Soal HOTS : Penentuan Genotipe Induk - Hereditas - Mendell

Main Ideas

The video explains how to infer parent genotypes from offspring data in Mendelian inheritance problems. The general strategy is to translate descriptions into dominant and recessive alleles, eliminate impossible crosses, and compare expected offspring with the evidence in the question.

Example 1: Round and Wrinkled Peas

• Round seeds are dominant (B); wrinkled seeds are recessive (b).
• Two round-seeded plants produce 5,674 round and 1,850 wrinkled offspring—approximately a 3:1 ratio.
• A wrinkled offspring must be bb, so each round parent must have contributed a recessive b allele. This rules out a parent with the genotype BB.
• The matching cross is Bb × Bb. It produces genotypes in a 1 BB : 2 Bb : 1 bb ratio, giving the observed 3:1 phenotype ratio.

Example 2: Plant Height and Flower Position

• The problem combines two traits:
  • T = tall; t = short
  • A = flowers in the leaf axil; a = flowers at the end of the stem
• A plant described as short with flowers at the end of the stem must be ttaa, since both traits are recessive.
• To identify the other parent, first record the traits and alleles clearly, then test candidate genotypes against the stated offspring proportion.
• The presenter uses the number of heterozygous gene pairs to estimate how many distinct gamete combinations a parent can produce: 2ⁿ, where n is the number of heterozygous pairs.
• In the described setup, a parent heterozygous for both traits (TtAa) crossed with ttaa can produce four equally likely offspring types. One is tall with flowers in the axil, so that phenotype occurs in one quarter of the offspring.

General Problem-Solving Lessons

• Convert descriptive traits into allele notation before working through a long question.
• Remember that a dominant phenotype can be either homozygous dominant or heterozygous; a recessive phenotype must be homozygous recessive.
• Use offspring ratios to test candidate parental genotypes and eliminate crosses that cannot produce the observed traits.
• For multiple traits, count heterozygous pairs to determine the number of possible gametes, then check the resulting offspring combinations.
• Organize the information first and practice these steps to make complex heredity questions easier to follow.

Speakers and Sources

• Kak Eni — biology lesson presenter, identified in the introduction.
• Bebisik Channel — the channel hosting the lesson.