Mendelian Genetics The Laws of Inheritance By Lisa
Mendelian Genetics: The Laws of Inheritance By Lisa Marie Meffert, Ph. D Morpho plelides Mark T. Hark, MD Bio. Ed. Online Bio. Ed
Mendel’s Research on Particulate Inheritance n n n Made pure breeding (parental) lines for different phenotypes of pea plants: n Plant height (tall vs. short) n Pea color (green vs. yellow) n Pea texture (round vs. wrinkled), etc. Gregor Mendel Crossed the pure lines to get F 1 generation n All of the F 1 individuals looked the same Crossed F 1 lines to get F 2 generation n ¾ of the F 2 individuals looked like one of the parental lines n ¼ of the F 2 individuals looked like the other parental line Pisum sativum Bio. Ed Online www. Bio. Ed. Online. org
Working out Mendelian Genetics n n n A Punnet square is bookkeeping tool. The allele is the specific form of hereditary particle passed on through male or female gametes. Allele capital letter T confers tallness. In this case, the tall parental line has all T’s. Allele lower case letter t confers shortness. The short parental line has all t’s. Cross a tall male with a short female. Bio. Ed Online www. Bio. Ed. Online. org
Crossing the Parental Lines: Male Contribution n First, the male passes on his alleles, one per gamete (reproductive cell). Bio. Ed Online www. Bio. Ed. Online. org
Crossing the Parental Lines: Female Contribution n Then, the female passes on her alleles, one per egg. Crossing these two parents yields all Tt offspring. Since T is dominant to t, all of the offspring are tall pea plants. Bio. Ed Online www. Bio. Ed. Online. org
Crossing the F 1 Generation n Crossing two homozygous individuals, TT and tt, yields all heterozygous offspring, Tt. This generation is referred to as F 1. Now, cross two individuals from the F 1 generation (Tt x Tt). First, the male pea plant passes on its alleles, one per gamete. Bio. Ed Online www. Bio. Ed. Online. org
Crossing the F 1 Generation n Now, the female passes on her alleles, one per egg. Genotypes of the F 1 n ¼ of the offspring are TT. n ½ of the offspring are heterozygotes (one T and one t). n ¼ of the offspring are tt. Phenotypes of the F 1 n ¾ are tall (at least one T). n ¼ are short (homozygous for t). Bio. Ed Online www. Bio. Ed. Online. org
Moving On to Two Traits at a Time n n n Keep T and t for tall and short plants, respectively. Add R and r for round and wrinkled seeds, respectively. A double heterozygote male produces four types of gametes. Bio. Ed Online www. Bio. Ed. Online. org
Cross with a Female Double Heterozygote n A double heterozygote female produces four types of eggs. Bio. Ed Online www. Bio. Ed. Online. org
Crossing the Double Heterozygotes n The male passes on his alleles, two per gamete. Bio. Ed Online www. Bio. Ed. Online. org
Crossing the Double Heterozygotes n The female passes on her alleles, two per egg. Bio. Ed Online www. Bio. Ed. Online. org
Double Heterozygote Cross: Assessing the Resultant Genotypes n n n At least one T yields tall stature. At least one R yield round seeds. Thus, there are 9 ways (gray) to produce tall, round -seeded offspring. Bio. Ed Online www. Bio. Ed. Online. org
Double Heterozygote Cross: Assessing the Resultant Genotypes n n n Again, at least one T yields tall stature. And one R is required for round seeds, so rr must produce wrinkled seeds. Thus, there are 3 ways (lighter gray) to produce tall, wrinkly seeded offspring Bio. Ed Online www. Bio. Ed. Online. org
The Third Phenotype in a Double Heterozygote Cross n n n Two t alleles yield short stature. At least one R produces round seeds. Thus, there are 3 ways (lightest gray) to produce short offspring with round seeds. Bio. Ed Online www. Bio. Ed. Online. org
The Fourth Phenotype in a Double Heterozygote Cross n n n Two t alleles yield short stature. Two r alleles produce wrinkled seeds. There is only 1 way to produce short offspring with wrinkled seeds. Bio. Ed Online www. Bio. Ed. Online. org
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