BIOSC-101 Lecture Notes - Lecture 12: Nondisjunction, Meiosis, Quantitative Trait Locus
9 Sep 2020
School
Department
Course
Professor
Biosc-101
Fundamentals of Biological Sciences
Class Notes
● Non-Mendelian Inheritance (Module 16)
○ Incomplete dominance
■ Incomplete dominance is a form of intermediate inheritance where one
allele for a specific is not completely expressed over the other allele in the
heterozygote
■ This results in a 3rd phenotype where the expressed physical trait is a
combination of the phenotypes of both alleles.
● Codominance
○ Codominant a gene where 2 different alleles are both expressed in a
heterozygous condition.
■ Example: A white flower and a red flower having offspring with red and
white spotted flowers.
● Both the red and the white phenotypes show up.
● Another example is with blood types.
● There is an A allele and a B allele for blood type
● If an individual has 2 A alleles, the have type A blood
● If they have 2 B alleles, the have B blood.
○ Polygenic Inheritance
■ Polygenic inheritance occurs when one phenotype is controlled by 2 or
more genes.
● Example: height, skin color, eye color, and weight
○ Human Inheritance (Module 17)
■ Patterns of Inheritance
● Humans have 46 chromosomes. Because they are diploid, this
means 23 pairs are chromosomes. Of those, 22 are autosomal.
● Autosomal refers to the chromosomes that are not sex
determining. A trait associated with alleles located on the
autosome (non sex chromosomes)
● The last pair of chromosomes are sex chromosomes which is a
chromosome involved in sex determination.
○ Ex: There are 2 types of chromosomes: X and Y. Males
have one X and one Y (XY), and females have 2 copies of
the X chromosome (XX).
● If the gene responsible for a disorder is present on a sex
chromosome, it is called a sex-linked disorder.
● Due to the fact that the male Y chromosome is very small and
contains only genes related to sex determination, most sex-linked
disorders are due to defective alleles on the X chromosome.
○ Sex-Linked Traits
■ The gene for seeing color is on the X chromosome.
■ The allele for color blindness is recessive, and the allele for normal vision
is dominant
Document Summary
Incomplete dominance is a form of intermediate inheritance where one allele for a specific is not completely expressed over the other allele in the heterozygote. This results in a 3rd phenotype where the expressed physical trait is a combination of the phenotypes of both alleles. Codominant a gene where 2 different alleles are both expressed in a heterozygous condition. Example: a white flower and a red flower having offspring with red and white spotted flowers. Both the red and the white phenotypes show up. There is an a allele and a b allele for blood type. If an individual has 2 a alleles, the have type a blood. If they have 2 b alleles, the have b blood. Polygenic inheritance occurs when one phenotype is controlled by 2 or more genes. Example: height, skin color, eye color, and weight. Because they are diploid, this means 23 pairs are chromosomes. Autosomal refers to the chromosomes that are not sex determining.
