1. NON-MENDELIAN INHERITANCE
Chapter 7

2. I Mendelian inheritance patterns
A. Involve genes directly influencing traits
B. Obey Mendel’s laws
1. Law of segregation
2. Law of independent assortment
C . Include
1. Dominant / recessive relationships
2. Gene interactions
3. Phenotype-influencing roles of sex and environment

3. II NON-MENDELIAN INHERITANCE
A. Many genes do not follow a Mendelian inheritance pattern
Sex-linked traits
Incomplete Dominance
Codominance
Multiple alleles
We will discuss additional and more bizarre non-Mendelian inheritance patterns

4. B. Polygenic Inheritance
Multiple genes produce 1 trait.
1. Example: Skin Color

5. C. Gene Linkage Genes are located on the same chromosome
1. Alleles cannot separate randomly according to the law of Random Segregation
2. Unless…crossing over during meiosis I moves them to a different chromosome.
We measure the distance between genes by the frequency of crossing over moving one of them to a new chromosome, called gene linkage mapping
Distant genes are separated by crossing over more often than nearby genes.

6. C. Gene Linkage C is farther away from A than B is
We figure this out because a higher percentage of gametes are ABc than are Abc.
In fruit flies, wings and body color are linked

7. d. MATERNAL EFFECT
Genotype of mother directly determines phenotype of offspring
Genotype of father and offspring are irrelevant
1. Explained by the accumulation of gene products mother provides to developing eggs

8. DMATERNAL EFFECT A. E. Boycott (1920s)
First studies of maternal effect involved phenotypes of water snail
Limnea peregra
Shell and internal organs can be either right- or left-handed
Determined by mitotic divisions of egg after fertilization
Right-handed orientation is more common and dominant

9. E. EPIGENETIC INHERITANCE
Gene expression is altered (1 gene affects another gene somewhere else)
May be fixed during an individual’s lifetime
1. Expression is not permanently changed over multiple generations
DNA sequence is not altered

10. 2. DOSAGE COMPENSATION
Only one copy of each sex chromosome is expressed; the other is deactivated.
This is because males and females have different numbers of sex chromosomes.
a. DNA in inactivated X chromosomes becomes highly compacted
A Barr body is formed
b. Most genes cannot be expressed

11. 2. DOSAGE COMPENSATION
Sex in birds is determined by Z and W sex chromosomes
Males are ZZ, females are ZW
The Z chromosome is large
So in birds, dosage compensation works by deactivating one of a males Z chromosomes.

12. 3. Genomic Imprinting Methylation generally inhibits expression
Can enhance binding of transcription-inhibiting proteins and/or inhibit binding of transcription-enhancing proteins
Methylation can increase expression of some genes
This happens during gamete formation

13. F. EXTRANUCLEAR INHERITANCE
Most genes are found in the cell’s nucleus
Some genes are found outside of the nucleus
Organelles like the chloroplast and mitochondria have their own DNA
1. We use mitochondrial DNA
to trace maternal lines of
inheritance