Biology Forums - Study Force

1) Which of the following statements best describes the events associated with the recombination of genes?

a. If the alleles in gametes after meiosis are different from those in the parents, the gametes are referred to as recombinant.

b. Any two genes located on the same chromosome are called linked genes.

c. If two genes are located on the same chromosome, the alleles on non-sister chromatids of homologous chromosomes will segregate together if a crossover does not occur between the two genes.

d. Crossovers are most likely to occur between linked genes that are close together.








2) Two genes called TE and X1 were studied in a lab. 45 out of 500 offspring from crosses involving these two genes had recombinant genotypes.

What is the recombinant frequency of the genes TE and X1?

a. 50%

b. 18%

c. 9%

d. 4.5%







3) Two genes, N and O, are 27 map units apart. If parents heterozygous for these genes were test crossed, and 500 offspring resulted, how many would be recombinants for genes N and O?

a. 140

b. 130

c. 315

d. 27

e. 135









4) The following recombination frequencies are calculated for four linked genes:

    Genes                         Recombination Frequency
   A and B                                      2%

  B and C                                      17%

 C and D                                       4%

 A and C                                       15%

 B and D                                      13%

What is the frequency of crossing-over between A and D?

a. 15%

b. 11%

c. 6%

d. 8%







5) The recombinant frequency of two genes, A and B, located on the same chromosome is 38%.

Parents heterozygous for genes A and B were test crossed, and 250 offspring resulted. How many of the offspring would have parental genotypes for genes A and B?

Record your answer as a whole number.  Answer





6) IMAGE ATTACHED ANSWER PLEASE






7) Scarlet (S), cream (Cr), and maroon (M) are three genes located on chromosome 3 of Drosophila melanogaster.

The distances between each pair of genes is given below.

   Gene Combination                            Map Units
         S and Cr                                             1.5

       Cr and M                                              9.5

         M and S                                              8.0

The sequence of these genes is

a. Cr S M or M S Cr

b. S Cr M or M Cr S

c. S M Cr or Cr M S










8) Use the following information to answer the next question.

In a testcross, the parent that is homozygous recessive for the genes being studied is called the testcross parent. The parent that has the dominant phenotype of the genes being studied is called the non-testcross parent.

Which of the following is NOT a reason that a testcross is a useful technique when studying the inheritance of a trait?

a. The gametes produced by the testcross parent are determined from the testcross progeny.

b. A testcross can determine if an individual with the dominant phenotype is homozygous or heterozygous.

c. The relative frequencies of the different phenotypes among the testcross progeny can be used to map linked genes.

d. Because the testcross parent can contribute only recessive alleles, the alleles contributed by the other parent will be expressed in the offspring of the testcross.









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10)  In Drosophila (fruit flies), jammed wings (J), daughterless (da), curly wings (Cy), star eyes (S), and a black body (b) are determined by genes located on the same chromosome.

   Gene Combination              Recombination Frequency
           J and Cy                                            34.9

          J and da                                             1.7

          S and Cy                                            4.8

           Cy and b                                            42.4

          S and da                                             38

          b and S                                               47.2

What is the map unit distance between b and da?

Answer  (map units)

Record your answer as a value rounded to one decimal place.










11) SEE THIRD IMAGE ATTACHED PLEASE

1)

https://biology-forums.com/index.php?topic=1922007.msg4959246

2)

9%

Explanation :

% of recombination = (number of recombinant / total offspring) *100

= (45/500) *100

=9 %

3)

Answer is 135

Distance between N and O = 27 mu
Recombination frequency between N and O = 27%
Assuming the genes are in coupling combination,

Parental cross: NnOo X nnoo
Progeny:
Total progeny = 500
Parental combinations = 73%
NO/no + no/no = 73% = 500*0.73 = 365
NO/no = no/no = 36.5% = 500*0.365 = 182.5

Recombinations = 27%
No/no + nO/no = 27% = 500*0.27 = 135
NO/no = no/no = 13.5% = 500*0.135 = 67.5

4)

Answer is 11%

Explanation- The frequency of crossing over between any two genes of the same chromosome is directly proportional to the distance between them. This frequency can be calculated to construct linkage maps.
# Recombination frequency is the genetic linkage between two alleles in a chromosome. The frequency tells us about the changes in crossing over between them.
# A recombination frequency of less than 50% indicates linked genes. A value of over 50% is unlinked genes.
# Low values show that they are close together.
# Here the distance between A and D is 11 map units. So their recombination(crossing over) frequency is 11%.

Hope that helps!