance expectation that asks students to develop and use a model, such as a Punnett square, a diagram or a simulation, to explain why asexual reproduction gives offspring with identical genetic information while sexual reproduction gives offspring with genetic variation. It is usually taught in grade 7 or 8 life science.
Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation.
Clarification Statement: Emphasis is on using models such as Punnett squares, diagrams, and simulations to describe the cause and effect relationship of gene transmission from parent(s) to offspring and resulting genetic variation.
Next Generation Science Standards · Disciplinary Core Idea: Heredity: Inheritance and Variation of Traits · Official standard
Students develop and use models to explain why offspring made by asexual reproduction (one parent) carry genetic information identical to their parent, while offspring made by sexual reproduction (two parents) show genetic variation. They draw chromosome diagrams, build Punnett squares, run a bean-draw simulation for a fictional animal, root plant cuttings and compare them with seedlings, and critique other students' models. All examples use plants, animals or fictional organisms, never students or their families, and all data sets are invented for teaching.
The NGSS Clarification Statement says: "Emphasis is on using models such as Punnett squares, diagrams, and simulations to describe the cause and effect relationship of gene transmission from parent(s) to offspring and resulting genetic variation." MS-LS3-2 has no official Assessment Boundary. Students do the practice of developing and using models: they build each model, use it to predict outcomes, compare predictions with data and revise models that contain errors.
Learning Objectives
By the end of this lesson, students will be able to:
Use a diagram to explain why offspring of asexual reproduction have genetic information identical to their one parent
Use a diagram and a Punnett square to explain why offspring of sexual reproduction get half their genes from each parent and so vary
Use a Punnett square to predict the chances of allele combinations and compare predictions with data
Run and interpret a simulation of gene transmission, and critique models that show it incorrectly
Prior Knowledge Required
Students should already be comfortable with:
Plants and animals have life cycles that include reproduction 3-LS1-1
Traits are inherited, and individuals of the same kind vary 3-LS3-1
Genes on chromosomes code for proteins that affect traits MS-LS3-1
Show two photos: a tray of young spider-plant offshoots (baby plants on runners) that all look alike, and a litter of kittens from the same two parent cats with different coat colors and patterns.
Warm-Up Prompt
"The baby plants all look like their one parent. The kittens look different from each other and from their parents. What do you think is different about how each group was made? What would you need to know to test your idea?"
Record ideas without correcting them. Students often say "one parent or two"; ask them why two parents would lead to differences. Return to this question at the end with the model.
Direct Instruction15-20 minutes
Key words.Genetic information is the set of genes an organism carries on its chromosomes (long strands of DNA in the nucleus). Most plant and animal cells have chromosomes in pairs, so they have two copies of each gene. The two copies may be the same or different versions; each version is called an allele and is written with a letter, such as A or a. Offspring are the young that an organism produces. In asexual reproduction, one parent makes offspring from its own body cells, which copy all of its chromosomes, so the offspring get identical genetic information. Offspring with identical genetic information are called clones. In sexual reproduction, two parents each make sex cells (eggs, sperm or pollen) that carry only one chromosome from each pair, chosen at random, and two sex cells join. So each offspring gets half its genes from each parent, in a new combination. Differences in genes among offspring are called genetic variation.
Models. A Punnett square is a grid that shows every way the alleles of two parents can combine. One parent's alleles go across the top, the other's down the side, and each box is one equally likely outcome. An allele is dominant if one copy is enough to show its trait; the other allele is recessive, and its trait shows only with two copies. A simulation is a model that acts out a process with chance, such as drawing beans from bags. Diagram 1 compares the two kinds of reproduction. Rare mutations (changes in genes) can make even a clone slightly different; MS-LS3-1 covers them.
Asexual reproduction: plantlets on a kalanchoe leaf
A kalanchoe plant grows tiny plantlets along the edges of its leaves. The plantlets drop off, root and grow into new plants. In the model, suppose the parent carries alleles A and a for one gene and B and b for another. A class potted 36 plantlets from one parent.
Result: Each plantlet is made from the parent's own cells, which copy all of the parent's chromosomes. So every plantlet has Aa Bb, the same genetic information as the parent and as each other: 36 of 36 match (100%). With one parent and exact copies, there is no source of new gene combinations.
Sexual reproduction: a Punnett square for squash color (Diagram 2)
In summer squash, the allele for white fruit (W) is dominant to the allele for yellow fruit (w): a plant with at least one W has white fruit. Two Ww plants, both with white fruit, are crossed. Invented data: 64 of their seeds grow into plants that bear fruit: 45 have white fruit and 19 have yellow fruit.
Result: Punnett square: WW, Ww, Ww, ww, so 3 in 4 offspring are expected to have white fruit and 1 in 4 yellow. Expected: 64 × 3/4 = 48 white and 64 × 1/4 = 16 yellow. Observed 45 and 19 are close; real counts scatter around the prediction. The yellow plants have a trait that neither parent shows, because each got one w from each parent.
One plant, two ways: strawberry runners and strawberry seeds
A strawberry plant with alleles Aa Bb sends out runners, stems that grow along the ground and root into new plants. It also makes seeds when its flowers are pollinated by another Aa Bb plant. A grower raises 12 runner plants and a tray of seedlings.
Result: Runner plants: all 12 are Aa Bb, identical to the parent. Seedlings: for gene A alone, a Punnett square gives AA, Aa or aa (3 combinations), and the same for gene B, so there are 3 × 3 = 9 possible combinations. A seedling matches the parent (Aa and Bb) with probability 1/2 × 1/2 = 1/4. Most seedlings differ from the parent and from each other.
A simulation: bean-draw offspring for a fictional animal
The Snorkid is a fictional animal with 3 genes on 3 chromosome pairs, and both parents are Aa Bb Cc. For each gene, each parent has a bag with one dark bean (the capital-letter allele) and one white bean. To make a sexual offspring, draw one bean from each bag of each parent without looking. To make an asexual offspring, copy both beans of every bag of one parent. A group made 16 offspring each way (invented results): asexual, 16 of 16 were Aa Bb Cc; sexual, 3 of 16 were Aa Bb Cc and the other 13 differed.
Result: Model prediction for a sexual offspring to match a parent: 1/2 for each gene, so 1/2 × 1/2 × 1/2 = 1/8, and 16 × 1/8 = 2 expected. Observed 3 of 16 = 18.75%, near the predicted 12.5% for so few offspring. Asexual offspring: 100% identical, as the model predicts.
After each example, ask: "How many parents? Did the offspring get copies of all the parent's genes or half from each parent? What does the model predict about how alike the offspring are?" Use Example 2 to show that a Punnett square predicts chances, not exact counts.
Guided Practice10-15 minutes
Pairs build two Punnett squares and one asexual model. In cats, the allele for short hair (L) is dominant to the allele for long hair (l).
Cross 1: two short-haired cats, both Ll. Draw the Punnett square and write the chance that a kitten has long hair.
Cross 2: a short-haired Ll cat and a long-haired ll cat. Draw the square and write the chance of a long-haired kitten.
For Cross 2, predict how many long-haired kittens to expect in a litter of 4. Explain why a real litter of 4 could have 0, 1, 3 or 4 long-haired kittens.
Garlic is usually grown by planting single cloves from a bulb. A farmer plants all 10 cloves from one bulb. Draw a model that shows the genes of the parent plant and the 10 new plants.
Write two sentences comparing how alike the kittens and the garlic plants are, and why.
Independent Practice10-15 minutes
Each student analyzes invented data about the Bloomworm, a fictional sea worm that can split in two (asexual) or mate (sexual). Both parent worms carry two different alleles for each of 4 genes. Scientists recorded whether each offspring had exactly the same allele pairs as its parents for all 4 genes.
Independent practice data (invented): 20 Bloomworm offspring of each kind
How the offspring were made
Same allele pairs as the parents for all 4 genes
Different in at least one gene
Splitting (asexual)
20
0
Mating (sexual)
2
18
Students find the percent of each group that matched the parents, use the model (1/2 for each gene) to predict the chance that a sexual offspring matches, and explain in a paragraph why the two groups differ so much. They end with one prediction: what would happen to the match rate if the worms differed in 8 genes instead of 4?
Closure5 minutes
Exit ticket: "Draw a quick model of one asexual and one sexual reproduction from today. Label where the offspring's genes came from, and write one sentence on why only one kind gives variation." Return to the warm-up photos and ask students to explain the plants and the kittens with their model.
Differentiation Strategies
For Struggling Students
Provide a Punnett square template with the parent alleles already in place, and color-code the dominant allele
Use paper strips for chromosomes so students can physically copy (asexual) or split (sexual) them
Give a sentence frame: "In ___ reproduction there is/are ___ parent(s), so the offspring get ___, which means they are ___."
For Advanced Students
Ask students to count the possible combinations for 4 genes when both parents are Aa Bb Cc Dd (3 × 3 × 3 × 3 = 81)
Have students pool class simulation data and explain why bigger samples land closer to the Punnett prediction
Ask students to argue when a farmer would choose cuttings and when a plant breeder would choose seeds
Assessment Guidance
What to Look For
Check that students explain the cause, not just the outcome: asexual offspring are identical because all chromosomes are copied from one parent; sexual offspring vary because each parent passes on a random one of each chromosome pair. Look for correct Punnett squares that list one parent's alleles on each side. Listen for students who treat Punnett predictions as exact counts or who think a sexual offspring is a half-and-half blend of its parents.
02
Classroom Activities
3 Activities
1
Bean Draw: Building Snorkid Offspring
25 minGroups of 3
Groups simulate asexual and sexual reproduction for the fictional Snorkid. Each parent has three paper bags, one for each gene, and each bag holds one dark bean (dominant allele) and one white bean (recessive allele).
Procedure
Trait key: gene A, ears (at least one dark bean: pointed; two white: round); gene B, tail (dark: striped; two white: plain); gene C, body (dark: green; two white: orange).
Asexual round: one parent "buds". Copy both beans of each of its bags onto the record sheet. Make 10 offspring this way.
Sexual round: without looking, draw one bean from each bag of parent 1 and one from each bag of parent 2. Record the pair for each gene, put the beans back and shake the bags. Make 10 offspring.
Draw one offspring of each kind. Safety: dried beans are not food; do not eat them, and pick up any that fall.
Sample Data (invented)
Eight groups pooled 80 sexual offspring: 11 had the same allele pairs as the parents for all three genes (Aa Bb Cc). All 80 asexual offspring matched their parent.
Discussion Questions
The model predicts that 1 in 8 sexual offspring match the parents. How many of 80 is that, and how close was the class?
Why do you put the beans back and draw without looking? What part of real reproduction does that stand for?
Did any sexual offspring show a trait that neither parent showed, such as an orange body? Explain how.
Modification for Distance Learning
Students use two coins per parent (heads for the dark allele) or an online random picker, and share results in a class spreadsheet.
2
Cuttings and Seeds: A Coleus Investigation
20 min, then 2 weeks of observationPairs
Coleus plants have leaves with bold color patterns. Pairs make stem cuttings from one named-variety plant (asexual reproduction by people) and compare them with seedlings the teacher grew from a mixed seed packet (sexual reproduction).
Procedure
With blunt scissors, cut a 10 cm stem tip just below a leaf joint. Remove the lowest leaves and stand the stem in a cup of water labeled with your names.
Sketch and describe the leaf pattern of the parent plant and of 10 seedlings: colors, edge shape and markings.
Over the next 2 weeks, check the cuttings for roots and compare their new leaves with the parent's leaves.
Safety: wash hands after handling the plants, and keep the plants away from pets at home.
Sample Data (invented)
All 12 rooted cuttings in one class grew leaves with the parent's pattern. The 10 seedlings showed 6 different leaf patterns.
Discussion Questions
Explain with a model why the cuttings match the parent plant.
Why do the seedlings differ from each other, even though they came from one seed packet of one kind of plant?
A garden center wants 200 plants that all look exactly like its best coleus. Which method should it use, and why?
Modification for Distance Learning
With an adult's permission, students root a cutting from a houseplant such as pothos in water, or use the teacher's photo series of the class plants.
3
Model Critique: Find and Fix the Error
15 minGroups of 3-4
Groups receive three models drawn by fictional students. Each model contains one error. Groups find the error, explain why it is wrong with evidence from the other models on this page, and redraw it correctly.
The Three Models
Model A (asexual): a parent sea anemone with 4 chromosome pairs splits in two, and the drawing gives each new anemone 2 chromosome pairs.
Model B (sexual): a diagram of two parent rabbits in which the baby rabbit gets all its chromosomes from the mother.
Model C (Punnett square): a square for Bb × bb in which the student wrote "Bb" across the top and "Bb" down the side.
Discussion Questions
How many chromosome pairs should each new anemone in Model A have, and why?
How should Model B change, and what does the change mean for variation among baby rabbits?
Fix Model C. What is the chance of a bb offspring in the corrected square?
Challenge Variation
Groups draw their own model with one hidden error and trade it with another group to find and fix.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: A Model of Gene Transmission in Asexual and Sexual Reproduction
Left: in asexual reproduction one parent passes on copies of all its chromosomes, so every offspring has the same alleles (Aa Bb). Right: in sexual reproduction each parent passes on one chromosome from each pair, chosen at random, so offspring get new combinations. The three offspring shown are three of the possible combinations from these parents.
Diagram 2: Punnett Square for Two Ww Squash Plants (Example 2)
Each parent passes on W or w with equal chance. The four boxes are equally likely, so 1 in 4 offspring are expected to be WW, 2 in 4 Ww and 1 in 4 ww. Because W is dominant, 3 in 4 are expected to have white fruit and 1 in 4 yellow fruit.
04
Homework Assignment
~30 min
MS-LS3-2 Homework: Identical or Varied Offspring?
Directions: All data sets are invented for practice. Draw models (diagrams or Punnett squares) where asked, and in every explanation say how many parents there are and where the offspring's genes come from.
Part 1: Asexual or Sexual? (Problems 1-3)
A quaking aspen tree can send up new trunks from its roots, so a whole hillside of trunks can be one connected organism, called a clone. In fall, all the trunks of one clone turn yellow within the same few days, while a clone on the next hillside may turn a week later. (a) Is growing new trunks from roots asexual or sexual reproduction? (b) Use a model to explain why the trunks of one clone change color together. (c) Aspens also make seeds from flowers that are pollinated by wind. Predict how a group of aspens grown from seed would compare in fall, and explain.
In many sheep breeds, the allele for white wool (W) is dominant to the allele for black wool (w). A Ww ram is mated with ww ewes. (a) Draw the Punnett square. (b) What is the chance that a lamb has black wool? (c) How many black lambs would you expect among 12 lambs? (d) One farm got 4 black lambs out of 12. Does this mean the model is wrong? Explain.
The Glimmer snail is a fictional snail in which a spiral shell (S) is dominant to a flat shell (s). Glimmer snails can mate, and they can also reproduce by splitting. (a) Two Ss snails mate. Draw the Punnett square and give the fraction of young expected to be SS, Ss and ss. (b) Of 40 young from such matings, how many would you expect to have flat shells? (c) An Ss snail splits to make 40 young. How many would have flat shells, and why?
Part 2: Simulations and Models (Problems 4-6)
A class ran a bean-draw simulation for one gene with two Aa parents and made 60 offspring (invented results): 12 AA, 34 Aa and 14 aa. (a) Find the percent of each combination. (b) Use a Punnett square to find how many of 60 the model predicts for each. (c) Explain why the results are not exactly equal to the prediction. (d) If one Aa parent had made 60 offspring by budding instead, how many would be Aa?
A rose grower has one rose plant with a perfect deep-red color that buyers love. A plant breeder wants a new rose that resists a leaf disease. (a) Which kind of reproduction should the grower use to make 300 plants with the same color, and how could she do it? (b) Which kind should the breeder use, and why? (c) Use the words "identical genetic information" and "genetic variation" in your answers.
A hydra is a tiny freshwater animal related to jellyfish. In warm water with plenty of food, a hydra grows buds on its side that break off as new hydras. When the water turns cold in fall, many hydras make eggs and sperm instead. (a) Draw a model of each kind of reproduction that shows where the offspring's chromosomes come from. (b) Which offspring will be identical to their parent? (c) Scientists propose that varied offspring are more likely to include some that survive a hard winter. Use your model to explain why variation could help.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Models
Diagrams and Punnett squares are complete and correct, with one parent's alleles on each side
Model drawn, with one error or missing labels
Cause and Effect
Explains that copying all genes gives identical offspring and that half from each parent, at random, gives variation
States the outcome without the cause
Predictions and Data
Correct chances and expected counts, and explains why data scatter around predictions
Correct chances but counts or the comparison with data missing
05
Quiz: 20 Questions
Interactive, with answers
Instructions
All data sets are invented, and all organisms are plants, animals or fictional species. Draw a Punnett square on scrap paper when a question gives parent alleles. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
Which of these is an example of asexual reproduction?
Answer: B
The yeast bud comes from one parent and copies all of its genetic information. Choices A and D involve two parents, so they are sexual reproduction. Choice C moves pollen between two plants, which leads to sexual reproduction.
Question 2 of 20 · Multiple Choice
Why do offspring made by asexual reproduction have genetic information identical to their parent?
Answer: A
With one parent and copied chromosomes, the offspring receive the same alleles. Choice B describes sexual reproduction. Choice D confuses environment with genes: offspring that live in the same place can still have different genes.
Question 3 of 20 · Multiple Choice
In sexual reproduction, how much of its genetic information does each parent pass to an offspring?
Answer: D
Each egg, sperm or pollen cell carries one chromosome of each pair, so each parent gives half. Choice A describes asexual reproduction. Choice B is wrong because sperm and pollen carry genes too.
Question 4 of 20 · Multiple Choice
In a fictional plant, purple flowers (P) are dominant to white flowers (p). A Pp plant is crossed with a pp plant. What is the chance that an offspring has white flowers?
Answer: C
The Punnett square has Pp, Pp, pp, pp, so 2 of 4 boxes, or 50%, are pp with white flowers. Choice B is the chance for two Pp parents. Choice D is the chance of purple flowers for two Pp parents. Choice A assumes the dominant P always wins, forgetting that the Pp parent passes on p half the time and the pp parent always passes on p, so pp offspring with white flowers appear.
Question 5 of 20 · Multiple Choice
One parent is AA and the other is aa for one gene. How many different allele combinations can their offspring have for that gene?
Answer: A
Every box of the Punnett square is Aa, because one parent can pass on only A and the other only a, so there is just 1 combination. Choice B counts the two alleles. Choice C is the answer for two Aa parents. Choice D counts the 4 boxes, which are all the same.
Question 6 of 20 · Multiple Choice
Two Rr plants are crossed, and r is recessive. About how many of 80 offspring would you expect to show the recessive trait?
Answer: A
The chance of rr is 1/4, and 80 × 1/4 = 20. Choice B uses 1/2, the chance of Rr. Choice C is the number expected to show the dominant trait (3/4 of 80). Choice D writes 1/4 as 25 (from 25%) instead of taking 1/4 of 80.
Question 7 of 20 · Multiple Choice
Three groups of 10 offspring are described. Which group was most likely made by asexual reproduction?
Answer: C
Offspring that match their single parent in every trait fit a model in which all genes are copied. Choices B and D describe two parents, which means sexual reproduction. Choice A shows variation, which asexual reproduction does not produce.
Question 8 of 20 · Multiple Choice
Two seedlings grew from seeds of the same two parent plants, but they look different. Which explanation fits the model of sexual reproduction?
Answer: A
Each sex cell carries a random one of each chromosome pair, so siblings get different combinations. Choice B is wrong because each seedling gets the same number of chromosomes. Choice C describes asexual reproduction.
Question 9 of 20 · Multiple Choice
Why can genetic variation among offspring help a population of plants?
Answer: D
If the plants differ, a new disease or a change in weather may kill some but not all of them. Choice C describes clones, which have no variation. Choice B is too strong: variation raises the chance that some survive, but it does not prevent disease.
Question 10 of 20 · Multiple Choice
Most bananas sold in stores come from plants grown from shoots of other banana plants, not from seeds. Why does this make a banana farm risky when a new plant disease arrives?
Answer: B
Growing from shoots is asexual, so the plants are clones. If the disease can kill one, it can kill nearly all of them. Choice C is false: shoots carry the parent's full set of genes. Choice D has no support in the model.
Question 11 of 20 · Multiple Choice
Two parents are both Aa Bb, with the two genes on different chromosome pairs. What is the chance that an offspring is aa bb?
Answer: C
The chance of aa is 1/4 and the chance of bb is 1/4, so the chance of both is 1/4 × 1/4 = 1/16. Choice B counts only one gene. Choice A adds 1/4 + 1/4 instead of multiplying. Choice D multiplies 1/4 by 1/2, as if one parent were bb.
Question 12 of 20 · Multiple Choice
In a class simulation with two Aa parents, 12 of 50 offspring were aa. What percent were aa, and how does it compare with the Punnett square prediction?
Answer: B
12 ÷ 50 = 24%, and the square (AA, Aa, Aa, aa) predicts 1 in 4, or 25%. Choice A writes the count as a percent. Choice C expects a chance model to give exact counts. Choice D is the share that were not aa, compared with a wrong prediction.
Question 13 of 20 · Multiple Choice
Which description is a correct model of sexual reproduction?
Answer: D
Each parent gives one of each pair, so the offspring again has complete pairs, half from each parent. Choice C would double the number of chromosomes. Choices A and B leave out one parent's contribution.
Question 14 of 20 · Multiple Choice
A gardener wants 50 African violet plants that are exactly like her best plant. What should she do?
Answer: D
Leaf cuttings grow into new plants by asexual reproduction, so they carry the same genes as the best plant. Choices A and C use sexual reproduction, which gives varied seedlings. Choice B gives seedlings from unknown parents.
Question 15 of 20 · Short Answer
The Fennow is a fictional fox in which a long tail (L) is dominant to a short tail (l). An LL Fennow mates with an Ll Fennow. Draw the Punnett square, give the chance of each allele combination, and predict how many of 8 young would have short tails.
Square: LL, LL, Ll, Ll. Chances: LL 1/2, Ll 1/2, ll 0. So 0 of 8 young would have short tails, because the LL parent always passes on L. A full answer adds that about half the young (Ll) still carry the short-tail allele and could have short-tailed young of their own.
Question 16 of 20 · Short Answer
Potato farmers usually plant pieces of potatoes, called seed potatoes, instead of true seeds. Use a model to explain why a field planted this way gives very similar plants, and name one risk.
A piece of potato grows into a new plant by asexual reproduction, copying all of the parent's chromosomes, so every plant in the field has identical genetic information. Risk: if a disease or pest can harm one plant, it can harm almost all of them, because none has different alleles that might resist it.
Question 17 of 20 · Short Answer
In the bean-draw simulation, why must students put the beans back and draw without looking? What would go wrong if a student always chose the dark bean?
Drawing without looking makes each allele equally likely to be passed on, which models the random way a chromosome from each pair ends up in an egg, sperm or pollen cell. If a student always chose the dark bean, every offspring would get the dominant allele from that parent, the results would no longer match the Punnett square, and the model would hide real variation.
Question 18 of 20 · Short Answer
A student writes: "A seedling gets half its genes from each parent plant, so it must look exactly halfway between its two parents." What is correct in this statement, and what is wrong?
Correct: each parent passes on half its genes, one chromosome of each pair. Wrong: the seedling is not a blend. Its traits depend on which alleles it got and which are dominant, so it may look like one parent, like neither (for example, two white-fruit Ww squash can give a yellow-fruit ww plant), or have its own mix of traits.
Question 19 of 20 · Short Answer
A sea anemone can reproduce by splitting down the middle into two anemones. Describe a model that shows where each new anemone's chromosomes come from, and explain whether the two will be genetically identical.
Model: draw the parent with its chromosome pairs, then two new anemones, each with a full copy of every pair, because the parent's cells copy their chromosomes before and while the body splits. Both new anemones are genetically identical to the parent and to each other, since there is one parent and no new combinations. Rare mutations are the only exception.
Question 20 of 20 · Short Answer
A parent that is Aa Bb makes 30 offspring by asexual reproduction. The same kind of organism, crossed Aa Bb × aa bb, makes 40 offspring by sexual reproduction. How many of the 30 asexual offspring are Aa Bb? How many of the 40 sexual offspring would you expect to be aa bb? Explain.
Asexual: all 30 are Aa Bb, because all genes are copied from one parent. Sexual: the chance of aa is 1/2 (Aa × aa) and of bb is 1/2 (Bb × bb), so aa bb has chance 1/2 × 1/2 = 1/4, and 40 × 1/4 = 10 expected.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does MS-LS3-2 mean?
MS-LS3-2 asks students to build and use models that explain why asexual reproduction makes offspring with identical genetic information and sexual reproduction makes offspring with genetic variation. The code means Middle School, Life Science, core idea 3 (Heredity: Inheritance and Variation of Traits), performance expectation 2.
What grade is MS-LS3-2 taught in?
It is a middle school standard for grades 6-8. Schools usually teach it in grade 7 or 8 life science, often right after MS-LS3-1 on mutations and before natural selection in MS-LS4.
Does MS-LS3-2 have an assessment boundary?
No. MS-LS3-2 has no official Assessment Boundary. The Clarification Statement names the models: Punnett squares, diagrams and simulations that show how genes pass from parent or parents to offspring and why variation results.
Are Punnett squares required for MS-LS3-2?
Punnett squares are one of the models named in the Clarification Statement, along with diagrams and simulations. Students should use at least one of them to explain cause and effect, not only to fill in boxes. One-gene squares with dominant and recessive alleles are enough at this level.
What is the difference between asexual and sexual reproduction?
Asexual reproduction has one parent, and the offspring get copies of all its genes, so they are clones. Sexual reproduction has two parents, and each passes on half its genes, one chromosome of each pair, so the offspring get new combinations.
Why do offspring in the same litter look different?
Each egg and sperm carries a random one of each chromosome pair, so every offspring gets a different mix of the parents' alleles. With many genes, the number of possible combinations is so large that two siblings almost never get the same set, unless they developed from the same fertilized egg.
Are clones always exactly identical?
Clones start with identical genetic information. Rare mutations can make small differences, and the environment, such as light or food, can change how traits develop. That is why a cutting in a dark corner may look paler than its parent even with the same genes.
What simulations work well for MS-LS3-2?
Drawing beans or paper chromosomes from bags, flipping coins for each allele, or using an online random picker all work. The key rule is that each parent passes on one allele per gene at random, and students compare their results with the Punnett square prediction.
Should students use their own families as examples?
No. This page uses plants, animals and fictional organisms, such as the Snorkid and the Bloomworm, so no student's family or traits are put on display. The models work the same way for any sexually reproducing organism.
What misconceptions do students have about reproduction and genes?
Common ones are that offspring are a blend halfway between the parents, that one parent (often the mother) gives more genes, and that a Punnett square gives exact counts. Another is that asexual reproduction only happens in tiny organisms; many plants and some animals, such as hydras and sea anemones, reproduce asexually.
07
Related Standards
6 standards
These standards connect to MS-LS3-2: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
3-LS1-1Prerequisite
Model that organisms have diverse life cycles that all include reproduction
Lesson coming soon
3-LS3-1Prerequisite
Use data to show that traits are inherited and vary within a group
Lesson coming soon
Alongside
MS-LS3-1Parallel
Model why gene mutations on chromosomes may change proteins and traits
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