Introduction to Mendelian Genetics Packet #19 Chapters 6 & 7 **There will be many questions…please be patient as some questions will be answered in future packets…Please write questions on question page provided to be answered at an appropriate time. Tuesday, January 01, 2019

Mendelian Genetics Who is Mr. Gregor Mendel? What is he famous for? Describe the experiments of Gregor Mendel Tuesday, January 01, 2019Tuesday, January 01, 2019

Introduction I Heredity Gene The biological similarity of offspring and parents Gene Region of DNA, found on the chromosome, that controls a discrete hereditary characteristic of an organism Tuesday, January 01, 2019Tuesday, January 01, 2019

Introduction II Allele Locus One of several alternate forms of a particular gene Locus Particular place along the length of a chromosome where a given gene is located Alleles/genes give rise to phenotypes. Tuesday, January 01, 2019Tuesday, January 01, 2019

Introduction III Genotype The specific allele composition of a cell The combination of alleles located on homologous chromosomes that determines a specific characteristic or trait. Remember, an allele is a different form of the same gene This is the reason why the alleles MUST be found on homologous chromosomes. Each of the homologous chromosomes will contain a version of the same gene (allele). Tuesday, January 01, 2019Tuesday, January 01, 2019

Introduction IV Phenotype The observable physical or biochemical characteristics of an organism, as determined by organism’s genetic makeup (genotype). Tuesday, January 01, 2019Tuesday, January 01, 2019

Introduction V Dominant Allele Recessive Allele An allele that expresses its phenotype effect even when combined with a recessive allele. Recessive Allele An allele whose phenotype effect is not expressed unless it is combined with another recessive allele. However, there are exceptions to this rule in specific genetic disorders. More to come in future packets…Please hold those questions until then. Remember, the alleles are on homologous chromosomes. Tuesday, January 01, 2019Tuesday, January 01, 2019

Introduction VI Genotype Variations A = dominant allele Homozygous dominant Two dominant alleles Heterozygous One recessive allele One dominant allele Homozygous recessive Two recessive alleles A = dominant allele A = recessive allele AA = homozygous dominant genotype Aa = heterozygous genotype aa = homozygous recessive genotype Remember, the alleles are on homologous chromosomes.

Incomplete Dominance Occurs when hybrids, with a heterozygous genotype, have an appearance between the phenotypes of the parental varieties. Remember, the alleles are on homologous chromosomes. Tuesday, January 01, 2019Tuesday, January 01, 2019

Incomplete Dominance II Tuesday, January 01, 2019Tuesday, January 01, 2019

Codominance Situation in which the phenotypes of both alleles are exhibited in a heterozygote Tuesday, January 01, 2019Tuesday, January 01, 2019

Epistasis Phenomenon in which one gene alters the expression of another gene that is independently inherited. Tuesday, January 01, 2019Tuesday, January 01, 2019

Epistasis II Tuesday, January 01, 2019Tuesday, January 01, 2019

Sex-Linked Genes Sex-linked genes Genes that are found on the sex chromosomes.

Multiple Alleles On some occasions, there is more than two alleles (forms) of a particular gene. Example: - Alleles for blood group. When discussing genotypes for blood groups, there are three alleles that one must consider i iA iB More to come on blood types later and how blood types are determined in a couple’s offspring and how blood groups impact the blood transfusions.

Punnett Squares Punnett Square A diagram used in the study of inheritance Shows the result of random fertilization in genetic crosses. Shows the probable results of crossing over. More to come in the next packet. Tuesday, January 01, 2019Tuesday, January 01, 2019

Mendel’s Laws

Mendel’s Laws When Mendel carried out his research, the processes of mitosis and meiosis had not yet been discovered. However, Mendel knew, through his experiments, that genes (alleles) existed. From Mendel’s research, he devised two laws. Principle of Segregation Principle (Law) of Independent Assortment

Principle of Segregation The principle states that in diploid organisms genes come in pairs and that when sex cells get produced each gamete gets one gene at random. The haploid cell contains one chromosome set. Since the cell contains only one chromosome set, it only contains one copy of every chromosome. Since the cell only contains one copy of every chromosome, it contains one copy of the each gene found on a particular chromosome.

Principle of Segregation II When developing this idea Gregor Mendel conducted a series on monohybrid (test) crosses using pea plants. A monohybrid is when only one allele is investigated.

Principle of Independent Assortment The Law of Independent Assortment states that the alleles (or separate members of a gene pair) separate independently to form the gamete. To do this, one must be comparing at least TWO traits. Dihybrid cross By doing so, the traits are transferred independent from one another. This allows for much more variation in the offspring since the alleles are randomly matched with the gamete from the other parent to form the zygote. According to how many traits are in question, the number of possible variations can become quite high.

Dihybrid Cross A dihybrid cross involves an investigation of two alleles at the same time.

Principle of Independent Assortment II Mendel concluded that alleles (traits) are transmitted to offspring independently of one another. If the genes are transmitted independently, then the genes are determined as being unlinked. If the genes are transmitted together, the majority of the time, then the genes are determined as linked genes. Hence, the principle of independent assortment does not apply. Independent assortment occurs because there are two ways in which two pairs of homologous chromosomes can be arranged at metaphase I of meiosis. The orientation of homologous chromosomes on the metaphase plate determines the way chromosomes are distributed into haploid cells.

Principle of Independent Assortment III This law holds true as long as the two genes (traits) in question are: - Located on separate chromosomes Not linked together if they are located on the same chromosome. Unlinked genes More to come later in AP Biology The principle of independent assortment allows/results in recombination The presence of new gene combinations not present in the parental (P) generation.

Principle of Independent Assortment IV The principle of independent assortment allows/results in recombination The presence of new gene combinations not present in the parental (P) generation.

Genetic Crosses

Monohybrid (Test) Cross

Examples

Dihybrid Crosses

Examples Parent #1 Genotype FfEe Parent #2 Genotype

Review