How is sex determined in human beings?
The male sex gametes have X and Y chromosomes, whereas the female sex gametes have two X chromosomes. When a sperm containing a Y chromosome fuses with the ovum containing X chromosome, the zygote develops into a male. When a sperm containing the X chromosome fuses with an ovum containing X chromosome, the zygote develops into a female. Thus the sex of an individual is determined by the sex chromosomes X and Y, which is present in the male chromosomes.
Which of the processes, sexual reproduction or asexual reproduction, brings about maximum variations in the offsprings ?
Choose the one term from the following which includes the other three :
broccoli, wild cabbage, cauliflower, cabbage
”The sex of the children is determined by what they inherit from their father and not their mother.” Justify.
Name five varieties of vegetables which have been produced from ‘wild cabbage’ by the process of artificial selection.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually ? Give reason for your answer.
Explain the mechanism of sex determination in humans. [All India]
Or
With the help of a flow chart explain in brief how the sex of a newborn is genetically determined in human beings. Which of the two parents, the mother or the father, is responsible for determination of sex of a child? [Foreign]
Define the term ‘evolution’. “Evolution cannot be equated with progress”. Justify this statement. [Delhi]
An individual cannot pass on to its progeny the experiences of its lifetime.” Justify the statement with the help of an example and also give reason for the same. [Foreign]
State one characteristic which shows that the birds are very closely related to dinosaurs.
Study the following cross and showing self-pollination in Flf fill in the blank and answer the question that follows
A man having blood group O marries a woman having blood group B and they have a daughter. What will be the blood group of the daughter ?
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics ?
Mendel said that the characteristics or traits of organisms are carried from one generation to the next by internal factors which occur in pairs. What is the modern name for these factors ?
Write the names of at least three inorganic molecules which helped in the origin of life on the earth.
The forelimbs of a frog, a bird and a man show the same basic design (or basic structure) of bones. What name is given to such organs ?
Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species ?
In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.
Does geographical isolation of individual of a species lead to formation of a new species? Provide a suitable explanation.
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better body design’ why or why not ?
Give an example of body characteristics used to determine how close two species are in terms of evolution and explain it. [All India]
Name one reptile in each case where higher incubation temperature leads to the development of : (a) male progeny, (b) female progeny.
What do the following symbols used in the topic on heredity represent ?
(a) TT
(b) tt
(c) XX
(d) XY
(a) What is the genotype of dwarf plants which always produced dwarf offspring ?
(b) What is the genotype of tall plants which always produced tall offspring ?
(c) What is the genotype of
(a) What do you understand by the term ‘variation’ ?
(b) Name two human traits which show variation.
Do genetic combination of mothers play a significant role in determining the sex of new born?
Can the wing of butterfly and the wing of a bat be considered homologous organs ? Why or why not ?
Who provided the evidence of DNA as the genetic material? Write the names of the components of the DNA molecule.
What are fossils? What do they tell us about the process of evolution? [All India(C): All India 2011]
Give one example each of characters that are inherited and the ones that are acquired in humans. Mention the difference between the inherited and the acquired characters. [Delhi]
What are homologous organs? Can the wing of a butterfly and the wing of a bat be regarded as homologous? Why? [All India]
What is meant by the term speciation? List four factors which could lead to speciation. [Delhi]
If the trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier ?