UD BISC 207 - Chapter 17 – Sex Chromosomes

Unformatted text preview:

Chapter 17 – Sex Chromosomes, Linkage, & OrganellesI. Sex-Linked Genes A. Sex chromosomes have small areas of homology (same genes) at their tipsB. X-Chromosome 1. Has over 1000 genes, Y has 502. X chromosome genes are “x-linked”3. Males only pass X-linked genes onto their daughters4. Males only need one copy of an X-linked recessive to show the recessive phenotypea. I.e. If a male has one X-chromosome with the recessive allele for color blindness, thereis no “normal” other X-chromosome containing the dominant allele for normal vision. In a female, the other X chromosome would “block” the one with the recessive allele.b. Red-green color blindness is a recessive X-linked traitC. Y Chromosome 1. The SRY gene on the Y chromosome sets the human embryo on the male development pathway2. Only sons inherit Y-linked genes3. Fathers pass Y-linked genes to all sons4. Only maleness & some male fertility traits are known to follow a Y-linked pattern of inheritanceII. Linked Genes A. Genes that are located close to each other on the same chromosomeB. Tend to be inherited as a groupC. Thomas Morgan’s Fruit Fly Experiment1. Uses different notation for dominant recessive for fruit fliesa. b+/c+ = dominantb. b/c = recessivebc Phenotypeb+c+b+c+bc Gray/Straightb+c b+cbc Gray/Curvedbc+bc+bc Black/Straightbc bcbc Black/CurvedGray Body Black BodyStraight Wings Curved Wingsb+b+c+c+ x bbccGray BodyStraight Wings Test Crossb+ b c+ c x bbccExpect what from this cross (^) if genes are unlinked ? Punnett Square: Expected outcome: 1:1:1:1 ratio of phenotypesExpect what if genes are linked ? (Inherited together) b+ b c+ c x bbccExpected Outcome: 1:1 ratio of phenotypesTest CrossGray Body/Straight WingsTest CrossGray Body/Straight Wingsbc Phenotypeb+c+b+ c +b c Gray/Straightbc b c b c Black/CurvedActual Findings from Experiment: Some new phenotypes (supports first cross, meaning genesare unlinked), but also found lots of parental phenotypes (supports second cross, meaning genesare unlinked)III. Morgan’s Experiment With Linked Genes (continued) A. Morgan proposed new phenotypes are due to crossing over (fig. 17.10)1. Used this to figure out relative location of genes on a chromosomea. Frequency of recombination is a measure of the distance between genes (Fig. 17.10a)b. Use recombination frequencies to estimate distance between genesi. Map Distance between 2 linked genes = (# recombinant offspring/total # of offspring) x 100ii. One map unit (aka centimorgans) = 1% recombination frequencyFig. 17.10IV. Extranuclear/Cytosolic DNA & Inheritance A. Not all DNA is in the nucleusB. Mitochondrial DNA (mtDNA)1. Single, circular chromosome2. In matrix3. Human mtDNA codes for 37 genes4. 10+ copies of genome per mitochondrion5. 37 mtDNA Genesa. 24 for tRNA & rRNAb. 13 genes for proteins for oxidative phosphorylationc. The other 1000+ protein types in mitochondria are coded for by genes now in nucleusi. Some of these were originally part of the mtDNAii. So, mitochondria are heavily dependent on nucleus for its DNA – why mitochondria can’t live outside the cell, even though they have their own DNA6. mtDNA is maternally inherited (mitochondrion of sperm cells are in its tail which never enter the egg)a. If the mitochondria of sperm are injected into the egg, the egg recognizes them as foreign and digests themC. cpDNA (Chloroplast)1. Single circular chromosome2. In stroma3. Multiple copies per chloroplast4. 110-120 genes, many for photosynthesis5. cpDNA is often but not always maternally inheritedV. Endosymbiotic theory A. 2 billion years agoB. Primordial eukaryotic cell engulfed but did not digest a bacteria (prokaryote) & resulted in the chloroplasts & mitochondria1. Prokaryote got a place to live & eukaryote got a source of ATP


View Full Document

UD BISC 207 - Chapter 17 – Sex Chromosomes

Documents in this Course
Chapter 6

Chapter 6

18 pages

Chapter 3

Chapter 3

17 pages

Load more
Download Chapter 17 – Sex Chromosomes
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Chapter 17 – Sex Chromosomes and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Chapter 17 – Sex Chromosomes 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?