(DSA5) Intro to Genetics

Question 1

What is the differnce between complete dominance, co-dominance, and incomplete dominance?

DSA5 S7

Answer 1

Complete dominance:

• two phenotypes; dominant and recessive
• if one copy of the dominant allele is present the phenotype is dominant. Recessive phenotype is only present with two copies of the recessive allele.

Co-dominant:

• three phenotypes
• If a copy of the allele is present, it is expressed. If both alleles are different, they are coexpressed equally and unchanged.

Incomplete dominance:

• three phenotypes
• heterozygotic phenotype is a blending of the charactheristics of the homozygotic couterparts

Question 2

What does the term lyonization refer to?

DSA5 S14

Answer 2

X-inactivation

Females only need one copy of their X chromosomes active in each cell so a copy is randomly inactivated. Descendents of that cell will maintain the same X chromsome inactivation.

The reason for this is dosage compensation. Males only have a single X chromosome that provides a sufficient amount of gene products for normal function. This is the same for females X chromosomes and thus one is inactivated so as to not have twice the number of necessary gene products.

The fur pattern of a calico cat is an example of this as the gene for coat color is on the X chromsome and results in the local activation of either the black or orange fur allele.

Question 3

What is mosaicism?

DSA5 S319

Answer 3

Result when an individual has cells of two different genotypes in their body. This typically occurs in aneuploidic syndromes (Down, Klienfelter, and Turner syndromes) where there is an odd number of chromosomes so each daughter cell from mitosis has a different number of chromosomes.

Ratio of normal to abnormal cells determines the severity of related disease.