Post on 12-Jan-2016
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
hairWomen 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 passedEx. 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