principles of law of inheritance
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Mendel’s principles of inheritance
Key principles of genetics were developed from Mendel’s studies on peas.
1. Fundamental theory of heredity
Inheritance involves the passing of discrete units of inheritance, or genes, from parents to offspring.
Mendel found that paired pea traits were either dominantor recessive. When pure-bred parent plants were cross-bred, dominant traits were always seen in the progeny, whereas recessive traits were hidden until the first-generation (F1) hybrid plants were left to self-pollinate. Mendel counted the number of second-generation (F2) progeny with dominant or recessive traits and found a 3:1 ratio of dominant to recessive traits. He concluded that traits were not blended but remained distinct in subsequent generations, which was contrary to scientific opinion at the time.
Mendel didn’t know about genes or discover genes, but he did speculate that there were 2 factors for each basic traitand that 1 factor was inherited from each parent.
We now know that Mendel’s inheritance factors are genes, or more specifically alleles – different variants of the same gene. In today’s genetic language, a pure-breeding pea plant line is a homozygote – it has 2 identical copies of the same allele. An F1 cross-bred pea plant is a heterozygote – it has 2 different alleles.
2. Principle of segregation
During reproduction, the inherited factors (now called alleles) that determine traits are separated into reproductive cells by a process called meiosis and randomly reunite during fertilisation.
Mendel proposed that, during reproduction, the inherited factors must separate into reproductive cells. He had observed that allowing hybrid pea plants to self-pollinate resulted in progeny that looked different from their parents. Separation occurs during meiosis when the alleles of each gene segregate into individual reproductive cells (eggs and sperm in animals, or pollen and ova in plants).
3. Principle of independent assortment
Genes located on different chromosomes will be inherited independently of each other.
Mendel observed that, when peas with more than one trait were crossed, the progeny did not always match the parents. This is because different traits are inherited independently – this is the principle of independent assortment. For example, he cross-bred pea plants with round, yellow seeds and plants with wrinkled, green seeds. Only the dominant traits (yellow and round) appeared in the F1 progeny, but all combinations of trait were seen in the self-pollinated F2 progeny. The traits were present in a 9:3:3:1 ratio (round, yellow: round, green: wrinkled, yellow: wrinkled, green).
Key principles of genetics were developed from Mendel’s studies on peas.
1. Fundamental theory of heredity
Inheritance involves the passing of discrete units of inheritance, or genes, from parents to offspring.
Mendel found that paired pea traits were either dominantor recessive. When pure-bred parent plants were cross-bred, dominant traits were always seen in the progeny, whereas recessive traits were hidden until the first-generation (F1) hybrid plants were left to self-pollinate. Mendel counted the number of second-generation (F2) progeny with dominant or recessive traits and found a 3:1 ratio of dominant to recessive traits. He concluded that traits were not blended but remained distinct in subsequent generations, which was contrary to scientific opinion at the time.
Mendel didn’t know about genes or discover genes, but he did speculate that there were 2 factors for each basic traitand that 1 factor was inherited from each parent.
We now know that Mendel’s inheritance factors are genes, or more specifically alleles – different variants of the same gene. In today’s genetic language, a pure-breeding pea plant line is a homozygote – it has 2 identical copies of the same allele. An F1 cross-bred pea plant is a heterozygote – it has 2 different alleles.
2. Principle of segregation
During reproduction, the inherited factors (now called alleles) that determine traits are separated into reproductive cells by a process called meiosis and randomly reunite during fertilisation.
Mendel proposed that, during reproduction, the inherited factors must separate into reproductive cells. He had observed that allowing hybrid pea plants to self-pollinate resulted in progeny that looked different from their parents. Separation occurs during meiosis when the alleles of each gene segregate into individual reproductive cells (eggs and sperm in animals, or pollen and ova in plants).
3. Principle of independent assortment
Genes located on different chromosomes will be inherited independently of each other.
Mendel observed that, when peas with more than one trait were crossed, the progeny did not always match the parents. This is because different traits are inherited independently – this is the principle of independent assortment. For example, he cross-bred pea plants with round, yellow seeds and plants with wrinkled, green seeds. Only the dominant traits (yellow and round) appeared in the F1 progeny, but all combinations of trait were seen in the self-pollinated F2 progeny. The traits were present in a 9:3:3:1 ratio (round, yellow: round, green: wrinkled, yellow: wrinkled, green).
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Mendel's law of inheritance are as follows: Law of segregation: During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene. Law of independent assortment: Genes for different traits can segregate independently during the formation of gametes.
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