WORKING GENETICS PROBLEMS
You absolutely have to know what the words mean:
phenotype
genotype
heterozygote
homozygote
gene
locus
allele
recessive
dominant
linked
sex linked (X linked
recessive)
zygote
gamete
test cross
P generation, F1, F2
And you have to know the answers to these questions:
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How many alleles for each gene in each adult?
How many alleles for each gene in each gamete produced by the adult?
If G = Yellow and g = Green, what are the possible genotypes for adults? What
are the possible phenotypes? What are the possible genotypes for gametes?
Finally, you must read each question carefully – what information is given to
you? What is being asked of you? If a question asks you for the phenotypes of
the F2 generation and you supply an answer like “WwGg” you have not given a
phenotype.
Here are some exercises to do together if you have a study group:
1. Do monohybrid cross (P generation = AA x aa) - note ratio of phenotypes in F2
generation
2. Cross a heterozygote with a homozygous recessive - note ratio
3. Bring in another locus – what kind of genotypes are possible when two loci are
involved? If G = Yellow and g = Green, and at another locus H = hairy and h =
hairless, what are the possible genotypes for adults? What are the possible
phenotypes? What are the possible genotypes for gametes?
4. Do a dihybrid cross (P generation = AABB x aabb) and note the ratio of offspring
in the F2 generation.
5. Do a test cross between a double heterozygote and a double recessive. Note ratio.
6. Do a cross involving incomplete dominance.
7. What does sex linked mean?
8. What are the possible genotypes for a female for red-green colorblindness?
9. What are the potential genotypes for a male?
10. What patterns of inheritance show that a trait is sex-linked?
11. What patterns of inheritance show that two different genes are linked?