Q26 of 27 Page 1

Aneuploidy of chromosomes in human beings results in certain disorders. Draw out the possibilities of the karyotype in common disorders of this kind in human beings and its consequences in individuals.

OR


In a dihybrid cross, white-eyed, yellow bodied female Drosophila was crossed with red-eyed, brown bodied male Drosophila. The cross produced 1.3 per cent recombinants and 98.7 progeny with parental type combinations in the F2 generation. Analyze the above observation and compare with the Mendelian dihybrid cross.

Aneuploidy refers to the failure of segregation of chromatids during cell division cycle results in the gain or loss of chromosomes.

Common disorders of this kind in human beings;


Down’s syndrome


• Caused due to the presence of an additional copy of chromosome number 21 9trisomy of 21)


• The affected individual is short statured with a small round head, furrowed tongue and partially opened mouth. Palm is broad with characteristic palm crease. Physical, psychomotor and mental development is retarded.


• Karyotype with 23 pairs of autosomes and 1 pair of sex chromosomes. (total of 24 pairs i.e. 47 chromosomes).


Turner’s syndrome


• Caused due to the absence of one X chromosome, i.e., 45 with X0,


• Affected female individuals are sterile as ovaries are rudimentary and may lack secondary sexual characters.


• Karyotype of 45 chromosomes.


OR


The genes determining the above characters are located on the X chromosome. When two genes in the dihybrid cross are situated on the same chromosome, the proportion of parental combination becomes much higher than the non-parental type of combination. The linkage is the physical association of genes on a chromosome. Recombination explains the non-parental gene combination. Genes on the same chromosomes are tightly linked (show low recombination), or it may be loosely linked (showed high recombination).


1.3 percent recombinants indicate that genes are loosely held, so there are less parental type characters and. 98.7 per cent progeny with parental type combination indicates genes were tightly held and less recombination.


In Mendelian dihybrid cross, the genes segregate independent of each other, and the F2 ratio was 9:3:3:1 (when two genes are independent).


More from this chapter

All 27 →
23

Study the given pedigree chart and answer the questions that follow:


(a) Is the trait recessive or dominant?


(b) Is the trait sex-linked or autosomal?


(c) Give the genotypes of the parents shown in generation I and their third child shown in generation II and the first grandchild shown in generation III.


OR


Haemophilia is a sex-linked recessive disorder of humans. The pedigree chart given below shows the inheritance of Haemophilia in one family. Study the pattern of inheritance and answer the questions given.


pedigree.png


(a) Give all the possible genotypes of the members 4, 5 and 6 in the pedigree chart.


(b) A blood test shows that the individual 14 is a carrier of haemophilia. The member numbered 15 has recently married the member numbered 14. What is the probability that their first child will be a haemophilic male.? Show with the help of Punnett square.

 24

(a) In a pond, there were 200 frogs. 40 more were born in the year. Calculate the birth rate of the population.

(b) Population in terms of number is not always a necessary parameter to measure population density. Justify with two examples.

 25

People living in the coastal areas are forced to evict their dwelling units as the sea has inundated into the land areas. State the possible reasons and suggest measures that could be taken to reduce the deleterious changes in the environment.

OR


A young sperm whale, 33-foot long was found dead off the coast. It had a large amount of human trash like trash bags, polypropylene sacks, ropes, net segments etc. amounting to 29 kilograms in its digestive system. The whale died because of inflammation of the abdominal lining. Analyze the possible reasons for such mishaps and suggest measures that can be taken to reduce such incidents.

 27

Differentiate between spermatogenesis and oogenesis.

OR


‘Parturition is induced by a complex Neuro endocrine mechanism’. Justify