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17. Genetic disorders are predominantly recessive because: (2pts)
a. mutant genes are able to persist in the population amongcarriers
b. offspring exhibiting dominant traits are always homozygous
c. they are linked to sex chromosomes
d. a & b
e. b & c


18. A scientist breeds Drosophila melanogaster to study commonmutations found in this species. The main mutation of interest issepia eyes. The P generation was a cross between Wildtype maleflies and female flies with sepia eyes. The following offspringwere found: (15 pts)
F1:
793 Wildtype & 801 sepia

F2:
813 Wildtype & 279 Sepia

Based on the F1 count, what was the probable genotype of themales used for the cross in the P generation?

What are the possible genotypes of the flies in the F1generation?

If you were to randomly cross one of the dominant phenotypemales from F2 with a recessive female, what is the probability thatthe first offspring in the next generation will beheterozygous?

Perform a Chi-Square analysis to see if the expected 3:1 ratiowas found for F2.

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Deanna Hettinger
Deanna HettingerLv2
28 Sep 2019

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Related questions

A cross is made between two true-breeding strains (P1generation) in Drosophila. The

following F2 data were obtained by intercrossing the F1 malesand females from this cross:

Phenotype # of flies

Claret eyes, wildtype bristles 255

Red eyes, frizzled bristles 248

Red eyes, wildtype bristles 497

Claret eyes, frizzled bristles 0

a) What were the phenotypes of the F1 males and F1 females thatwere crossed to produce the

F2 generation?

b) What were the genotypes of the F1 males and F1 females thatwere crossed to produce the F2

generation?

c) Explain whether a student can conclude that claret eyes aredetermined by a recessive allele of

an autosomal gene.

d) Can the student conclude that the 2 genes are syntenic (onthe same chromosome)? Explain.

e) Indicate the genotypes of the gametes that will be producedby the F1 males and females.

f) Illustrate, using appropriate symbols and convention, thegenotypes of the two true-breeding

parents of the F1 generation.

g) Predict the expected number of male and female flies in eachof the 4 phenotypes in a

population of 2000 flies, if the F1 male is crossed to a femalefrom a tester strain with claret

eyes and frizzled bristles.


The genes for sepia eye color, short bristles, and dark body coloration are on the same chromosome of Drosophila melanogaster. Each gene has two alleles: wild type, which is dominant, or mutant, which is recessive.

se+ is dominant and causes red eyes; se is recessive and causes sepia eyes

sb+ is dominant and causes long bristles; sb is recessive and causes short bristles

b+ is dominant and causes gray body coloration; b is recessive and causes dark body coloration

The sepia gene and short bristle gene are separated by 32 map units; the short bristlegene and the dark body gene are separated by 13 map units. The sepia gene and dark bodygene are separated by 45 map units.

If you crossed a fly, which was homozygous for the wild type allele of each gene with a homozygous recessive fly for each gene, the F1 generation would entirely consist of flies that had the wild type traits, but were heterozygous for each gene.

If you were to cross these heterozygous F1flies to recessive homozygous flies, how many flies would you predict to have the double cross-over phenotype? (You will show all of your work and phenotypic classes in the next problem. Just show the NUMBER of double cross-over flies predicted by the map unit data here. Round to a whole number)

If you were to cross these heterozygous F1flies to recessive homozygous flies, how many flies would you predict to observe in each of the eight predicted phenotypic categories with respect to these three genes (given the map units above) if there were 1,000 total offspring? Please show work and show all phenotypic classes!

8. Working on a genetics experiment with Drosophila, you can count the F2 generation of the dihybrid cross between a female fly who has wildtype eyes and vestigial wings and a male who has white eyes but normal wings. An F1 female is then crossed to a true breeding male who has white eyes and vestigial wings. You obtain the following count for the F2 generation (4.0 pts): 64 wildtype (red eyes, normal wings)

896 wildtype eyes, vestigial 932 white eyes,

wildtype wings 75 white eyes, vestigial

a) Calculate the recombination frequency between eye color and wing traits.

11. A dog breeder has noticed some of his male dogs have begun to show a genetic defect, keratitis, in which the cornea of their eyes are easily inflamed, resulting in poor eye sight. The genes controlling this trait are unknown but it is assumed to be a sex-linked gene that it is also recessive. Dogs also have a gene, B, that controls coat color, where black is dominant, B, and yellow is recessive, b. Suppose that the breeder mates a male dog who is normal (XY) and black (heterozygous), with a female dog that is a carrier of keratitis (XXR) and yellow. (5pts)

a)Summarize the possible phenotypes of the offspring (include sex).

b)What are the chances of producing a dog with keratitis?

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