Fundamentals Of Genetics Chapter 4 PDF

BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY OCTOBER 2024 CHAPTER 4: VARIATIONS OF THE MENDELIAN INHERITANCE INTR...

BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY OCTOBER 2024 CHAPTER 4: VARIATIONS OF THE MENDELIAN INHERITANCE INTRUCTOR Student CHRISTOFER DIWA BS PSYCH III  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY MENDELIAN INHERITANCE?  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY MENDELIAN INHERITANCE?  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY VARIATIONS OF THE MENDELIAN INHERITANCE 1.Incomplete Dominance 2.Codominance 3.Lethal Genes 4.Multiple Alleles 5.Polygenes 6.Epistasis  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY GENE INTERACTION Gene interactions refer to the ways in which different 2 or more genes influence each other’s expression and contribute to a particular phenotype Allelic or Non-epistatic Gene Interaction and Non-allelic or Epistatic Gene Interaction  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY GENE INTERACTION Gene interactions are divided into two categories: 1. Allelic or Non-epistatic Gene Interaction: This gene interaction occurs between the alleles of a single gene The phenotypic ratios diverge from Mendelian ratios because specific alleles can often be equally or partially dominant to each other or due to the lethal alleles. a. Incomplete dominance b. Codominance c. Lethal alleles/genes d. Multiple alleles  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY I. INCOMPLETE DOMINANCE Definition: A form of inheritance where the phenotype of a heterozygote is an intermediate blend of the phenotypes of both homozygous parents. Deviation from Mendel’s Principle of Dominance: Unlike Mendel’s concept where one allele completely masks the other, incomplete dominance shows a blend of both parental traits. Phenotypic Result: A third, distinct phenotype is produced that is intermediate between the two parental phenotypes (neither dominant nor recessive). 1:2:1  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY I. INCOMPLETE DOMINANCE MECHANISM OF INCOMPLETE DOMINANACE Dosage Effect: The heterozygote produces less of the gene product (usually a protein) compared to the homozygote for the dominant allele. Gene Expression: Both alleles contribute to the phenotype, but the gene products from the alleles are not enough to fully express either trait.  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY I. INCOMPLETE DOMINANCE EXAMPLE: FLOWER COLOR IN SNAP DRAGON Parental Generation: Red-flowered plant: CRCR White-flowered plant: CWCW F1 Generation: Heterozygous offspring (CRCW): All plants are heterozygous Phenotypic Expression: Intermediate phenotype: Offspring display pink flowers Reason for Pink Color: ⚬ The red allele (CR) only partially contributes to the flower color ⚬ The white allele (CW) also contributes but not fully ⚬ The result is a blend, or an intermediate trait, between red and white-pink  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY I. INCOMPLETE DOMINANCE Example: Incomplete Dominance in Andalusian Chicken Feather Color Parental Generation: ⚬ Black-feathered chicken: CBCB ⚬ White-feathered chicken: CWCW F1 Generation: ⚬ Heterozygous offspring (CBCW): All offspring have blue-gray (or "blue") feathers Phenotypic Expression: ⚬ Intermediate phenotype: Heterozygous chickens show blue- gray or slate-colored feathers. ⚬ Reason for Blue-Gray Color: ￭ The black allele (CB) doesn’t fully dominate the white allele (CW). ￭ Instead, the black pigment is diluted, resulting in a softer, blue-gray color. ￭ This color is a mix between black and white, with neither allele being completely dominant  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY I. INCOMPLETE DOMINANCE Why Blue, Not Gray?: ⚬ The blue-gray feathers are not a simple average of black and white. The color arises from the partial expression of black pigment, which, when reduced or diluted, often results in a bluish tone due to the way light interacts with the diluted black pigment ⚬ This effect creates a more blueish slate tone, rather than a pure gray, which is a combination of black and white at an equal intensity  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY SAMPLE PROBLEMS: INCOMPLETE DOMINANCE In a certain breed of rabbits, the allele for black fur (B) is incompletely dominant to the allele for white fur (W). A gray-furred rabbit (BW) is crossed with a white-furred rabbit (WW). If the cross produces 16 offspring, what are the expected genotypes and phenotypes of the 16 offspring?  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY II. CODOMINANCE Definition: A form of inheritance where both alleles in a heterozygous organism are fully and equally expressed. Phenotypic Result: The organism exhibits traits from both alleles simultaneously, with no blending of traits. 1:2:1 Contrast with Incomplete Dominance: ⚬ In codominance, traits from both alleles are visible and distinct. ⚬ In incomplete dominance, the traits blend into an intermediate phenotype.  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY II. CODOMINANCE Mechanism of Codominance: Chromosomal Level: ⚬ Both alleles at a specific locus of homologous chromosomes remain active and contribute equally to the phenotype ⚬ Unlike Mendelian inheritance, where one allele may be recessive, neither allele is suppressed in codominance Expression Level: ⚬ Both alleles independently code for proteins, which are co-expressed. ⚬ The proteins produced by each allele function independently but are both observable in the phenotype ⚬ No reduction in the output or activity of either allele’s protein product  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY II. CODOMINANCE Example: Codominance of Blood Types A and B Alleles: ⚬ IA allele: Codes for the A antigen (a glycoprotein) on the surface of red blood cells. ⚬ IB allele: Codes for the B antigen (a different glycoprotein) on the surface of red blood cells. ⚬ i/IO Genotype: ⚬ IAIB: The individual inherits both the IA and IB alleles. Phenotype: ⚬ Blood type AB: Both A and B antigens are produced and expressed equally on the surface of red blood cells.  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY II. CODOMINANCE Example: Codominance in Sickle-Cell Anemia Alleles: ⚬ HbA allele: Codes for normal hemoglobin (HbA) ⚬ HbS allele: Codes for mutated, sickle-shaped hemoglobin (HbS) Genotype: ⚬ HbAHbS: Heterozygous individuals carry both normal and mutated alleles. Phenotype: ⚬ Co-expression: Both normal and sickle-shaped hemoglobin proteins are produced. ⚬ Red Blood Cells: These cells contain both normal and abnormal hemoglobin. Effects on Health: ⚬ Mild Symptoms: Individuals with the HbAHbS genotype usually do not have severe symptoms but may experience mild sickling under low oxygen conditions (e.g., during intense physical activity or at high altitudes).  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY II. CODOMINANCE When hemoglobin S is exposed to low oxygen levels, it polymerizes (clumps together), causing the red blood cells to change from their normal round, flexible shape to a rigid, sickle (crescent) shape.  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY SAMPLE PROBLEMS: CODOMINANCE In humans, the allele for normal hemoglobin (HbA) and the allele for sickle-cell hemoglobin (HbS) are codominant. In individuals with the heterozygous genotype (HbAHbS), both normal and sickle-shaped red blood cells are present in the bloodstream, a condition called sickle cell trait. If a person with sickle cell trait (HbAHbS) has a child with someone who has normal hemoglobin (HbAHbA), what are the possible genotypes and phenotypes of their offspring?  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY III. LETHAL GENES Definition: Lethal genes refer to alleles that cause the death of an organism when present in a particular combination. These genes can disrupt vital biological processes, leading to non-viable offspring. Lethal genes can cause embryonic lethality. Other genes, can cause death later in life. Types of Lethal Genes: 1. Recessive Lethal Genes: ⚬ In this case, an individual must inherit two copies of the lethal allele (homozygous) for the gene to be fatal  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY III. LETHAL GENES Types of Lethal Genes: 1.Recessive Lethal Genes: ⚬ Example: The yellow coat color in mice is controlled by a recessive lethal gene. When two heterozygous, yellow-coated mice are crossed (Yy), one-quarter of the offspring inherit two copies of the lethal allele (yy), leading to death in the embryonic stage. ⚬ Genotypic Outcome: A 1:2 phenotypic ratio is observed (1 normal-colored: 2 yellow-colored), rather than the usual 3:1 Mendelian ratio. This skewed ratio results from the absence of homozygous lethal individuals in the surviving population.  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY III. LETHAL GENES Types of Lethal Genes: 2. Dominant Lethal Genes: ⚬ A dominant lethal allele is fatal when present even in a single copy, meaning heterozygous and homozygous dominant individuals do not survive. These alleles are rare because individuals carrying the allele typically die before reaching reproductive age. ⚬ In rare cases, dominant lethal alleles don’t impact viability until later in life, after reproductive maturity thus passing the lethal genes to the offspring ⚬ Example: HUNTINGTON’S DISEASE  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY III. LETHAL GENES Huntington's Disease: In Huntington's disease, the gene responsible for the disorder is a dominant lethal gene. Individuals with one copy of the mutated allele (Hh) survive to adulthood but eventually develop the disease, while homozygous individuals (HH) experience more severe symptoms, though both forms are ultimately fatal.  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY III. LETHAL GENES  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY III. LETHAL GENES Types of Lethal Genes: 2. Dominant Lethal Genes: Creeper Chickens Example: ⚬ Creeper Chickens: In chickens, the "creeper" allele (CP) is lethal in its homozygous form (CPCP). Heterozygous chickens (Cp+) exhibit a short-legged phenotype ⚬ homozygous individuals die before hatching.  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY III. LETHAL GENES ⚬ Manx Cats: In Manx cats, the gene responsible for their taillessness is a dominant lethal gene. Homozygous Manx cats (MM) are not viable, so only heterozygous cats (Mm) survive and exhibit the characteristic tailless trait  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY SAMPLE PROBLEMS: LETHAL GENES Achondroplasia is a form of dwarfism caused by a dominant allele (A), but the homozygous genotype (AA) is lethal before birth. Heterozygous individuals (Aa) display the achondroplasia phenotype, while homozygous recessive individuals (aa) have normal height. If two individuals with achondroplasia (Aa) suppose to have 4 children, how many of them will have a normal height?  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY IV. MULTIPLE ALLELES Definition: Multiple alleles refer to a situation where more than two alternative forms of a gene (alleles) exist for a particular trait within a population. While an individual organism can only carry two alleles for any given gene (one from each parent), multiple alleles mean that there are more than two possible versions of the gene circulating in the population. This leads to greater genetic variation for that trait.  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY IV. MULTIPLE ALLELES KEY CHARACTERISTICS OF MULTIPLE ALLELES 1.More than Two Alleles in the Population: Unlike Mendelian inheritance, where only two alleles (dominant and recessive) control a trait, multiple alleles involve three or more alleles for a single gene. However, any individual organism still only inherits two alleles for that trait. 2.Hierarchies of Dominance: Often, with multiple alleles, there is a dominance hierarchy among the alleles, meaning some alleles may be completely dominant, partially dominant, or recessive to others. This can lead to more complex inheritance patterns. 3.Increased Phenotypic Variety: Multiple alleles contribute to a wider range of possible phenotypes for a given trait. This allows for more diversity within the population and can make traits more variable than they would be with just two alleles.  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY IV. MULTIPLE ALLELES EXAMPLE: ABO Blood Group System in Dominance Hierarchy: Humans IA = IB (codominant to each other) The ABO blood group is a classic example of IA > i (A allele dominates O allele) multiple alleles: IB > i (B allele dominates O allele) IA codes for the A antigen on red blood cells IB codes for the B antigen i (or IO) codes for no antigen (O blood type) These three alleles—IA, IB, and i—determine an individual's blood type: only two of these alleles will be present in an individual.  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY IV. MULTIPLE ALLELES Dominance Hierarchy: C (full color) is the most dominant allele EXAMPLE: Coat Color in Rabbits cch (chinchilla) is partially dominant and lies Another example of multiple alleles can below C in the hierarchy be found in the coat color of rabbits: ch (Himalayan) is less dominant than cch C (wild type (full color), dominant) c (albino) is the most recessive allele cch (chinchilla, partially dominant) ch (Himalayan, less dominant) C > cch > ch > c c (albino, recessive) The combinations of these alleles produce different coat colors: CC, Ccch, or Cch gives full color cchcch, cchch, or cchc gives chinchilla coloration chch or chc gives Himalayan cc gives albino  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY IV. MULTIPLE ALLELES  BENGUET STATE BACHELOR OF SCIENCE IN PSYCHOLOGY UNIVERSITY SAMPLE PROBLEMS: MULTIPLE ALLELES In rabbits, coat color is determined by a gene with multiple alleles. The alleles follow a hierarchy of dominance: C (dominant, full color) c^ch (chinchilla, partial color) c^h (Himalayan, color on extremities) c (recessive, albino, no color) The dominance relationship is: C > c^ch > c^h > c A rabbit breeder crosses a rabbit with genotype C c^h (full color) with another rabbit with genotype c^ch c (chinchilla). Using a Punnett square, determine the genotype, phenotype, and phenotypic ratio of the offspring.