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

2024
Views:

152

Pages:

13
Author:

5CelestialChronicle

Sex-Linked Characteristics Objectives  Students will be able to: 1) Comprehend how inheritance plays a role in sex- linked genes 2) Explain the difference between sex- linked, limited, and influenced inheritance 3) Compare the difference between simply-inherited and polygenic traits Randomness of Inheritance  First off genetics are random in nature  Prior to Mendel’s findings, the most widely accepted thought involved a blending theory of inheritance  No way to predict the combination of genes in a gamete  Randomness of inheritance is critical from an evolutionary standpoint and important to the success of artificial selection Inheritance  For a number of traits, gene expression differs in males and females  The causes fall under 3 categories: 1) Sex-Linked 2) Sex-Limited 3) Sex-Influenced Sex-Linked Traits  The pattern of inheritance for genes located on sex chromosomes  Females- XX Males- XY  X and Y chromosomes are members of a pair, but are quite different from each other - lacking corresponding regions of DNA - Males are hemizygous *having only one gene of a pair Sex-Linked Inheritance  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 Sex-Linked Inheritance Females OO Males Oo OO = Orange O = Orange Oo = Tortoiseshell o = non-orange Oo = non- orange Sex- Influence Inheritance  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 on cattle is a sex-influenced inheritance The allele for scurs is dominant in males and recessive in females A male with one copy will be scurred, 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 Sex-Limited inheritance  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 Traits  Simply- Inherited and Polygenic traits  Simply Inherited are traits that are affected by only a few genes - Coat Color, Horns  Qualitative or categorical - Either/ or expression - Measured with numbers or continuous - white- spotting in cats (1-9 numerical rating)  Typically affected very little by environment Traits  Polygenic traits;  Affected by many genes with no gene having an occurring influence -Growth rate, milk production, ribeye area  Typically quantitative or continuous in expression - phenotypes are usually described by numbers - weaning weights, milk yield, ribeye area  Greatly influenced by environment - Lack of fed, Heat/cold stress What is more important  Polygenic traits are more important - Growth rate, fertility, milk production - traits that determine productivity and profitability  But, Some markets are sensitive to simply- inherited traits - Coat/feather color, Polled, Genetic defects are usually simply-inherited