You are studying a cell which, before the S phase of the cell cycle, has 8 chrom

Question

You are studying a cell which, before the S phase of the cell cycle, has 8 chromosomes and 2.4 picograms (2.4 × 1012 grams) of DNA. Complete the following table with the expected number of chromosomes, chromatids, homologous pairs and the amount of DNA in each area or pole of the spindle at each of the stages indicated. (1/2 mark per box, 10 marks total)

Chromosomes

Chromatids

Homologous pairs

DNA amount

Prophase (Mitosis)

Anaphase (Mitosis)

Prophase I (Meiosis)

Anaphase I (Meiosis)

Anaphase II (Meiosis)

Including examples, compare and contrast the following: (4 marks each; 16 marks total)

Genotype and phenotype

Codominance and epistasis

Crossing-over and independent assortment

Crossing-over and independent assortment

A particular type of pond organism usually reproduces asexually. However, in later summer and as winter approaches it tends to reproduce sexually. Explain why this organism would use two different methods of reproduction. (6 marks)

A female Drosophila (fruit fly) heterozygous for red eyes and grey body was crossed with a male homozygous for scarlet eyes and ebony body. The two genes are linked on the same chromosome. The following offspring were produced. How many map units would separate them? (Show all your work.) (4 marks)

Red eyes, grey body

38

Red eyes, ebony body

13

Scarlet eyes, grey body

15

Scarlet eyes, ebony body

34

In a certain breed of domestic fowl, pea comb is dominant to single comb but feather colour shows absence of dominance. Black feathers and white feathers are homozygous, whereas the heterozygote gives blue feathers. From crosses between birds heterozygous for both genes, what proportion of the offspring would you expect to be: (Define the alleles and show all your work.) (12 marks)

Pea-combed

Black-feathered

Blue-feathered

Pea-combed and blue-feathered

Single-combed and white-feathered

A particular X-linked gene is a recessive lethal that causes death and reabsorption of the embryo at an early stage. A heterozygous female married a man expressing the dominant trait. Define the alleles and show your work in answering the following questions: (5 marks)

What proportion of their offspring would be expected to be females?

What proportion of the offspring would be expected to be carriers of the gene?

Look at the following pedigree. Circles represent females; squares represent males. Coloured circles and squares represent affected individuals. Horizontal lines represent matings; vertical lines represent offspring produced from a mating. (13 marks total)

What is the mode of inheritance? Referring to the applicable numbered individuals, explain your reasoning. Your choices are autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, Y-linked. (8 marks)

What are the genotypes of the following individuals (be sure to define the alleles): 4, 5, 8, 11. (5 marks)

List 4 features of an ideal organism to study genetics. (4 marks)

Explain the roles of bicoid, the segmentation genes, and homeotic genes in development of an embryo. (10 marks)

Answer the following questions about stem cell research: (11 marks total )

Differentiate between multipotent, pluripotent and induced pluripotent stem cells. Include an example of each. (6 marks)

Outline the advantages and disadvantages of iPS cells. (5 marks)

Write a short paragraph (not more than 200 words) describing the genetic disorder known as maple syrup urine disease (MSUD). In your discussion, include answers to the following questions:

Use your own words to write a coherent paragraph in complete sentences. Cite your sources following the citation instructions in Jan A. Pechenik’s A Short Guide to Writing about Biology. (9 marks)

How is maple syrup urine disease inherited?

Why is it called maple syrup urine disease?

Briefly explain what causes this disease.

How many births in North America result in infants with MSUD?

Chromosomes

Chromatids

Homologous pairs

DNA amount

Prophase (Mitosis)

Anaphase (Mitosis)

Prophase I (Meiosis)

Anaphase I (Meiosis)

Anaphase II (Meiosis)

Explanation / Answer

Please find the answers below:

Answer 1: As mitosis is an equational cell division whereas meiosis is reduction cell division, the number of chromosomes and DNA remains same in mitosis whereas it reduces to half in meiosis. Further, the number of chromatids per chromosomes remains same in mitosis whereas it splits into half in meiosis. Thus, the answers can be found as below:

Phase Chromosomes Chromatids Homologous pair DNA amount Prophase 8 16 8 2.4 pg Anaphase 16 16 8 2.4 pg Prophase I (Meiosis) 8 16 8 2.4 pg Anaphase I (Meiosis) 8 16 8 2.4 pg Anaphase II (Meiosis) 8 8 No pairs 1.2 pg

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