Extention And Modification

Question 1

Incomplete dominance def

Answer 1

When the heterozygote has a phenotype intermediate between the phenotypes of the two homozygotes. As long as the heterozygotes phenotype can be differentiated and falls within the range of two homozygotes, considered incomplete dominance. Ex. Red and white flower make shades of pink, purple and white fruit make violet fruit.

Question 2

Codominance def

Answer 2

The phenotype of the heterozygote is not intermediate between the phenotypes of the homozygotes, rather, the heterozygote simultaneously express the phenotype of both homozygotes. Ex is MN blood has both M and N antigen on the red blood cell.

Question 3

Complete dominance def

Answer 3

Phenotype of the heterozygote is the same as the phenotype of one of the homozygotes.

Question 4

What levels can phenotype frequently be observed at?

Answer 4

Anatomical level, physiological level, molecular level.the type of dominance exhibited depends on the level of phenotype examined

Question 5

3 Characteristics of dominance

Answer 5

1. Dominanace is a result of interactions between genes at the same locus, dominanace is allergic interaction
2. Dominance does not alter the way in which the genes are inherited, it only influences the way in which they are expressed as a phenotype. The allergic interaction that characterizes dominance is therefore interaction between the products of the genes.
3. Dominance is frequently in the eye of the beholder meaning that the classification of dominance depends on the level at which the phenotype is examined.

Question 6

Incomplete penetrance def

Answer 6

When the genotype doesn’t produce the expected phenotype. Seen in polydactyly, the condition of having extra fingers or toes. Some people possess the allele for polydactyly but have a normal number of fingers , not fully penetrant .

Question 7

Penetrance def

Answer 7

The percentage of individual organisms having a particular genotype that express the expected phenotype. Ex. Examined 42 people having an allele for polydactyly and found that only 38 of them were polydactylous, the percentage would be 0.90.

Question 8

Expressivity def

Answer 8

The degree to which a trait is expressed. Polydactyly exhibits variable expressivity as some possess extra fingers whereas some only have a small tag of extra skin.

Question 9

Lethal allele def

Answer 9

Causes death at an early stage of development, often before birth, and some genotypes may not appear among progeny. An example, found in snapdragons, the aura strain in these plants have yellow leaves. Many leather alleles are in nature are recessive

Question 10

Multiple alleles def

Answer 10

More than two alleles are present within a group of organisms, the locus has multiple alleles. Ex. At a locus that determines the feather pattern of mallard ducks. Restricted, MRM or MRmd, Mallard Mmd, dusky, mdmd

Question 11

Number of genotypes possible equation

Answer 11

[n(n+1) / 2] n is the number of different alleles at a locus

Question 12

Gene interaction def

Answer 12

Interaction between the effects of genes at different loci . The products of genes at different loci combine to produce new phenotype that are not predictable from the single-locus effects alone.

Question 13

Epistasis def

Answer 13

The effects of gene interaction is that one gene masks the effects of another gene at a different locus. The gene that does the masking is the epistatic gene, the gene whose effect is masked is a hypo static gene.

Question 14

Recessive epistasis ex

Answer 14

Recessive epistasis is seen in the genes that determines coat colour in Labrador retrievers. The dogs may be black, or yellow. The coat colours are determines by interactions between genes at two loci.

Question 15

Dominant epistasis def

Answer 15

Only a single copy of an allele is required to inhibit the expression of the allele at a different locus.