Genetics Answers

8. A heterozygous brown-eyed human female who is a carrier of color blindness marries a blue-eyed male who is not color-blind. Color blindness is a sex (X)-linked trait. Assume that eye color is an autosomal trait and that brown is dominant over blue. What is the probability that...
a) they will have a child with brown eyes?
b) they will have child that is color blind?
c) they will have a blue eyed, colorblind female? d) their first 2 children will be colorblind?

9. Imagine that a newly discovered, recessively inherited disease is expressed only in individuals with type O blood, although the disease and blood group are independently inherited. A normal man with type A blood and a normal woman with type B blood, both of whom are heterozygous with respect to the disease gene, already have one child with the disease. The woman is now pregnant for a second time. What is the probability that the second child will also have the disease?

Probability rules can be used to solve genetics problems. An organism that has the genotype AaBbCC is crossed with an organism that has the genotype AaBbCc. Assume all genes are on separate sets of chromosomes (that is, they are not linked).
a) What is the probability that any of the offspring will have the genotype AABBCC?
Hint: To get the answer, first determine the probability of each allele in the gametes (i.e. egg and sperm). Next, determine the individual probabilities of getting AA offspring from the monohybrid cross. Then do the same to determine the probabilities of getting BB offspring and CC offspring. Finally, multiply these probabilities together.
b) What is the probability that any of the offspring will have the genotype AabbCc?

5. A black guinea pig crossed with an albino guinea pig produces 12 black offspring. When the albino is crossed with a second black one, 7 blacks and 5 albinos are obtained.
a) What is the best explanation for these observations (i.e. what is the mode of inheritance)?
b) Given your answer for a)...
* What is the genotype of the first black guinea pig? 

* What is/are the genotype(s) of the gametes produced by this black guinea pig? 

* What is the genotype of the albino? 

* What is/are the genotype(s) of the gametes produced by this albino? 

* What is/are the genotype(s) of the offspring from this cross? 

* What is the genotype of the second black guinea pig? 


6. A rooster with grey feathers is mated with a hen of the same phenotype. Among their offspring, 15 chicks are gray, 6 are black, and 8 are white.
a) What is the mode of inheritance for feather colors in chickens?
b) What phenotypic ratio would you predict in the offspring from the mating of a gray rooster and a black hen?

3. To solve genetics problems in which genotypes are given, you must first determine what types
of gametes each organism can produce. To this end, list the kinds of gametes that individuals with each of the following genotypes can produce. Assume the genes are unlinked.
a) AaBB
b) AaBbCC
4. If an organism is heterozygous for two traits that are tightly linked, how many genotypes are possible in the gametes produced from a single germ-line cell? Assume that no crossing over occurs.

2. a) Mendel's law of independent assortment has its basis in which of the following events of meiosis?
* Synapsis of homologous chromosomes in prophase I 

* Crossing over 

* Random alignment of tetrads relative to other tetrads at the metaphase plate 

* Separation of homologs at anaphase I 

* Separation of cells following telophase II 

b) Mendel's law of segregation has its basis in which of the following phases of nuclear division?
* Prophase I of meiosis 

* Prophase II of meiosis 

* Metaphase I of meiosis 

* Anaphase I of meiosis 

* Anaphase of mitosis 


How are genotypic value, breeding value and gene combination value related?

Meiosis is divided into nine stages, each playing a vital role in the cellular division responsible for making gametes. Which of the following occurs in the meiosis stage known as telophase

Malignant tumors are sometimes treated with drugs that halt mitosis, and thus stop the production of new cancer cells. Two such drugs, vincristine sulfate and vinblastine sulfate, interfere with the formation of spindle fibers. How could this action halt mitosis? Antibiotics such as mitomycin C and inorganic compounds such as cis-platinum also can be used to stop the growth of tumors. These drugs interfere with DNA synthesis in treated cells. How could this action halt mitosis?

In a population of 50 individuals, there are 12 AA genotypes, 29 Aa genotypes, and 9 aa genotypes. Assuming the inheritance of allele A and a is complete dominance and that A is the dominant allele.

a) Calculate the number of individuals in the population expressing the dominant phenotype.

b) Calculate the proportion of each of the genotypes observed.

c) Calculate the proportion of the A allele and the a allele.

d) State the equation of Hardy-Weinburg equilibrium. Using the allelic
proportions that you calculated above, calculate the proportions of each
genotype that you would expect under Hardy-Weinburg Equilibrium.

In a human, polydactyly is autosome dominant disease. The blood groups of system ABO are determined by three allelic genes: i0, IA, IB. The blood groups of a human being are i0i0 - I(0); IAIA or IAi0 - II(A); IBIB or IBi0 - III(B); IAIB - IV(AB). In a family, a mother had I blood group and polydactyly, the father had IV blood group and normal structure of hand. There was born a child with first blood group and normal structure of hand. Determine the parental genotypes and the probability of a child with III blood group and polydactyly.