Mendel and the Gene Idea

Question 1

4 concepts that explained the 3:1 phenotypic ratio that Mendel saw in the F2 generation of his experiment

Answer 1

1st concept - alternative versions of genes(alleles) account for variations in inherited characters
2nd concept - for each character an organism inherits 2 alleles, one from each parent
3rd concept - If 2 alleles at a locus differ, the dominant allele determines organisms appearance and the recessive has no noticeable effect on appearance
4th concept - The 2 alleles for a heritable character separate during gamete formation and end up in different gametes (law of segregation)

Question 2

Dominant vs Recessive allele

Answer 2

Dominant determines organisms appearance (capital letter)
Recessive has no noticeable effect on appearance (lower case letter)

Question 3

Differentiate between genotype and phyenotype

Answer 3

Genotype - genetic makeup (heterozygous, homozygous)
Phenotype - physical appearance (color, trait)

Question 4

Homozygous and Heterozygous

Answer 4

Homozygous - 2 identical alleles
Heterozygous - 2 different alleles

Question 5

Monohybrid cross

Answer 5

Both parents heterozygous for one trait (Rr x Rr)

Question 6

Dihybrid cross

Answer 6

Both parents heterozygous for both traits (RrYy x RrYy)

Question 7

Complete Dominance

Answer 7

Occurs when phenotypes of the heterozygote and dominant homozygote are identical

Question 8

Incomplete Dominance

Answer 8

The phenotype of F1 hybrids is somewhere between the phenotypes of the 2 parental varieties (blending of traits)
ex. red(RR), pink(Rr), and white plant(rr)

Question 9

Co-dominance

Answer 9

2 dominant alleles affect the phenotype in separate distinguishable ways (no blending)
ex. roan cattle (mixture of white and pigmented hairs)
ex. blood type AB

Question 10

Epistasis

Answer 10

2 or more genes affect one phenotype
ex. coat color of Labrador dogs B and E gene (no pigment E gene) homozygous recessive gene

Question 11

Pleiotropy
How is it different from epistasis

Answer 11

The ability of a single gene to have multiple phenotypic effects
ex. in tigers and Siamese cats the gene that controls fur pigmentation also influences connections between cat’s eyes and brain
ex. sickle cell anemia, can cause rapid destruction of sickle cells leading to anemia, clumping of cells causing interference with blood circulation, accumulation of red blood cells in spleen leading enlargement
In epistasis more than one gene determines a phenotype, while in pleiotropy, one gene determines multiple phenotypes

Question 12

Norm of reaction (environmental impact of phenotype)

Answer 12

Phenotypic range of a genotype influenced by the environment
ex. hydrangea flowers of the same genotype range from blue-violet to pink depending on soil acidity