Give your opinion about probable suggestions which can be given to pair of contenders before marriage in order to prevent the spread of a genetic disease from the society already known to you?

In order to prevent the spread of a genetic disease, the pair of contenders must do genetic counselling so that the risk of a disorder may be prevented. Genetic counselling gives you knowledge about how genetic conditions might affect you or your family. The genetic counsellor or other healthcare professional will manage your personal and family health history. They can use this information to decide how likely, it is that you or your family member has a genetic condition. Based on this information, the genetic counsellor can assist you to decide whether a genetic test might be right for you or your relative.

‘Different genotypes produce the same phenotype’ – Justify the statement in the form a table by taking an example from the result of dihybrid cross of pea plant?

A dihybrid cross describes a mating experiment between two organisms that are identically hybrid for two traits. Mendel also worked with and crossed pea plants that differed in two characters, as is seen in the cross between a pea plant that has seeds with yellow colour and round shape and one that had seeds of green colour and wrinkled shape. Mendel found that the seeds resulting from the crossing of the parents, had yellow coloured and round shaped seeds. Let us use the genotypic symbols Y for dominant yellow seed colour and y for recessive green seed colour, R for round shaped seeds and r for wrinkled seed shape. The genotype of the parents can then be written as RRYY and rryy. The gametes RY and ry unite on fertilisation to produce the F 1 hybrid RrYy. When Mendel self hybridised the F 1 plants he found that 3 / 4 th of F 2 plants had yellow seeds and 1 / 4 th had green. In the table, we can see the genotype of RRYY, RrYY, RRYy, RrYy are different, but their phenotype is the same example–Yellow Round.

Show with the help of cross, who is more important among parents in determining the sex of their offspring?

From the cross, we can conclude that the father is more important in determining the sex of the offspring because of the X chromosome fertilises the mother gametes then the offspring will be a girl and if the Y chromosome fertilises the mother gametes then the offspring will be a boy.

A colour blind female married a normal male. Judge the probability of colour blindness among their children in the first filial generation. Show with the help of a cross how the first law of Mendel is deviated in the case of Four-O'clock plant in F2 generation.

Colour blindness is an X-linked recessive disorder. One copy of the affected gene in males in each cell is sufficient to cause the disorder. Females with two copies of the affected gene show the disorder (Xc Xc ). Females heterozygous (Xc X) for this trait are normal but serve as a carrier of the disease. According to the question, the female is colour blind (Xc Xc) and the father is normal (XY). The affected mother will inherit the disease to 100% sons (Xc Y) while the 100% daughter will be normal but will serve as a carrier. The chart is given below: Parent generation: XcXc x XY Gametes Xc Xc X XXc (carrier girl) XXc (carrier girl) Y XcY (colour blind boy) XcY (colour blind boy) The monohybrid cross in Four o’clock plant is an example of incomplete dominance. It is also called semi-dominance or partial dominance. Incomplete dominance is a phenomenon when neither of the alleles of a gene is fully dominant over the other. The resulting hybrid is an intermediate between the two parents. According to Mendels first law, the varieties gives 1:2:1 genotypic ratio and phenotypic ratio in F2 generation which is 3:1 in otherwise dominant traits. This is because the heterozygous genotypes do not show the dominant trait but, they are blend of dominant and recessive phenotype. A cross between two pure breeding genotypes that differ in two pairs of traits followed by selfing of F1 hybrid. F2 phenotypic ratio: 1/4 Red : 1/2 Pink : 1/4 White

Tabulate three pairs of dominant-recessive traits of pea plants as selected by Mendel. State the first law of Mendel as deducted from the experiment of a monohybrid cross.

Traits Dominant Recessive Height of plant Tall (TT, Tt) Dwarf (tt) Seed shape Round (RR, Rr) Wrinkled (rr) Seed colour Green (YY, Yy) Yellow (yy) Monohybrid cross: In this experiment, Mendel took two pea plants of opposite traits (one dwarf and one tall) and crossed them. He found the first generation offsprings were tall and called it F1 progeny. Then he crossed F1 progeny and obtained both tall and short plants in the ratio 3:1. Mendel even conducted this experiment with other contrasting traits like green peas vs yellow peas, round vs wrinkled, etc . In all the cases, he found that the results were similar. From this, he formulated the laws of segregation and dominance. Law of Segregation: The law of segregation states that during the production of gametes, two copies of each hereditary factor segregate so, that offspring acquire one factor from each parent. In other words, allele pairs segregate during the formation of gamete and re-unite randomly during fertilization. This is also known as Mendel’s third law of inheritance.

Find the probable gametes to be produced from the hybrid plant YyRr produced at F 1 generation in a dihybrid cross experiment.

A cross between the two pure breeding parents or the homozygous parents in which the pattern of inheritance of two pairs of contrasting characters is observed simultaneously is called a dihybrid cross. In a dihybrid cross, the parents carry different pairs of alleles for each trait. One parent carries a homozygous dominant allele, while the other one carries a homozygous recessive allele. The offsprings produced after the crosses in the F1 generation are all heterozygous for specific traits.

One day students read an article in a newspaper about Thalassemia and were very scared to know the fate of a thalassemia patient. Give a list of the kind of measures they have to use to eradicate this disease from the population.

Thalassaemia is an inherited blood disorder where the body produces an inadequate amount of haemoglobin. Haemoglobin is a protein molecule that has oxygen in the red blood cells. It results in the extreme destruction of red blood cells that leads to anaemia. Anaemia is a condition in which the haemoglobin or red blood cells are less than the regular count. It is an inherited disease that is mainly caused due to abnormal haemoglobin synthesis. It is transferred by one of the parents who are a carrier of this disease due to either deletion of particular key gene fragments or a genetic mutation.

With the help of a cross, determine how the sex of offspring of a human is identified.

In humans, sex is determined by sex chromosomes (XX females, XY males). The X and Y chromosomes harbour dramatically different numbers and sets of genes (about 1 , 000 genes on the X and only a few dozen genes on the Y), yet they originated from ordinary autosomes during the early evolution of mammals. Most human chromosomes have a maternal and a paternal copy, and we have 22 such pairs. But one pair, called the sex chromosomes, is odd in not always being a perfect pair. Women have a perfect pair of sex chromosomes, both called X. But men have a mismatched pair in which one is a normal-sized X while the other is a short one called Y. So women are XX, while men are XY. All children will inherit an X chromosome from their mother regardless of whether they are boys or girls. Thus, the sex of the children will be determined by what they inherit from their father. A child who inherits an X chromosome from her father will be a girl, and one who inherits a Y chromosome from him will be a boy.

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 16 - Heredity and Common Genetic Diseases>West Bengal Board-2018>Q 16

MEDIUM

10th West Bengal Board

IMPORTANT

Earn 100

Colour of seed or shape of seed of a pea plant-taking these two characters Mendel performed Dihybrid cross. Write the genotypes of pea plant having yellow and round seeds produced in the F2 generation of the experiment. State the law of independent assortment of Mendel.

Important Questions on Heredity and Common Genetic Diseases

MEDIUM

10th West Bengal Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 16 - Heredity and Common Genetic Diseases>West Bengal Board-2018>Q 17

State the opposite traits for each of the characters of flowers of the pea plant chosen by Mendel for his experiment. “For developing the scientific ideas on heredity the experiments performed by Mendel on pea plants are epoch-making”- Mention three reasons behind his success in performing the experiment.