General Biology 1 Fall 2024 Past Paper PDF

General Biology 1 Fall 2024 Patterns of Inheritance – part 2 Prof : Dr. Vincent Gagnon Book Raven, Biology, 13th edition  Patterns of Inheritance Study guide: Topic...

General Biology 1 Fall 2024 Patterns of Inheritance – part 2 Prof : Dr. Vincent Gagnon Book Raven, Biology, 13th edition  Patterns of Inheritance Study guide: Topic References (13th Ed) Section 13.4, Figure 13.10, Deduce a pattern of inheritance using a family pedigree 13.11 Identify and understand the concepts of patterns of inheritance. Compare and contrast patterns of inheritance, and interpret the phenotypic ratio's in the offspring of a heterozygous cross for each pattern. Solve problems related to the following patterns For both autosomal and sex-linked Section 12.2, 12.3 and situations: 12.5, Table 12.1 Complete dominance (Simple dominance) Incomplete dominance Lab and VGL actvities Codominance Multiple alleles Hierarchal dominance (VGL) Circular dominance (VGL) Recognize the following patterns of inheritance as variations of Mendelian inheritance: Epistaisis Section 12.5, Table 12.1 Pleiotropy Polygenic (continuous variation) Understand and give examples of the effect on gene expression by the environment. Section 12.5, Table 12.1  Patterns of Inheritance Pedigree: A pedigree is a family tree that describes the interrelationships of parent and children across generations. Inheritance patterns of particular traits can be traced and described using pedigrees. How to read a pedigree ▪ Male are squares and female are circles. ▪ Normal individual are white and affected individual are coloured or black. ▪ Horizontal line linking the center of a square and circle represent mating. ▪ Offspring of this mating are link to their parents by horizontal and vertical lines.  Patterns of Inheritance Pedigree: We will see 3 examples of pedigree 1) Dominant trait pedigree 2) Recessive trait pedigree 3) Sex-link trait pedigree  Patterns of Inheritance Pedigree: 1) Dominant trait pedigree Example: juvenile glaucoma (autosome chromosome). - Disease causes degeneration of optic nerve leading to blindness. - Males and females affected equally, since it’s on an autosome chromosome. Question: The disease is a dominant alleles, so why don’t all the offspring in this pedigree have the disease?  Patterns of Inheritance Pedigree: 1) Dominant trait pedigree Example: juvenile glaucoma (autosome chromosome). - Disease causes degeneration of optic nerve leading to blindness. Answer: The male of generation I EGEg EgEg is an heterozygote for the allele. Therefore he as one good EgEg EgEg EGEg EGEg EgEg and one mutated allele (EGEg) where capital G is EGEg EGEg EGEg the mutated allele that give you glaucoma.  Patterns of Inheritance Pedigree: 2) Recessive trait pedigree Example: Albinism (autosome chromosome) - Condition in which the pigment melanin is not produced. - Cause by the nonfunctional allele of the enzyme tyrosinase. - Males and females affected equally, since it’s on an autosome chromosome. - Most affected individuals have unaffected parents. - The carrier (half colour) are not always present in a pedigree.  Patterns of Inheritance Pedigree: 3) Sex-link trait pedigree Example: Hemophilia (sex chromosome) - It’s an inherited genetic disorder that impairs the body's ability to Hemophilia Pedigree make blood clots. - The mutations causing the disease is a recessive allele located on the X sexual chromosome (sex-linked). - Males more affected than females. By looking at a pedigree you should be able to determine if it’s a dominant or recessive allele and if it’s sex link or not.  Patterns of Inheritance Pedigree: Example: Hemophilia The Royal hemophilia pedigree. Queen Victoria’s daughter Alice introduced hemophilia into the Russian and Austrian royal houses.  Patterns of Inheritance The Mendel legacy Although Mendel's results did not receive much notice during his lifetime, three different investigators independently rediscovered his pioneering paper in 1900, 16 years after his death. However, scientists attempting to confirm Mendel's theory often had trouble obtaining the same simple ratios he had reported. Mendel's simple ratios were not always observed for other traits examined. A number of assumptions are built into Mendel's model that are oversimplifications. Mendel’s model of inheritance assumes that: ▪ Each trait is controlled by a single gene. ▪ Each gene has only 2 alleles (ex.: purple or white). ▪ There is a clear dominant-recessive relationship between the alleles. Most genes do not meet these criteria!  Patterns of Inheritance Extensions to Mendel model The ranges of dominance and recessive relationships 1) Complete dominance (Simple dominance, Mendel model) 2) Incomplete dominance Red White Pink 3) Codominance  Patterns of Inheritance Extensions to Mendel model The ranges of dominance and recessive relationships 1) Complete dominance (Simple dominance, Mendel model) Mendel’s model of inheritance assumes that: ▪ Each trait is controlled by a single gene. ▪ Each gene has only 2 alleles (ex.: purple or white). ▪ There is a clear dominant-recessive relationship between the alleles.  Patterns of Inheritance Extensions to Mendel model 2) Incomplete dominance Heterozygote is intermediate in phenotype between the 2 homozygotes. Red flowers × white flowers = pink flowers. If pink F1 are self-crossed, they will yield progeny the same as the Mendelian monohybrid genotypic ratio (1 red: 2 pink: 1 white).  Patterns of Inheritance 3) Codominance Most genes in a population possess several different alleles, and often no single allele is dominant; instead, each allele has its own effect, and the heterozygote shows some aspect of both allele in their phenotype. The alleles are said to be codominant. Example: Human ABO blood group The blood type depend on the carbohydrate sugars present at the surface of the red blood cell (those are the antigens). Codominance with multiple alleles: ▪ 3 alleles of the I gene (IA, IB, and i). Codominance: ▪ IA and IB are dominant to i, but codominant to each other. You don’t need to remember the name of the antigen sugars  Patterns of Inheritance 3) Codominance Most genes in a population possess several different alleles, and often no single allele is dominant; instead, each allele has its own effect, and the heterozygote shows some aspect of both allele in their phenotype. The alleles are said to be codominant. Example: Human ABO blood group Blood Alleles Antigen Sugars Donates and Receives Type IAIA or IAi Receives A and O A Galactosamine (IA dominant to i) Donates to A and AB IBIB or IBi Receives B and O B Galactose (IB dominant to i) Donates to B and AB IAIB Both galactose and Universal receiver Donates AB (codominant) galactosamine to AB ii Receives O O None (i is recessive) Universal donor You don’t need to remember the name of the antigen sugars  Patterns of Inheritance 3) Codominance Most genes in a population possess several different alleles, and often no single allele is dominant; instead, each allele has its own effect, and the heterozygote shows some aspect of both allele in their phenotype. The alleles are said to be codominant. Example: Human ABO blood group The incompatibility between blood type come from the antibody contain in the plasma of the blood that target the antigen (sugars) at the surface of the blood cell.  Patterns of Inheritance 3) Codominance Example: Human ABO blood group  Patterns of Inheritance Extensions to Mendel model The ranges of dominance and recessive relationships 1) Polygenic inheritance: 2) Pleiotropy 4) Environmental 3) Epistasis  Patterns of Inheritance Extensions to Mendel model The ranges of dominance and recessive relationships 1) Polygenic inheritance: Occurs when multiple genes are involved in controlling the phenotype of a trait. The phenotype is an accumulation of contributions by multiple genes. These traits show continuous variation and are referred to as quantitative traits. Example: Human height  Patterns of Inheritance Extensions to Mendel model The ranges of dominance and recessive relationships 1) Polygenic inheritance: Example: Colour of the skin is affected by multiple genes.  Patterns of Inheritance What is the main difference between multiple alleles and polygenic inheritance. Polygenic inheritance Multiple Alleles Polygenic traits are determined by several genes. Multiple alleles are more than two alternative forms of a single gene that determine a trait.  Patterns of Inheritance Extensions to Mendel model 2) Pleiotropy Refers to an allele which has more than one effect on the phenotype Pleiotropic effects are difficult to predict, because a gene that affects one trait often performs other, unknown functions  Patterns of Inheritance Extensions to Mendel model 2) Pleiotropy example: The gene responsible for the blue color of a cat's eye also makes it deaf in one ear.  Patterns of Inheritance Extensions to Mendel model 2) Pleiotropy example: In the fruit fly Drosophila, the vestigial gene plays a critical role in wing development. Homozygous flies for the recessive form of the vestigial gene (vg), will develop short wings The vg gene is also pleiotropic: ▪ Changes the number of egg strings in a fly's ovaries. ▪ Alters the position of bristles on a fly's scutellum. ▪ Decreases the length of a fly's life. https://www.nature.com/scitable/topicpage/pleiotropy-one-gene- can-affect-multiple-traits-569/  Patterns of Inheritance Extensions to Mendel model 2) Pleiotropy example: In 1936, researchers Walter Landauer and Elizabeth Upham observed that chickens that expressed the dominant frizzle gene produced feathers that curled outward rather than lying flat against their bodies Chickens and the Frizzle Trait: ▪ Abnormal body temperatures. ▪ Higher metabolic and blood flow rates. ▪ Laid fewer eggs. https://www.nature.com/scitable/topicpage/pleiotropy-one-gene- can-affect-multiple-traits-569/  Patterns of Inheritance Extensions to Mendel model 3) Epistasis: The expression of one gene can affect the phenotypic expression of another. Example: the colour of a Labrador dog depend on the pigment, but also of the gene the for pigment deposition. B = black pigment b = brown pigment E = pigment deposition e = no pigment deposit  Patterns of Inheritance Extensions to Mendel model 3) Epistasis: Example: Crossed two true-breeding corn varieties, each lacking anthocyanin pigment. If this was a simple Mendelian trait, we would expect colorless seeds, but instead, all of the F1 plants produced purple seeds. When crossing F1 plants to produce an F2 generation that consisted of 56% pigmented seeds, and 44% colorless seeds. Epistasis was involve, since the colour emerge from the action of two enzymes (A and B). If one is absent the seed is colourless.  Patterns of Inheritance Extensions to Mendel model 4) Environmental influence Phenotypes may be affected by the environment. Example: Coat color in Himalayan rabbits and Siamese cats. Allele produces an enzyme that allows pigment production only at temperatures below 33oC.  Patterns of Inheritance Extensions to Mendel model 4) Environmental influence Hydrangea flower colour change according to soil pH pH: Acid pH: Basic  Patterns of Inheritance Extensions to Mendel model