Day 1 Mendelian Inheritance

Question 1

1. Explain and distinguish between Mendel’s Laws of Inheritance

Answer 1

1) Law of Segregation of genes: Every organism has two individual alleles for each trait, alleles segregate during meiosis such that each gamete only contains one of these alleles; off spring gets one of each allele from their parents
2) Law of Independent Assortment: alleles for separate traits are passed independently from one another from parents to offspring
3) Law of Dominance: Recessive alleles are masked by dominant alleles

Question 2

2. Discuss how the following two principal factors determine the inheritance patterns seen in single-gene disorders: a) quality of the phenotype (dominant vs. recessive), and b) location of the gene locus (autosomal vs. sex chromosome).

Answer 2

a) dominant traits will be much more frequent and will not skip generations; recessive traits can and are much less common
b) X-linked traits—will not be male to male transferred (Transferred from father to son)—but can manifest in daughter if dad has trait (and always will if its X dominant), if present in mother if one allele has the mutation/disease it will manifest in 50% of boys (regardless if recessive/dominant)

Question 3

3. Recognize and distinguish between the major modes of Mendelian Inheritance, including autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive.

Answer 3

I’d say just look at some pedigrees for this. I sort of addressed it in the past question.

Question 4

4. Explain and compare various ‘threats’ to Mendelian inheritance patterns, particularly the threats due to variability in penetrance, expressivity, and pleiotropy.

Answer 4

Penetrance: Fraction (or percent) of individuals who have the genotype but actually show the disease

Expressivity: The degree in which a trait is expressed/severity

Pleiotropy: Different than variable expressivity, one gene having more than one effect (effects are unrelated)