9 Genetic Material
Big Ideas
- Traits are determined by GENETIC and ENVIRONMENTAL factors.
- There are PATTERNS in the way genetic information is STORED, EXPRESSED, and PASSED ON.
Big Questions
- What are the patterns in these processes?
- What are the outcomes of these processes?
- How can understanding these patterns help us determine what factors are genetic and which are not?
- What is the difference between DNA and RNA?
- Why do organisms have so many similarities, and yet so many differences?
- Where do organisms get their traits?
Genetics
All living things have genetic material that is structured in a similar pattern across species that helps organisms to perform necessary functions related particularly to passing traits from one generation to the next (figure 21). Humans can utilize information about genetic material to identify organisms and ailments. Genetic material is held in six main structures that work together to complete multiple functions.
Figure 21: Genetic Material Structures
| Structures | Functions |
|
|
Interaction
Click here to interact with genetic material. While interacting with DNA ask yourself these questions:
- How does the structure of the DNA relate to its function?
- What makes DNA an important part of living organisms?
Genetic Structures
How does this connect to the NGSS Progression
DCI: LS1 A: Structure and Function: Science concepts start macro in grade band K-2 and 3-5 as students compare and contrast external structures across species and then what can be internal structures related to their functions across species. Students use this concept base to help them make connections as they dive into micro structures and their functions in grade band 6-8.
| K-2 | 3-5 | 6-8 | |
| LS1.A Structure and function | All organisms have external parts that they use to perform daily functions. | Organisms have both internal and external macroscopic structures that allow for growth, survival, behavior, and reproduction. | All living things are made up of cells. In organisms, cells work together to form tissues and organs that are specialized for particular body functions. |
Implementation into the Classroom
DNA paper models – students engage with developing DNA models from memory as they use basic shapes. Split the students into two groups, plant DNA and animal DNA. Encourage students to work with partners to construct the DNA molecule. Then have groups compare with each other. Provide students expert books for them to compare their designs to.
Chickens and Humans – show students images of a chicken and a human. Ask students what they notice about the structures that are on both organisms. Keep track on the board of what students say in two columns, one for structure and function. Have students compare the functions across species to help them see the relationships. For example, chicken feet look much different than human feet (structure), but their functions are similar (walking/running).
Cell Types- provide students with an image of a plant cell and an animal cell. Ask students what they notice that is similar and different. Ask students how the cells come together to make organs.
Deoxyribonucleic Acid (DNA)
DNA is one of the basic building blocks of all eukaryotic living things. It provides the genetic material that codes for the development, characteristics, and function of an organism. DNA is structured through the hydrogen bonding of four bases molecules (adenine (A), cytosine (C), guanine (G), and thymine (T)) and a sugar-phosphate backbone (figure 22 and 23). The bases bond in a set pattern of pairs where adenine will bond with thymine and guanine bonds with cytosine creating a double strand. As the bonded bases and backbone interact electrical charges caused by the atomic structure cause the DNA to make a spiral structure known as a double helix.
Figure 22: DNA Structure
DNA
Accumulate more information about the structure of DNA.
|
Structure |
Function |
|
|
Figure 23: DNA Structure
(Ball, 2020)
Gene
A string of base pairs within DNA make up a gene. Genes can be anywhere from a few base pair to thousands of base pairs long (figure 24). A strand of DNA can contain a variety of different genes that encode for specific characteristics or functions for the organism.
Figure 24: Gene Located on a DNA Strand
(Novartis, 2021)
|
Structure |
Function |
|
|
Chromosomes
DNA is a large molecule that, if stretched out, reaches lengths of up to 5 feet long in humans! For the DNA to fit in the cell’s nucleus it is stored around a protein structure known as a histone. As the DNA is wound up it starts to form a rod shape known as a chromatid. When paired up, the two chromatids create a chromosome. Chromosomes contain the entire or part of the entire DNA of an organism (figure 25). This means that chromosomes are the “large” structure that holds all genetic material for an eukaryotic organism.
Figure 25: Break Down of a Chromosome
|
Structure |
Function |
|
|
Alleles
In some cases, genes can come in one, two, or more forms known as alleles. These alleles can be found at the same location (locus) on chromosomes and encode for the same overall characteristic or function, but are structured by slight differences in the DNA due to mutations that have occurred over time (figure 26). These differences are known as alleles and are often characterized as dominant and recessive. Dominant alleles provide a masking of all other genes that correspond to that same allele. The alleles that are masked are known as recessive alleles. Alleles often work in pairs, one on each corresponding chromosome. This pairing of alleles is known as a genotype and most commonly expressed by a letter (capital (i.e. T) for dominant, lower case (i.e. t) for recessive) when representing the genotype. When there are two of the same alleles together the genotype is referred to as homozygous and defined further by identifying it as dominant or recessive (i.e. AA = homozygous dominant, aa = homozygous recessive). If the two alleles are different the genotype is heterozygous (i.e. Aa). It is important to note that alleles (both dominant, both recessive, or dominant and recessive) are expressed at the same time. Genotypes (and by default alleles) can come together in varying patterns that will be discussed in the Genetic Functions section.
Figure 26: Alleles and Punnet Squares
(Brookes, 2008)
|
Structure |
Function |
|
|
Ribonucleic Acid (RNA)
RNA is a piece of genetic material that has similar structural patterns to DNA as it has four bases and a sugar-phosphate backbone. However, RNA is single stranded, has ribose, and contains one different base, uracil (U) (figure 27). Within some prokaryotes RNA provides all genetic material needed for cellular processes; while in other prokaryotes and eukaryotes RNA functions as an intermediate molecule between DNA and gene expression (traits- characteristics that are observed) through the process of transcription. During transcription DNA is transcribed into RNA which then leaves the nucleus and enters the cytoplasm of the cell. It is here that RNA performs its function of developing proteins through the process of translation.
Transcription vs Translation
To learn more about the processes of transcription and translation watch these videos:
Figure 27: DNA and RNA Structure
(Sponk, 2010)
|
Structure |
Function |
|
|
Protein
The process of translation creates long chains of amino acids that correspond to the DNA that was first transcribed. The chains of amino acids are then folded (figure 28) into the necessary structure and sent to different parts of the cell or body to perform a function. These folded strands of amino acids are known as proteins. Proteins provide a variety of traits within a cell that include structural, mechanical, biochemical, and signaling.
Figure 28: Protein Folding
(Shields, 2021)
|
Structure |
Function |
|
|
Phenotype
Hair color, eye shape, feather length, leaf shape, hormones. All of these are phenotypes–the DNA outcome (trait) that we can observe with our sense or enhancement of our senses. Phenotypes are acted upon through the environment and provide ways for organisms to blend in, stick out, or to protect themselves. In many cases, phenotypes can also be an indicator of health or sexual viability. Phenotypes can also be in the form of hormones such as estrogen, testosterone, insulin, adrenaline, etc. The main thing to know is that phenotypes are the end result of DNA. Below are five typical patterns in which we observe phenotypes:
Simple dominance → a mendelian genetic pattern where the dominant gene is expressed over the recessive and where the recessive gene is masked by the dominant gene OR is expressed when the genotype is homozygous recessive.
Incomplete dominance→ With a heterozygous genotype, the dominant trait is not fully expressed but in the homozygous dominant genotype it is. For example, red (R) and white (r) alleles in a flower expressed as red with a homozygous dominant phenotype (RR), pink with a heterozygous phenotype (Rr) and white with a homozygous recessive phenotype (rr) (Figure 29).
Figure 29: Incomplete Dominance Inheritance Pattern
(Kilo, 2012)
Codominance→ both the recessive and dominant traits are expressed at the same time resulting in each characteristic showing up in the heterozygous genotype. For example, red (R) and white (r) resulting in a striped plant (figure 30).
Figure 30: Codominance Inheritance Pattern
(Cruz, 2005)
Polygenic→ when there are multiple genes that make up a phenotype and are expressed at the same time. For example: hair color, eye color, and skin color (figure 31).
Figure 31: Polygenic Inheritance Pattern
(OpenStax, 2016)
Multiple Allele→ multiple alleles (more than 2) exist for a particular gene and therefore make up a variety of phenotypes resulting from many possible genotypes. For example, coat color in the organism below has four different possible alleles (C, cch, ch, c). (figure 32)
Figure 32: Multiple Allele Inheritance Pattern
(OpenStax, 2016)
|
Structure |
Function |
|
|
Teacher Time Out: Variation of Traits
How does this connect to the NGSS Progression
DCI: LS3.B: Variation of Traits: Grade band K-2 focuses on comparing parent to offspring utilizing external structures that can be seen. This phenomena is further investigated in grade band 3-5 and 6-8 as students begin to discover the underlying cause (genetics, inheritance, and environment) to the similar but different characteristics of parent to offspring.
|
|
K-2 |
3-5 |
6-8 |
| LS3.B Variation of traits | Young organisms are very much, but not exactly, like their parents and also resemble other organisms of the same kind. | Different organisms vary in how they look and function because they have different inherited information; the environment also affects the traits that an organism develops. | In sexual reproduction, each parent contributes half of the genes acquired by the offspring resulting in variation between parent and offspring. Genetic information can be altered because of mutations, which may result in beneficial, negative, or no change to proteins in or traits of an organism. |
Implementation into the Classroom
Lady Bug Similarities – Students can be shown images of parents and offspring of lady bugs. Engage students in discussion on what they notice about each picture. Keep track of these up on the board. Help students notice that the offspring look like their parents, but may have a different number, shape, or shade of spots. Help students recognize that even siblings look a little different.
Fit Your Environment – Show students different habitats and different animals. Have students develop claims back with evidence to determine which organism lives where and why. Ask probing questions to engage students in conversation about the benefits of how organisms look and their environment.
Genetic Functions
The overall function of genetic material is to create an organism that is able to have structures that can function to keep the organism alive and to pass on genetic information (DNA → RNA → Protein → Trait) to the next generation. This process is known as reproduction through meiosis and cell replication through mitosis.
Reproduction
All living organisms are capable of reproduction either sexually or asexually. Asexual reproduction allows for an organism to reproduce without another member of its species. This type of reproduction tends to occur in species that have reduced mobility (e.g. tulips, potatoes, amoebas, bacteria, sea anemones, etc.). When asexual reproduction occurs an organism creates a clone of itself through a serious of steps known as mitosis (figure 33) which passes on all traits both advantageous and detrimental to the offspring. Mitosis is also used within a species as they heal and grow, creating cells to replace old ones.
Figure 33: Steps of Mitosis
(Kultys, 2008)
The other method of reproduction is sexual reproduction. This requires genetic material from two different members of the same species (e.g. humans, ginkgo trees, bears, lions, etc.). In order to facilitate sexual reproduction, some cells go through a series of steps known as meiosis (figure 34). Through this process the sex gametes (sperm and egg) are created and have only half of the typical number of chromosomes for the species. When mating, each individual contributes a gamete which provides half the chromosomes, or genetic material, for the offspring to have a complete set.
Figure 34: Steps of Meiosis
(Kultys, 2008)
Teacher Time Out: Growth, Development, and Inheritance
How does this connect to the NGSS
DCI: LS1.B: Growth and Development of Organisms: Students begin to develop an awareness of how behaviors relate to survival in grade band K-2, and how these behaviors are often found in parents and offspring. In grade band 3-5 students observe the phenomena of life cycles and the need for reproduction. These two grade bands allow for a base understanding for students in grade band 6-8 to put behaviors and reproduction together as they further their understanding of how genetics and environment play a role in development.
|
|
K-2 |
3-5 |
6-8 |
| LS1.B Growth and development of organisms | Parents and offspring often engage in behaviors that help the offspring survive | Reproduction is essential to every kind of organism. Organisms have unique and diverse life cycles. | Animals engage in behaviors that increase the odds of reproduction. An organism’s growth is affected by both genetic and environmental factors. |
Implementation into the Classroom
An initial engagement activity where students are shown the phenomena of genetics and politics. Students then organize a list of characteristics on a continuum of completely genetic to completely environmental.
An investigation and engineering activity where students explore their own phenotypes and potential genotypes as they work with a partner to develop a baby.
Genetic Material and the Environment
Nature versus nurture. Which one is truly more important? Do your genes control who you are, or is it the environment? Are you predisposed to end up like your parents? Does one have more pull over the other? These are questions that are often asked and are still being asked by many scientists. However, it is thought that both genetics and the environment play a role in the way organisms look, act, and their ability to survive. DNA is the basic unit of life that encodes for the proteins that make up characteristics (traits) of an organism. Yet, it’s the environment that interacts with those traits which can lead to the alteration of the gene pool of a population. Thus, the environment can impact genes. New research on genetics has shown that there may be genes that are influenced by the environment known as epigenetics. The concept of environmental interaction and genetics will be discussed in more detail in the Evolution section.
Epigenetics
Investigate epigenetics as you read this article.