Extended Response

Explain the purpose of a testcross. In your answer, please specifically address: A. What the importance is of the genotype of the tester in the cross. B. The genotypes of both individuals in the testcross. C. The outcome genotypes and phenotypes in the testcross progeny

A. This is crucial because the recessive genotype ensures that any observed phenotypic variation in the progeny is due entirely to the genotype of the other parent. It serves as a "baseline" to reveal whether the tested individual is homozygous dominant or heterozygous.

B. The tester will have the genotype aa (homozygous recessive).

• The individual being tested will have either:

  • Homozygous dominant (AA)

  • Heterozygous (Aa)

C. If the tested individual is homozygous dominant (AA):**

• All offspring will have the Aa genotype.

• All offspring will display the dominant phenotype.

• If the tested individual is heterozygous (Aa):**

  • Offspring genotypes will be a 1:1 ratio of Aa and aa.

  • Phenotypes will also show a 1:1 ratio of the dominant and recessive traits.

Explain the process of clonal evolution. Please specifically address: A. What is meant by the term ‘clonal evolution’. Why is this process referred to as ‘clonal’? B. The role(s) of ‘driver’ mutations. What types of genes are likely to be mutated? C. The role(s) of ‘passenger’ mutations. Explain why passenger mutations are observed ?

Clonal evolution is a biological process associated with the development and progression of diseases, especially cancer.

A. It refers to the process where cell populations acquire mutations over time, creating clones with selective advantages. It is called "clonal" because it originates from a single cell lineage.

B. These mutations drive disease progression by providing a selective advantage. They often affect oncogenes, tumor suppressor genes, or DNA repair genes.

C. These mutations do not contribute to disease progression but accumulate alongside driver mutations due to high mutation rates and instability in the cells

A trihybrid parental cross between two true-breeding mice that differ in traits for ear shape, color, and coat pattern. Sort the alleles independently using the three Punnett squares and provide the predicted outcomes.

We calculate each trait independently using separate Punnett squares for the F1 cross (EeCcPp × EeCcPp). Here's a summary:

1. Ear Shape Punnett Square (Ee × Ee):

• Genotypes: 1 EE, 2 Ee, 1 ee (ratio 1:2:1).

• Phenotypes: 3 dominant ear shape : 1 recessive ear shape.

2. Color Punnett Square (Cc × Cc):

• Genotypes: 1 CC, 2 Cc, 1 cc (ratio 1:2:1).

• Phenotypes: 3 dominant color : 1 recessive color.

3. Coat Pattern Punnett Square (Pp × Pp):

• Genotypes: 1 PP, 2 Pp, 1 pp (ratio 1:2:1).

• Phenotypes: 3 dominant coat pattern : 1 recessive coat pattern.

Step 4: Combine Predicted Outcomes

To find the overall ratios of phenotypes, multiply the independent probabilities:

• Dominant for all traits: 3/4×3/4×3/4=27/643/4 \times 3/4 \times 3/4 = 27/64.

• Dominant for two traits, recessive for one: 3/4×3/4×1/4=9/643/4 \times 3/4 \times 1/4 = 9/64 (and similar combinations, totaling 27/64+27/64+27/6427/64 + 27/64 + 27/64).

• Fully recessive for all traits: 1/4×1/4×1/4=1/641/4 \times 1/4 \times 1/4 = 1/64.

A parental cross between two true-breeding mice that differ in traits for ear shape, color, and fur. Furled (F) is dominant to round (f). Black (B) is dominant to tan (b). Tufted (T) is dominant to hairless (t). Mouse #1 is true-breeding for Furled, black, tufted ears; Mouse #2 is true-breeding for round, tan, hairless ears. Your F2 generation does NOT follow your predictions obtained in #27, so you perform a testcross utilizing one of the F1 progeny. Making use of a testcross, determine the order of the three loci. Calculate the coefficient of coincidence and interference

Step 1: Testcross Setup

The parental genotypes are:

• Mouse #1: FFBBTT (homozygous dominant for all three traits).

• Mouse #2: ffbbtt (homozygous recessive for all three traits).

The F1 offspring are:

• All FfBbTt (heterozygous for all traits).

A testcross involves crossing an F1 individual (FfBbTt) with a homozygous recessive tester (ffbbtt). This allows us to observe phenotypic ratios that reflect recombination between the loci.

Recombination frequency between loci is calculated as:

Recombination frequency=Number of recombinant progenyTotal number of progeny×100\text{Recombination frequency} = \frac{\text{Number of recombinant progeny}}{\text{Total number of progeny}} \times 100

Use this to determine the map distances (in centimorgans, cM) between pairs of loci

The CoC is calculated as:

CoC=Observed double crossovers / Expected double crossovers

From his work from 1856-1863 crossing pea plants, Mendel came to two final conclusions: I. The principle of segregation (his 1 st law); II. The principle of independent assortment (his 2 nd law). Compare and contrast Mendel’s 1 st and 2 nd Laws

• Principle of Segregation (1st Law): States that alleles for a single gene separate during gamete formation, ensuring each gamete carries only one allele. It applies to inheritance of one trait.

• Principle of Independent Assortment (2nd Law): States that alleles of different genes distribute independently during gamete formation, creating new combinations of traits. It applies to inheritance of multiple traits.

During Meiosis, there are two mechanisms that function to introduce genetic variation to the resulting gametes. Please explain in some detail: A. Each of the two mechanisms. B. What would be the consequence, for each, if it did not occur, for example due to mutation (please, do not just say “no variation”)

• Crossing Over (Prophase I): Homologous chromosomes exchange genetic material, creating recombinant chromosomes and increasing genetic diversity. Without it, offspring would inherit the same parental alleles, reducing diversity and adaptability.

• Independent Assortment (Metaphase I): Chromosome pairs align randomly, ensuring different combinations of maternal and paternal chromosomes in gametes. Without it, gametes would have fixed, identical combinations of chromosomes, reducing diversity and increasing risk of genetic disorders.