Chapter 5: HereditySection 2: Genetics Since Mendel Minersville Area School District Mr. Motuk Room 124
Incomplete Dominance Neither allele for a trait is dominant. The phenotype produced is intermediate between the two homozygous parents. This results in a blendingof the two traits. Example:RR = Red Flowers WW= White Flowers RW = Pink flowers
Incomplete Dominance B= Allele for Black Fur W= Allele for White Fur So if we had incomplete dominance: BB would be homozygous Black Fur WW would be homozygous White Fur BW would be heterozygous GREY Fur
Multiple Alleles More than two alleles that control a trait are called multiple alleles. Traits controlled by multiple alleles produce more than three phenotypes. An excellent example of multiple alleles is human blood type. a. Blood types exist in four possible phenotypes: A, B, AB, and O.
Blood Type Alleles IA= type A blood IB= Type B blood i= Type “O” blood A Blood is dominant over “O” blood (i). B blood is dominant over “O” blood (i). A blood is codominant with B blood. (both show up)
Blood Type Genotypes
Polygenic inheritance A group of gene pairs acts together to produce a trait, which creates more variety in phenotypes. Many human traits are controlled by polygenic inheritance, such as hair and eye color.
Mutations Mutations are genes that are altered or copied incorrectly. A mutation can cause harmful, beneficial, or have no effect. Chromosome disorders Caused by more or fewer chromosomes than normal. Down Syndrome is caused by an extra copy of chromosome # 21.
Recessive Genetic Disorders Both parents have a recessive allele responsible for the disorder and pass it to their child. Because both parents are heterozygous they DON’T show any symptoms. Cystic fibrosis is a homozygous disorder. What is Cystic Fibrosis?(Journal Entry)
Sex Determination Chromosomes that determine the sex of an organism are XX in females and XY in males. Females produce eggs with X chromosomes only. Males produce sperm with either an X or a Y chromosome. The male determines the sex of the offspring.
Sex-linked Disorders An allele inherited on an X or Y chromosome is a sex linked gene. Color blindness is a sex linked disorder caused by a recessive allele on the X chromosome. a. Color blindness is more common in men than women. Why? A pedigree follows a trait through generations of a family.
How to use a Pedigree Males are represented by squares. Females are represented by circles. Completely filled in circle or square shows that the trait can be seen in that person. A half colored in circle or square indicates a carrier. Carriers are heterozygous for the trait, and the trait is not seen in that individual. People represented by empty circles or squares do not have the trait and are not carriers.
Example of a Pedigree (Pedigree worksheet to follow)