Biology 3721 Genetics Test 1

Front 1

Ch 2 Essential Concepts

Back 1

Discret units called genes control the appearance of inherited traits

Front 2

Ch 2 Essential Concepts

Back 2

genes comein alternative forms called alleles that are resposible for the expression of different forms of a trait

Front 3

Ch 2 Essential Concepts

Back 3

body cells of sexually reproducing organisms carry two copies of each gene. When the two copies of a gene are the same allel, the individual in homozygous for that gene. When the two copies of a gene are different alleles, the individual is heterozygus for that gene

Front 4

Ch 2 Essential Concepts

Back 4

The genotype is a description of that alleic combination of the two copies of a gene present in an individual.The phenotype is the observable form of the trait that the individual expresses.

Front 5

Ch 2 Essential Concepts

Back 5

A cross between two parental lines (P) that are purebreeding for alternative aleles of a gene will produce a first filial (F1) generation of hybrids that are heterozyous. The phenotype expressed by these hybrids is determined by the dominant allele of the pair and the phenotype is the same as that expressed by individuals homozygous for dominant allele. The phenotype associated with the recessive allele will reappear only in the F2generation in individuals homozygous for this allele. In crosses between F1 heterozygotes, the dominant recessive phenotypes will appear in the F2 generation in a ratio of 3:1

Front 6

Ch 2 Essential Concepts

Back 6

The two copies of each gene segregate during the formation of gametes. As a result, each egg and each sperm or pollen grain contains only one copy, and thus, only one allele, of each gene. Male and female gametes unite at random at fertilization. Mendel described this process as the law of segregation

Front 7

Ch 2 Essential Concepts

Back 7

The segregation of alleles of any one gene is independent of the segregation of the alleles of other genes. Mendeldescribed this process as the law of independent assortment. According to this law, crosses between Aa Bb F1 dihybrids will generate F2 progeny with a phenotypic ratio of 9 (A- B-) : 3 (A- bb) : 1 (aa bb)

Front 8

Incomplete Dominance

Back 8

the hybrid does not resemble either pure-breeding parent. F1 hybrids that differ from both parents often express a phenotype that is "INTERMEDIATE" between those of both pure-breeding parents. In the F2 a ratio of 1:2:1 (for snapdragons; red:pink:white)

Front 9

Codominance

Back 9

the hybrid resembles both pure-breeding parents in the F1 which means that neither the "spotted" or "dotted" allele is dominant or recessive to the other. With spotted and dotted pure-breeding parents the F2 have a ration of 1:2:1 (spotted: spotted/dotted: dotted)