Intro to Mendelian Inheritance

Question 1

1st Law: The Law of Segregation

Answer 1

at meiosis, alleles segregate from each other so that each gamete (egg or sperm) receives one copy from each allele

Question 2

2nd Law: The Law of Independent Assortment

Answer 2

the segregation of each set of alleles in meiosis is independent of the segregation of other alleles during meiosis

Question 3

Discuss the two principal factors that determine the inheritance patterns seen in single-gene disorders

Answer 3

Quality of the phenotype (dominant vs. recessive) and

Location of the gene locus (autosomal vs. sex chromosome)

Question 4

If a phenotype is dominant, it is expressed when

Answer 4

only one chromosome of a pair carries the mutant allele for the given gene (the other chromosome in the pair is the wild-type)

Question 5

If a phenotype is recessive, it is expressed

Answer 5

only when both chromosomes in a pair carry mutant alleles (not necessarily the same mutant allele)

Question 6

Genes found on autosomes behave according to the _______ and normally affect males and females _______

Answer 6

rules for the quality of phenotype

equally

Question 7

Genes found on sex chromosomes demonstrate

Answer 7

characteristic patterns of inheritance (i.e. X-linked dominant, X-linked recessive and Y-linked dominant)

Question 8

penetrance

Answer 8

• –probability that a gene will have a phenotypic expression at all
• –all or none concept–the gene is expressed or it isn’t
• –commonly influenced by age (age dependent penetrance)

Question 9

expressivity

Answer 9

• –severity of expression of a phenotype with the same genotype
• –variations in expressivity are explained by a variety of factors (environment, gender, modifier genes, etc.)

Question 10

pleiotropy

Answer 10

description of a genotype that causes defects in several different body systems resulting in a variety of phenotypic effects

Question 11

Threats to Mendelian Inheritance

Answer 11

Penetrance
Age dependent penetrance  
Expressivity
Sex Influence and Sex Limitation 
Environmental factors 
Stochastic Effects
Modifier genes
Phenocopies
Pleiotropy