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Bicoid protein is encoded by an autosomal gene and is essential to the development of the anterior part of Drosophila embryos. In the absence of bicoid protein embryos are headless! You cross a male fly in which both bicoid alleles are non-functional (bcd-/bcd-) to a female that is heterozygous for the mutant allele (bcd-/bcd+). In case you’re wondering, they both have heads.

a) How is this even possible: how does this mutant male have a head?

b) What fraction of embryos from this cross will have heads?

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Related questions

1. The eye color of wild-type Drosophila flies is red. Differentmutations in a single or in multiple genes lead to flies with whiteeyes. Mutations in the w gene on the X chromosome lead to whiteeyes instead of the normal red. You have isolated both a white-eyedmutation (designated W-1) that gives a dominant phenotype, and awhite-eyed mutation (designated w-2) that gives a recessivephenotype.

(a) A white-eyed male from the W-1 line is crossed to awild-type female. What color eyes will the female progeny from thiscross have?

(b) What color eyes will the male progeny from the cross in part(a) have?

(c) One of the female progeny from the cross in part (a) ismated to a white-eyed male from the w- 2 line. What fraction of thewhite-eyed progeny from this cross will be female?

2. The body color of Drosophila adult flies is regulated bymultiple genes, including the autosomal ebony gene. Ebony body (e)is recessive to the wild type (yellowish) body (e+). A second gene,which is X-linked, controls bristle shape. Normal bristle shape(f+) is dominant to the mutant forked bristles (f). A female withforked bristles that is heterozygous for the body color gene ismated with an ebony body male (his bristles are normal).

(a) What are the genotypes of the parents?

(b) Using a Punnett square, determine the expected proportionsof each possible progeny phenotype. Since there is a sex-linkedgene here, be sure to include consider sex as part of thephenotype.

3. Describe in your own words what a balancer chromosome is andwhy it is important in fly genetics (you will have to do someresearch for this one!)

The drosophila alleles for black body (instead of the normal tancolor, which is the wild type) and curved wings (instead of thewild-type straight wings) are both recessive and on chromosome 2.Gene “C” designates color, with alleles C representing the dominanttan allele and c representing the recessive black allele, whilegene “W” designates the wing shape gene with W being the dominantstraight allele and w the recessive curved allele. You need todiscover how close together these two genes are on chromosome 2.You place one male from a pure breeding stock and one female from apure breeding stock (these are the ‘parental’ or ‘generation zero’(G0) flies) into vial 1. The offspring of this cross (cross 1)hatch in vial 1. These offspring (Generation 1, G1) areheterozygous for both genes. You perform the cross from the abovequestion and get 500 offspring in vial 2 (these are the G2 flies).Among these G2 flies, 65 have tan bodies and curved wings, 70 haveblack bodies and straight wings, 190 have black bodies and curvedwings, and 175 have tan bodies and straight wings. What are thegenotypes of offspring with parental phenotypes? What are thegenotypes of the recombinant offspring? wo true breedingparents (G0) gave rise to the doubly heterozygous (G1) flies invial 1. What were the genotypes of these parents? Whatis the percent of recombinants for these two genes? Ifthe two genes were actually on different chromosomes, whatphenotypic distribution would you expect in the G2 flies (insteadof 65 tan curved, 70 black straight, 190 black curved, and 175 tanstraight)? If the two genes were actually on differentchromosomes and you crossed the heterozygous flies to each other(did a self cross) what phenotypic distribution would you expectfrom the offspring?

Ploidy refers to the number of complete sets of chromosomes (genes) present in a cell. The number of chromosomes in a complete set is a fixed characteristic of a species. Humans are diploid with two sets of 23 chromosomes. Fruit flies are diploid with two sets of 4 chromosomes. Sexually reproducing organisms are diploid, each somatic cell of an organism has two complete sets ("di" is a prefix indicating 2.). To complete a life cycle and reproduce new members of a species, mating is required. Mating brings a donation from a male and a donation from a female together. However, if the male and female cells remain diploid, the fertilization will result in a tetraploid zygote. In general, these are not viable. A mechanism is needed to form special haploid cells, gametes. The diploid set is split precisely into two complete haploid sets. That mechanism is meiosis.

The complete set of chromosomes of a species is also the complete set of genes of a species, the genome. (Yes, there is a minor contribution from mitochondria and chloroplasts. Inheritance of this information is "cytoplasmic".)

Please answer the following questions:

1. How many chromosomes in a brain cell of a fruit fly? How many chromosomes are in a liver cell of a human? Explain both answers.

2. How many chromosomes are in a fruit fly unfertilized egg? How many chromosomes are in a human egg? Explain both answers.

3. Why is meiosis necessary for sexually reproducing organisms? How many chromosomes are in a human zygote? Relate the two answers.

4. What is a gene allele? Suppose there is a gene called "bingo" and it is present once in a complete haploid set. How many alleles of "bingo" does a diploid individual have? How many copies or versions of the gene "bingo" are present in a diploid individual?

5. Modern DNA sequencing clearly identifies alleles by showing the different DNA sequence of each allele. These alleles may be termed structural alleles (I coined the term for this problem.). Classical genetics only dealt with phenotypes or visible traits. As a result, alleles of genes were identified by functionality, usually normal or non-functional. Using your knowledge of gene structure and gene expression, postulate a relationship between structural alleles and functional alleles. (include relative amounts; more, less, or equal).

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