Genetics of Inheritance
Genetics of Inheritance 40763 - BMS 110 - B
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This 9 page Class Notes was uploaded by tess2019 on Thursday October 8, 2015. The Class Notes belongs to 40763 - BMS 110 - B at Missouri State University taught by Ivy J Fitzgerald in Fall 2015. Since its upload, it has received 19 views. For similar materials see Introduction to the Biomedical Sciences in Biomedical Sciences at Missouri State University.
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Date Created: 10/08/15
Genetics of Inheritance Monday August 17 2015 1228 PM Terminology Genotype genetic alleles present Phenotype physical characteristics Dominant one copy of allele causes phenotype Recessive two copies ofallele necessary to cause phenotype Allele version alternative form of a gene Homozygous contains two ofthe same alleles Heterozygous contains two different alleles Autosomal not sexlinked For humans allele is on one of chromosomes 122 Sexlinked on chromosomeX or Y Gregor Mendel Mendel carefully crossbred pea plants and recorded the frequency of the phenotypes that resulted Peas are normally selffertilizing so no sexlinked traits Did work mid18005 work found 1900 Punnett Squares Punnett squares are used to calculate the expected ratio of genotypes and phenotypes niuon 39ll o nayon39lc39 Tennhinge EIVCII LI IC Pal CI IL SCI IULYPCD 0 A square with 4 boxes is drawn if 1 trait is being analyzed 0 Parent 139s alleles are written across the top of the box one over each column 0 Parent 239s alleles are written along the side of the box one next to each row Mendel39s Laws of Inheritance Law of Segregation Every individual has a pair ofalleles for each trait 0 These alleles separate during gamete formation 0 Each gamete only gets one allele Law of Independent Assortment Alleles for different genes end up in gametes independently of each other Law of Dominance Dominant alleles mask recessive alleles Thomas Hunt Morgan 1900 Bred fruit flies o Havesex linked traits SexLinked Traits Sexlinked traits show different patters of phenotypic expression based on sex Males XY 0 Hemizygous one copy of each chromosome 0 Females XX 0 For genes on the Y chromosome males always show them and females never show them 0 For genes on the X chromosome males show recessive trait when females are heterozygous and have dominant phenotype 0 Chromosome letter is written with superscript capital letter dominant allele or lowercase letter recessive allele Pedigrees Pedigrees are family tree that shows sex phenotype and relationship of each member of the tree Males are represented as squares Women are represented as circles Anyone who has the mutational phenotype are filled in Anyone who does not have the mutation is not filled in 0 Still could be carriers of the recessive trait Horizontal line means they are married Vertical line means the linked people below are their offspring To identify the inheritance shown in a pedigree follow these steps 1 Look at how frequent affected people are is the affected phenotypes rare or common 2 Look at the ratio of affected men to affected women is it about 5050 oris it sexskewed i If more women have it 3 Make a guess ofthe inheritance type 4 Draw a Punnett square for the parents based on yourguess and see if the children in the pedigree match your guess 5 lfthe Punnett square and the pedigree don39t match guess again and check with another square 6 lfthe square and the pedigree match you39re done What39s yourguess o lfthe affected phenotypeis rare guess it39s recessive o lfthe affected phenotypeis common guess it39s dominant o lfthe ratio of affected men to affected women is close to 5050 guess autosomal o If more ofthe affected people are of one sex than the other guess sex aned Sexlinked Pedigree Mutation on X or Y chromosome Mutation on X chromosome can be dominant or recessive Show mutation with superscript letter 0 DominantX39V39 o Recessive Xm Women need to have at least one dominant mutation to show the phenotype and two recessive mutations to show the phenotype Remember men are hemizygousforthe X chromosome so if they have a mutation on the X chromosome they show it regardless if it39s dominant or recessive Ylinkedall men along the male lineage are affected and no women are affected Xlinkedeither males orfemales can be affected 0 Xlinked recessive men are affected much more frequently than women 39 Affected men have carrier daughters who have 50 affected sons 0 Xlinked dominant affected men have affected daughters and unaffected sons 39 Affected women have 50 affected children Sex Chromosomes 1100 genes on the X chromosome 0 5060 genes on the Y chromosome 0 Many nonsex related genes on X chromosome 0 Hemophilia Fragile X Congenital night blindness Duchenne muscular dystrophy High blood pressure 0 Pattern baldness What if an Xlinked dominanttrait is lethal 0 Women are mosaics 39 One X is active and the other isn39t in each cell 39 Which X is active varies bt cells 39 Women may be okay if mutant X is turned offin critical tissues 0 lncontinentia pigmentiis an Xlinked dominant trait 39 Embryonic lethal for males III The only males with incontinentia pigmentihave a mild mutation or have an extra X chromosome 39 Women can live with it 0000 NonMendelian Genetics NonMendelian genetics inheritance doesn39t follow Mendel39s law of independent assortment or of dominance Common in humans Polygenictraits phenotype controlled by more than one gene Looomlnance Codominance both alleles on both chromosomes are expressed Color of someflowers 0 Two alleles for color 39 One for red pigment R 39 One for white pigment W o A flower with 39 2 white alleles white flower I 1 white 1 red allele pink flower I 2 red alleles red flower 39 Pink flowers make 12 as much red pigment as red flowers 1 R vs 2 R III Look at how many alleles that make pigment you have 0 Blood types 0 Three alleles in population A makes A antigen dominant B makes B antigen dominant 0 makes no antigen recessive People with one A allele and one B allele make both antigens Blood donation 39 Group 0 III No antigens on red blood cells so won39t elicit an immune response if transfused into another person universal donors 39 Group AB III No antibodiesin plasma so won39t elicit an immune responseif blood is transfused from another person universal recipients III Another antigen is found on some people39s red blood cells Rh factor Rh have Rh on RBC Rh don39t have Rh on RBC People wo Rh will make antibodies against Rh 0 So Rh people can39t accept Rh blood People with Rh do NOT have antibodies against Rh 0 Rh people CAN accept Rh blood OOOOO Incomplete Penetrance Incomplete penetrance individuals with the genotype may vary in how strongly the phenotype shows up or at all Epistasis Epistasisthe expression ofone gene is controlled by another gene 0 Two or more genes interact to determine a phenotype Mousefur color determined bya gene Bb o B black pigment dominant o b brown pigment recessive Whether or nota mouse makes pigment in its fur is determined by a gene Cc o C pigment dominant o c no pigment recessive fa mouse gets two cc genes it will be white regardless ofwhat color it should be with Bb gene Albino gene prevents color of pigment IVIuItigenic Multigenic phenotypeis controlled by multiple loci Human skin color Linked Genes Independent assortment alleles for different traits segregate into haploid gametes independently of other traits Genes that are close together on a chromosome do NOT exhibit independent assortment o The chances of recombination occurring bt two genes that are close together is small Recombination frequency lt50 Mosaic Mosaic individual has more than one genotype 0 Women are mosaics o In women one X chromosome is inactivated 0 Random inactivation of X chromosome process in cells so women are mixed 0 Inactive chromosomes forms Barr body Calico cats are female mosaics 0 Fur color is gene on X chromosome 0 Males are hemizygous 39 One X chromosome so one color 0 Females have two X chromosomes which may have different color genes 0 Each cell will express only one of the X chromosome color genes 0 So cat will have patches oforange and patches of black fur calico fa mutation arises during fetal development this results in a mosaic individual Mosaics contain genomic differences bt cells but all cells arose from same zygote Chimera Iffraternal twin zygotes fuse this creates one chimeric individual 0 Common first step for making transgenic laboratory animals Mosaics and chimeras Snachan and Read HMG 1999 Mosaic caused by genetic mutation cells more closely related Chimera caused by fusion of two zygotes lVlutations f lllJJ uene VUIaI0nS 7 affects one gene Small deletions duplications mutations Types of gene mutations O 0 Silent mutation nucleotide codon is changed but codon still encodes the same amino acid Missense mutation nucleotide codon is changed so it encodes a different amino acid Nonsense mutation nucleotide in codon is changed so it doesn39t encode any amino acid eg a stop codon Examples of gene mutations O 0 DNA polymerase mistakes 39 Human DNA polymerase makes an error about once every 100000000 base pairs 39 Error correction reduces this rate to 10000000000 base pairs 39 The human genome contains 6000000000 base pairs I A lot of cell divisions from first cell to full body 39 There are about 400 cell divisions bt the male zygote and the sperm he produces III 124 mutations per sperm cell 39 There are about 30 cell divisions bt the female zygote and the eggs she produces III 9 mutations per egg 39 A baby inherits about 133 mutations their parents did not inherit DNA looping 39 DNA loops out and a nucleotide gets an extra base added or omitted Chromosome mutations Larger region of chromosomeis changed deleted duplicated inverted translocated Affects multiple genes Types of mutations O O Deletion loss of a portion ofa chromosome Duplication a portion of a chromosome gets copied more than once resulting in multiple copies ofthe chromosomal region Inversion a portion ofthe chromosome gets flipped around Translocation movement of a portion ofone chromosome onto another chromosome Genome mutations Affectschromosomenumbermonosomytrisomy Caused by nondisjunction o Nondisjunctionthefailure of chromosomes to disjoin separate normally during meiosis Monosomy one copy of a chromosome Trisomy three copies ofa chromosome 0 Only three autosomal chromosomes present in the triplicate are not embryonic lethal o Trisomy 13 Patau Syndrome 39 Severe intellectual disability 39 Physical abnormalities in many parts ofthe body 39 Survival daysweeks 510 livegt 1 year 0 Trisomy 18 Edwards Syndrome 39 Physicalabnormalities 39 Severe intellectual disability 39 Survival miscarriage 1 month 510 livegt 1year o Trisomy 21 Down Syndrome 39 Mild to moderate mental retardation 39 Potential physiological defects heart intestine 39 Life expectancy of about 50 years 0 Usually embryonic lethal causing a miscarriage by the 10th week of pregnancy
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