Exam 1: Lecture 2

Question 1

Benefits of Drosophila for Research

Answer 1

• small size
• quick generation time
• small genome (4 chromosomes)
• easy husbandry

Question 2

Mutations

Answer 2

• one of fist discovered was white eyes
• location of gene was genetically mapped to one of 4 chromosomes
• called white gene

Question 3

Recombination

Answer 3

• Process by which alleles of different genes that reside on the same chromosome are brought together or separated
• Morgan repeated Mendel’s experiments with Drosophlia and noticed that if two genes reside on the same chromosome then the alleles of those genes did not assort completely independently

Question 4

Linked Genes

Answer 4

• some combinations of alleles were inherited together at a great frequency than other combinations
• genes that are more closely positioned on a chromosome are more tightly linked together than genes that reside at further distances from each other.

Question 5

Morgan

Answer 5

-generated the first genetic map, coined the concept of recombination and discovered that recombination frequency correlates directly with the distance between two genes

Question 6

Seymour Benzer Experiment

Answer 6

• he used a virus that infects only bacterial cells: the bacteriophage
• phage will inject its genomic DNA into the bacterial cell upon attachment
• existing replication machinery within the bacterial cell will generate thousands of new phage genomes which will then be transcribed and translated into phage coat proteins by the host transcription and translation machinery
• viral genomes will be packaged into phage coats and the new bacteriophage particles will lyse the host cell and proceed to infect neighboring bacterial cells

Question 7

Seymour Benzer Findings in Other Studies

Answer 7

• produced and mapped hundreds of mutations to each of genes that are located within bacteriophage genome
• studies on intragenic recombination Seymour focused on a special class of mutants called rII.
• these mutants fail to lyse certain bacterial cell strains such as E. coli K12l

Question 8

Benzer Recombination Studies

Answer 8

• if two strains of bacteriophage are co-infected into E. coli cells the viral genomes can undergo recombination
• if the two strains contained mutations within different genes then recombination would produce phage genomes that contained intact copies of both genes and the phage could lyse the bacterial cells (this is called complementation)
• proposed that if recombination did actually occur within a single gene then he would be able to recover new phage particles
• did experiments on very large scale
• appearance of plaques meant lysis happened
• Benzer did in fact recover wild type phage particles after he had co-infected E.coli K12l cells with the r103 and r104 T4 strains. Each harbored a different mutation with the rIIA gene. This result indicates that the gene is not indivisible and that recombination can occur anywhere along a chromosome

Question 9

Recombination and Meiosis

Answer 9

• occurs between non-sister chromatids of homologues
• occur simultaneously at thousands of positions along the chromosome
• results in genetic diversity as new allelic combinations are created at each generation

Question 10

X-linked Genes

Answer 10

• inhereited in sex-dependent matter
• if homozygous red-eyed female are mated to white males then 100% of F1 progeny will have red eyes
• if a white eyed female is mated to a red eyed male then 100% of the F1 females will have red eyes but 100% of the males will have white eyes
• white gene encodes a membrane associated protein called a transporter which allows for various molecules to cross membrane barriers.
• if gene on Y chromosome, males always get the trait

Question 11

Other Eye Color Mutants

Answer 11

• some of these genes code for proteins that move membrane vesicles within a cell
• few of the mammalian counterparts to these genes move vesicles filled with neurotransmitters.
• mutations within these genes cause several diseases such as Hermansky-Pudlak Syndrome and schizophrenia

Question 12

Co-dominance

Answer 12

• neither allele of same gene is dominant or recessive to other
• heterozygous individuals for co-dominant alleles will show both parental phenotypes
• red and white rhododendron and ABO blood types (AA mates with BB child is AB)

Question 13

Incomplete Dominance

Answer 13

• impatients flowers, cross red homozygote and white homozygote get pink flower
• also prevalent in eggplants