Genetics Notes: Patterns of Inheritance & Pedigrees

I. Other Patterns of Inheritance: **Not all traits are completely dominant** A. Incomplete 1. Pattern of inheritance in which heterozygous offspring show a between the of the parents (in the middle) 2. NEITHER is expressed fully 3. Examples: a. Snapdragon : i. + flower = flower b. Cow : i. Red () bull + white cow = (Pink) cow 4. Punnett Square Example: a. Knowing that a certain flower shows a pattern of incomplete dominance, create a Punnett Square showing a cross of TWO PINK flowers. b. r = red; w = white

B. Codominance 1. Pattern of inheritance where both in the heterozygous offspring are FULLY expressed 2. Example: Human a. = Letters; Phenotype = Blood Type b. Type A: AA, AO (homozygous & heterozygous) c. Type B: BB, BO (homozygous & heterozygous) d. Type AB: AB (ONLY heterozygous) e. Type O: OO (ONLY homozygous) 3. Punnett Square Example: a. Knowing that blood type shows a pattern of codominance, cross a person with TYPE O blood and one with TYPE AB blood. Name:______Date:______

C. Sex-linked 1. Phenotypic expression of an allele that is dependent on the of the individual 2. Carried on either sex (X or Y) a. Remember: Female = XX; Male = XY b. Many more carried on the X chromosome, so many more X-linked traits than Y-linked traits i. Examples: Hemophilia, Color-blindness ii. FEMALES: If have only healthy X, it dominates over the infected X. iii. MALES: If have only one infected X, Y can’t dominate over it. 3. Punnett Square Example a. Knowing that is a sex-linked trait, cross a CARRIER FEMALE with a NON-INFECTED MALE. b. Determine the probability of this couple having a color- blind child.

D. Polygenic Traits 1. One trait is controlled by TWO or MORE genes 2. Example: a. E. Multiple Alleles 1. More than two alleles for the same Name:______Date:______

2. Example: a. Human blood type (phenotypes produced by 3 different alleles)

F. Pleiotropy 1. Single gene affects MORE than one trait 2. Examples: a. Sickle cell disease b. Marfan’s syndrome II. Pedigree A. Chart that shows how a trait and the genes that control it are passed through a family 1. Most knowledge of human comes from studying patterns of heredity in populations and families 2. Best way to trace these patterns is by creating a pedigree B. Symbols: Symbol Description

Unaffected male

Unaffected female

Affected male

Affected female

Deceased (dead) male


Deceased (dead) female

Possibly affected male or unknown

Possibly affected female or unknown

Carrier male of autosomal recessive disorder

Carrier female of autosomal recessive disorder

Connected Symbols:

Twins Married couple

Divorced Couple Siblings

Pedigree Example: I



I Although Jane and Joe Smith have dimples, daughter, Clarisse does not. Joe’s dad has dimples, but his mother and his sister, Grace, do not. Jane’s dad, Mr. Renaldo, her brother, George, and her sister, Emily, do not have dimples but her mother does.