(a) List any two pairs of visible contrasting characters of garden pea plants used by Mendel for his experiments stating the dominant and recessive characters in each pair. OR (b) In human beings, the probability of getting a male or a female child is $50\%$. Explain with the help of a flow diagram only.

Option (a)

Two pairs of visible contrasting characters of garden pea plants used by Mendel:

1. Plant Height:

• Dominant character: Tall ($T$)
• Recessive character: Short/Dwarf ($t$)

1. Seed Shape:

• Dominant character: Round ($R$)
• Recessive character: Wrinkled ($r$)

(Other valid pairs include: Flower colour - Violet (Dominant) / White (Recessive))

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Option (b)

In human beings, the sex of a child is determined genetically. Females have a perfect pair of sex chromosomes ($XX$), while males have a mismatched pair ($XY$).

#### Flow Diagram of Sex Determination in Human Beings:

``diagram {"xrange": [-1.0, 1.0], "yrange": [-13.44, 1.44], "lines": [{"from": [0.0, 0.0], "to": [0.0, -3.0], "label": ""}, {"from": [0.0, -3.0], "to": [0.0, -6.0], "label": ""}, {"from": [0.0, -3.0], "to": [0.0, -9.0], "label": ""}, {"from": [0.0, -6.0], "to": [0.0, -12.0], "label": ""}, {"from": [0.0, -9.0], "to": [0.0, -12.0], "label": ""}], "points": [{"x": 0.0, "y": 0.0, "label": "Parents: Father (XY) x Mother (XX)"}, {"x": 0.0, "y": -3.0, "label": "Gametes: Sperm [X] or [Y] | Egg [X]"}, {"x": 0.0, "y": -6.0, "label": "Sperm [X] + Egg [X] -> XX (Female Child)"}, {"x": 0.0, "y": -9.0, "label": "Sperm [Y] + Egg [X] -> XY (Male Child)"}, {"x": 0.0, "y": -12.0, "label": "Probability: 50% Girl (XX) : 50% Boy (XY)"}]} ``

Explanation:

• The mother produces only one type of gamete (egg) containing the $X$ chromosome.
• The father produces two types of gametes (sperm): $50\%$ carry the $X$ chromosome and $50\%$ carry the $Y$ chromosome.
• Fertilization of an $X$-egg by an $X$-sperm results in a female child ($XX$).
• Fertilization of an $X$-egg by a $Y$-sperm results in a male child ($XY$).
• Thus, the probability of getting a male or a female child is exactly $1:1$ or $50\%$.