Answers to Hands-on Pg 65-69

Objective Questions

1	A	9	D
2	B	10	D
3	B	11	A
4	A	12	D
5	D	13	C
6	B	14	B
7	B	15	C
8	A	16	C

Structured Questions

Section A

1. (a) (ii) Tall plants with coloured flowers

(b) (i) Dihybrid cross

(ii) TtCc

(d)(i)

Gametes	TC	Tc	tC	tc
tc	TtCc	Ttcc	ttCc	ttcc

(ii) A plant which is heterozygous for tallness and coloured flowers has the genotype TtCc. The plant produces four types of gametes, TC, Tc, tC and tc. When the plant is crossed with another plant which is homozygous recessive, the gametes combine at random to produce plants with TtCc, Ttcc, ttCc and ttcc as their genotypes.

(e) To obtain consistent results as pure-breeding plants are able to produce offspring which have received identical genes from the parents. When self-fertilised, they are able to produce offspring having exactly the genes they have inherited.

2. (a) (i) Genes are carried on the sex chromosomes and passed down to the next generation.

(ii) Usually are carried on the X chromosome and it mostly affects the males

(b) Bakri’s mother must be a carrier with the genotype X^HX^h in which ‘h’ is the recessive gene for haemophilia. Bakri inherits X^h from his mother and the Y chromosome from his father.

(c) One of them inherits X^H from her father and X^H from her mother. The other one inherits X^H from her father and X^h from her mother. Both are normal but genotypically, one of them is a carrier.

(d) Males are determined by the presence of the X and Y chromosomes. Sex-linked genes are absent in the Y chromosomes. Therefore, the presence of one sex-linked gene in the X chromosome will affect the male as compared to the female who

needs genes to be present in both X chromosomes for her to be affected.

(e)

Gametes	Xh	Y
XH	XHXh	XHY
Xh	Xh Xh	XhY

(f) 100%

Answers to Hands-on Pg 63-64

Aim : To illustrate Mendel’s first law using coloured buttons

Colours of buttons	Number of pairs	Trait represented by buttons
Red and red	24	Tall
Red and white	53	Tall
White and white	23	Dwarf

Discussions:

1. Red
2. Gamete
3. Tall plant. Red button represent the gene for tallness which is dominant. Therefore when it is paired with a white button which is recessive, then a tall plant is produced.  A dominant gene expresses itself even when it is in the heterozygous condition.
4. The ratio of tall : dwarf is 3:1.  This is because an organism’s characteristic is determined by a pair of genes which will separate and be carried in a gamete and the dominant gene will express itself.

Conclusion :

Mendel’s first law is illustrated by separating the buttons before pairing them again which shows that a characteristic in an organism is represented by a pair of genes. The genes will separate and each gene is carried by a gamete.

Genetics and Variations

Protein Synthesis-Transcription and Translation

Protein synthesis- Translation