Question

Q1. Fill in

In 2016, The American Sheep Industry Association released data showing that the nation's 88,000 sheep producers generated a total economic impact of $5.8 billion. Some of the issues that impact the profitability of sheep include their coat color, how quickly they gain weight, and whether they are resistant to infection caused by parasitic worms called nematodes. In the UK last year, approximately 100 million dollars were spent on reducing and curing worm infections in sheep. A team of researchers led my Riggio and Matika are working on understanding the genetics of sheep in order to increase profitability. While sheep have hundreds of thousands of genes on their total of 54 chromosomes (n=27), the researchers are focusing on 3 genes. The NR gene is correlated with nematode resistance and is located on chromosome 14. Only individuals with two recessive copies show resistance to nematode infection. The GTH gene is correlated with growth rate and overall bodyweight. The researchers would like to have sheep grow quickly so they are ready for market sooner. Individuals with GG or Gg grow the fastest and reach market weight sooner than individuals with gg. Finally, there are two genes involved in coat color. They are both on chromosome 3, meaning they are linked. The first determines if the individual is Black (BB or Bb) or brown (bb). The second determine if there are white spots on the coat. The spotting gene shows no spotting with the NN genotype, spotting only on the head with the SN genotype, and spotting covering a majority of the body with the SS genotype.

Q1 Fill in the table below to help you keep track of the genes.  

Chromosome #           Possible Alleles             Possible Genotypes                 Resulting Phenotyp

3                                       B or b                            BB or Bb or bb Black, black, brown

Coat Color S or N   

13

Growth Rate                  G or g

14

Nematode Resistance      R or r

Q2. In order to confirm that the NR gene controls resistance to infection from nematodes, the researchers want to perform a study to test their idea that individuals with the genotype “rr” have a lower risk of getting infected by nematodes than individuals with RR or Rr genotypes.

a. What is the null hypothesis for the study?

b. What is the alternative hypothesis for the study?

The methods used in the study are explained below:

The genotype of 300 baby sheep were determined prior to the study and approximately the same number of genotype RR, Rr and rr were used. They were raised in the same pastures and fed similar food. Fecal samples were collected from the rectum of the baby sheep at approximately 16, 20 and 24 weeks of age. Fecal egg counts of nematodes were measured on four replicates of each fecal sample and the average of the four replicates at each time point was used for analyses.

Q3. Draw a figure that would show support for the alternative hypothesis. Make sure to clearly label your axes, values (tick marks), and include an appropriate figure legend below the figure.

Q4. One of the sheep in the study is Dolly. She is brown with spotting on her head. She is heterozygous for the growth rate gene and shows resistance for nematode infection.

a. What is the genotype of Dolly?

b. Draw one of Dolly’s cells during metaphase of mitosis. Show chromosomes 3, 13, and 14. Label all the alleles. Label sister chromatids once in your model. Label homologous pairs once in your model.

c. Describe what the products of mitosis would be for Dolly.

d. Describe one reason why Dolly would need to perform mitosis.

A new Spartan sheep farm is starting to increase their flock and they are going to breed two sheep to produce a variety of colors and high resistance to nematode infection.

A female named Sally with the genotype: Bb NN rr GG with a male, Buster, with the genotype bb SN rr Gg

Q5. Draw a puffy stick chromosome model showing for chromosomes 3, 13, and 14 for Buster before DNA replication. Clearly show the locus for the genes and label the particular alleles.

Q6

a. Are there homologous pairs in this model? State Yes or No and explain you know.

b. Are there identical sister chromatids in this model? State Yes or No and explain.

Q7. Draw puffy stick chromosome models showing the homologous pairs for chromosomes 3, 13, and 14 Buster during metaphase of Meiosis I. Represent the two possible alignments of the chromosomes, due to independent assortment in A) and B). Clearly label all alleles for all genes. Also, label the sister chromatids and homologous chromosomes in at least 1 instance in your drawings if they are present.

Q8. Draw puffy stick chromosome models showing the homologous pairs for chromosomes 3, 13, and 14 Buster during metaphase of Meiosis II for alignment A above AND then the final products.   Clearly show the locus for the genes and label the particular alleles.

Meiosis II, Alignment A:

Final Products of Meiosis II for Buster in Alignment A:

Q9. For Q7 and Q8, Write haploid or diploid next to each model. Then below explain how you know the difference:

Q10. In the space below, draw the Punnett square for the cross between Sally and Buster

Sally with the genotype: Bb NN rr GG              Buster, with the genotype bb SN rr Gg

Q11. What would be the expected percentage or fraction of the offspring that would be brown with spotting on the head, be resistant to nemotodes and be heterozygous dominant for growth rate?

Q12. If you had 5 generations in a row of sheep that either had no spotting or had spotting only on the head and then a baby sheep appeared with spotting all over the body, what is one possible explanation? Explain your thinking.

Q13. If these scientists wanted to put the “n” allele into goats to help fight nematode infection, would they be doing gene editing or creating a genetically modified organism? Explain?

Only need questions 5-13 if you can understand it

Answer 1

ANSWER 1 :-

Chromosome number	Possible alleles	Possible genotypes	Resulting phenotype
3 (Coat colour)	B or b	'BB' or 'Bb' or 'bb'	(BB - Black Bb - Black bb - Brown)
13 (Spotting)	S or N	'SS' or 'SN' or 'NN'	(SS - Spots on major portion of body SN - Spots on head NN - No spots)
14 (Growth rate)	G or g	'GG' or 'Gg' or 'gg'	(GG - Fast growth rate Gg - Fast growth gg - slow growth rate)
Nematode resistance	R or r	'RR' or 'Rr' or 'rr'	(RR - No resistance Rr - No resistance rr - resistance)

ANSWER 2 :-

Null Hypothesis :

There is no statistically significant relationship between having genotype 'rr' and having lower risk of getting infected by the nematodes as compared to genotypes 'RR' and 'Rr'.

Alternate Hypothesis :

There is a statistically significant relationship between having genotype 'rr' and having lower risk of getting infected by the nematodes as compared to the genotype 'RR' and 'Rr'.

ANSWER 3 :-

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