Transcript X n Y
Sex influenced traits • The gene is NOT on a sex chromosome, but SEX affects the phenotype • Ex-baldness-dominant in males, recessive in women – If ‘B’ represents bald and ‘b’ is hairy then Men must be bb to keep hair Women can be Bb or bb to keep hair • Caused by a gene that is located on a SEX chromosome (X or Y) • Most SEX-linked Traits are found on the X chromosome X-linked diseases • Most are recessive • Examples-hemophilia, red-green colorblindness • Males are more likely to have these because they cannot be carriers • Why? • Males are XY-if their ‘X’ has a bad gene, there is nothing on the ‘Y’ to dominate over it How A Sex-linked trait is passed Ex. Red-Green Colorblindness (x-recessive) • n N • XNXN=Normal • XNXn=CARRIER, but IS NOT colorblind • XNY=Normal • XnY=HAS red-green colorblindess Passing colorblindness • Carrier mom XNXn • Normal Dad XNY XN Xn XN XNXN XNXn Y XNY XnY X-linked genes are on the X chromosome Autosomal genes-NOT on the X or Y chromosomes Other X-linked traits • Orange and Black Alleles are on the X chromosome in cats • White is on another chromosome • In every cell, only 1 X chromosome is active (other X is Barr Body) • Result-some cells make black fur, some orange Multifactorial and polygenic traits • Polygenic-more than one pair of alleles determines phenotype- -eye color • Multifactorial-genes AND environment determine phenotype –weight and height Epistasis • Multiple alleles (more than 2 involved) • One allele causes the other to act differently) • Example-E is brown unless B is present