Bio 321 F13 lecture 3 v2

Xwy hemizygotes to generate white

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ll be white eyed females Ÿ༉25% of offspring will be red eyed males Ÿ༉25% of offspring will be white eyed males females: 50% red eyed Ÿ༉X+Xw heterozygotes 50% white eyed Ÿ༉XwXw homozygotes males 50% red eyed Ÿ༉X+Y hemizygotes 50% white eyed Ÿ༉XwY hemizygotes rela0ve size of X compared to rest of genome varies widely •  D. melanogaster and related species –  1 of 5 major chromosome arms =>~20 of genes are X- linked •  ~3000- 3500 of the ~17000 genes •  Homo sapiens –  X is one of 23 chromosomes •  one of the smaller ones •  ~1400- 1700 of the ~21000 genes •  ~7% of the genes what about the Y chromosome •  D. melanogaster –  Y is very small and mostly repe00ve, non- coding DNA –  12 genes known (as of 2008) –  Y is not necessary for viability (X0 males develop normally soma0cally) –  Y required for fer0lity (XO males are infer0le) •  H. sapiens –  231- 344 genes (es0mates vary) –  X0 humans Turner syndrome (Ullrich- Turner syndrome) •  females with short stature and many other morphological and developmental abnormali0es –  infer0le •  incidence: 1:2000 – 1:5000 flies vs. humans •  both have XY genotypic sex determina0on •  Different mechanisms –  Drosophila uses X:A ra0o •  females 1:1 (2 X chromosomes, 2 copies of each autosome) •  males 1:2 (1 X chromosome, 2 copies of each autosome) •  Y chromosome genes irrelevant to soma0c development –  humans – Y chromosome genes play many vital roles in development •  SRY (sex- determining region on Y) gene and others the heterogame0c sex and new muta0ons •  most new muta0ons, if recessive, and on autosomes, are lost –  even advantageous ones –  ini0al frequency = 1/2N (N = pop size) –  rare alleles almost completely in heterozygotes •  recessive phenotype not expressed –  dri3 determines their fate •  but if on the X are expressed in males –  most muta0ons are deleterious => stronger purifying selec0on on X in males –  faster evolu0on of X linked genes...
View Full Document

This note was uploaded on 10/01/2013 for the course BIO 321 taught by Professor John during the Spring '12 term at SUNY Stony Brook.

Ask a homework question - tutors are online