6.3 “Mendel and Heredity” Vocabulary: Standards: Bio.LS3:2 Explain how protein formation results in phenotypic variation and discuss how changes in DNA can lead to somatic or germline mutations. Bio.LS3:3 Through pedigree analysis, identify member genotypes. Use mathematical thinking to predict the likelihood of various types of trait transmission. Vocabulary Term Trait Purebred Law of Segregation Definition Characteristic that is inherited. Type of organism whose ancestors are genetically uniform. Mendel’s first law, stating that (1) organisms inherit two copies of genes, one from each parent, and (2) organisms donate only one copy of each gene in their gametes because the genes separate during gamete formation. Image Genetics Study of the heredity patterns and variation of organisms. Cross Mating of two organisms. 6.3 “Mendel and Heredity” Summary Notes: Key Concept: Mendel's research showed that traits are inherited as discrete units. Objectives: ● Describe the patterns of inheritance that Mendel’s data revealed. ● Summarize Mendel's law of segregation. Mendel Laid the groundwork for genetics: - Traits are distinguishing characteristics that are inherited, such as eye color, leaf shape, and tail length. - Traits are hereditary, or passed down from one generation to the next. - Genetics is the study of biological inheritance patterns and variation in organisms. - The groundwork for much of our understanding of genetics was laid in the middle of the 1800’s by an Austrian monk named Gregor Mendel. About Gregor Mendel: ❏ A mathematician ❏ Austrian monk ❏ He bred thousands of pea plants, carefully counting and recording his results and from his data. ❏ He was able to correctly predict the results of meiosis long before chromosomes were discovered. ❏ He recognized that traits are inherited as discrete units from the parental generation, like different colored marbles mixed together that can still be picked out separately. ❏ By recognizing that organisms inherit two copies of each discrete unit, what we now call genes, Mendel also described how traits were passed between generations. Mendel’s data revealed patterns of inheritance: ● Mendel made three key choices about his experiments that played an important role in the development of his laws of inheritance: 1. Control over breeding 2. Use of purebred plants 3. Observation of “either-or” traits that appeared in only two alternate forms. ● Experimental Design: Pea Plants because they reproduce quickly and the control of how they would mate. ★ (Background knowledge of Pea Plants): The sex organs of a plant are in its flowers, and pea flowers contain BOTH male and female reproductive organs. In nature, the pea plant typically self-pollinates (mates with itself). ● ● ● If a line of plants has self-pollinated for long enough, that line becomes genetically uniform, or purebred. Mendel was able to mate plants with specific traits by interrupting the self-pollination process (refer to 6.8 image). Mendel chose 7 traits to follow: pea shape, pea color, pod shape, pod color, plant height, flower color, and flower position. Results: ● The mating of two organisms is called a cross.(Refer to image 6.9 to see a an example.) ● In this example, Mendel crossed a purebred purple pea plant with a purebred white pea plant. ● Results showed: F1= all purple flowers F2= some purple and some white flowers ● P= Parental generation F1= first filial (offspring) generation F2= second filial(offspring) generation ● Like he had anticipated with the F1 generation, the white trait had not disappeared in the cross, but simply had been hidden or masked, therefore was able to show back up in F2 generation. Conclusions: ● Mendel drew three important conclusions from his experiment. 1. Traits are inherited as discrete units, which explained why individual traits persist without being blended or diluted over successive generations. 2. Organisms inherit two copies of each gene, one from each parent. 3. Organisms donate only one copy of each gene in their gametes, Thus, the two copies of each gene segregate, or separate, during gamete formation. ● Number 2 and 3 made up Mendel’s First Law, better known as the Law of Segregation. 6.4 “Traits, Genes, and Alleles” Vocabulary Vocabulary Term Definition Gene Specific region of DNA that codes for a particular protein. Allele Homozygous Heterozygous Any of the alternative forms of a gene that occurs at a specific place on a chromosome. Characteristic of having two of the same alleles at the same locus of sister chromatids. Characteristic of having two different alleles that appear at the same locus of sister chromatids. Image Genome Genotype Phenotype Dominant All of an organism's genetic material. Collection of all of an organism’s genetic information that codes for traits. Collection of all of an organism’s physical characteristics. Allele that is expressed when two different alleles are present in an organism’s genotype. Recessive Allele that is not expressed unless two copies are present in an organism’s genotype. 6.4 “Traits, Genes, and Alleles”: Summary Notes: Standards: Bio.LS3:2 Explain how protein formation results in phenotypic variation and discuss how changes in DNA can lead to somatic or germline mutations. Bio.LS3:3 Through pedigree analysis, identify member genotypes. Use mathematical thinking to predict the likelihood of various types of trait transmission. Key Concept: Genes encode proteins that produce a diverse range of traits. Objectives: ● Explain how there can be many versions of one gene. ● Describe how genes influence the development of traits. The same gene can have many versions: ● Think of a gene as a piece of DNA that provides a set of instructions to a cell to make a protein. ● Each gene has a (locus) or a specific “location, position, or address” on a pair of homologous chromosomes. ● An allele is any of the alternative forms of a gene that may occur at a specific locus. ● Your cells have two alleles for each gene: one on each of the homologous chromosomes on which the locus for that gene is found. (Got one from each parent) ● Homozygous- describes two of the SAME alleles at a specific locus. EX: both code for white flowers (HH or hh) ● Heterozygous- describes two DIFFERENT alleles at a specific locus. EX: one might code for white flowers, the other for purple flowers (Hh) Genes influence the development of traits: ● A genome is all of an organism’s genetic material. ● You have a unique genome unless you have an identical twin. ● A genotype typically refers to the genetic makeup of a specific set of genes. EX: Plant Height ( T= tall t= short) Homozygous- dominant = TT ● A phenotype is the physical characteristics or traits that make up an individual organism. EX: the plant is tall ● ● Dominant and Recessive Alleles: A dominant allele is the allele that is expressed when two different alleles or two dominant alleles are present. A recessive allele is the allele that is only expressed when two copies are present. ● ● ● ● ● A dominant allele is not necessarily better or stronger than a recessive allele, nor does it mean that it occurs most often in the population. An allele is dominant in a heterozygote simply because it is expressed and the other allele is not. Alleles are often represented with letters. (HH or Hh or hh) EX: Homozygous Dominant : HH Heterozygous: Hh Homozygous Recessive: hh Alleles and Phenotype: Because some alleles are dominant over others, two genotypes can produce the dominant phenotype. There are many factors that contribute to certain alleles being dominant over one another. Refer to page 182 of text for more information on this subject area. We will also cover it in more depth in Chapter 7. 6.5 “Traits and Probability” Vocabulary Vocabulary Term Definition Punnett square Model for predicting all genotypes resulting from a cross, or mating. Image Monohybrid cross Testcross Cross, or mating, between organisms that involves only one pair of contrasting traits. Cross between an organism with an unknown genotype and an organism with a recessive phenotype. Dihybrid cross Cross, or mating, between organisms involving two pairs of contrasting traits. Law of independent Assortment Mendel’s second law, stating that allele pairs separate from one another during gamete formation. Probability Likelihood that a particular event will happen. 6.5 “Traits and Probability” Summary Notes: Standards: Bio.LS3:2 Explain how protein formation results in phenotypic variation and discuss how changes in DNA can lead to somatic or germline mutations. Bio.LS3:3 Through pedigree analysis, identify member genotypes. Use mathematical thinking to predict the likelihood of various types of trait transmission. Key Concept: The inheritance of traits follows the rules of probability. Objectives: ● Describe monohybrid and dihybrid crosses. ● Explain how heredity can be illustrated mathematically. Punnett squares illustrate genetic crosses: ● R.C. Punnett developed the Punnett Square. ● Punnett square is a grid system for predicting all possible genotypes resulting from a cross. ● From a punnett square we can find the ratio of genotypes in a generation and if we also know how the genotype corresponds to the phenotype, we can find the ratio of phenotypes in that generation as well. A monohybrid cross involves one trait: ● A monohybrid cross examines the inheritance of only one specific trait. ● Predicts genotypic and phenotypic ratios. ● A testcross is a cross between an organism with an unknown genotype and an organism with a recessive phenotype. (Refer to page 185 of text for more information.) ● ● Rule 1: Homozygous- Homozygous Cross between a Homozygous dominant and Homozygous recessive: (FF) X (ff) Result= 100% Heterozygous (Ff) ● ● Rule 2: Heterozygous- Heterozygous Cross between a Heterozygous and Heterozygous: (Ff) X (Ff) Result= 25% Homozygous dominant, 50% Heterozygous, and 25% Homozygous recessive (ff). Genotypic ratio= 1:2:1 Phenotypic ratio= 3:1 ● ● ● ● ● Rule 3: Heterozygous-Homozygous Cross between a Heterozygous and a Homozygous recessive: (Ff) X (ff) Result= 50% Heterozygous (Ff) and 50% Homozygous recessive (ff) Genotypic ratio= 1:1 Phenotypic ratio= 1:1 Cross between a Heterozygous and a Homozygous dominant: (Ff) X (FF) ● ● A dihybrid cross involves two traits: ● A dihybrid cross examines the inheritance of two different traits. ● Mendel conducted a second experiment using a dihybrid cross. ● The law of independent assortment, states that allele pairs separate independently of each other during gamete formation, or meiosis. (Different traits appear to be inherited separately.) Mendel’s 2nd Experiment: ❏ Dihybrid cross between purebred plants. ❏ He crossed a purebred plants (yellow with round peas) X (green with wrinkled peas) ❏ Result of F1 generation= All would be Heterozygous and look the same. (yellow with round peas) ❏ He then allowed the F1 generation to self pollinate again and then obtained the following results of: 9 yellow/round, 3 yellow/wrinkled, 3: green/round, and 1 green/wrinkled. ❏ This resulted in the 9:3:3:1 phenotypic ratio, which continued into the F2 generation as well. ❏ The ratio will change if the original parent crosses are changed. ● Link for dihybrid cross setup: http://www.biology.arizona.edu/mendelian_genetics/problem_sets/dihybrid_cross/03t.html Heredity patterns can be calculated: ● Probability is the likelihood that a particular event will happen and predicts the average number of occurrences, not the exact number of occurrences. 6.6 “Meiosis and Genetic Variation” Vocabulary: Vocabulary Term Definition Crossing Over Exchange of chromosome segments between homologous chromosomes during Meiosis I. Image Genetic Linkage Tendency for genes located close together on the same chromosome to be inherited together. 6.6 “Meiosis and Genetic Variation” Summary Notes: Standards: Bio.LS3:2 Explain how protein formation results in phenotypic variation and discuss how changes in DNA can lead to somatic or germline mutations. Bio.LS3:3 Through pedigree analysis, identify member genotypes. Use mathematical thinking to predict the likelihood of various types of trait transmission. Key Concept: Independent assortment and crossing over during meiosis result in genetic diversity. Objectives: ● Describe how sexual reproduction creates unique gene combinations. ● Explain how crossing over during meiosis increases genetic diversity. Sexual Reproduction creates unique genes: ● An advantage of sexual reproduction is that it gives rise to a great deal of genetic variation. ● The variation results largely from: 1. The independent assortment of chromosomes during meiosis 2. The random fertilization of gametes. ● Since any sperm can fertilize any egg, the total number of possible combinations is the product of or more than 70 trillion different combinations of chromosomes. ● Independent assortment and fertilization play key roles in creating and maintaining genetic diversity in all sexually reproducing organisms. ● The number of possible chromosome combinations varies by species. ● Sexual reproduction creates unique genes resulting in organisms with unique phenotypes. Crossing over during meiosis increases genetic diversity: ● Independent assortment creates a lot of variation within a species. ● Crossing over is the exchange of chromosomes segments between homologous chromosomes during prophase I of meiosis I. ● Crossing over helps create even greater variation amongst a species. ● ● ● ● Crossing over happens any time a germ cell divides and it can occur many times within the same pair of homologous chromosomes. Because crossing over results in new combinations of genes, it is also called recombination. Some genes on the same chromosome are close together and others are far apart. The farther apart two genes are located, the more likely they are to be separated when crossing over happens. Thus, genes located close together tend to be inherited together, which is called genetic linkage. Refer to page 191 of text for more information on genetic linkage.
