The document discusses Gregor Mendel's experiments with pea plants to study genetic inheritance. It defines key terms like alleles, genes, loci, genotype, and phenotype. It describes Mendel's pea plants and the seven traits he studied. Mendel performed crosses between pea plants and found that the traits in the offspring (F2 generation) followed a consistent ratio, around 3 dominant to 1 recessive for each trait.

1. CHAPTER 2: GENETIC INHERITANCE

2. Concept review… Genetic inheritance Terms & concepts Mendel’s experiment Pisum sativum – garden pea Monohybrid crosses Dihybrid crosses Law of segregation Law of independent assortment Deviation from Mendel’s Law Codominance Incomplete dominance Multiple allele Polygene Lethal allele Linked gene Genetic mapping Pedigree analysis

3. Important terms… allele genes locus genotype phenotype dominant recessive homozygous heterozygous true-breed

4. OBJECTIVE Define terminologies used in genetic inheritance. Describe the characteristics of Mendel’s pea plants.

5. Terms used in genetic inheritance Alleles: all the different molecular forms of the same genes Genes: units of information about specific traits and they are passed from parents to offspring/ small section of DNA that codes for a particular protein. Cells with a diploid chromosome number (2n) have pairs of genes, on pairs of homologous chromosomes.

6. Locus Each gene has a specific location locus on a chromosome . P Q p q

7. There are two loci , one is for flower color and the other is for stem length

8. Two terms help keep the distinction clear between genes and the traits they specify. Genotype Particular genes and individual carries / the genes that an organism inherits from its mother and father. Phenotype An individual’s observable traits/ the protein used by these genes that determine the organism’s physical characteristic. Eg: Phenotype : tall Genotype : TT @ Tt

9. An allele is said to be dominant when its effect on a trait masks that of any recessive allele paired with it. We used capital letters for dominant alleles and lowercase letters for the recessive one. Example, A and a. So, the homozygous dominant has a pair of dominant alleles (AA), homozygous recessive has a pair of recessive alleles (aa) and heterozygous has a pair of non-identical allele (Aa).

10. True-breed @ pure-breed Organisms that are homozygous for any given genotype and therefore pass it on to all their progeny in a cross with a similar homozygote

11. P : parental generation F1 : first-generation offspring F2 : second-generation offspring

12. TYPES OF CROSSES Test cross A cross between a recessive homozygous and an organism of dominant phenotype , but unknown genotype. If an organism displays a dominant characteristic, it may possess 2 dominant alleles (homologous) or a dominant and recessive allele for that characteristic (heterozygous) To find out which in the case, the organism is crossed with one displaying the recessive characteristic. If all the offspring show the dominant characteristic then the organism is homozygous, but if half show the recessive characteristic, then the organism is heterozygous.

13. Self cross Male and female from the same plants /generation Back cross A mating between individuals of the parental generation (P) and the first generation (F1) in order to identify hidden recessive alleles.

14. Reciprocal cross A cross reversing the roles of males and females to confirm the results obtained from an earlier cross. For example, if a pollen (male) from tall plants in transferred to the stigma (female) of dwarf plants in one cross, the reciprocal cross would use the pollen of dwarf plants to pollinate the stigmas of tall plants.

15. P : X b X b x X B Y color blind normal G : X b X b X B Y F1 : X B X b X B X b X b Y X b Y EARLIER CROSS B – normal b – color blind normal female Color blind male Phenotype ratio : 1 normal : 1 color blind

16. P : X B X B x X b Y normal color blind G : X B X B X b Y F1 : X B X b X B X b X B Y X B Y RECIPROCAL CROSS Female carrier Normal male Phenotypic ratio : All normal

17. Mendel’s Experiment Gregor Mendel studied the inheritance of characteristics in garden peas ( Pisum sativum ). He chose peas because : they were easy to grow they had a short life cycle their pollination could be controlled they have easily observable characteristics .

18. He studied 7 characteristics, each of which has two contrasting alternatives. seed shape : round / wrinkled seed color : yellow / green pod shape : inflated / constricted pod color : yellow / green flower color : purple / white flower position : axial / terminal plant height : tall / dwarf

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20. Mendel’s Experimental Result Character Dominant vs F 2 Ratio recessive Seed shape R x r 5474 : 1850 2.96 :1 Seed color Y x y 6022 : 2001 3.01 :1 Flower color P x p 705:224 3.15 : 1 Pod shape I x i 882:299 2.95 : 1 Pod color G x g 428:152 2.82 : 1 Flower position A x a 651:207 3.14 : 1 Plant height T x t 787:277 2.84 : 1

21. It shows 7 characters studied in garden pea crosses and the data obtained. F 2 generation showed close to 3:1 ratio of characteristics.