Genetic Recombination

Question 1

What were the contributions of Fredrich Meichser to DNA?

Answer 1

1844 - 1895 He was the first to identify nucleic acids. He worked with puss fluid (lymphocytes) and was able to see and isolate the material from the large nucleus. He came to the conclusion that the materials in the nucleus are made of 2 products: proteins and nucleic acids (this was pre deoxyribonucleic acid structure)

Question 2

How did Wihelm Roux’s analysis of dividing cells contributory to the discovery of DNA?

Answer 2

1850 - 1924. Saw that dividing cells did not lead to an even distribution of organelles in new sister cells, however the nucleus always lead to an even distribution of nucleic acids and proteins.

Question 3

Hershey and Chase experimented with bacteriophages that led to the conclusion that genetic material found in the nucleus was in fact the nucleic acids and not the proteins. What was the use of radioactive S-35?

Answer 3

This allowed the fluorescent tagging of amino acids incorporated into the bacteriophage protein coat. While S-35 allows incorporation of the tag into proteins, it is not incorporated into DNA. The tagging allowed Hershey and Chase to conclude that proteins are not the genetic material inherited by offspring.

Question 4

Hershey and Chase experimented with bacteriophages that led to the conclusion that genetic material found in the nucleus was in fact the nucleic acids and not the proteins. What was the use of radioactive P-32?

Answer 4

The fluorescent tagging of P-32 allowed this molecule to be incorporated into the backbone of DNA. While this radioactive molecule identified DNA, it did not identify proteins. This tagging allowed Hershey and Chase to conclude that DNA were in fact the genetic material inherited by offsprings.

Question 5

Explain why the results of Hershey and Chase’s experiments found only some DNA to be tagged with some P-32, while some DNA do not have this fluorescent tag.

Answer 5

Not seen in all the DNA, because some nutrients came from the bacteria.

Question 6

Watson and Crick’s collaboration utilizing the work of others allowed …

Answer 6

For the identification of the double helix of DNA and DNA’s nitrogenous bases (A, T, C, and G).

Question 7

Contrast an allele and a gene.

Answer 7

Genes make up a chromosome. Alleles are different versions of the same gene and normally mirror one another on homologous chromosome

Question 8

Contrast a nonhomologous chromosome from a homologous chromosome.

Answer 8

Non-homologous chromosomes - these are the sex chromosomes and are non mirroring like the other chromosomes.

Question 9

How to determine if indv is a male or female?

Answer 9

Y chromosomes cause one to automatically be a male.

Two X - female

Question 10

Overall the sex chromosomes or the nonhomologous chromosomes are genetically poor. Among the 80 or so genes found on the Y chromosome, what important gene helps play a role in the formation of testes?

Answer 10

The SRY gene

Question 11

Sex linked diseases are?

Answer 11

These diseases tend to be recessive and found on the X chromosome. Such examples are color blindness and hemophilia.

Question 12

What is the proportional of sex linked diseases in women compared to men? Why?

Answer 12

If m - the allele frequency of the mutation on the x chromosome than women = m^2. In males, if the X chromosome has it, then the male will have one as well. The Y chromosome is unable to have a complementary allele to dominate the recessive mutation - known as sex linked diseases. In females, both X chromosomes have to have the genetic mutation if the mutation was recessive

Question 13

A chromatid undergoes replication in order to start the process of meiosis. After the chromatid is replicated, it is attached to its replicant at the centromere still. What is this new form of the chromatid called?

Answer 13

The replicated chromatid is still considered one chromosome as well as they are 2 copies of the same chromosome.

Question 14

During prophase I, what phenomenon is seen with the replicated homologous chromosomes?

Answer 14

Synapsis occurs, the process in which the replicated chromatids pair up with one another to form a tetrad - 4 chromatids of 2 chromosomes.

Question 15

What is the synaptonemal complex?

Answer 15

A railroad like protein complex forms in the middle of the tetrad called the synaptonemal complex. The complex helps aid the chromosomes in crossover or switching of genetic material downward of the chiasm during prophase I to achieve genetic recombination AKA crossing over. THis is achieved in breaking bonds and switching places

Question 16

What is the importance of genetic recombination?

Answer 16

This allows variation in genes

Question 17

True or false: Recombinant gametes are gametes that mirror the parent chromosomes.

Answer 17

False. These gametes produced have a different genetic profile from the parent chromosome which was achieved as a result of crossing over. These are non identical chromatids

Question 18

You’re asked to analyze some fruit flies and found that the genes for the wing phenotype and the color of the fly are found to be on the same chromosome. Meaning the two genes are …
A. Sex linked genes
B. Linked Genes
C. Synaptonemal complex
D. Independent Genes

Answer 18

B. Linked genes - Wing gene and color gene is linked to one another, therefore they are founded on the same chromosome
Independent Genes - Are genes not on the same genes and by Mendel’s law of independent assortment, these two genes will be sorted independent of the other (therefore does not depend the others movement)

Question 19

You’re assessing a homologous chromosome replicate. You tag one chromosome with a red fluorescent and the other with a blue fluorescent isotope. After replication, sister chromatids produced are
A. Red - No color
B. Red - Green 
C. Green - Red
D. Red - Blue

Answer 19

A. Red-no color Individual chromatids of the same chromosome should replicate independent of its indv chromosome. During replication, the complementary nucleotides added onto each indv chromatid will not be tagged, therefore leading to one strand with color and the other with none.

Question 20

True or false: Non sister chromatids are not homologous chromosomes.

Answer 20

False. Non sister chromatids are not necessarily the nonhomologous chromosomes. After crossing over in the tetrad, the chromatids will no longer be identical to one another meaning they are no longer sister chromatids to one another.

Question 21

The phase in which sister chromatids are separated from one another is:
A. Prophase I 
B. Metaphase I 
C. Metaphase II
D. Anaphase I

Answer 21

C. Metaphase II. During meiosis II Metaphase II, sister chromatids are separated from one another. This is the final separation in forming haploid gametes

Question 22

The stage at which the recombined homologous chromosomes are separated from one another is:
A. Prophase I 
B. Metaphase I 
C. Metaphase II
D. Anaphase I

Answer 22

B. Metaphase I. During meiosis I, metaphase I, homologous chromosomes are separated from one another to produce n cells.

Question 23

Crossovers can be seen in a number of ways in a number of orders and times. How do you name a crossover?

Answer 23

Number of strands involved in cross over - Number of cross over - crossover.
Therefore 3 strand double crossover - 3 chromatids are involved and double because 2 crossovers occured

Question 24

Does recombo occur over at the sex chromosomes?

Answer 24

Typically no. This process may not be the wisest process and can lead to nonfunctional chromosomes.
Sex chromosomes do have regions called pseudoautosomal regions. Crossing over does occur in these regions, but no crossover is seen in the male specific region

Question 25

Synapsis results in the formation of a tetrad. A tetrad is composed of four: 
A. Genes 
B. Loci
C. Chromatids
D. Chromosomes

Answer 25

C. Chromatids

Question 26

True or false: A tetrad is a crossed over chromosome.

Answer 26

True. This is the 4 chromatid structure seen in the process of synapsis.

Question 27

Describe the relationship between genetic recombination and genetic mapping.

Answer 27

Genetic Recombination can be used to find the distance of genes between one another on a chromosome. When one does this for all genes, one can calculate all the positions of the genes in relation to one another - genetic mapping

Question 28

What determines the identification of genetic material as a chromosome?

Answer 28

The centromere. Therefore even during replication, when a chromatid has been replicated to form a sister chromatid, these two structures are still considered one chromosome because there is only one centromere

Question 29

In assessing the chromosome 11, you find that the allele related to Sickle cell anemia allele and the cystic fibrosis allele are 7 map units away from one another. After a few days more studying the chromosome, you note that the albinism allele is 20 m.u away from the Sickle Cell Anemia allele. Which genes are more likely to recombine?

Answer 29

Recombination AKA the separation of two linked genes as a result of crossing over - chances are determined by distance between two genes. The increase in distance, the increase in recombination. Therefore the sickle cell anemia allele and the albinism allele are more likely to recombine by 9% more of the time meiosis happens.

Question 30

Bladder Cancer allele founded on Chromosome 11 is 20 m.u away from Porphyria allele. Meaning
A. 80% chance of these two genes to recombine
B. 20% chance for these two genes to recombine
C. 20% chance for these two genes to not recombine
D. 80% chance for these two genes to not recombine

Answer 30

B. 20% of the time meiosis happens, recombination will occur with respect to these two genes. [note: Centimorgan - unit of measurement on a chromosome. AKA a genetic map unit. AKA m.u
The distance bt genes for which one product of meiosis in 100 is recombinant. Therefore is 2 genes are 1 centimorgan apart, therefore 1/100 times or 1% of the time of meiosis occurs, these genes will be recombinant or separated and not be on the same chromosome any more]

Question 31

What is the genotype for the F1 generation offspring for parents with genotype of GGnn and ggNN?

Answer 31

Female gametes: Gn
Male gametes: gN
F1 generation: GgNn - heterozygous genotype - 100% of offspring has this genotype

Question 32

In an experiment producing flowers, you create a F1 generation of AaBb from Ab & aB parental gametes. If we were to mate the F1 generations with a homozygous recessive plant, what would be the expected distribution of F2 offspring if the two traits are linked and no crossing over took place?

Answer 32

Gametes produced would be 50% Aabb and 50% aaBb. Because there is no crossover, use the same parental gamete genotype Ab and aB to crossover with ab gamete (from the homozygous recessive indv)

Question 33

In an experiment producing flowers, you create a F1 generation of AaBb from Ab & aB parental gametes. If we were to mate the F1 generations with a homozygous recessive plant, and got the following stats, what is the recombination frequency between the two genes. What is the distance in recombination units

895 Aabb
905 aaBb
110 aabb
90 AaBb

Answer 33

The genotype aabb and AaBb are offsprings as a result of recombination.
110+90 = the total number of offsprings that are recombinant
200/2000 = 1/10 or 10% recombination between these two genes AKA 10% of the offsprings are a result of recombination

Question 34

What is a locus?

Answer 34

A locus is the particular point on a chromosome where a gene is situated.

Question 35

The phenomenon in which genes located near each other on a chromosome are inherited together is known as what?

Answer 35

Linkage

Question 36

During what stage of prophase I of meiosis does crossing over occur?

Answer 36

In diplonema, the chiasmata are clearly visible and thus indicating crossing over will occur.