Heredity PDF

HEREDITY: Inheritance and Variation  What comes into your mind, when you hear the word heredity? GENOTYPES CONTROL PHENOTYPES Genotype is described as: Totality of the genetic makeup of an individual Combination of alleles found in a homologous...

HEREDITY: Inheritance and Variation  What comes into your mind, when you hear the word heredity? GENOTYPES CONTROL PHENOTYPES Genotype is described as: Totality of the genetic makeup of an individual Combination of alleles found in a homologous chromosome Represented as symbols of the alleles When two similar alleles are represented in pair is called homozygous When two different alleles are represented in pair is called heterozygous Dominant allele is the allele that is expressed in a heterozygous condition while recessive allele is the allele that is not expressed Phenotype is described as set of observable characteristic traits MENDEL’S LAW OF INHERITANCE GREGOR MENDEL (1822-1884) Father of the Modern Genetics Experimented the pea plant breeding Law of Dominance, Law of Segregation, Law of Independent Assortment  Punnett Square A diagram that is used to predict genotypes of a particular breeding experiment and is developed by Reginald Punnett. capital letters represent dominant alleles and lower case letters to recessive alleles With this tool, the known genotypes of each parent are shown to help predict the possible genotypes of their offspring. It shows how alleles are inherited or passed on to offspring from parents. Monohybrid cross Dihybrid cross Mendelian Laws 1. Law of Dominance- one of the pairs of inherited traits will be dominant and the others recessive unless both the factors are recessive. 2. Law of Segregation- when any individual produces gametes, the copies of a gene separate so that each gamete receives only one copy. 3. Law of Independent Assortment- also known as “Inheritance Law” states that alleles of different genes assort independently of one another during gamete formation.  Difference Between Recessive and Dominant Traits Dominant Trait Recessive Trait Expression in an Individual Dominant traits are always expressed when the Recessive traits are expressed only if both the connected allele is dominant, even if only one copy connected alleles are recessive. If one of the alleles is exists dominant, then the associated characteristic is less likely to manifest Representation in Literature Dominant allele is denoted by a capital letter Recessive allele is denoted by a small letter Examples in Humans V-shaped hairline Straight hairline Almond-shaped eyes Round eyes Right handedness Left handedness Detached earlobes Attached earlobes Dark hair Blond hair, red hair Brown eyes Blue eyes (can also be a polygenetic trait)  ACTIVITY. Determine which of each pair of traits are dominant. 1. Dwarfism and tall stature 2. Right-handed and left-handed 3. Blood type A and Blood type O 4. Ability to roll the tongue and inability to roll the tongue 5. With dimples and without dimples 6. Widow’s peak and straight hair line 7. Long eyelashes and short eyelashes 8. Free earlobes and attached earlobes 9. Wide eyes and narrow eyes 10. Broad lips and thin lips Answer Self-check on page 21. (Table 7-3) Non-Mendelian Patterns of Inheritance 1. Codominance- expression of two dominant alleles that results to simultaneous expression of both alleles in the phenotype of the heterozygous individual. Example: ABO blood type, roan (chicken) 2. Incomplete Dominance- expression of a phenotype intermediate to either homozygous parent. An example is when white roses are crossed with red roses, the result are pink roses. What is the difference between Codominance and Incomplete dominance?  Lethal Genes A gene which brings about the death of the organism carrying it. Lethal genes constitute the most common class of gene changes (that is, mutations) and are reflections of the fact that the fundamental function of genes is the control of processes essential to the growth and development of organisms. In higher diploid forms lethals are usually recessive and expressed only in homozygotes. Dominant lethals, expressed in heterozygotes, are rapidly eliminated and thus rarely detected. Recessive zygotic lethals are retained with considerable frequency in natural populations of cross-fertilizing organisms, while gametic lethals (those affecting normal functioning of eggs and sperm among animals, or the pollen and ovules of plants) are subject to stringent selection and are accordingly rare. Recessive lethal genes Multiple Alleles Multiple alleles is a type of non-Mendelian inheritance pattern that involves more than just the typical two alleles that usually code for a certain characteristic in a species. With multiple alleles, that means there are more than two phenotypes available depending on the dominant or recessive alleles that are available in the trait and the dominance pattern the individual alleles follow when combined together. POLYGENIC INHERITANCE Trait controlled by two or more genes. Polygenic traits often show a wide range of phenotypes. Example: The wide range of skin color in humans comes about partly because more than four different genes probably control this trait. SEX LINKED INHERITANCE and SEX LIMITED PATTERN ✓Sex linked traits are determined by genes located on the sex chromosomes and sex-limited traits are determined by genes located on autosomes and express only in one sex. ✓Example of sex linked traits are Hemophilia, color blindedness while sex limited pattern are milk production and sperm production. Pleiotropy These is a condition where one genes affects (multiple genes) in various organs of the body. Example of this is Marfan Syndrome, a human genetic disorder affecting the connective tissues. This disease commonly affects the eyes, heart, blood vessels and skeleton. Albinism, Phenylketonuria, Autism, Sickle Cell Anemia and Schizophrenia.