Mendel’s Legacy 9.1

Background on Gregor Mendel: Austrian monk Austrian monk Studied science & math at the University of Vienna Studied science & math at the University of Vienna Formulated the Laws of Heredity in the early 1860's Formulated the Laws of Heredity in the early 1860's Did a statistical study of traits in garden peas over an eight year period

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

Genetics - study of heredity Traits – any characteristic that can be passed from parent to offspring Traits – any characteristic that can be passed from parent to offspring E.g. height, eye color E.g. height, eye color Heredity – passing of traits from parent to offspring Heredity – passing of traits from parent to offspring

Pollination – when pollen grains which contain sperm are produced in the male reproductive parts anther of a flower are transferred to the female reproductive part stigma which holds the ovary where the eggs are Pollination – when pollen grains which contain sperm are produced in the male reproductive parts anther of a flower are transferred to the female reproductive part stigma which holds the ovary where the eggs are Ovary

Self-pollination – pollination of same flower or flower on same plant Self-pollination – pollination of same flower or flower on same plant Cross-pollination – involves 2 separate plants Cross-pollination – involves 2 separate plants Types of pollination:

Mendel’s experiments Pure plants always produce offspring with that trait Pure plants always produce offspring with that trait A strain refers to plants that are pure for a specific trait e.g. all having yellow flower A strain refers to plants that are pure for a specific trait e.g. all having yellow flower P 1 generation – each parental strain P 1 generation – each parental strain

Terms to know Genotype - gene combination for a trait (e.g. RR, Rr, rr) Genotype - gene combination for a trait (e.g. RR, Rr, rr) Phenotype - the physical feature resulting from a genotype (e.g. tall, short) Phenotype - the physical feature resulting from a genotype (e.g. tall, short) The trait that is expressed or shows) The trait that is expressed or shows) Gene – segment of DNA on a chromosome that controls a particular hereditary trait Gene – segment of DNA on a chromosome that controls a particular hereditary trait Allele – each alternative form of a gene (paired) Allele – each alternative form of a gene (paired)

Alleles – are two forms of a gene (dominant & recessive) Alleles – are two forms of a gene (dominant & recessive) Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R) 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 lowercase letter (r) Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r) More terms

Mendel cross-pollinated two strains and tracked each trait through two generations (e.g. TT x tt ) The offspring of this cross were all hybrids showing only the dominant trait & were called the First Filial or F1 generation Trait - plant height Trait - plant height Alleles - T tall, t short Alleles - T tall, t short P 1 cross TT x tt genotype -- Tt tt phenotype -- Tall TTtTt genotypic ratio --all alike TTtTt phenotypic ratio- all alike alike

He cross-pollinated F 1 generation – (first filial) offspring of P1 F 1 generation – (first filial) offspring of P1 Hybrid - only showing the dominant trait Hybrid - only showing the dominant trait (filial means having or assuming the relation of a child or offspring) (filial means having or assuming the relation of a child or offspring) Plants allowed to cross-pollinate produced F 2 generation – offspring of F 1 Plants allowed to cross-pollinate produced F 2 generation – offspring of F 1

Mendel then crossed two of his F1 plants and tracked their traits; known as an F1 cross Trait - plant height Trait - plant height Alleles - T tall, t short Alleles - T tall, t short F 1 cross Tt x Tt genotype -- TT, Tt, tt Tt phenotype -- Tall & short TTTTt genotypic ratio --1:2:1 tTttt phenotypic ratio- 3:1

When 2 hybrids were crossed, 75% (3/4) of the offspring showed the dominant trait & 25% (1/4) showed the recessive trait; always a 3:1 ratio When 2 hybrids were crossed, 75% (3/4) of the offspring showed the dominant trait & 25% (1/4) showed the recessive trait; always a 3:1 ratio The offspring of this cross were called the F2 generation The offspring of this cross were called the F2 generation

50% (1/2) of the offspring in a test cross showed the same genotype of one parent & the other 50% showed the genotype of the other parent; always a 1:1 ratio Trait - Plant Height Alleles - T tall, t short F 2 cross TT x Tt F 2 cross tt x Tt Tt Tt TTTTt tTttt TTTTt tTttt genotype - TT, Tt genotype - TT, Tt genotype - tt, Tt phenotype - Tall phenotype - Tall phenotype - Tall & short phenotype - Tall & short genotypic ratio - 1:1 genotypic ratio - 1:1 phenotypic ratio – all alike phenotypic ratio – all alike phenotypic ratio - 1:1 phenotypic ratio - 1:1

Mendel then crossed a pure & a hybrid from his F2 generation; known as an F2 or test cross Why???

16 Test Cross A mating between an individual of unknown genotype and a homozygous recessive (bb) individual will give info on the unknown genotype. Example: bbC__ x bbcc BB = brown eyes Bb = brown eyes bb = blue eyes CC = curly hair Cc = curly hair cc = straight hair bCb___bc

Problems: Work the P1, F1, and both F2 crosses for all of the other pea plant traits & be sure to include genotypes, phenotypes, genotypic & phenotypic ratios Mendel's traits included: Mendel's traits included: a. Seed shape --- Round (R) or Wrinkled (r) b. Seed Color ---- Yellow (Y) or Green (y) c. Pod Shape --- Smooth (S) or wrinkled (s) d. Pod Color --- Green (G) or Yellow (g) e. Seed Coat Color --- Gray (G) or White (g) f. Flower position --- Axial (A) or Terminal (a) g. Plant Height --- Tall (T) or Short (t) h. Flower color --- Purple (P) or white (p) a. Seed shape --- Round (R) or Wrinkled (r) b. Seed Color ---- Yellow (Y) or Green (y) c. Pod Shape --- Smooth (S) or wrinkled (s) d. Pod Color --- Green (G) or Yellow (g) e. Seed Coat Color --- Gray (G) or White (g) f. Flower position --- Axial (A) or Terminal (a) g. Plant Height --- Tall (T) or Short (t) h. Flower color --- Purple (P) or white (p)

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Law of Segregation - states that each genetic trait is produced by a pair of alleles which separate (segregate) during reproduction states that each genetic trait is produced by a pair of alleles which separate (segregate) during reproduction Rr Rr

21 Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then ”recombined" at fertilization, producing the genotype for the traits of the offspring.

Law of Independent Assortment states that each factor (gene) is distributed (assorted) randomly and independently of one another in the formation of gametes during meiosis states that each factor (gene) is distributed (assorted) randomly and independently of one another in the formation of gametes during meiosis R r Y y RYRyrYry

Molecular genetics - The study of the structure and function of chromosomes and genes The study of the structure and function of chromosomes and genes

Mendel also crossed plants that differed in two characteristics (Dihybrid Crosses) e.g. seed shape & seed color differed in two characteristics (Dihybrid Crosses) e.g. seed shape & seed color

In the P1 cross, RRYY x rryy, all of the F1 offspring showed only the dominant form for both traits; all hybrids, RrYy Traits: Seed Shape & Seed Color Alleles: R round Y yellow r wrinkled y green P 1 Cross: RRYY x r r yy P 1 Cross: RRYY x r r yy ry Genotype: RrYy RrYy RY Phenotype: Round yellow seed Round yellow seed Genotypic ratio: All alike All alike Phenotypic ratio: All Alike All Alike

Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure (homo=same,alike,man) Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure (homo=same,alike,man) Heterozygous genotype - gene combination of one dominant & one recessive allele (e.g. Rr); also called hybrid Heterozygous genotype - gene combination of one dominant & one recessive allele (e.g. Rr); also called hybrid (hetero=different, other, opposite) combinations

When Mendel crossed 2 hybrid plants (F1 cross), he got the following results: RYRyrYry RY RRY Y RRY y RrY Y RrY y Ry RRY y RRy y RrY y Rry y rY RrY Y RrY y rrY Y rrYy ry RrY y Rry y rrYyrryy Traits: Seed Shape & Seed Color Alleles: R - round Y- yellow R - round Y- yellow r - wrinkled y green

Genotypes Genotypic ratio Penotype Phenotypic ratio RRYYRRYyRrYYRrYy1224 Round yellow seed 9 RRyyRryy12 Round green seed 3 rrYYrrYy12 Wrinkled yellow seed 3 rryy1 Wrinkled green seed 1

Problem: Choose two other pea plant traits and work the P1 and F1 dihybrid crosses. Be sure to show the trait, alleles, genotypes, phenotypes, and all ratios. Choose two other pea plant traits and work the P1 and F1 dihybrid crosses. Be sure to show the trait, alleles, genotypes, phenotypes, and all ratios.

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References n_genetics.htm n_genetics.htm n_genetics.htm n_genetics.htm