INHERITANCE (PRELIM).pdf

CYTOGENETICS INHERITANCE b) For each characteristic or trait an organism inherits two alternative - the patterns governing how genetic...

CYTOGENETICS INHERITANCE b) For each characteristic or trait an organism inherits two alternative - the patterns governing how genetic forms of that gene, one from each information is transmitted from parent. generation to generation are collectively c) If the two alleles differ, then one, the known as the principle of inheritance. dominant allele, is fully expressed in - inheritance is not subtyping. the organism’s appearance. The other, the recessive allele has no Austrian Monk, Creationist Gregor Mendel noticeable effect on the organism’s - Mendel’s laws (1865) went unnoticed appearance. until 35 years later, when they were d) The two genes for each character simultaneously and independently segregate during gamete production. discovered by Hugo De Vries in the Netherlands, Erich von Tschermak in III. Law of Independent Assortment Austria, and Carl Correns in Germany. - alleles of different genes pass randomly to offspring. MENDEL’S THREE LAWS OF HEREDITY - in the gametes, alleles of one I. Law of Dominance [Unit gene separate independently Inheritance] of those another gene, and - each trait is determined by two thus all possible combinations factors (alleles), inherited one of alleles are equally probable from each parent. Each of these - the emergence of one trait will factors exhibit a characteristic not affect the emergence of dominant, co-dominant, or another. recessive expression, and those that are dominant will mask the Mendel concluded that each organism expression of those that are carries two copies of its expressed recessive. phenotype. If one differs from the other on the same phenotype one will II. Law of Segregation inevitably dominate the other. - the two alleles of a gene are never transmitted together from one This law was later found to have parent to an offspring. This means important exceptions: if two genes are that, in humans, an individual egg very close to each other on a or sperm is formed with only one chromosome, they tend to be passed allele of each gene. down together. - each of the two inherited factors (alleles) possessed by the parent DEFINITION OF TERMS will segregate and pass during Genotype meiosis into separate gametes - the genetic makeup of an organism. (eggs or sperm), which will each carry only one of the factors. Phenotype - the external appearance of an organism- This specific law has four parts, which caused by the genotype. are: a) Alternative versions of genes or Gene Pool alleles account for variation in - all of the genes and their alleles present inherited characteristics. in a population. Genome Lesson 3: Inheritance Earl Adriane A. Gabato  CYTOGENETICS - entire genetic material of an organism. Hybrid - receive different alleles for a trait from each parent. GENES - composed of DNA (deoxyribonucleic acid), whose building blocks, the nucleotides, code for the multitude of proteins in the human body, including enzymes and structural proteins. - in 2001, estimates place the number of human protein-coding genes between 25,000 and 35,000. Genotype - defined as the subset of alleles of an individual. - composed of alleles, and produces phenotype. - includes type homozygous dominant (MM genotype), homozygous recessive (mm genotype), and heterozygous (Mm genotype). Phenotype - characteristics of an individual and living thing. - produced by genotype environment, and is composed of traits. - includes heritable traits, and acquired traits. Alleles - different forms of a trait; one form of a gene. - examples of traits: eye color, skin color, height, hair texture. - examples of alleles: brown or blue, albino or pigmented, tall or short, curly or straight. Lesson 3: Inheritance Earl Adriane A. Gabato  CYTOGENETICS Dominant Sample Problem - the fully expressed gene, has full control Mother (Aa) x Father (Aa) on the phenotype. - What are the genotypes of the offspring? Recessive - If the dominant gene is attached - gene is completely masked in the earlobes and the recessive gene is phenotype. unattached earlobes, what are the phenotypes of the offspring? Dominant alleles are denoted by a capital letter (A). Recessive alleles are denoted by a lower-case letter (a). APPLICATION TO BLOOD TYPE PUNNET SQUARE - antigen on surface = gives the person his blood phenotype. Lesson 3: Inheritance Earl Adriane A. Gabato  CYTOGENETICS AUTOSOMAL INHERITANCE A gene on one of the 22 pairs of autosomes-that is, the non-sex-determining chromosomes-is called an autosomal gene. Similarly, a trait or ABO BLOOD TYPES: disease associated with that gene is an *O= recessive autosomal trait. *A, B= dominant *AB= co-dominant Autosomal conditions are the most common and are equally likely to occur in males or females. Genotypes: Phenotypes: Antigen: Anti- Autosomal Traits are further classified as either bodies: dominant or recessive. 1. AO Type A A Anti-B (Heterozygous 1. Autosomal Dominant Inheritance A) - Autosomal dominant traits are 2. AA Type A A Anti-B those in which a single copy of an (Homozygous allele is enough fort he trait to be A) expressed or shown in the 3. BO Type B B Anti-A phenotype of the animal. (Heterozygous - dominant conditions are those B) that are expressed in 4. BB Type B B Anti-A heterozygotes. (Homozygous B) 5. OO Type O None Anti- A & Anti- B 6. AB Type AB A&B none Sample Problem: Mother Heterozygous B x Father Type AB − What are the genotypes & phenotypes of the offspring? Lesson 3: Inheritance Earl Adriane A. Gabato  CYTOGENETICS 2. Autosomal Recessive Inheritance - all daughters of an affected father - Autosomal recessive traits will also be affected but none of require that the individual have 2 his sons will be affected (unless copies of the trait to express the the mother is also affected). phenotype. - in addition, the mother of an - the genes for autosomal recessive affected son is also affected (but traits are also located on the necessarily the other way round). autosomes, but the mutant, disease-causing alleles are recessive to normal alleles; thus, if one normal allele is present, it is usually sufficient to prevent any expression of the disease. X-LINKED INHERITANCE X-linked inheritance is often referred to as sex- linked inheritance. Females have two X chromosomes (XX) and males have X and Y (XY). Smaller Y chromosome has only a very few genes as compared to the larger X. A distinguishing feature is the lack of male-to- male transmission, because a father transmits only his Y chromosome, not his X, to his sons. 1. X-Linked Dominant Inheritance - works differently depending upon whether the mother or father is the carries of a gene that causes a disease or disorder. Lesson 3: Inheritance Earl Adriane A. Gabato  CYTOGENETICS 2. X-Linked Recessive Inheritance 3. Mitochondrial Inheritance - expressed in males (who are - refers to additional genes in cell’s necessarily hemizygous for the mitochondria. gene mutation because they have - because mitochondria are almost only one X chromosome); and exclusively passed from parent to - expressed in females who are child in the egg and not in the homozygous for the gene sperm, a hallmark of mutation. mitochondrial inheritance is - carrier females do not usually transmitted from an affected express the phenotype. woman to all of her children. Lesson 3: Inheritance Earl Adriane A. Gabato