Genetics - Probabilities, etc. Flashcards
Consider Tt x Tt.
What fraction of the progeny will demonstrate the dominant trait? Recessive?
What fraction of the progeny will be homozygous dominant? Recessive? Heterozygous?
3/4 = dominant trait; 1/4 recessive 1/4 = homozygous dominant; 1/4 = homozygous recessive; 1/2 = heterozygous
Consider TT x Tt.
What fraction of the progeny will demonstrate the dominant trait? Recessive?
What fraction of the progeny will be homozygous dominant? Recessive? Heterozygous?
All = dominant trait; no recessive trait demonstrated 1/2 = homozygous dominant; no homozygous recessive; 1/2 = heterozygous
Consider Tt x tt
What fraction of the progeny will demonstrate the dominant trait? Recessive?
What fraction of the progeny will be homozygous dominant? Recessive? Heterozygous?
1/2 = dominant; 1/2 recessive
No homozygous dominant; 1/2 = homozygous recessive; 1/2 = heterozygous
Individual #1 with phenotype B is crossed to an individual with phenotype b. B is dominant to b. All of the offspring have phenotype B.
What are the genotypes of the individuals that were crossed? Explain.
BB x bb.
Parent #2 has to be bb due to the demonstration of a recessive phenotype.
Parent #1 BB - if Bb, then 1/4 of the offspring would demonstrate the bb recessive phenotype.
A tall plant with blue flowers (Tt Bb) is crossed with a tall plant with white flowers (TT bb). What is the probability of obtaining progeny with the genotype TTbb?
TT = 1/2; bb = 1/2
So…
1/2 * 1/2 = 1/4
Consider parents heterozygous for A, B, C, D, and E.
What is the probability that progeny will be homozygous recessive for all 5 genes?
Prob for each = 1/4
(1/4)^5 = 1/1024
Consider parents heterozygous for A, B, C, D, and E.
What is the probability that progeny will be AaBBCcddEE? (use a calc)
Aa = 1/2; BB = 1/4; Cc = 1/2; dd = 1/4; EE = 1/4
So…
1/2 * 1/4 * 1/2 * 1/4 * 1/4 = 1/256
Consider parents where one is heterozygous for A, B, C, D, and E, and the other is homozygous dominant at all 5 loci.
What is the probability that progeny will be AaBBCcDDEE?
(1/2)^5 = 1/32
What is the probability that in the cross Aa Bb x aa Bb that progeny will be aa BB?
aa = 1/2; BB = 1/4
So….
1/8
T or F: if the professor presents a multiple choice question where all but one of the answers you know is true, but one of the answers seems doubtful, you should choose an option comparable to “all of the above”
True… he does a lot of “all are true”, B & D are true, etc..
Beginning with a monohybrid cross of two true-breeding parents (AA X aa), what proportion
of the F2 generation will be homozygous recessive?
A. 1/8
B. 1/4
C. 1/3
D. 1/2
E. Cannot be determined from the information provided.
B. 1/4
Beginning with a dihybrid cross of two true-breeding parents (AABB X aabb), you recover progeny in the F2 generation in the phenotypic ratio of 9:3:3:1. This indicates that the alleles show ____ assortment. This is true because the genes are located on ____ chromosomes.
independent; different.
Junior scientist crossed a female Drosophila with genotype Zz with a male Drosophila having genotype ZZ. The Z gene encodes an enzyme that is essential for the earliest stages of development. To determine whether mutations of the Z gene are dominant or recessive, she should
Cannot be determined with a backcross - backcrosses require Zz x zz, but zz are non-viable.
How did Mendel obtain a true-breeding P1 generation in his pea plants?
He bred 2 generations to confirm all progeny matched the parents.
The effect of Barr body formation in mammals is that? What is the mechanism in flies?
It inactivates the production of proteins on one of the X chromosomes (from an XX) in order to equalize, or limit over-production, of X-linked products.
In flies, the one X double produces.
