* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download File - fiserscience.com
Quantitative trait locus wikipedia , lookup
Genomic imprinting wikipedia , lookup
Hardy–Weinberg principle wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Gene expression programming wikipedia , lookup
X-inactivation wikipedia , lookup
Gene expression profiling wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Genome (book) wikipedia , lookup
Designer baby wikipedia , lookup
Chapter 4 Lecture Concepts of Genetics Tenth Edition Extensions of Mendelian Genetics • Mendel’s work at start of 20th century well known • Other biologists verify with crosses of other organisms • Exceptions were observed • Extensions to Mendel’s principles of heredity © 2012 Pearson Education, Inc. Cuenot’s Mice • Cuenot worked with coat color in mice which come in many colors: – Black, gray, brown, white, yellow – But no true breeding yellow mice ever obtained © 2012 Pearson Education, Inc. Genes and Alleles Interact to Produce Phenotypes • • • • • Existing alleles subject to mutation Give rise to new alleles Single gene can have many alleles A single gene many phenotypic effects Single character may be controlled by many genes • Expression of gene is affected by interactions with other genes and with environment © 2012 Pearson Education, Inc. • Alternative forms of a gene are called alleles • Mutation is the source of alleles • The wild-type allele is the one that occurs most frequently in nature • The other alleles of that gene are mutant • Genes with more than one allele are polymorphic – New phenotypes result from changes in functional activity of gene product • Eliminating enzyme function • Changing relative enzyme efficiency • Changing overall enzyme function © 2012 Pearson Education, Inc. Multiple alleles for coat color in rabbits • C gene for coat color • 4 alleles • C > cchd > ch > c © 2012 Pearson Education, Inc. Dominance not always complete • Many genes have alleles that are neither dominant nor recessive to one another • Heterozygotes have an intermediate phenotype • Incomplete Dominance • Phenotype ratio = Genotype ratio © 2012 Pearson Education, Inc. Incomplete Dominance © 2012 Pearson Education, Inc. © 2012 Pearson Education, Inc. Figure 4.1 Codominance • Two alleles of a gene both produce their phenotypes when present in a heterozygote • Ex: ABO blood group in humans • Gene I encodes an enzyme involved in attaching sugars to the surface or RBC • Three alleles of the I gene: IA IB and i (IO ) © 2012 Pearson Education, Inc. Genes interact when they are expressed • Many traits characterized by a distinct phenotype are affected by more than one gene • In gene interaction, the cellular function of numerous gene products contributes to the development of a common phenotype © 2012 Pearson Education, Inc. • The term epistasis describes the situation in which a gene can mask or modify the phenotypic effects of another gene • Epistatic interactions often arise because two (or more) different proteins participate in a common cellular function – For example, an enzymatic pathway Colorless precursor Enzyme C The recessive c allele encodes an inactive enzyme © 2012 Pearson Education, Inc. Colorless intermediate Enzyme P Purple pigment The recessive p allele encodes an inactive enzyme • If an individual is homozygous for either recessive allele, it will not make any functional enzyme C or enzyme P – Therefore, in the previous example, the flowers remain white © 2012 Pearson Education, Inc. © 2012 Pearson Education, Inc. © 2012 Pearson Education, Inc. Labrador retrievers Allele B (black) is dominant to b (brown) Allele E (pigment deposition in hair) is dominant to e (no deposition so hair is yellow) © 2012 Pearson Education, Inc. Labrador Retrievers © 2012 Pearson Education, Inc. The Expression of a Genotype May Be Influenced by Environmental Effects • Temperature-sensitive allele: – An allele whose product is functional only at a certain temperature. Two parameters describe the effects of genes and environment on phenotype 1) Penetrance – proportion of individuals in a group with a given genotype that actually show the expected phenotype – Ex: BRCA1 mutant allele, some people do not develop breast cancer – The mutation is said to be incompletely penetrant © 2012 Pearson Education, Inc. 2) Expressivity – degree or range to which a genotype is expressed in an individual – Ex: BRCA1 mutant allele. A woman with the mutant allele may develop both breast and ovarian cancer as part of the phenotype, but another woman with same mutation may only get breast cancer. – The mutation is said to have variable expressivity © 2012 Pearson Education, Inc. Genes are carried on chromosomes • A gene is a sequence of DNA that resides at a particular site on a chromosome called a locus • Genes that reside on a single chromosome are genetically linked together and this affects pattern of inheritance © 2012 Pearson Education, Inc. • X,Y system used for sex determination by many animal and plant species • X is a large chromosome and encodes many genes • Y is a small chromosome with few genes (not homologous to X in the traditional sense but has pairing region for synapsis) © 2012 Pearson Education, Inc. Thomas Hunt Morgan and the Fly Room • Early 20th century, Columbia University • Fruit fly – Drosophila melanogaster © 2012 Pearson Education, Inc. © 2012 Pearson Education, Inc. Figure 4.12 © 2012 Pearson Education, Inc. Figure 4.13 • Thomas Hunt Morgan (1910) showed the Xlinked inheritance in his studies of the white eyed mutation in Drosophila • The inheritance pattern was clearly related to the sex of the parent carrying the mutant allele • Reciprocal crosses between white eyed and red eyed flies did not yield identical results • White locus is present on the X chromosome rather than one of the autosomes © 2012 Pearson Education, Inc. Interesting video to watch on Morgan’s flies • Calvin Bridges: http://library.cshl.edu/exhibits/bridges/_pag es/page1_about.html • The Fly Room movie: http://www.theflyroom.com © 2012 Pearson Education, Inc. • Genes present on the X chromosome exhibit unique patterns of inheritance due to the presence of only one X chromosome in males and two in females • Males cannot be either homozygous or heterozygous for X linked genes – they have only one copy of a gene in a diploid cell - hemizygous © 2012 Pearson Education, Inc. • Many traits controlled by X chromosomelinked traits – Red/green color blindness – Hemophilia – Only females are carriers of recessive alleles © 2012 Pearson Education, Inc. © 2012 Pearson Education, Inc. Figure 4.14 • Lethal X-linked recessive disorders are observed most often in males • Only females can be heterozygous carriers that do not develop the disorders • For example: Duchenne muscular dystrophy – Muscles slowly degenerate leading to paralysis – Onset prior to the age of 6 and lethal around 30 © 2012 Pearson Education, Inc. Concept Check Hemophilia (reduced blood clotting) is an X-linked recessive disease in humans. A woman with hemophilia mates with a man who exhibits normal blood clotting. What is the probability that their child will have hemophilia? Concept Check Hemophilia (reduced blood clotting) is an X-linked recessive disease in humans. A woman with hemophilia mates with a man who exhibits normal blood clotting. What is the probability that their child will have hemophilia? 1/2 © 2012 Pearson Education, Inc. © 2012 Pearson Education, Inc.