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BIOL 202 5.5 Genetic Mapping There are a number of genes in the mtDNA - many involved with energy production - some play roles in heredity - chromosomal inheritance is 50% male and 50% female - organelle DNA: male contribution is low o random distribution—no spindle dividing it get a segregation of mitochondria into 2 daughters if the dominant allele is on the L at time of division and recessive on R, then one daughter will only have dominant and one only recessive not so much of a problem if somatic cells but if germ cell, and 1 egg only has recessive alleles and 1 only dominant alleles, may be problematic o see this in variegated plants genes that encode the machinery for the green pigments are in chloroplasts division causes a mosaic o mostly end up with at 5050 split o areas that are white, the chloroplasts didn’t get the dominant green-pigmentmaking allele: most parts are variegated; parts that are all green have all dominant; parts that are all white have all recessive - important for human diseases o many don’t seem to have nuclear heritability—appear to be completely maternally-related map to mitochondria if a dominant mutation in a mother’s mitochondria, will pass it to ALL of her offspring the males never pass on the mutation to his kids all the daughters/women will pass mutation on to all her kids - phenotype of mutations o mitochondrial chromosome is tiny o a lot are diseases related to energy and metabolism Scientific basis - Model organism is neurospora o When they sporulate, all contain an ascus with 8 indiv haploid spores all in a linear array BIOL 202 - Form like this because of cell division Divides in vertical plain can tell where the cells came from can also follow chromosomes and how they move because of this ordered division o can mark a chromosome with dominant allele, e.g. with GFP by following ascus, can see where dominant allele is Cytoplasmic inheritance o Poky phenotype Poky spores grow slowly Inheritance of poky wasn’t nuclear Found it’s from mitochondria Saw that females with poky passed it onto all spores but chromosomes were moving properly But when males with poky, didn’t pass the gene on— chromosomes still moving properly non-nuclear inheritance Genetic Mapping - genes move independently because on different chromosomes or far apart on the same chromosome - when genes move together, are considered genetically linked o physically linked, too bc on single piece of DNA - created genetic maps of linkages - Studying genes on plants o Found many single-gene traits Some linked, some not Some genes (linked) didn’t move as Mendel predicted Could count chromosomes: individual linkage groups mapped to different chromosomes - Bateson and Punnett o Tried to replicate Mendel’s experiments with different pea plants Mated purebreeding red flower and long pollen and purebreeding white flower and short pollen pea plants Expected (phenotypes move independently o all in F1 were red with long pollen o in F2, got a mix of styles Actual o Got something very different: no 9:3:3:1 o 2 of 383 not due to chance o the phenotypes are moving together get preference for parental phenotypes; recombinant phenotypes relatively rare - Why recombination or lack therof? o To prove linkage, did a test cross of RrLl and rrll Allows to see the parental chromosome phenotype BIOL 202 - - End up with red, long and white, short phenotypes if the chromosomes don’t break If the chromosomes break, could get cross between the 2 chromosomes recombinant phenotypes See mostly parental phenotype and very little recombinant Recombinant frequency (RF) o = (# of recombinants)/(total number of progeny) o 1% recombinant frequency = 1 centimorgan (1 cM) = 1 genetic map unit (m.u.) o RF of 2 unlinked genes is 50% o For linked genes, is less than 50% Morgan did most of the linkage analysis studies, on drosophila o Found easily seen phenotypes; mapped them Single genes, straight up dominance; but also linked genes Can combine maps to figure out order of genes Drosophila genetics - nomenclature: o + = WT o lowercase = recessive - crossing a recessive (purple eyed, vestigial winged) with a dominant (red eyed and normal winged) gives a normal fly in F1 - can see crossovers - recombination doesn’t occur at the same rate over distances - if genes A, B and C; and if A and B are physically close to each other, less likely to get a recombination between A and B Note: when unclear if 2 genes are on the same chromosome, use “” to denote this (e.g. RRLL) If on same chromosome, use “;” (e.g. RR;LL) If on the same chromosome, use a “/” (e.g. RR/LL) Three point testcross - can look at 3 genes at one time o e.g. vermillion (recessive to WT) cv controls existence of a vein on a fly’s wings ct is a cut mutant: wing has a cut in it o cross normal red-eyed, veined trihybrid female with recessive all should end up with a 1:1:1:1:1:1:1:1 ended up with mostly ones like mom cv and ct is 6.4 m.u. apart; ct and v are 13.2 m.u. apart - Recombination between 2 genes is invisible without a 3rd gene in between them o Ones with least frequency would have had double recombinance o Because of this, may end up marking as WT even if there is some crossing over, if doesn’t appear in phenotype BIOL 202 2 tightly linked genes (i.e. no crossing over), always end up with parental phenotype Centromere mapping with linear tetrads - in neurospora, can tell where the recombination occurred - can dissect out the spores and count recombinants Chi-square analysis and linkages - non-significant p value means the genes are linked -