Lecture 6 - Extensions to Mendel’s Rules

Question 1

What is genetic linkage and why is it an exception to Mendel’s rules?

L6 S31

Answer 1

Alleles that are located closely to one another on the same chromosome don’t segregate as independently

Question 2

What does the term polygenetic mean?

L6 S34

Answer 2

A trait that’s phenotype is controlled by multiple sets of genes.

Question 3

Differentiate between complete dominance, incomplete dominance, and codominance.

L6 S40-42

Answer 3

Complete dominance:
-phenotype of the heterozygote is the same as one homozygote

Incomplete dominance:
-phenotype of the heterozygote is intermediate between the two homozygotes

Codominance:
-phenotype of the heterozygote includes includes phenotype of both homozygotes

Question 4

What is penetrance and expressivity?

L6 S43

Answer 4

Penetrance:
-percentage of individuals with a specific genotype that express the expected phenotype

Expressivity:
-degree to which a characteristics is expressed

Question 5

Assume that long fingers are inherited as a recessive trait with 80% penetrance.
Two people heterozygous for long fingers mate. What is the probability that their first child will have long fingers?

L6 S46

Answer 5

20% = 1/4 * 80%

Question 6

What is a lethal allele and how does it affect Mendelian genotypic/phenotypic ratios?

L6 S47

Answer 6

Lethal alleles cause death during development. Because of this, the lethal phenotype and genotype will no be observed in fully developed organisms.

Question 7

What blood types are possible among the children of a cross between a man who is blood-type A and a woman who is blood-type B?

L6 S52

Answer 7

Because the father and mother could be homozygous or heterozygous (AA or AO and BB or BO), the children could possibly be any blood type (genotypes AO, BO, or OO with phenotype A, B, or O respectively)

Question 8

What is gene interaction?

L6 S54-55

Answer 8

The phenotype of a gene is affected by the genotype of a gene at a different location.