Genetics - Prelim Module - PDF

ZOOLOGY (GENETICS) Prelim Module BS Psychology | Prof: Dan Bryan Dandan| 2nd YR |2ND SEM |SY 24-25 |Created by Bantolio, Airin LESSON 1: GENETICS Key discovery...

ZOOLOGY (GENETICS) Prelim Module BS Psychology | Prof: Dan Bryan Dandan| 2nd YR |2ND SEM |SY 24-25 |Created by Bantolio, Airin LESSON 1: GENETICS Key discovery In 1953, scientists discovered the double-helix structure WHAT IS GENETICS? of DNA, using data from other scientists. This revealed  In the last century, the reason why some people how DNA stores genetic information. inherit certain traits while others do not, has been subject of much research. Surprisingly enough, the Significance answer lies within the cell! The discovery of DNA’s structure revolutionized biology  branch of biology that deals with heredity and and genetics, allowing for a better understanding of variation of organisms. inheritance and evolution. Chromosomes From a chemical perspective, DNA is a polymer of  Chromosomes carry the hereditary nucleotides, in other words, a polynucleotide. A information(genes) polymer is a compound formed by many simple  Arrangement of nucleotides in DNA units connected to each other.  DNA -> RNA->Proteins Composition NUCLEUS  Double helix structure:  Under the microscope, DNA resembles a twisted ladder with two strands the most evidentpart of containing groups of four nitrogenous bases: Adenine the cell is the nucleus. It is alsothe most (A), Cytosine (C), Guanine (G), and Thymine (T). crucial part of it.  Base pairing:  It is located in the The bases are paired in the helix, specifically A pairs center of the with T, and C pairs with G. cell,surrounded by a membrane which NUCLEOTIDES keepsall the chromosomes inside.  Nucleotides are the basic units of DNA, composed of a phosphate group (P), a sugar CHROMOSOMES (deoxyribose), and a  Inside each cell, there nitrogenous base (A, are 23 pairs of C, G, or T) that chromosomes. encodes genetic  They are structures that are difficult to see information. under the microscope;  The human genome has only 4 letters: however, they become o Purine bases: more evident when the  Adenine A and Guanine G cell is divided. o Pyrimidine bases:  Thymine T and Cytosine C DNA (Deoxyribonucleic Acid) 1. Purines  In chemical terms, DNA  A purine is a heterocyclic aromatic organic is a polymer of compound, consisting of a pyrimidine ring fused to nucleotides. In other an imidazole ring. words, a  Structure: Purines have a double-ring structure (a polynucleotide. A larger, fused structure made up of a six-membered polymer is a compound formed by many simple ring and a five- membered ring). units connected to Examples: each other. o Adenine (A) o Guanine (G) Found in: Discovery of DNA o Both DNA and RNA. Early mention  Function: During the mid – 1980s and early 1990s, scientists o Purines pair with pyrimidines through hydrogen explored trait inheritance in organisms through bonds to maintain the stability of the DNA and RNA experiments with peas and flies. However they were not structure. able to get to complete understanding of control o Adenine (A) pairs with Thymine (T) in DNA (or mechanisms. Uracil(U) in RNA) via two hydrogen bonds. o Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.  ZOOLOGY (GENETICS) Prelim Module BS Psychology | Prof: Dan Bryan Dandan| 2nd YR |2ND SEM |SY 24-25 |Created by Bantolio, Airin 2. Pyrimidines You can see it’s made up of only four letters: A, T, C, and  Pyrimidine is a heterocyclic aromatic organic G (the 4 nucleotides) compound similar to benzene  Structure: Pyrimidines have a single-ring structure Importance in cell division (smaller, six-membered ring).  DNA replication is crucial during cell division Examples: (mitosis and meiosis) as it ensures that each o Cytosine (C) daughter cell receives an exact copy of the genetic o Thymine (T) (found in DNA) information. Without accurate replication, genetic o Uracil (U) (found in RNA, replaces Thymine) errors and cellular dysfunctions could occur.  Found in: o Cytosine is in both DNA and RNA. DNA, genes, and chromosomes: o Thymine is in DNA only.  DNA is the molecule that forms genes, and multiple o Uracil is in RNA only. genes are grouped into chromosomes. Function: Chromosomes are present in the nucleus of every  Pyrimidines pair with purines to ensure proper cell and contain all the genetic information of an base pairing: organism.  Cytosine pairs with Guanine (G).  Thymine (or Uracil in RNA) pairs with GENES AND CHROMOSOMES Adenine (A). Same, but different Chromosome Genes Basic Functions of DNA Chromosomes are Genes are segments of Information storage structures formed by DNA that contain  DNA stores the genetic information that determines DNA and proteins that instructions for protein the characteristics and functions of an organism. house multiple genes in synthesis and determine Replication the cell nucleus. hereditary traits.  DNA can make exact copies of itself, which is essential for cell division and growth. Transcription and translation  DNA is transcribed into RNA and then translated WHAT ARE ALLELES? into proteins, which control cellular activities. An allele is each of the two or more versions of a gene. Inheritance  DNA is inherited from generation to generation and An individual inherits two alleles is responsible for passing traits from parents to An individual inherits two alleles for offspring. each gene; one from the father and Replication the other from the mother. DNA replication process  DNA replication is the process by which the DNA molecule is duplicated before a cell divides. It begins Alleles are located at the same position with the separation of the two complementary DNA within homologous chromosomes. strands, followed by the construction of new complementary strands from available nucleotides. It is essential for cell reproduction and inheritance. ALLELES Homozygous Steps of DNA replication  If both alleles are identical, the 1. Strand separation: individual is homozygous for this gene. The two DNA strands unwind and separate, Ex. PP breaking the hydrogen bonds between Heterozygous complementary bases (A-T, C-G).  If both alleles are different, the individual is 2. Complementation: Free nucleotides pair with the heterozygous for this gene. exposed bases on each strand, following the rules of Ex. Pp complementarity. 3. Formation of new strands: Two new DNA strands TERMINOLOGIES IN GENETICS are formed, one for each original strand, using the  Gene paired nucleotides as building blocks.  Allele 4. Two DNA molecules: The result is the formation of  Dominant and Recessive Allele two DNA molecules, identical to the original, ready  Genotype and Phenotype for cell division.  Heterozygous and Homozygous & Hemizygous Here's an example of a DNA sequence:  Hybrid, Monohybrid, Dihybrid...ATGGACGTTACTAAGGATCCACTAG...  F1, F2 Generations  Reciprocal Cross, Backcross and Test Cross  ZOOLOGY (GENETICS) Prelim Module BS Psychology | Prof: Dan Bryan Dandan| 2nd YR |2ND SEM |SY 24-25 |Created by Bantolio, Airin William Bateson  MONOHYBRID CROSS - a cross between two  biologist who founded and named the science of individual organism which differ from each other genetics and whose work provided a basis for the with respect to ONE pair of allele under study modern understanding of heredity. He is the and the  DIHYBRID CROSS – a cross between two individual chief populariser of the ideas of Gregor Mendel organism which differ from each other with respect following their rediscovery in 1900. to TWO pairs of allele under study.  Bateson co-discovered genetic linkage with Reginald o Ex. Punnett and Edith Saunders, and he and Punnett Yellow Round Seed Green Wrinkled Seed founded the Journal of Genetics in 1910, Bateson YYRR X yyrr also coined the term "epistasis" to describe the genetic interaction of two independent loci. Terminologies: F1 and F2 Generation  F - filial meaning 'offspring' Terminologies: Genotype and Phenotype  F1 - “first filial generation" or the initial cross  GENOTYPE: the genetic makeup (constitution) of an between two genetically distinct plants organism  F2 - cross is the next generation, or the result of  PHENOTYPE: the physical features/ appearance of crossing two sister seedlings from the F1 cross. an organism  Phenotype is the expression of genotype. Terminologies: Reciprocal Cross  Phenotype is produced not only by the  RECIPROCAL CROSS In genetics, a reciprocal cross is genotype but also by the interaction between a breeding experiment designed to test the role of genotype and environmental factors parental sex on a given inheritance pattern. All  EXAMPLE: parent organisms must be true breeding to properly o Trait: Height carry out such an experiment. o Phenotype: Tall and Dwarf o For example, if the pollen (male) from tall plants o Genotype: TT or Tt or tt is transferred to the stigmas (female) of dwarf plants in one cross, the reciprocal cross would Terminologies: Heterozygous, Homozygous, use the pollen of dwarf plants to pollinate the stigmas of tall plants Hemizygous  HETEROZYGOUS: inherited different forms of a particular gene from each parent. Terminologies: Backcross  HOMOZYGOUS: the degree to which both copies of  BACKROSS - is a crossing of a hybrid with one of its a chromosome or gene have the same genetic parents or an individual genetically similar to its sequence parent, in order to achieve offspring with a genetic  HEMIZYGOUS: is a condition in which only one copy identity which is closer to that of the parent. It is of a gene or DNA sequence is present in diploid used in horticulture, animal breeding and in cells. production of gene knockout organisms. Heterozygous Homozygous o For example, the cross between first filial Tall : TT Tall : Tt heterozygote tall (Tt) pea plant and pure tall Dwarf : tt (TT) or pure dwarf (tt) pea plant of the parental generation Hemizygous: Genes on X chromosome in male (have one X and one Y chromosomes) Genes on Y Terminologies: Test Cross chromosomes (only one Y chromosome in male).  TEST CROSS is an experimental cross of an individual organism of dominant phenotype but unknown Terminologies: HYBRID, MONOHYBRID, DIHYBRID genotype and an organism with a homozygous  Hybridization is the process of producing a hybrid. recessive genotype (and phenotype). This also refers to the process of producing offspring o For example, consider the following example by mating two parents from different varieties or Suppose you have a purple and white flower species. and purple color (P) is dominant to white (p). o Example: Liger - a hybrid animal which is an The white flower must be homozygous for the offspring of a lion and a tiger. recessive allele, but the genotype of the purple  HYBRID - offspring of parents that differ in flower is unknown. It could be either PP or Pp. A genetically determined traits. testcross will determine the organism's  MONOHYBRID - a hybrid between two species that genotype. only have a difference of one gene.  DIHYBRID - describes a mating experiment between WHAT ARE GENES? two organisms that are identically hybrid for two  In humans, genes vary in size from a few hundred traits DNA bases to over 2 million bases.  Genes are composed of segments of DNA, the molecule that encodes genetic information in cells.  ZOOLOGY (GENETICS) Prelim Module BS Psychology | Prof: Dan Bryan Dandan| 2nd YR |2ND SEM |SY 24-25 |Created by Bantolio, Airin  Some act as instructions to produce molecules o Carl Corens (Germany) called proteins, and many of them do not o Hugo deVries (Holland) apparently encode. o Erich von Tsechermak (Austria)  A gene is the fundamental physical and functional unit of heredity Mendel’s Peas  Mendel looked at seven traits or characteristics of Terminologies: Gene pea plants:  a unit of heredity which is transferred from a parent  Some traits Mendel saw: to offspring and is held to determine some –Pea Shape characteristic of the offspring. –Pea Color  Danish botanist Wilhelm Johannsen coined the –Pod Color word gene in 1909. –Pod Shape  Consist of continuous segment of DNA –Stem Length (Deoxyribonucleic acid)  In eukaryotes, the gene occupies in the specific MENDEL’S PRINCIPLES OF INHERITANCE position on the chromosomes called locus (loci). Heredity was believed to involve a blending of GREGOR JOHANN MENDEL attributes  Austrian Monk, born in what is now Czech Republic in 1822  Son of peasant farmer, studied Theology and was Like the way two colors ordained priest Order St. Augustine. Went to the mix to give an intermediate color university of Vienna, where he studied botany and learned the Scientific Method  Worked with pure lines of peas for eight years How did the dark hair  Prior to Mendel, heredity was regarded as a skip a generation? "blending" process and the offspring were essentially a "dilution" of the different parental characteristics.  The Modern Concepts of genetics took birthfrom his work on Pisum sativum (Garden Pea, 1856-1864)  Mendel published his results in the annual Greg’s Diary proceedings of Natural History Society of Brunnin  Heredity must be based on discrete units of 1886 Publication ” Experiments in Plant inheritance! Hybridizations (German)  These units of inheritance were later called genes.  In 1866 he published Experiments in Plant Hybridization, (Versuche über Pflanzen- Hybriden) in The Gene Theory of Inheritance which he established his three Principles of Inheritance  He tried to repeat his work in another plant, but didn’t work because the plant reproduced asexually!  Work was largely ignored for 34 years, until 1900, when 3 independent botanists rediscovered Mendel’ s work.  Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance. He  deduced that genes come in pairs and are inherited  Mendel studied pea plants  as distinct units, one from each parent. Mendel  Mendel knew nothing about chromosomes  tracked the segregation of parental genes and their Why pea plants?  appearance in the offspring as dominant or  Multiple variable traits that are clearly visible recessive traits.  Generations are short and offspring are many  He recognized the mathematical patterns of  Mendel just removed the stamens from certain inheritance from one generation to the next. plants Mendel's Laws of Heredity are usually stated using 3  Mating is easy to control (cross-fertilization) principles Rediscovery of Mendel’s Original Work  In 1900, three (3) botanist independently rediscover Mendel’s work, a generation after Mendel published his papers.  ZOOLOGY (GENETICS) Prelim Module BS Psychology | Prof: Dan Bryan Dandan| 2nd YR |2ND SEM |SY 24-25 |Created by Bantolio, Airin Hybridization Monohybrid Cross - Law of Segregation  Hybridization is the process of producing a hybrid. This also refers to the process of producing offspring by mating two parents from different varieties or species Only flower color is F1 generation being assessed (first filial) Dihybrid Cross – Law of Independent Assortment Two traits can be assessed at once F2 generation (second filial) MENDEL’S LAWS  The law of Segregation  The law of independent assortment Both genotypes = heterozygous  The law of Dominance Both phenotypes = dominant The Law of Segregation Gametes: Y, y, R, r  Each trait we inherit, like eye color or hair type, Phenotypic distribution =9:3:3:1 is controlled by two versions of a gene (one 9 = both traits dominant from each parent). During reproduction, the 3 = seed color dominant parents’ genes are randomly split so that the 3+ seed shape dominant egg or sperm gets only one version (not both). 1 = both traits recessive When the egg and sperm join during fertilization, the baby ends up with one version  These results prove that the of the gene from each parent, creating the pair. traits are determined separately The Law of Independent Assortment  Gametes have a random  The Law of Independent Assortment means that 25% 25% 25% 25% combination of the possible genes controlling different traits (like eye color and alleles for the two traits height) are passed down independently of each  Heredity is therefore pure probability other.  For example, just because you inherit your The rules of probability allow us to predict phenotypic mom's eye color doesn’t mean you’ll also distributions for any combination. inherit her height. Each trait is passed on More complex patterns of inheritance exist without affecting the others. Two traits for flower color are Every trait is controlled by a gene expressed simultaneously Like flower color Organisms have two version of each gene Genotype = nucleotide sequence Mendelian Genetics Have Since Been Extended Phenotype = visibly expressed trait  Certain alleles are not completely dominant or recessive Mendel deciphered this without knowing about DNA  some genes have more than two alleles Only the dominant allele is expressed  A single gene can produce multiple phenotypes True-breeding plants have two identical alleles Detached Earlobes Attached Earlobes The Law of Dominance:  The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.  Gametes have only one allele Straight thumb Hitchiker’s thumb  The offspring have two alleles (one from each parent)  ZOOLOGY (GENETICS) Prelim Module BS Psychology | Prof: Dan Bryan Dandan| 2nd YR |2ND SEM |SY 24-25 |Created by Bantolio, Airin  Treatment focuses on managing symptoms, including: o Medications for movement disorders and psychiatric symptoms. o Physical therapy, speech therapy, and Tounge roll Unable to do tongue roll counseling.  Ongoing research is exploring gene-silencing therapies and other experimental approaches. Prognosis:  Huntington's disease is progressive, meaning symptoms worsen over time.  Life expectancy after symptom onset is typically 15– 20 years. LESSSON 3: RELATED TO MENDELLIAN Tay-Sachs Disease (Recessive Inheritance) PATTERN OF INHERITANCE Cause:  Tay-Sachs is caused by a mutation in the HEXA gene Autosomal Dominant on chromosome 15.  One mutated allele causes the disorder.  The mutation leads to a deficiency of the enzyme  Two mutated alleles are required for the disorder beta-hexosaminidase A, which breaks down a fatty substance called GM2 ganglioside. Huntington’s Disease (Dominant Inheritance)  The buildup of GM2 ganglioside in the brain leads to Cause: progressive neurological damage.  HD is caused by a mutation in the HTT gene located Symptoms: on chromosome 4.  Symptoms typically appear in infancy (3– 6 months)  The mutation involves an excessive repetition of a and worsen over time. DNA sequence called CAG trinucleotide repeat  Neurological Symptoms: Loss of motor skills, within the gene. muscle weakness, seizures, and exaggerated startle  More than 40 repeats of this sequence typically response. result in the development of the disease.  Cognitive Symptoms: Gradual loss of awareness, Symptoms: responsiveness, and intellectual abilities.  Symptoms usually appear between the ages of 30  Physical Symptoms: Vision and hearing loss, and 50, though they can occur earlier or later. difficulty swallowing, and cherry-red spots in the  Symptoms worsen over time eyes.  and include: Inheritance: o Motor Symptoms: Involuntary movements  Tay-Sachs disease is autosomal recessive, meaning: (chorea), impaired coordination, difficulty with  Both parents must be carriers (Tt) to pass on the voluntary movements. disease. o Cognitive Symptoms: Difficulty concentrating,  Each child has a 25% chance of having Tay-Sachs, a memory loss, impaired decision-making, and 50% chance of being a carrier, and a 25% chance of dementia in later stages. being unaffected. o Psychiatric Symptoms: Depression, anxiety, Diagnosis: irritability, mood swings, and, in some cases,  Enzyme testing: Measures beta-hexosaminidase A psychosis. activity in blood. Inheritance:  Genetic testing: Detects mutations in the HEXA  Huntington's disease is autosomal dominant, gene. meaning:  Prenatal testing: Can identify carriers and affected o A person with the disease has a 50% chance of fetuses. passing the mutation to each child. Treatment o Both males and females are equally likely to  There is currently no cure for Tay-Sachs disease. inherit and transmit the disease.  Treatment focuses on managing symptoms and Diagnosis: providing supportive care, including:  Genetic testing can confirm the presence of the CAG repeat expansion in the HTT gene. o Seizure medications.  Family history, physical examination, and o Physical therapy and feeding support. neurological evaluations also play a role. o Palliative care for end-stage disease. Treatment:  There is no cure for Huntington 's disease.  ZOOLOGY (GENETICS) Prelim Module BS Psychology | Prof: Dan Bryan Dandan| 2nd YR |2ND SEM |SY 24-25 |Created by Bantolio, Airin Albinism (Recessive Inheritance)  Psychiatric Symptoms:  Albinism is a rare genetic condition characterized by o Anxiety, depression, and emotional instability, a lack of melanin, the pigment responsible for the especially in individuals diagnosed later or not color of skin, hair, and eyes. It is caused by adhering to treatment. mutations in genes that affect melanin production, Diagnosis: leading to reduced or absent pigmentation.  Newborn screening detects elevated Albinism occurs in all ethnic groups and affects both phenylalanine levels. Early detection prevents males and females equally. complications. Treatment: Types of Albinism  Low-phenylalanine diet: Avoiding high- protein 1. Oculocutaneous Albinism (OCA): foods like meat, fish, dairy, eggs, and certain o Affects the skin, hair, and eyes. artificial sweeteners (aspartame). o It is inherited in an autosomal recessive pattern,  Special medical formula provides essential nutrients meaning an individual must inherit two copies without phenylalanine. of the mutated gene (one from each parent).  Regular monitoring of phenylalanine levels. 2. Ocular Albinism (OA):  Emerging treatments, such as enzyme replacement o Primarily affects the eyes, with little or no therapy or gene therapy, are under research. impact on skin and hair pigmentation. o Usually inherited in an X-linked recessive manner, affecting mostly males. LESSON 4: UNDERSTANDING NON- Symptoms:  Skin: Pale skin that is highly sensitive to sunburn MENDELIAN INHERITANCE  and UV damage.  Hair: White, light blonde, or very light brown WHAT IS NON-MENDELIAN INHERITANCE? hair, depending on the type of albinism.  Non-Mendelian inheritance refers to genetic  Eyes: patterns that do not follow Mendel’s laws of o Light-colored eyes (blue, green, or gray). dominant and recessive traits. o Vision problems, such as reduced sharpness,  Because some traits are influenced by multiple sensitivity to light (photophobia), involuntary alleles, incomplete dominance, codominance, gene eye movements (nystagmus), and misaligned interactions, or environmental factors. eyes (strabismus).  Increased Risk of Skin Cancer: Due to the lack Types of Non-Mendelian Inheritance Covered: of melanin, which offers protection from UV  Incomplete Dominance rays.  Codominance  Multiple Alleles PKU (Phenylketonuria, Recessive Inheritance)  PKU (Phenylketonuria) is a rare inherited metabolic INCOMPLETE DOMINANCE disorder caused by mutations in the PAH gene  In incomplete dominance, the heterozygous (phenylalanine hydroxylase). This gene produces an phenotype is a mix or intermediate between two enzyme that breaks down phenylalanine, an amino homozygous phenotypes. acid found in protein-containing foods. Without this  Neither Allele is completely dominant over the enzyme, phenylalanine builds up to toxic levels in other. the body, leading to severe health and developmental problems. HOW DOES INCOMPLETE DOMINANCE APPLY TO  PKU is inherited in an autosomal recessive pattern, HUMAN? meaning a person must inherit two defective copies Incomplete dominance can be observed in some human of the gene (one from each parent) to develop the traits and conditions. condition. 1. Hair Texture Symptoms:  Straight hair (SS) × Curly hair (CC) = Wavy hair (SC)  Neurological and Cognitive Symptoms:  Individuals with one allele for straight hair and one  Intellectual disability (if untreated). for curly hair tend to have wavy hair, which is a mix  Delayed development, behavioral problems, of both textures. and poor concentration.  Physical Symptoms: 2. Skin Color o Musty odor due to the buildup of  While skin color is determined by multiple genes phenylalanine. (polygenic inheritance), incomplete dominance o Fair skin and hair (due to reduced melanin plays a role. production).  When individuals with very light skin and very dark o Small head size (microcephaly). skin have children, their offspring often have an intermediate skin tone.  ZOOLOGY (GENETICS) Prelim Module BS Psychology | Prof: Dan Bryan Dandan| 2nd YR |2ND SEM |SY 24-25 |Created by Bantolio, Airin 3. Lip Shape GENOTYPE: 1 CC; 2 CS; 1 SS  Some studies suggest that the shape of lips can PHENOTYPE: 1 Curly hair; 2 Wavy hair; 1 Straight hair follow an incomplete dominance pattern. 25% BB – 50% BW – 25% WW  A parent with thick lips and a parent with thin lips may have children with medium-sized lips. CONCLUSION  Incomplete dominance is an important genetic 4. Voice Pitch concept that explains why some traits appear as a  Some researchers propose that vocal pitch in mix rather than strictly following dominant- humans can be influenced by incomplete recessive inheritance. dominance, where deep and high-pitched voices  In humans, traits such as hair texture, skin tone, and blend into an intermediate range. even certain diseases show incomplete dominance patterns, contributing to the diversity of human WHY DOES INCOMPLETE DOMINANCE HAPPEN? characteristics.  The reason incomplete dominance occurs is that  Understanding these principles helps in fields like one functional allele does not produce enough genetics, medicine, and evolutionary biology. protein (such as a pigment or enzyme) to fully express a dominant trait. CODOMINANCE  This leads to an intermediate expression instead of a  Codominance is a pattern of inheritance where both full dominant phenotype. alleles in a heterozygous individual are fully  In contrast, in Mendelian inheritance, the dominant expressed without blending. allele typically produces enough functional protein  Unlike incomplete dominance, where the to completely mask the recessive allele. heterozygous phenotype is an intermediate between the two homozygous forms, codominance TRIVIA ABOUT INCOMPLETE DOMINANCE results in both traits appearing distinctly in the Incomplete Dominance and Co-dominance organism.  Incomplete dominance is different from codominance!  In codominance, both traits are fully visible (like in HOW DOES INCOMPLETE DOMINANCE APPLY TO AB blood type), whereas in incomplete dominance, HUMANS? the traits blend together. Codominance is evident in several human traits and  Heterozygous individuals may have advantages! In genetic conditions some cases, blending traits can offer a biological 1. ABO Blood Group System advantage, such as increased survival or  The most well-known example of codominance in adaptability. humans is the ABO blood group system. Blood type  Selective breeding in agriculture uses incomplete is determined by the presence of specific antigens dominance! Breeders use this principle to develop (proteins) on the surface of red blood cells, intermediate traits in crops and livestock. controlled by a single gene with three alleles: SAMPLE PROBLEM 1 If two blue-feathered Andalusian chickens (BW × BW) are crossed, what percentage of their offspring will have white feathers?  BB (Black feathers)  WW (White feathers)  BW (Blue-gray feathers) → A mix of black and white feathers B W How Codominance Works in Blood Types B BB BW  Type A (IAIA or IAi): Only A antigens are expressed. W BW WW  Type B (IBIB or IBi): Only B antigens are expressed. GENOTYPE: 1 BB; 2 BW; 1 WW  Type O (ii): No antigens are present. PHENOTYPE: 1 black feather; 2 blue-gray feathers; 1  Type AB (IAIB): Both A and B antigens are expressed white feathers equally, making this an example of codominance. 25% BB – 50% BW – 25% WW  "I" stands for Isoagglutinogen, referring to the antigens found on the surface of red blood cells. SAMPLE PROBLEM 2  These antigens (A and B) determine a person's If two wavy-haired individuals (CS × CS) have children, blood type. what are the expected hair textures in their offspring?  The gene responsible for these antigens is called the C S I gene or ABO gene. C CC CS S CS SS  ZOOLOGY (GENETICS) Prelim Module BS Psychology | Prof: Dan Bryan Dandan| 2nd YR |2ND SEM |SY 24-25 |Created by Bantolio, Airin MULTIPLE ALLELES IN HUMAN INHERITANCE  Humans have several traits governed by multiple alleles, but an individual can still inherit only two alleles (one from each parent) because we have two copies of each gene. However, at the population level, more than two possible alleles exist. 1. ABO Blood Group System (Classic Example of Multiple Alleles)  The ABO blood system in humans is one Example of a Codominant Blood Type Cross of the best examples of multiple alleles.  Medical Importance: Blood type determination is  Gene: ABO gene (located on chromosome 9) crucial for blood transfusions, as AB individuals can  Alleles: receive blood from any group (universal recipients), o IA (A allele) → Produces A antigen while O individuals can donate to all but can only o IB (B allele) → Produces B antigen M receive O blood. o i (O allele) → Produces no antigen  Sickle Cell Trait (Partial Codominance) Another WHY DOES MULTIPLE ALLELE INHERITANCE MATTER? human example is sickle cell anemia, caused by  Blood transfusions depend on ABO compatibility. mutations in the hemoglobin gene (HBB gene). The o Type O (ii) = Universal donor (no antigens, so it two alleles are: won’t trigger an immune  HA: Normal hemoglobin response).  Hs: Mutated hemoglobin, leading to o Type AB (IAIB) = Universal  sickle-shaped red blood cells recipient (has both A and B antigens, so it can How Codominance Works in Sickle Cell Trait receive any blood type)  HaHa (Normal Hemoglobin): All red blood cells are Genotype Rh Type Antigen on Antibody in normal. RBC Plasma  HsHs (Sickle Cell Anemia): All red blood cells are RR or Rr Rh+ Rh (D) None sickle-shaped, causing severe health issues. (Positve) antigen rr Rh- No Rh May  HaHs (Sickle Cell Trait): Both normal and sickle- (Negative) antigen develop shaped red blood cells are present in the anti-Rh if bloodstream, showing codominance. exposed to Rh+ blood Medical Importance:  Individuals with HAHs (sickle cell trait) usually do  Rh Factor (+ or -) not suffer from severe symptoms but have o The Rh blood group system is determined by the increased resistance to malaria. presence (Rha+) or absence (Rha -)of the Rh (D)  This is an example of heterozygote advantage, antigen on red blood cells where codominance contributes to survival in malaria-prone regions (e.g., Africa).  Type O - is the universal donor, while Type AB+ is the universal recipient because it has no antibodies SUMMARY against A, B, or Rh antigens.  Codominance plays an important role in genetic Recipient Blood Type Can Receive From Type A+ A+, A-, O+, O- diversity, especially in blood type compatibility, Type A- A-, O- disease resistance, and immune function. While not Type B+ B+, B-, O+, O- as common as dominant/recessive inheritance, Type B- B-, O- codominance allows for the coexistence of multiple Type AB+ (Universal All Blood Types functional traits in the same individual. Recipient) Type AB- AB-, A-, B-, O- MULTIPLE ALLELES Type O+ O+, O- Type O- (Universal Donor) O- Only  In genetics, multiple alleles refer to a situation where a gene has more than two possible versions 2. Human Eye Color (Influenced by Multiple (alleles) in a population. Unlike simple dominant- recessive inheritance (where a gene has only two Alleles) alleles, like tall vs. short in Mendel’ s pea plants),  Eye color is polygenic (influenced by multiplegenes), multiple alleles create more variation in traits. but one major gene, OCA2, has multiple alleles that help determine eye color:  Brown (B) = Dominant  Blue (b) = Recessive  ZOOLOGY (GENETICS) Prelim Module BS Psychology | Prof: Dan Bryan Dandan| 2nd YR |2ND SEM |SY 24-25 |Created by Bantolio, Airin  Green (G) and Hazel (H) CONCLUSION = Intermediate alleles with varying dominance  Multiple alleles increase genetic diversity in a  Possible Allele Combinations: population. o BB, Bb → Brown Eyes  They explain why humans have a broad range of o bb → Blue Eyes physical traits, from eye color and hair color to o BG → Green Eyes blood types and skin tone. o BH → Hazel Eye  They show that inheritance is more complex than just dominant and recessive traits.  Since multiple genes interact, eye color is not determined by a single allele, but rather by a complex interaction of dominant, recessive, and intermediate alleles.  Hair color is controlled by genes like MC1R, which has multiple alleles influencing the production of eumelanin (brown/black pigment) and pheomelanin (red/yellow pigment). 3. Human Hair Color (Influenced by Multiple Alleles  Alleles of MC1R:  B (Brown/Black hair, dominant)  b (Blonde, recessive)  r (Red, recessive, associated with high pheomelanin production)  Possible Combinations:  BB → Black Hair  Bb → Brown Hair  bb → Blonde Hair  rr → Red Hair (only ifboth parents pass “r”)  Hair color inheritance is incomplete dominance and polygenic, meaning multiple genes affect shade and texture. 4. Human Skin Colo (Multiple Alleles + Polygenic Inheritance)  Skin color is determined by melanin production, which influenced by multiple genes. There are several alleles controlling melanin levels, making skin color highly variable across populations.  Genes like MC1R, SLC24A5, TYR, and OCA2 contribute to light vs. dark skin.  Different alleles in these genes lead to varying amounts of melanin. Unlike blood type, skin color inheritance is complex and influenced by environmental factors (e.g., sun exposure). INTERESTING FACTS ABOUT MULTIPLE ALLELES  The gene for freckles (MC1R) has multiple alleles; some cause freckling, while others don’t.  ABO blood type mutations exist, and some rare variants cause blood types like Bombay phenotype (hh), where a person appears to have type O even if they carry an A or B allele.  There are over 1500 known MC1R variants, which is why hair and skin color vary so much