University:
Sam Houston State University
Course:
BIOL 2413 | General Zoology
Academic year:

2024
Views:

144

Pages:

11
Author:

StellarSymphony

 Involve genes that are carried only on the X or Y chromosomes  These are involved in determining the sex of animals.  The female genotype is XX, while the male genotype is XY.  The X chromosome is larger and longer than the Y chromosome, which means a portion of the X chromosome does not pair with genes on the Y chromosome.  The sex of an animal may determine whether a gene is dominant or recessive (Ex. Scurs in polled European cattle).  Sex-linked traits in females are recessive and covered by dominant genes.  A certain portion of the Y chromosome does not link with the X chromosome.  The traits on this portion of the Y chromosome are transmitted only from fathers to sons.  The expression of certain genes, which are carried on the regular body chromosomes of animals, is also affected by the sex of the animal.  In poultry, the male has the genotype XX, while the female has the genotype Xw.  An example of a sex-linked trait in poultry is the barring of Barred Plymouth Rock chickens.  If barred hens are mated to nonbarred males, all of the barred chicks from this cross are males, and the nonbarred chicks are females. Photo courtesy of Wikipedia.  Ex- Tortoise shell color in cats - mixture of color that appears in patches * orange, white, black, gray, tabby * much white called calico - always female (almost) - Locus for orange color occurs on the X chromosome Females OO Males Oo OO = Orange O = Orange Oo = Tortoiseshell o = non-orange Oo = non- orange Modes of gene expression differ between males and females  An allele may be expressed as a dominant in one sex and a recessive in the other  Scurs for cattle is a sex-influenced inheritance  The allele for scurs is dominant in males and recessive in females  A male with one copy will have scurs, but a female must have 2 copies  Genotype Males PP SS Polled PP Ss Polled PP ss Polled Pp SS Scurs Pp Ss Scurs Pp ss Polled pp SS Horned pp Ss Horned Females Polled Polled Polled Scurs Polled Polled Horned Horned  Phenotypic expression is limited to one sex  Ex. Milk production, and scrotal circumference  These genes are not necessarily on the sex chromosomes but are only expressed in the male or female  Thought to be hormonally conditioned  Discuss genetic inheritance.  Investigate principles of inheritance.  Demonstrate how inheritance plays a role in sex-linked genes  Explain the difference between sexlinked, limited, and influenced inheritance