3.) (2pts each, 4 points total) A newly discovered species of Daphnia (D. voltro

Question

3.) (2pts each, 4 points total) A newly discovered species of Daphnia (D. voltronil) has 2n- 20 chromosomes mates with a closely related Daphnia species (D. zeldai) that has 2n 12 chromosomes. How many would there be in each indicated cross? r 3n ln a. Allotetraploidy including D. yoltroni and D. zeldal b.) Autotriploidy in D. edai 3 3 (3 points) Most aneuploidies for autosomes in humans will be spontaneously aborted, and those that reach live chromosome 21. Although individuals with Down syndrome experience a range of disabilities, many can live semi-independent lives with low-intensity care. Explain why there is such a discrepancy between other human trisomies and trisomy 21. 4. birth have severe abnormalities. However, Down syndrome is caused by aneuploidy of sis

Explanation / Answer

3. An allotetraploid is a hybrid that has chromosomes which are 4 times that of a haploid organism . These are formed as a result of both chromosome sets of each parent being present in the gamete.

The fusion of such gametes results in the formation of an individual with the sum of the whole set of parents' chromosome.

D.voltrani has 2n = 20 chromosomes .

It mates with D. zeldal which has 2n= 12 chromosomes.

When the two mate, the resultant individual will have 20 + 12 = 32 chromosomes .

Autotriploidy is a phenomenon in which the individual has three sets of chromosomes, all with the same karyotype . So each chromosome in a triploid occurs in groups of 3 homologues i.e the chromosomes are trisomic. During meiosis the groups of three homologous chromosomes synapse, two chromosomes at one place at a time.

Autotriploidy in D.zeldal  will result in an individual with 3 sets of n chromosomes

Here, 2n = 12 , therefore n= 6

So, the new individual will have 3 * 6 = 18 chromosomes.

4. Humans have 23 pairs of chromosomes of which 22 pairs are autosomes and one pair is sex chromosome . This is the normal condition . Sometimes due to nondisjunction in Meiosis 1 or Meiosis 2 , a pair of chromosomes fail to separate, resulting in one gamete with an extra chromosome and the other with one less number of chromosome. This condition is called ' aneuloploidy '. If such gametes get fertilised, they result in individuals with severe genetic defects. Many a times, such fetuses are naturally aborted before the full term of pregnancy.

Each pair of homologus chromosome is different from others. In humans , trisomy of chromosome pairs numbered 21, 18, 16 , 22, 8, 9 etc have been reported. Each condition will produce different complications and syndromes because the different chromosome carry different genes which are responsible for different characteristics.

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