Genetics by Mendel 1 ONE GENE WITH TWO ALLELES CONTROLING TWO CONTRASTING/ ALTERNATIVE FORMS OF A SPECIFIC TRAIT IS CALLED MENDELELIAN GENETICS

Introduction Genetics is the study of genes. Genetics is the study of genes. Inheritance is how traits, or characteristics, are passed on from generation to generation. Inheritance is how traits, or characteristics, are passed on from generation to generation. Chromosomes are made up of genes, which are made up of DNA. Chromosomes are made up of genes, which are made up of DNA. Genetic material (genes,chromosomes, DNA) is found inside the nucleus of a cell. Genetic material (genes,chromosomes, DNA) is found inside the nucleus of a cell. Gregor Mendel is considered “The Father of Genetics“ Gregor Mendel is considered “The Father of Genetics“  Mendel's work was not recognized until the turn of the 20th century the turn of the 20th century

Mendelian Genetics Dominant traits- traits that are expressed. Dominant traits- traits that are expressed. Recessive traits- traits that are covered up. Recessive traits- traits that are covered up. Alleles- the different forms of a characteristic. Alleles- the different forms of a characteristic. Punnett Squares- show how crosses are made. Punnett Squares- show how crosses are made. Probability- the chances/ percentages that something will occur. Probability- the chances/ percentages that something will occur. Genotype- the types of genes (Alleles) present. Genotype- the types of genes (Alleles) present. Phenotype- what it looks like. Phenotype- what it looks like. Homozygous- two of the same alleles. Homozygous- two of the same alleles. Heterozygous- two different alleles. Heterozygous- two different alleles.

Genes  Alleles - two forms of a gene (dominant & recessive)  Dominant – ‘stronger’ of two genes expressed in the hybrid; represented by a capital letter (R)  Recessive - gene that shows up less often in a cross; represented by a lower case letter (r) 4

Gregor Mendel Austrian Monk. Austrian Monk. Experimented with “pea plants”. Experimented with “pea plants”. Used pea plants because: Used pea plants because: They were available They were available They reproduced quickly They reproduced quickly They showed obvious differences in the traits They showed obvious differences in the traits Understood that there was something that carried traits from one generation to the next - “FACTOR”.

6 Gregor Mendel ( ) Father of genetics Responsible for the Laws governing Inheritance of Traits

Mendel cont…… In the mid-1800s, the rules underlying patterns of inheritance were uncovered in a series of experiments performed by an Austrian monk named Gregor Mendel.

Gregor Johann Mendel  Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea plants  He found that the plants' offspring retained traits of the parents  Called the “Father of Genetics" 8

Site of Gregor Mendel’s experimental garden in the Czech Republic 9

Mendel's Plant Breeding Experiments Gregor Mendel was one of the first to apply an experimental approach to the question of inheritance. For seven years, Mendel bred pea plants and recorded inheritance patterns in the offspring. Particulate Hypothesis of Inheritance Parents pass on to their offspring separate and distinct factors (today called genes) that are responsible for inherited traits.

Mendel’s Pea Plant Experiments 11

Why peas, Pisum sativum?  Can be grown in a small area  Produce lots of offspring  Produce pure plants when allowed to self- pollinate several generations  Can be artificially cross- pollinated 12

Reproduction in Flowering Plants  Pollen contains sperm Produced by the stamen Produced by the stamen  Ovary contains eggs Found inside the flower Found inside the flower 13 Pollen carries sperm to the eggs for fertilisation Self-fertilisation can occur in the same flower Cross-fertilisation can occur between flowers

Mendel’s Experimental Methods  Mendel hand-pollinated flowers using a paintbrush He could snip the stamens to prevent self-pollination He could snip the stamens to prevent self-pollination Covered each flower with a cloth bag Covered each flower with a cloth bag  He traced traits through the several generations 14

15 How Mendel Began Mendel produced pure strains by allowing the plants to self- pollinate for several generations

Mendel was fortunate he chose the Garden Pea Mendel probably chose to work with peas because they are available in many varieties. The use of peas also gave Mendel strict control over which plants mated. Fortunately, the pea traits are distinct and were clearly contrasting.

To test the particulate hypothesis, Mendel crossed true- breeding plants that had two distinct and contrasting traits—for example, purple or white flowers. What is meant by “true breeding?” Mendel cross-fertilized his plants by hand. Why is it important to control which plants would serve as the parents?

For each monohybrid cross, Mendel cross-fertilized true-breeding plants that were different in just one character—in this case, flower color. He then allowed the hybrids (the F1 generation) to self-fertilize.

Typical breeding experiment P generation (parental generation) F1 generation (first filial generation, the word filial from the Latin word for "son") are the hybrid offspring. Allowing these F1 hybrids to self-pollinate produces: F2 generation (second filial generation). It is the analysis of this that lead to an understanding of genetic crosses.

Eight Pea Plant Traits WITH THEIR CONTRASTING ALLELES  Seed shape --- Round (R) or Wrinkled (r)  Seed Colour ---- Yellow (Y) or Green ( y )  Pod Shape --- Smooth (S) or wrinkled ( s )  Pod Colour --- Green (G) or Yellow (g)  Seed Coat Colour ---Gray (G) or White (g)  Flower position---Axial (A) or Terminal (a)  Plant Height --- Tall (T) or Short (t)  Flower colour --- Purple (P) or white ( p ) 20

Mendel studies seven characteristics in the garden pea

: Statistics indicated a pattern.

23  Mendel stated that physical traits are inherited as “particles”  Mendel did not know that the “particles” were actually Chromosomes & DNA Particulate Inheritance

Genetic Terminology  Trait - any characteristic that can be passed from parent to offspring  Heredity - passing of traits from parent to offspring  Genetics - study of heredity 24

Types of Genetic Crosses  Monohybrid cross - cross involving a single trait e.g. flower colour  Dihybrid cross - cross involving two traits e.g. flower colour & plant height 25

Punnett Square Used to help solve genetics problems 26

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More Terminology  Genotype - gene combination for a trait (e.g. RR, Rr, rr)  Phenotype - the physical feature resulting from a genotype (e.g. red, white) 28

Genotype & Phenotype in Flowers 29 Genotype of alleles: R = red flower r = yellow flower All genes occur in pairs, so 2 alleles affect a characteristic Possible combinations are: GenotypesRR Rrrr PhenotypesRED RED YELLOW

Genotypes  Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure  Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure  Heterozygous genotype - gene combination of one dominant & one recessive allele (e.g. Rr); also called hybrid 30

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33 Mendel’s Experimental Results

Did the observed ratio during the experiments match the theoretical ratio? 34 The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled Mendel’s observed ratio was 2.96:1 The discrepancy is due to statistical error The larger the sample the more nearly the results approximate to the theoretical ratio (see seed colour)

Generations  Parental P 1 Generation = the parental generation in a breeding experiment.  F 1 generation = the first-generation offspring in a breeding experiment. (1st filial generation) From breeding individuals from the P 1 generation From breeding individuals from the P 1 generation  F 2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation) From breeding individuals from the F 1 generation From breeding individuals from the F 1 generation 35

Following the Generations 36 Cross 2 Pure Plants TT x tt Results in all Hybrids Tt Cross 2 Hybrids get 3 Tall & 1 Short TT, Tt, tt

Monohybrid Crosses 37

P 1 Monohybrid Cross  Trait: Seed Shape  Alleles: R – Roundr – Wrinkled  Cross: Round seeds x Wrinkled seeds  RR x rr 38 R R rr Rr Genotype:Rr Genotype: Rr PhenotypeRound Phenotype: Round Genotypic Ratio:All alike Genotypic Ratio: All alike Phenotypic Ratio: All alike F1F1

P 1 Monohybrid SUMMARY  Homozygous dominant x Homozygous recessive  Offspring all Heterozygous (hybrids)  Offspring called F 1 generation  Genotypic & Phenotypic ratio is ALL ALIKE 39

F 1 Monohybrid Cross  Trait: Seed Shape  Alleles: R – Roundr – Wrinkled  Cross: Heterozygous Round seeds x Round seeds  Rr x Rr 40 R r rR RR rrRr Genotype:RR, Rr, rr Genotype: RR, Rr, rr PhenotypeRound & wrinkled Phenotype: Round & wrinkled G.Ratio:1:2:1 G.Ratio: 1:2:1 P.Ratio: 3:1 F2F2

F 1 Monohybrid SUMMARY  Heterozygous x heterozygous  Offspring: 25% Homozygous dominant RR 50% Heterozygous Rr 25% Homozygous Recessive rr  Offspring called F 2 generation  Genotypic ratio is 1:2:1  Phenotypic Ratio is 3:1 41

42 What Do the Peas Look Like?

…And Now the Test Cross  Mendel then crossed a pure & a hybrid from his F 2 generation  This is known as an F 2 or test cross  There are two possible test crosses: Homozygous dominant x Hybrid Homozygous recessive x Hybrid 43

F 2 Monohybrid Cross (1 st )  Trait: Seed Shape  Alleles: R – Roundr – Wrinkled  Cross: Round seeds x Round seeds  RR x Rr 44 R R rR RR RrRR Rr Genotype:RR, Rr Genotype: RR, Rr PhenotypeRound Phenotype: Round Genotypic Ratio:1:1 Genotypic Ratio: 1:1 Phenotypic Ratio: All alike

F 2 Monohybrid Cross (2nd)  Trait: Seed Shape  Alleles: R – Roundr – Wrinkled  Cross: Wrinkled seeds x Round seeds  rr x Rr 45 r r rR Rr rrRr rr Genotype:Rr, rr Genotype: Rr, rr PhenotypeRound & Wrinkled Phenotype: Round & Wrinkled G. Ratio:1:1 G. Ratio: 1:1 P.Ratio: 1:1

F 2 Monohybrid SUMMARY  Homozygous x heterozygous(hybrid)  Offspring: 50% Homozygous RR or rr 50% Heterozygous Rr  Phenotypic Ratio is 1:1  Called Test Cross because the offspring have SAME genotype as parents 46

Practice Your Crosses Work the P 1, F 1, and both F 2 Crosses for each of the other Seven Pea Plant Traits 47

Genetic traits in humans can be tracked through family pedigrees The inheritance of many human traits follows Mendel’s principles and the rules of probability Figure 9.8A

Family pedigrees are used to determine patterns of inheritance and individual genotypes Figure 9.8B Dd Joshua Lambert Dd Abigail Linnell D_ Abigail Lambert Female Dd Elizabeth Eddy D_ John Eddy ?D_ Hepzibah Daggett ? ? ddDd ddDd Male Deaf Hearing dd Jonathan Lambert

Genetic Practice Problems 50

Breed the P 1 generation tall (TT) x dwarf (tt) pea plants 51 T T tt

Solution: 52 T T tt Tt All Tt = tall (heterozygous tall) produces the F 1 generation tall (TT) vs. dwarf (tt) pea plants

Breed the F 1 generation tall (Tt) vs. tall (Tt) pea plants 53 T t Tt

Solution: 54 TT Tt tt T t Tt produces the F 2 generation 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt 1:2:1 genotype 3:1 phenotype 3:1 phenotype tall (Tt) x tall (Tt) pea plants