Biology Olympiad: University Stage I of the 2013 All-Ukrainian Olympiad
On March 18, the first (university) stage of the 2013 All-Ukrainian Biology Olympiad was held at the Faculty of Biology. Eight participants took part - thanks to them for their courage! The results of the Olympiad are presented here, along with comments on the genetics problem.
On March 18, the first, university stage of the All-Ukrainian Biology Olympiad was held at the Faculty of Biology. The Olympiad consisted of three tasks: a theoretical open-ended question (D.A. Shabanov), a genetics problem (E.A. Kiosya), and a practical task on invertebrate zoology and ecology (V.A. Baranov).
Si-ri
grades
"Si-ra"
Re-calculation
Result
Code Surname, Name Course
Theo-
Task
Practice
Σ
Theo-
Task
Practice
Sum Mes- to
Sakun Yuliia III
5
1
18
24
4
1
7
12
2 Drogvalenko Nikolay I
6
4
19
29
6
4
8
18
III
3 Meleshko Elena IV
6
4
13,5
23,5
6
4
0
10
6 Vegerina Anastasiya III
3
0
20
23
0
0
10
10
7 Mironov Roman IV
3
2
20
25
0
2
10
12
8 Polshvedkina Yuliya II
5
8
18
31
4
8
7
19
III
9 Ostras Daniil III
8
8
18
34
10
8
7
25
II
10 Sapozhnikova Valeria II
6
10
20
36
6
10
10
26
I
When recalculating grades, the worst result was equated to 0, the best - to 10, the rest changed proportionally and were rounded to whole numbers. This recalculation method, according to the jury, allows for a more or less equal "weight" of the tasks; however, this recalculation method did not change the list of winners. According to a letter from Zhytomyr, our university's team must consist of 2 participants, regardless of previous results. Valeria Sapozhnikova and Daniil Ostras will go to the next stage in Zhytomyr. The tasks were given in Ukrainian, and the participants answered mainly in Russian. Since Yevhen Oleksandrovych gave the answer to the problem in Russian, its conditions will also be presented in Russian. (I hope to post the other two tasks and comments on them here as well). Task No. 2. Problem. A pedigree shows the inheritance of a rare genetic disease in four generations of one family. 1). What type of inheritance does this genetic disease follow? 2). What is the probability of the proband (marked with an arrow) having children with this genetic disease, assuming her spouse is healthy and not related to her? Explain your answer. Answer: Let's start by testing the hypothesis of monogenic inheritance of this disease. As is known, there are six types of inheritance for monogenic genetic diseases: (1) autosomal dominant, (2) autosomal recessive, (3) Y-chromosome linked, (4) X-chromosome linked recessive, (5) X-chromosome linked dominant, and (6) mitochondrial. We exclude Y-chromosome linked inheritance because both males and females are affected among the sick. The hypothetical defective allele cannot be X-chromosome linked dominant, because the principle of criss-cross inheritance is not observed in the pedigree (the disease should always be passed from affected fathers to daughters and never to sons). Affected fathers' daughters (II-5 and III-8), as we can see, are healthy. Similarly, we can explain why it cannot be an X-chromosome linked recessive allele. If it were, women II-1, II-3, III-2, III-3, III-5, IV-1, and IV-3 could not have inherited the disease from their affected mothers (as they would have received an X chromosome with a normal dominant allele from their healthy fathers and would have been healthy carriers). Perhaps our hypothetical allele is autosomal? In principle, this is probably possible. By postulating either an autosomal dominant or autosomal recessive mode of inheritance, we can assign genotypes to all individuals in the pedigree without any direct contradiction. However, statistically, this hypothesis appears extremely unconvincing. For the autosomal hypothesis to hold true, all marriages in this pedigree must be represented as crosses between heterozygotes and a recessive homozygote. In this case, we would expect about 50% of affected children in each marriage. However, we do not see such segregation in any of the six marriages of individuals in generations II and III. Instead, either all children are healthy, or all are affected. Furthermore, autosomal recessive inheritance requires assuming that all healthy spouses of affected individuals (I-1, II-2, II-4, II-6, III-6, and III-7) are heterozygotes for this rare disease. This is very difficult to believe. Only mitochondrial inheritance remains. And it fits our pedigree perfectly. Since mitochondria in humans are inherited only through the maternal line, all children of affected mothers can be affected, and all children of affected fathers (with a healthy mother) must be healthy. This is exactly what we observe. Some participants suggested a "cytoplasmic" mode of inheritance, which is generally close in meaning (since almost all studied cases of cytoplasmic inheritance in humans are due to mitochondrial DNA inheritance).