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- Students will recognize that traits are inherited from parents.
- Students will demonstrate that sexual reproduction produces variation, which allows organisms to adapt to changing environment.
- Students will be able to compare and contrast genotype and phenotype.
- Students will be able to distinguish between dominant and recessive alleles.
- Students will create their own sexually reproducing organism. They will choose four traits that the organisms will pass on to their offspring. Based on these traits, they will determine what the genotypes and the phenotypes of the offspring will be. They will create three different offspring.
- Students will compare and contrast the parents to the offspring and the offspring to one another. This will lead them to the conclusion that sexual reproduction creates variation.
- Copies of worksheet (1 per group).
- Slips of scratch paper.
- Colored pencils, markers, or crayons.
- This activity worked well with some of the more artistic students in the class who generally do not enjoy science laboratory activities. Some of the students seemed to be disturbed by the open ended nature of the activity. They did not know what to draw or how to begin. They wanted the activity to be more structured. The students practice thinking about genotype and phenotype, which lead nicely into following concepts, such as Punnett squares.
- Engage: Put students into small groups (2 to 4) and give each group a heredity related vocabulary word (e.g. heredity, inheritance, adaptation, DNA). Ask each group to make a list of all of the associations that they have with their word. Discuss the responses as a class.
- Explore: Give students an image of a litter of puppies (and the parents). Ask them to compare and contrast the appearance of the dogs. This could be done using merle coloring in dogs (an example can be found at Elementary Merle Genetics). Discuss their responses as a class.
- Explain: Give the students a short lecture on the inheritance and the heredity of traits (including ideas about alleles, dominance patterns, and Punnett squares). Discuss their association with the genetics words now that they have a new context and their observations about the dogs.
- Elaborate: Individually or in pairs, have the students complete the Genetic Traits and Heredity activity and worksheet.
- Evaluate: Have the students come up with environmental changes that would impact their organisms. Students should discuss how this change would impact the genotypes and phenotypes of the current generation of the organism, the following generation, five generations from the current generation, and 100 generations from the current generation. Have the students discuss what would happen at each of those stages if the environment changed back to the original state.
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- Students need to be familiar with the following concepts before completing the activity (this may be accomplished through a short lecture prior to beginning the activity): 1) Heredity and inheritance of traits, 2) Recessive and dominant alleles, 3) Genotype and phenotype, 4) Homozygous and heterozygous, 5) Adaptation.
- The concept of heredity and the ability to pass on traits from one generation to the next is central to genetics, as well as to evolution. This activity will cover inheritable traits, dominant and recessive traits, genotypes and phenotypes, and Punnett squares.
- In nature, there are two basic methods of passing genetic information from one generation to the next: sexual reproduction and asexual reproduction. In asexual reproduction, one parent makes an exact copy (or clone) of itself. This is commonly done through splitting one cell in half (binary fission), budding, or fragmentation. Asexual reproduction is used by bacteria, many plants and fungi, and some animals (generally simpler organisms). Some organisms can reproduce either sexually or asexually depending on conditions of their life history phase. In some cases, more advanced organisms, such as sharks, have shown the ability to reproduce asexually (through a process called parthenogenesis).
- Sexual reproduction involves combining the genetic material from two parents. Sexual reproduction increases the variability in the gene pool by combining the DNA from these two different organisms. This allows important information to be passed down through many generations. An offspring will get half of its DNA from its mother and half of its DNA from its father. The offspring’s mother got half of her DNA from her mother and half from her father. This pattern goes back through countless generations. Because the DNA is combined in many new ways (by having DNA from two individuals combining to form the offspring), new characteristics can be formed. This is significant because this variability will make the species more able to survive if the environment changes.
- All aspects of an organism are controlled by its DNA. This includes things that we can see and things that we can’t. When thinking about heredity, it is often helpful to focus on the things that we can see. Traits are characteristics of an organism that have natural variety. So, this doesn’t really apply to things like how cells divide because this is similar among all cells. Additionally, traits generally refer to things that we can see (eye color, skin color, hair color, attached earlobes, tongue rolling). Each version of a trait is called an allele. For example, eye color is a trait. The alleles for eye color are brown eyes and blue eyes.
- Each offspring gets one set of alleles for each trait from its mother and one from its father. Each parent has two sets of alleles (one from each parent) that it could potentially pass on to his/her offspring (although each parent will only pass on one allele for each trait). This is the basis of sexual reproduction and variability. Every organism that is a result of sexual reproduction has two copies of every gene. So, each organism has two copies of each gene (one from each parent) that it can pass along from to its offspring (which will be combined with the DNA from another organism when they reproduce). As a parent, only one copy of each allele that a parent possesses will be passed to each offspring. This is why siblings are often similar, but not identical.
- Each organism that is the result of sexual reproduction has 2 copies of each allele. The interaction of these alleles will determine the trait that we see. The alleles can be the same (homozygous) for a given trait or different (heterozygous) for a given trait.
- The way that alleles interact is referred to as the dominance pattern for a given trait. In humans, the allele for brown eyes is dominant to the allele for blue eyes. Brown hair is dominant to blonde hair. In Gregor Mendel’s early genetics experiments, purple flowers on pea plants were dominant to white flowers. The dominant allele is the one that is expressed (what we see).
- It is possible for someone to be a carrier of a recessive allele, but not show the trait. This is how two parents with brown eyes can have a child with blue eyes. This would occur if someone is heterozygous for a given trait (one allele for blue eyes and one allele for brown eyes). Only the dominant allele (brown eyes) will be expressed, and the recessive allele (blue eyes) will be hidden. However, because the individual carries the recessive allele and in sexually reproducing organisms, the parent randomly passes one allele to each offspring, it is possible for offspring to show versions of traits not seen in the parents.
- This difference between what your genes say and what you look like are referred to as your genotype and your phenotype. Genotype is what your genes (alleles) actually say. The genotype always includes two alleles. The genotype can be homozygous dominant (two alleles for brown eyes), homozygous recessive (two alleles for blue eyes), or heterozygous (one allele for brown eyes and one allele for blue eyes). However, the phenotype is what you look like. It only includes the version of the trait that you see (either blue or brown).
- Dominance patterns aren’t always completely straightforward. Incomplete dominance occurs when two alleles combine to form a phenotype that is different from each of the parents. A well known example of this is in snapdragons. White and red flowers both exist, but when an individual has a white allele and a red allele, the phenotype is pink flowers.
- In genetics, we use Punnett squares to determine the possible genotypes and phenotypes that can result from a given cross of parents. It allows us to determine the probability that certain parents will have offspring with a certain trait. This is important when thinking about things like genetic diseases if a couple is considering having children. Punnett squares work by placing each possible allele associated with each box. The top represents the two alleles that one parent can pass on to offspring and the left side represents the two alleles that the other parent can pass on. The boxes are filled with the possible allele combinations. In general, this is done using letters to represent a given trait. Capital letters represent dominant traits and lower case letters represent recessive traits. Only one letter is used, even if the alleles don’t start with the same letter. For example, if you are looking at white flowers and purple flowers, one could use P to represent purple alleles and p to represent white flowers (even though there is no p in white). In the case of incomplete dominance, one letter represents the trait and superscripts represent each possible allele. An example of this scheme is seen in the gummy bear genetics activity.
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Asexual Reproduction
Sexual Reproduction
Alleles from Parents
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- Time Frame: Designed to take up 55 minutes of a 90 minute period.
- Biology Standard 2c: "Students know how random chromosome segregation explains the probability that a particular allele will be in a gamete."
- Biology Standard 2d: "Students know new combinations of alleles may be generated in a zygote through the fusion of male and female gametes (fertilization)."
- Biology Standard 2e: "Students know why approximately half of an individual’s DNA sequence comes from each parent."
- Biology Standard 2g: "Students know how to predict possible combinations of alleles in a zygote from the genetic makeup of the parents."
- Biology Standard 3a: "Students know how to predict the probable outcomes of phenotypes in a genetic cross from the genotypes of the parent and the mode of inheritance (autosomal or X-linked, dominant or recessive)."
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SIO Cafe
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Design EarthRef.org
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