Heredity And Mendel's First Law

Übersicht

Why does a black bull crossed with a black cow sometimes throw a red calf. Why do two hornless goats occasionally produce a horned kid. The answer is not chance: it is heredity, the orderly passing of traits from parent to offspring, and it follows rules precise enough to predict on paper before a single mating takes place.

In this lesson you will learn the vocabulary breeders and examiners share: gene, allele, dominant, recessive, genotype and phenotype. You will then meet Mendel's first law, the law of segregation, and use it to solve monohybrid cross problems on real farm traits, coat colour and the polled condition, working out exactly what a planned mating is likely to produce.

Ziele

  1. Define heredity
  2. State Mendel's first law of inheritance
  3. Explain the terms gene, allele, dominant and recessive
  4. Solve a simple monohybrid cross problem using Mendel's first law
  5. Explain the application of Mendel's first law to animal breeding

Lektionshinweis

A herder in Sokoto mates a black bull with a black cow, and one calf is red. A goat farmer near Abeokuta mates two hornless does, and still gets a horned kid. Neither is unlucky: both outcomes are exactly what heredity predicts, and a breeder who understands the rule can say, before the mating, roughly how many of each type to expect.

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  1. In cattle, black coat colour (B) is dominant over red coat colour (b). What is the phenotype of an animal with genotype Bb? A. Red B. Black C. A mixture of red and black D. Cannot be determined Answer: B
  2. The actual pair of alleles an animal carries for a gene is called its: A. Phenotype B. Genotype C. Allele D. Chromosome Answer: B
  3. Mendel's first law states that: A. Genes for different traits assort independently B. The two alleles of a gene separate during gamete formation C. Dominant alleles always outnumber recessive alleles D. Offspring always resemble one parent exactly Answer: B
  4. Two heterozygous polled goats (Pp) are mated. What phenotype ratio is expected among the offspring? A. 1 polled : 1 horned B. 1 polled : 3 horned C. 3 polled : 1 horned D. All polled Answer: C
  5. An animal carrying two identical alleles for a gene, such as BB, is described as: A. Heterozygous B. Homozygous C. Recessive D. Hybrid Answer: B