Prepared By:Montalbo, Daniel Justin B.De Castro, Ralph Louis R.
Mendel’s Law of Segregation states that there are two alleles for every gene determining a specific characteristic, and these alleles are segregated into separate gametes during reproduction. When the 2 different alleles occur together in one individual (heterozygote), the dominant allele will be the one that is expressed in the phenotype of the individual. The Law of Addition is used to combine probabilities, when there are 2 or more ways to arrive at a given outcome. The Law of Multiplication is used to combine probabilities of 2 or more different events that need to occur in combination. Mendel’s Law of Independent Assortment says that 2 or more different genes, if found on separate chromosomes, are determined independently of each other. Many characteristics have been found to follow patterns of inheritance that are modifications of Mendel’s rules.
• pure • forked line• gene breeding • polygenes• allele • hybrid • contributor• dominant • homozygous y allele• recessive • heterozygous • non- contributor• character • P (parental y allele generation)• trait • continuous • F1 (first filial variation• phenotyp generation) • discontinuo e • F2 (second us variation• genotype filial generation) • Punnett
CHARACTERS TRAITS• Pre-Mendel beliefs in genetics: blending theory• Augustinian monk and science teacher• Why Pisum sativum? – Pea plants available in many varieties • character (heritable feature) • trait (character variant) – Perfect flowers • cross-pollination and self-pollination – Short generation time – Many offspring
MONOHYBRID CROSSinheritance of a single trait P Generation (true-breeding x parents) Purple White flowers flowers F1 Generation (hybrids) All plants had purple flowers self-pollination F2 Generation 705 plants 224 plants
Allele for purple flowers Alternative versions of genes exist Homologous (alleles)Locus for flower-color gene pair of › Dominant chromosomes › Recessive Organism inherites Allele for white flowers 2 alleles › Dominant is fully expressed › Recessive has no visible effect Law of segregation › 2 alleles for one character separate and go to different gametes
True-breeding plants have identical P Generationalleles. x Purple flowers White flowersGametes each contain only one allele PP ppfor the flower-color gene. Every gamete Appearance:produced by one parent has the same allele. Genetic makeup: P p Gametes:F1 hybrids have a Pp combination.Purple-flower allele is dominant, F1 Generationall hybrids have purple flowers. Purple flowersHybrid plants produce gametes, Appearance: Genetic makeup: Pptwo alleles segregate: half thegametes receiving the P allele and 1 /2 P 1 /2 p Gametes:the other half the p allele.Punnett square: shows all possible F1 spermcombinations of alleles in offspring P pfrom an F1 x F1 (Pp x Pp) cross. F2 Generation PEach square represents an equally probable PP Ppproduct of fertilization. F1 eggs p Pp ppRandom combination of the gametesresults in the 3:1 ratio that Mendel 3 :1observed in the F2 generation.
• Homozygous – identical alleles, true-breeding• Heterozygous – different alleles• Phenotype – physical appearance• Genotype – genetic make- up
APPLICATIONAn organism displaying the dominant phenotype can either Xbe homozygous or heterozygous for the trait. A test-cross willhelp determine which. Dominant phenotype, Recessive phenotype, unknown genotype: known genotype: TECHNIQUE PP or Pp? pp The individual with the unknown genotype is crossed with a homozygous individual expressing the recessive trait (white flowers in this example). By observing the If Pp, If PP, phenotypes of the offspring resulting from this then 1⁄2 offspring purple then all offspring cross, we can deduce the genotype of the purple-flowered purple: and 1⁄2 offspring white: parent. p p p p RESULTS P P Pp Pp Pp Pp P p Pp Pp pp pp
Illustrates the inheritance of two characters Produces four phenotypes in the F2 generation Law of Addition - combines probabilities for mutually exclusive events The Law of Multiplication - combines probabilities of 2 or more independent events that need to occur together
1. Codominance – two dominant alleles affect phenotype in separate ways – both alleles manifest – e.g. roan coloring in horses – both red and white2. Incomplete dominance – phenotype of offspring is between phenotypes of two parents – e.g. red and white parents give rise to pink offspring3. Multiple alleles – genes with more than two alleles that control the phenotype – e.g. ABO blood type system has 3 alleles--A,B,i. A and B are codominant, i is recessive to both