Genetics380_2009_Lecture9_28_3slides

Genetics380_2009_Lecture9_28_3slides - Sept. 28, 2009...

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1 Sept. 28, 2009 Extensions and Modifications of Mendel’s Basic Principles Reading: Chapter 5 of textbook. Original crosses by Cuenot (small numbers) NonYellow X NonYellow -> NonYellow yy X yy -> yy Yellow X Non Yellow -> 1:1 Yy X yy -> Yy:yy Yellow X Yellow -> 3 Yellow : 1 NonYellow Yy X Yy -> 3 Y_ : 1 yy Could never get a true breeding Yellow line 2/3 Yellow 1/3 Non Yellow 2:1 Ratio
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2 Modifications and extensions of Mendel’s Basic Principles • Lethal Alleles and Phenotypic Ratios • Multiple alleles at a single locus • Interaction of genes in pathways • Sex influences • Anticipation • Environment Lethal Alleles • 2:1 ratio is almost always produced by a recessive lethal allele. • Yellow coat color in mice: – Effect on survival – Effect on coat color • Tailless, a recessive lethal allele in cats. • Dominant lethal alleles? PLEIOTROPY: One gene affects more than one phenotype.
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3 Multiple Alleles There may be more than two alleles present in a group , but the individual genotype still consists of only two alleles. Allelic series Genotype Phenotype M R M R restricted M R M restricted M R m d restricted MM mallard M m d mallard m d m d dusky Co-dominance and the ABO blood group I A = I B > i Alleles at the ABO locus determine what sugars are added to compound H, which is expressed on the surface of a red blood cell.
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4 Interactions of Genes in Pathways • Effects of genes at different loci (genes that are not allelic) • At the molecular level, organisms operate similarly to an assembly line in a factory. • Series of pathways in which each step is controlled by a gene product: – Biosynthetic pathways – Signal transduction pathways – Developmental pathways RECALL FROM LECTURES 1 and 2: A mutant gene causes albinism Most humans (AA or Aa) have some amount of the skin and hair pigment, melanin. A few people, called albinos (aa), completely lack melanin. Recall from Lecture 4: MC1R gene encodes the melanocortin receptor. When activated, increased production of eumelanin and decreased pheomelanin, resulting in black/brown fur in mice. In humans, most redheads are mcr1/ mcr1. 10-20% are MCR1/ mcr1. Types and frequency of MCR1 mutations vary widely among human populations. Hair color (1) amt. of melanin produced (2) Relative amts. Of eumelanin (brown/ black) compared with pheomelanin (red/yellow). Melanin products against harmful effects of sunlight.
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5 Let’s do a dihybrid cross and consider the red hair phenotype of mcr1 mcr1 Aa MCR1mcr1 X Aa MCR1mcr1 9 A_MCR1_ 3 A_mcr1mcr1 3 aa MCR1_ 1 aa mcr1 mcr1 Interactions of Genes in Pathways • Effects of genes at different loci (genes that are not allelic) “Inborn errors of metabolism” Archibald Garrod (1857-1936) Alkaptonuria (AKU), or black urine disease: homogentisic acid (or alkapton) secreted in patient’s urine In unaffected, homogentisic acid is converted to maleylacetoactic acid.
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This note was uploaded on 10/03/2010 for the course RUT 146:356 taught by Professor Gol during the Spring '10 term at Rutgers.

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Genetics380_2009_Lecture9_28_3slides - Sept. 28, 2009...

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