Randomness of Inheritance Part 1

Inheritance Objectives  Discuss randomness in genetics.  Investigate principles of inheritance.  Comprehend how inheritance plays a role in sex-linked genes  Explain the difference between sexlinked, limited, and influenced inheritance 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 Considering Multiple Traits •Commonly, there are multiple traits that need to be considered when mating animals. •For example, consider that cattle can be horned or polled and white-faced or red-faced. •The horns and red-faced coloring are recessive traits. Considering Multiple Traits If two individuals with two pairs of heterozygous genes (each affecting a different trait) are mated, the expected genotypic and phenotypic ratios would be: Genotypes – 1 PPWW, 2 PPWw, 2 PpWW, 4 PpWw, 1 PPww, 2 Ppww, 1 ppWW, 2 ppWw, and 1 ppww; Considering Multiple Traits Phenotypes •9 polled, white-faced; •3 polled, red-faced; •3 horned, white-faced; and • 1 horned, red-faced offspring. MalecJ � PW Pw pW PW рр:Сг pp;f? Рр;;г Ot Pw рру рру Рру ф ctS Е (polled, whitefaced) (polled, whitefaced) (polled, whitefaced) (polled, whitefaced) (polled, coloredfaced) (polled, whitefaced) pw Рру (polled, whitefaced) Рру (polled, coloredfaced) ф pW Рр:Сг Pp;f? pp:s? рр::;? pw Рру Рру (polled, whitefaced) (polled, whitefaced) (polled, whitefaced) (horned, whitefaced) (horned, whitefaced) pp:fr pp::cr (polled, coloredfaced) (horned, whitefaced) (horned, coloredfaced) Sex-Linked Traits •Sex-linked traits involve genes that X or Y are carried only on the chromosomes, which are involved in determining the sex of animals. •The female genotype is XX, while the male genotype is XY. Sex-Linked Traits 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. Sex-Linked Traits •Additionally, 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. •Sex-linked traits are often recessive and are covered up in the female mammal by dominant genes. Sex-Linked Traits •The expression of certain genes, which are carried on the regular body chromosomes of animals, is also affected by the sex of the animal. •The sex of an animal may determine whether a gene is dominant or recessive (Ex. Scurs in polled European cattle). Sex-Linked Traits •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. Sex-Linked Traits If barred hens are mated to nonbarred males, all of the barred chicks from this cross are males, and the non-barred chicks are females. Photo courtesy of Wikipedia. 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