Genetics Savvas Reading PDF

# Mendel's Observations - Like all other organisms, the cardinals in Figure 1 pass their traits to their offspring. - To better understand heredity, the passing of traits from parents to offspring, it is important to learn about the history behind the science. - In the 1800s, a European monk named...

# Mendel's Observations - Like all other organisms, the cardinals in Figure 1 pass their traits to their offspring. - To better understand heredity, the passing of traits from parents to offspring, it is important to learn about the history behind the science. - In the 1800s, a European monk named Gregor Mendel studied heredity. - Mendel's job at the monastery was to tend the garden. - After several years of growing pea plants, he became very familiar with seven possible traits the plants could have. - Some plants grew tall, while others were short. - Some produced green seeds, while others produced yellow. ## Mendel's Experiments - Mendel's studies became some of the most important in biology because he was one of the first to quantify his results. - He collected, recorded, and analyzed data from the thousands of tests that he ran. - The experiments Mendel performed involved transferring the male flower part of a pea plant to the female flower part to get a desired trait. - Mendel wanted to see what would happen with pea plants when he crossed different traits: short and tall, yellow seeds and green seeds, and so on. - Because of his detailed work with heredity, Mendel is often referred to as the “father of modern genetics.” ## Hands-on Lab - Explore how human height is inherited. ### Academic Vocabulary - In Latin, *quantus* means "how much." - Have you heard the word *quantify* used before? - Does it remind you of any other words? ## Passing on Traits - Figure 1 Male and female northern cardinals share many traits, but also have several that make them unique. ## Parents and Offspring - When Mendel cross-pollinated, or crossed, a tall plant with a short one, all of the offspring were tall. - The tall plant and short plant that were crossed are called the parent plants, or P generation. - The offspring are called the F₁, or first filial generation. - The term *filial* originates from the Latin terms *filius* and *filia*, which mean "son" and "daughter," respectively. ## Mendel's Experiments - Mendel examined several traits of pea plants. - Through his experimentation, he realized that certain patterns formed. - When a plant with green peas was crossed with one with yellow peas, all of the F₁ offspring were yellow. - However, when he crossed these offspring, creating what is called the second filial generation, or F₂, the resulting offspring were not all yellow. - For every four offspring, three were yellow and one was green. - This pattern of inheritance appeared repeatedly when Mendel tested other traits, such as pea pod shape shown in Figure 2. - Mendel concluded that while only one form of the trait is visible in F₁, in F₂ the missing trait sometimes shows itself. ## Pea Pod Shape Figure 2 - Which pod shape in the P generation that has the dominant trait? - The figure depicts three generations of pea pods, starting with the *P* generation, then the *F₁* generation, and finally the *F₂* generation. - In the *P* generation, the pea pods are either smooth or pinched. - In the *F₁* generation, all of the pea pods are smooth. - In the *F₂* generation, there are both smooth and pinched pea pods. ## Plan It! - Consider five other traits that Mendel investigated. - Explain how you could repeat Mendel's procedure for one of these traits and what the likely results would be of your investigation. ### Trait | Dominant | Recessive ------- | -------- | -------- seed shape | round | wrinkled seed color | yellow | green pod color | green | yellow flower color | purple | white pod position on stem | side of stem | top of stem ## Alleles Affect Inheritance - In Mendel's time, people had no knowledge of genetic material or its ability to carry the code for an organism's traits. - However, Mendel was still able to formulate several ideas about heredity from his experiments. - He called the information that carried the traits *factors*, because they determined what was expressed. - He also determined that for every trait, organisms receive one factor from their mother and one factor from their father. - He concluded that one factor can mask the expression of the other even if both are present at the same time. ## Genes and Alleles - Today, the term *factor* has been replaced with *gene* or *allele*. - Alleles are the different forms of a gene. - Pea plants have one gene that controls the color of the seeds. - This gene may express itself as being either yellow or green through a combination of yellow alleles and green alleles. - When crossed, each parent donates one of its alleles for seed color to the offspring. - The allele that each parent donates is random. - An offspring's seed color is determined by the combination of both alleles. ## Alleles and Inheritance - An organism's traits are controlled by the alleles it inherits. - A *dominant allele* is one whose trait always shows up in the organism when the allele is present. - A *recessive allele*, on the other hand, is hidden whenever the dominant allele is present. - If one parent donates a dominant allele and the other donates a recessive allele, only the dominant trait will be expressed. ## Reading Check - Determine Conclusions What conditions would have to occur for an offspring to express the recessive trait? ## Academic Vocabulary - How is *factor* used differently in math and science? ## Hands-On Lab - Investigate Explore cross-pollination by examining the parts of a flower. - Download the worksheet to complete the activity. ## Reflect - Think about a time when you saw a baby animal, such as a puppy or kitten. - Think about the traits it inherited from its parents. - How could you determine which traits were dominant and which were recessive? - Discuss the question with a classmate and record your ideas in your science notebook. ## Literacy Connection - Determine Conclusions How did Mendel come to the conclusion that an organism's traits were carried on different alleles? - Highlight the sentence that answers this question. ## Writing Alleles - The traits we see are present because of the combination of alleles. - For example, the peas in Figure 3 show two different colors. - Pea color is the gene, while the combinations of alleles determines how the gene will be expressed. - To represent this, scientists who study patterns of inheritance, called geneticists, use letters to represent the alleles. - A dominant allele is represented with a capital letter (G) and a recessive allele with a lowercase letter (g). - When an organism has two of the same alleles for a trait, it is called a purebred. - This would be represented as GG or gg. - When the organism has one dominant allele and one recessive allele, it is called a hybrid. - This would be represented as Gg. - Remember that each trait is represented by two alleles, one from the mother and one from the father. - Depending upon which alleles are inherited, the offspring may be a purebred or a hybrid. ## Mendel's Work - Mendel's work was quite revolutionary. - Prior to his work, many people assumed that all traits in offspring were a mixture of each parent's traits. - Mendel's experiments, where traits appeared in the F₂ generation that were not in the F₁ generation, disproved this idea. ## Dominating Color - Figure 3 Mendel discovered that yellow is the dominant pea seed color, while recessive pea seed color is green. - Fill in the correct alleles in the labels in the photos. - Then complete the statements, using the letters G and g as needed. ### Apply Concepts - What are the alleles for the green pea seed? - Would it be a purebred or a hybrid? - Download to complete the activity. # Genotype - You are already familiar with the terms *purebred* and *hybrid*. - These terms refer to *genotype*, an organism's genetic makeup or combination of alleles. - As shown in Figure 4, the genotype of a purebred green seed pea plant would be gg. - Both alleles are the same (purebred) and they are recessive because green is the recessive trait in terms of seed color. - The hybrid genotype for this trait would be Gg. ## Phenotype - The expression of an organism's genes is called its *phenotype*, the organism's physical appearance or visible traits. - The height, the shape, the color, the size, the texture-whatever trait is being expressed, is referred to as the phenotype. - So, a pea plant with the phenotype of yellow seed color could have two possible genotypes, GG or Gg. ## Genotypes and Phenotypes for Seed Color - Figure 4 The phenotype of an organism is explained as physical characteristics we see, while the genotype describes the combination of alleles that are inherited. - The figure depicts four pea pods, each with a different genotype. - The genotype of each pea pod is shown inside the pod, along with the corresponding seed color. - The figure highlights the four possible genotypes: GG, Gg, gg. - The corresponding phenotypes are also shown in the figure. - The GG genotype is homozygous dominant and results in yellow seeds. - The Gg genotype is heterozygous and also results in yellow seeds. - The gg genotype is homozygous recessive and results in green seeds. ## Reading Check - Determine Differences Explain how genotypes and phenotypes are different. ## Chromosomes and Genes - Gregor Mendel's ideas about inheritance and probability can be applied to all living things. - Mendel determined that traits are inherited using pieces of information that he called factors and we call genes. - He observed and experimented with genes in pea plants. - He discovered how genes, such as those in ducks (Figure 1), were transferred from parents to offspring and how they made certain traits appear. - However, Mendel did not know what genes actually look like. - Today, scientists know that genes are segments of code that appear on structures called *chromosomes*. - These threadlike structures within a cell's nucleus contain DNA that is passed from one generation to the next. - These threadlike strands of genetic material have condensed and wrapped themselves around special proteins. - This provides support for the chromosome structure. - Chromosomes are made in the beginning of the *cell cycle*, the series of events in which a cell grows, prepares for division, and divides to form daughter cells. - During this time, the chromosome gets its characteristic X shape. ## Academic Vocabulary - Identify and describe something that has a particular structure. ## Hands-on Lab - Investigate Investigate genetic crosses in imaginary creatures. - Download the worksheet to complete the activity. ## Number of Chromosomes - Every cell in your body other than the sex cells has the same number of chromosomes. - In humans, this number is 46. - Other organisms have different numbers of chromosomes, and there is a great variety. - For example, mallard ducks have 80 chromosomes. - All sexually-reproducing organisms form sex cells, which have half the number of chromosomes that body cells have. ## Genes on Chromosomes - Every living thing needs instructions to live. - Without these instructions, living things would not be able to grow and function. - These instructions are located on genes. - As you can see in Figure 2, genes are located on chromosomes. - In humans, between 20,000 and 25,000 genes are found on the 46 chromosomes. - Chromosomes are different sizes. - Larger chromosomes contain more genes than smaller chromosomes. - Each gene contains instructions for coding a particular trait. - There are hundreds to thousands of genes coding traits on any given chromosome. - For many organisms, these chromosomes come in sets. ## Scales of Genetic Material Figure 2 - Order the structures from smallest to largest by writing the numbers 1 through 5 in the blank circles. - Number 1 is the smallest. - Download to complete the activity. ## Academic Vocabulary - What is the difference between an object's structure and its function? ## Make Meaning - Why do sex cells contain only half the number of chromosomes needed for offspring? - Explain what would happen if sex cells contained the same number of chromosomes as body cells. ## Chromosome Pairs - During fertilization, you receive 23 chromosomes from your father and 23 chromosomes from your mother. - These chromosomes come in pairs, called homologous chromosomes, that contain the same genes. - Two alleles -one from the mother and one from the father-represent each trait. - However, the alleles for these genes may or may not be the same. - Some of the alleles for how the gene is expressed may be dominant or recessive. - In Figure 3, the offspring that received these chromosomes inherited two different forms of a gene-allele A from one parent and allele a from the other. - The individual will be *heterozygous* for that gene trait. - Because more than one gene is present on the 23 pairs of chromosomes, there is a wide variety of allele combinations. ## Reading Check - Integrate with Visuals How would geneticists-people who study genes-know whether the organism in Figure 3 is homozygous or heterozygous for a certain trait by examining its chromosome pair? ## A Pair of Chromosomes Figure 3 - Circle all the pairs of alleles that would be homozygous for a trait. - Download to complete the activity. - The figure shows a pair of chromosomes, each with a gene represented by a letter. - The alleles for each gene are shown as uppercase or lowercase letters. - For example, the first gene shown is represented by the letter A and the alleles are A and a. - For a pair of alleles to be homozygous, they must be the same. - So, the homozygous pairs of alleles that should be circled are: GG, BB, CC, DD, EE, FF, and GG. # Math Toolbox - **Model with Mathematics**: Fill in the table with the appropriate chromosome number for the missing body cell or sex cell. - **Constuct Graphs**: Complete the line plot below. - Place an X for each organism whose body cell chromosome number falls within the given range. - The table shows the number of chromosomes in body cells and sex cells for several organisms. - The graph shows the body cell chromosome distribution for each organism. - The graph has seven columns representing the number of chromosomes: 0-20, 21-40, 41-60, 61-80, 81-100. - Each organism is represented by an "*X*" in the appropriate column, based on its body cell chromosome number. - The organisms are: house cat, mallard duck, corn, peanut, horse, oak tree, sweet potato, camel, and chicken. ### Organism | Body Cells | Sex Cells ------- | -------- | -------- House cat | 38 | 19 Mallard duck | 80 | 40 Corn | 20| 10 Peanut | 40 | 20 Horse | 32 | 16 Oak tree | 12 | 6 Sweet potato | 90 | 45 Camel | 78 | 39 Chicken | 78 | 39