Question

Please explain how these work: map units, map location, chromosome number and division arrangements. I have the correct answer to these questions I just need an explanation to find the answer.

Assume that, regarding a particular gene, one scored 30 second-division asocspore arrangements and 70 first-division arrangements in Neurospora. What would be the map distance between the gene and the centromere? Answer: 15

Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and straw body. The F1 Lobe females were then backcrossed with homozygous smooth abdomen, straw body males and the following phenotypes:

smooth abdomen, straw body 820

lobe 780

smooth abdomen, lobe 42

straw body 58

smooth abdomen 148

lobe,straw body 153

What is the coefficient of coincidence? Answer: zero

Give the gene order and map units between these loci. Answer: lobe is in the middle smooth abdomen-5-lobe-15-straw body.

Please explain all three answers and the concepts. Will rate!

Answer 1

Answer:

• In Neurospora during a \n experiment, a cross involving a pair of alleles 30% of asci show second division segregation, shows that 30% of zygotes had crossing over during meiosis, and remaining 70% show first division segregation.
• Since there are four chromatids in each tetrad, the 50% asci resulted from 30 x 4 = 120 original chromatidsout of which 60 are crossover chromatids.
• the remaining 60 chromatids are non-crossover chromatids.
• In 70% of zygotes, they did not have crossing over, which means that 70 x 4 = 280 are non-crossover chromatids.
• The actual number of non-crossover chromatids is larger because 280 + 60= 340 non-crossover chromatids.
• Therefore, if the original 100 tetrads or asci 340 are non-crossover chromatids and 60 are crossover chromatids.
• Since 100 tetrads or asci also mean 400 chromatids, the percentage of crossover chromatids will be
• (60/400) x 100 = 15%.
• Thus, there was 15% crossing over between the gene and the centromere.
• We can also say that the gene in question is 15 map units apart from the centromere.

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