Loyola University Chicago
BIOL 283-004: Genetics
Assignment 3: Pedigrees, Sex Chromosomes, and Linkage
20 points
Due date: Monday 9 May 2022
If you are planning to fill in the blanks within this sheet, please use RED as your font color so I can see
your answers more easily.
1. Chickens use the ZW system for sex determination. One proposed mechanism for sex
determination involves a dosage-dependent effect involving the Z-linked gene, DMRT1
(doublesex and mab3-related transcription factor 1). Given this, fill in the following blanks to
correctly predict the genotypes of ♀ and ♂ chickens regarding the DMRT1 gene. You may
assume that all alleles of DMRT1 in this scenario are wt.
♀: Z____________/____________ (fill in the superscript and the blank to the right of the slash)
♂: __________/___________ (fill in both blanks with the correct nomenclature; to add superscripts, use
the keyboard combination, “[CTRL + SHIFT + =/+]” or select the superscript option from the Font tools
on the Home menu)
2. Consider the following pedigree and answer the following questions:
a. Based on the information provided, what mode of inheritance is likeliest?
_____________________
b. Given what you answered for 2a, what do you expect the genotypes with regard to the trait
being followed in this pedigree of the following individuals (Please use correct gene
nomenclature):
1. I, 2 ________
2. I, 3 ________
3. II, 2 ________
4. II, 9 ________
5. III, 2 ________
6. III, 3 ________
c. Which individual in the study was the first in the family to be diagnosed with the condition
being tracked? ________________
3. You have established linkage in a trihybrid cross involving genes, A, B, and C. In all three genes,
the wt allele encodes functional gene products, while LOF mutants at each locus are recessive.
From your initial cross, your F1 generation was uniformly phenotypically dominant with regard
to all three characters. Based on the following data, predict the genotypes of the P generation
individuals that went into the cross and fill in the blanks on the map indicating the correct order
of the three loci. Don’t forget to use proper nomenclature for the gene symbols. For this
problem, you can assume that these loci are all autosomal.
Progeny Phenotypes
aBc
AbC
aBC
Abc
Numbers
244
238
24
14
P: ________________________ x __________________________
________
________
_________
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