Patterns of Inheritance PDF

Preview

Summary

Biology 1010 taught by James Bradshaw: lecture 15 notes on the basics of how genetics work and punnette squares....

Description

Lecture 15 Patterns of Inheritance - Chromosomes - Composed of genes - Each gene has a specific location on the chromosome (locus) - Genes - Sequence of nucleotides that encode a polypeptide chain - Allele - Different nucleotide sequences at the same locus on two homologous chromosomes Genes and Traits - Alleles - Dominant allele: exerts its effect whenever present - Recessive allele: is masked if dominant allele present - Only manifested if they have two of the recessive alleles - Most common allele not always the dominant one - Blue eyes common in northern Europe but recessive - Genotype: genetic makeup - Homozygous: identical - Homozygous recessive- tt - Homozygous dominant- TT - Heterozygous- one of each- Tt - Phenotype: trait expression - TT- tall - Tt- tall - tt- short Mendel’s Laws - Gregor Mendel was a 19th century Austrian monk who derived a series of laws that described the genetic patterns of heredity from one generation to the next. - These laws account for the variability between members of a family. - Mendel derived these laws from his experiments with pea plants. Mendel’s Law of Segregation - 2 alleles of each gene are packaged into separate gametes - Each gamete only contains 1 of the 2 alleles - When there is a heterozygous parent there is a 50/50 chance of which allele they pass on to their offspring - The punnett square is the application of the law of segregation Mendel’s Law of Independent Assortment - Alleles of different genes move independently into gametes - Alleles for one gene do not influence the segregation of alleles for another gene - Independent assortment also happens in metaphase I as one of the three recombination

processes Exceptions to Mendel’s Law - Looking at two traits that are influenced by two genes that are on the same chromosome - Genes A and B are far apart; crossing over is more likely to separate these alleles - Genes B and C are close together; crossing over is less likely to separate these alleles Family Pedigrees - From a pedigree, the pattern of inheritance for a genetic trait can be determined - This information can allow the genetic counselor to estimate the probability that a child might inherit a genetic disorder Genetic Disorders of Interest - The field of medical genetics focuses on genetic disorders caused by single gene mutations - Several of these disease are well-known and have been thoroughly studied Autosomal Disorders - Autosomal disorders are caused by mutated alleles on the autosomal chromosomes, not the sex chromosomes - Some autosomal disorders are recessive while others are dominant - For the recessive inheritance they need to have two recessive alleles to get the disease - Normal phenotypes means you don’t have the disease/disorder Sex-Linked Inheritance - Don’t look at the Y chromosome - Recessive disorders (don’t worry about dominant) - Color blindness - Hemophilia - Men are more prone to sex-linked disorders - Since it is recessive women are less prone because we have two X chromosomes and follows the same rules as the other disorders - Draw sex chromosomes first so you remember there is no allele on the Y chromosomes - If mother is colorblind she will pass that on to all her male offspring Beyond Mendel’s Laws - Mendel’s study of inheritance dealt with simple, independently-segregating traits - There are other patterns of inheritance other than the dominance/recessive relationship Mendel observed - Sometimes alleles aren’t dominant and recessive but are both dominant; you get an incomplete dominance with an intermediate phenotype that is just a combination of the two where you get something in the middle. - In humans, they are either round and make straight hair or they are flat and that makes curly hair. The intermediate phenotype is wavy as it has incomplete dominance because both curly and straight hair are dominant - In a flower, one is red and one is white which are both dominant genes so they combine

and create a pink colored offspring, 50% chance pink, 25% chance for red or white (called four o’clock flowers) Multiple-Allele Traits - For some factors, such as human blood type, there are more than two alleles - I^A= A antigen on red blood cells - I^B= B antigen on red blood cells - i= neither A or B antigen on red blood cells - Blood type O is without A and B - Some can have A and B which makes AB - ABO genes has three different alleles where two are dominant and one is recessive - Codominance means that neither allele is dominant over each other and both are expressed independently - In order for a child to be O, one parent has to be i i and the other parent must be heterozygous with only one i - RH factor affects - or +, if you have it your positive and if you don’t you don’t have it Alleles and Traits - Mendel’s alleles - Dominant - Recessive - Very simple and only one of each gene - Incomplete Dominance - Codominance - Polygenic - Many genes, one trait - Pleiotropy - One gene can influence multiple traits - Genetic heterogeneity - Multiple genotypes/identical phenotypes - Same phenotype but have mutations on different genes - Epistasis - One gene affects the expression of another - Albinism, having an A offspring with both parents having O - One genes supersedes all other genes Environmental and Phenotype - Fingerprints are 90% environmentally influenced - Blood type is 100% genetic influenced - We are both influenced by our environment and our phenotypes - Siamese cats and himalayas rabbits have black spots due to colder temperatures in their environment to help keep those extremities or spots warmer with their core cooler...