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Chapter 3

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University at Buffalo
APY 107
Niki Bertrand

Genetics: From Genotype to Phenotype Genotype – genetic make up of an organism; specific set of alleles an organism carries Phenotype – the physical features of an organism; physical traits under genetic influence There are two types of genes: Structural genes- the ones that carries the information to make proteins Surrounded by regulatory regions – contain regulatory genes Similar between species Regulatory genes – initiate, promote, or terminate transcription Guide the expression of structural genes Do not code for proteins themselves Think that regulatory genes are the most critical in determining the form of the organism Chimpanzees and humans have 98% similar regulatory genes All of these similarities come from regulatory genes From Genotype to Phenotype The ABO Blood Type System Recessive, dominant and co-dominant alleles ABO refers to the protein that is found on the blood cell and refers to the gene on chromosome 9 The gene has three alleles: A,B,O O- absence of protein We have two copies of a gene We can be heterozygous (2 different alleles) or homozygous (2 same) The allele has to be expressed twice then its recessive If the allele can be expressed once then its dominant Sometimes both can be expressed – co-dominant People who have A and B Obesity: A complex interaction Genes, environment, and phenotype There are genes that are linked to this Likely a combination of alleles that make someone more prone to be obese Environment plays a huge factor Availability of food Mendelian Genetics Before Mendel Blending Inheritance Darwin supported even though he didn’t know about him Based on two assumptions: parent contributes equally to the offspring the contributions that have are at each successive generation particular nature of heredity called it particulate inheritance Gregor Mendel Particulate inheritance Dichotomous variation – the traits differ in two ways Purple flowers or white flowers Only look at traits one at a time Developed a series of postulates for his theory about inheritance Punnett Squares – are a way to look at ratio of genotypes, phenotypes Mendel’s Postulates a. Hereditary characteristics i. Controlled by particulate unit factors (genes) that exist in pairs in organisms because in diploid organisms, the chromosomes come in pairs ii. Each individual receives one copy of each chromosome from each parent, thus he or she receives one of his/her pair of genes from each parent b. Dominant and recessive i. when an individual have two different alleles, responsible for two characteristics, only one is expressed, one is dominant and one is recessive c. Law and segregation i. During formation of gametes, the alleles will separate randomly so that each cell receives one or others with equal likelihood d. Law of independent assortment i. During gamete formation, the segregating pair of alleles will assort independently on one another ii. Complex di-hybrid crosses were performed and picked two traits Punnett Squares Monkeys Big ears & Little ears EE, Ee & ee Fluffy mohawks and slick mohawks MM, Mm, & mm Ratio : 9:3:3:1 Independent Assortment 9=dominance 3= dominant & recessive 3=recessive & dominant 1= recessive and recessive Linkage and Assortment Linkage Two genes on a single pair of homologs; exchange occurs between two non- sister chromatids Crossing over Mutation – occurs in the replication of DNA and become established in the daughter cell Point Mutation – single base in the gene is changed Sickle Cell –when you have sickle cell, it alters the bound shape of the RBC. Sickle cell can clog and decrease life span of the blood cell. not a fatal disease autosomal recessive – has to have two alleles in order for it to be present people who are heterozygous for this are affected it by it a little No Mutation (TTC - Lysine) Silent Mutation (TTT - Lysine) Nonsense Mutation (ATC - STOP) Missense Conservative (TCC – Argine) Nonconservative (TGC- Thr) Trinucleotide Repeat Disease: insertion of one or more nucleotide bases Huntington’s Disease – caused by the repeat sequence of CAG and can be repeated 40-180 times. depending on the # of repeats, that’s how long it takes to show up as a phenotypic trait the more repeats you have the more proteins are being made which is why it will show up sooner Autosomal dominant disease Single Chromosome Mutations Deletion – deletion of a nucleotide base Insertion – adding a fragment in Inversion – when a chromosome fragment breaks off and reattaches itself in
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