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#	Question	Answer
1	What topics are examined in this unit?	Structure and function of DNA, and the story and theory of evolution.
2	Which branch of biology deals with inheritance and variation?	Genetics.
3	During which period did humans recognize that sexual reproduction causes variation?	Around 8000–1000 B.C.
4	Who conducted hybridisation experiments on garden peas?	Gregor Mendel.
5	What is a true-breeding line?	A line that shows stable trait inheritance and expression after continuous self-pollination for several generations.
6	Which plants did Mendel cross in his monohybrid experiment?	Tall pea plants and dwarf pea plants.
7	What are the possible allele combinations for height in pea plants?	TT, Tt, and tt.
8	What is phenotype?	The observable expression of a trait, such as tall or dwarf.
9	Why are capital and small letters used for alleles?	To represent dominant and recessive forms of the same gene.
10	What is a monohybrid cross?	A cross between TT and tt involving one character.
11	Which allele is present in gametes of tall TT plants?	T allele.
12	Who developed the Punnett Square?	Reginald C. Punnett.
13	What proportion of fertilisations produce tt genotype?	1/4.
14	What is a test cross?	A cross between an organism showing dominant phenotype and a recessive parent to determine genotype.
15	State the second point of the Law of Dominance.	Factors occur in pairs.
16	Which plant is used as an example of incomplete dominance?	Snapdragon (Antirrhinum sp.).
17	How many copies of each gene are present in diploid organisms?	Two copies.
18	When are two alleles considered equivalent?	When both produce the same phenotype.
19	What is present on the plasma membrane of red blood cells in ABO blood groups?	Sugar polymers.
20	Why can multiple alleles be observed only at the population level?	Because an individual can possess only two alleles at a time.
21	What is the seed shape of bb seeds after maturation?	Wrinkled.
22	How is the 9:3:3:1 ratio derived?	By combining 3:1 ratio for seed shape with 3:1 ratio for seed colour.
23	What proportion of gametes carries allele R?	50 percent.
24	What are the four types of gametes produced by RrYy plants?	RY, Ry, rY, and ry.
25	What important similarity exists between chromosomes and genes?	Both occur in pairs and segregate during gamete formation.
26	What did Sutton and Boveri conclude from chromosome behaviour?	Pairing and separation of chromosomes lead to segregation of factors (genes).
27	Why was Drosophila melanogaster suitable for genetic studies?	It could be grown easily in the laboratory on simple synthetic medium.
28	What type of crosses did Morgan perform in Drosophila?	Dihybrid crosses involving sex-linked genes.
29	What is linkage?	Physical association of genes on the same chromosome.
30	Which gene pair in Drosophila showed 37.2% recombination?	White and miniature wing genes.
31	Which scientist carried out several dihybrid crosses in Drosophila?	Thomas Hunt Morgan.
32	What did Morgan discover about genes located on the same chromosome?	Some genes are tightly linked while others are loosely linked.
33	Who used recombination frequency to map genes?	Alfred Sturtevant.
34	Why does Cross A show stronger linkage?	Because recombination frequency is lower.
35	What are polygenic traits?	Traits controlled by three or more genes.
36	Which alleles are responsible for dark skin colour?	Dominant alleles A, B, and C.
37	What is pleiotropy?	A condition where a single gene affects multiple phenotypic traits.
38	What are the phenotypic effects of phenylketonuria?	Mental retardation and reduced hair and skin pigmentation.
39	In XO sex determination, what types of sperm are produced?	Some with X chromosome and some without X chromosome.
40	Which organism is an example of XO type sex determination?	Grasshopper.
41	Which organisms are mentioned as having XY sex determination?	Humans and Drosophila.
42	Which organisms are examples of male heterogamety?	Humans and Drosophila.
43	What is the sex determining mechanism in humans?	XY type.
44	What determines the sex of a child in humans?	Genetic makeup of the sperm.
45	What is the chromosome number in female honey bees?	Diploid, 32 chromosomes.
46	Besides recombination, what else produces variation in DNA?	Mutation.
47	What are frame-shift mutations caused by?	Insertions or deletions of DNA base pairs.
48	Why are controlled crosses not possible in humans?	Ethical and biological limitations.
49	Into which two categories are genetic disorders broadly classified?	Mendelian disorders and chromosomal disorders.
50	Can Mendelian disorders be dominant or recessive?	Yes.
51	What is the frequency of colour blindness in males?	About 8 percent.
52	Under what condition can a daughter become colour blind?	If the mother is a carrier and the father is colour blind.
53	Why is haemophilia rare in females?	The mother must be a carrier and the father haemophilic.
54	What is the probability that a carrier parent transmits the mutant HbS gene?	50 percent.
55	What type of inheritance does phenylketonuria show?	Autosomal recessive inheritance.
56	Why are phenylalanine derivatives excreted in urine?	Due to poor absorption by the kidney.
57	What is the main effect of abnormal globin synthesis in thalassemia?	Formation of abnormal haemoglobin causing anaemia.
58	What happens when more α-globin genes are affected?	Fewer alpha globin molecules are produced.
59	How does thalassemia differ from sickle-cell anaemia?	Thalassemia is a quantitative defect, while sickle-cell anaemia is a qualitative defect.
60	How many chromosomes are present in a normal human cell?	46 chromosomes.
61	Who first systematically studied inheritance?	Gregor Mendel.
62	Do characters blend in heterozygous condition according to Mendel?	No, characters do not blend.
63	What is genotype?	Genetic constitution or factors controlling characters.
64	What are sex-linked genes?	Genes linked to sex chromosomes.
65	What are the sex chromosomes in female birds?	ZW.
66	What causes polyploidy?	Increase in a whole set of chromosomes.
67	Which organism did T.H. Morgan use for genetics experiments?	Drosophila melanogaster.