Mendelian Genetics Introduction to Genotype and Phenotype Gregor

Mendelian Genetics Introduction to Genotype and Phenotype

Gregor Mendel (1822 -1884) Responsible for the Laws governing Inheritance of Traits copyright cmassengale 2

Gregor Johann Mendel §Austrian monk §Studied the inheritance of traits in pea plants §Developed the laws of inheritance §Mendel's work was not recognized until the turn of the 20 th century copyright cmassengale 3

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" copyright cmassengale 4

Site of Gregor Mendel’s experimental garden in the Czech Republic copyright cmassengale 5

Particulate Inheritance §Mendel stated that physical traits are inherited as “particles” §Mendel did not know that the “particles” were actually Chromosomes & DNA copyright cmassengale 6

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 copyright cmassengale 7

Genotype is… our genetic make-up we cannot see our genes! We get one copy of our genes from our mother and one from our father. The genes on these chromosomes might code for different forms of the same trait. Different forms of genes are called alleles. Image retrieved from http: //www. emunix. emich. edu/~rwinning/genetics/inherit 2. htm

Genotype is determined… by how the parent’s alleles combine during reproduction. Here, the mother has only the “a” form of the gene, while the father has only the “A” form of the same gene. In this scenario, the offspring can have only one genotype: Aa Image retrieved from: http: //www 1. geneticsolutions. com/Page. Req? id=3844: 1873

Determining Genotypes Here, each parent has both the “A” and the “a” allele for this gene. The offspring can have any of the following genotypes: AA, Aa or aa Image retrieved from: http: //www 1. geneticsolutions. com/Page. Req? id=3844: 1873

So what? The genotype of an organism is the code for the physical features of the organism (phenotype) Phenotype is the physical appearance of the organism For example, the allele, “A” might code for a normal skin pigment, while the “a” allele might code for albinism.

What is the relationship between genotype and phenotype? Image retrieved from http: //www. bbc. co. uk/schools/gcsebitesize/biology/variationandinheritance/0 dnaandgenesrev 5. shtml

Image retrieved from http: //bio 1151. nicerweb. com/doc/class/bio 1151/Locked/media/ch 14/14_06 Phenotype. Vs. Genotype_L. jpg

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) 14

How is phenotype determined? Generally, certain alleles of a gene completely override other alleles of the same gene (they are completely dominant). The allele for a tall plant is dominant in this example. If the tall parent has only tall alleles, all of its offspring will receive a tall allele from this plant. Since the tall allele is dominant to the short allele, all of the offspring will be tall. Image retrieved from http: //web. pdx. edu/~cruzan/Kid

Punnett Square Used to help solve genetics problems 16

copyright cmassengale 17

Designer “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 lowercase letter (r) 18

Genotype & Phenotype in Flowers Genotype of alleles: R = red flower r = yellow flower All genes occur in pairs, so 2 alleles affect a characteristic Possible combinations are: Genotypes RR Rr rr Phenotypes RED YELLOW 19

Genotypes § 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 20

Types of Genetic Crosses § Monohybrid cross - cross involving a single trait e. g. flower color § Dihybrid cross - cross involving two traits e. g. flower color & plant height copyright cmassengale 21

P 1 Monohybrid Cross Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Wrinkled seeds RR x rr r r R Rr Rr Genotype: Rr Phenotype: Phenotype Round Genotypic Ratio: All alike Phenotypic Ratio: All alike 22

P 1 Monohybrid Cross Review § Homozygous dominant x Homozygous recessive § Offspring all Heterozygous (hybrids) § Offspring called F 1 generation § Genotypic & Phenotypic ratio is ALL ALIKE 23

F 1 Monohybrid Cross Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Round seeds Rr x Rr R RR Rr rr Genotype: RR, Rr, rr Phenotype: Phenotype Round & wrinkled G. Ratio: 1: 2: 1 P. Ratio: 3: 1 copyright cmassengale 24

Given alleles T(tall) and t(short)… -What are the possible genotypes of a tall plant? -What are the possible genotypes of a short plant? -What would be the phenotype of TT? -What would be the phenotype of tt? -What would be the phenotype of Tt?

Mendel’s Pea Plant Experiments copyright cmassengale 26

In a famous experiment, a man named Gregor Mendel mated pea plants. When he mated a pure bred smooth seed with a pure bred wrinkled seed, he found that the wrinkled seed phenotype only occurred about 25% of the time. This happened because the allele for smooth seeds (S) is dominant to the allele for wrinkled seeds (s). Image retrieved from http: //www. accessexcellence. org/RC/VL/GG/mendel. html

Why peas, Pisum sativum? §Can be grown in a small area §Produce lots of offspring §Produce pure plants when allowed to selfpollinate several generations §Can be artificially cross-pollinated copyright cmassengale 28

Mendel’s Experimental Methods Mendel hand-pollinated flowers using a paintbrush He could snip the stamens to prevent selfpollination Covered each flower with a cloth bag He traced traits through the several generations copyright cmassengale 29

How Mendel Began Mendel produced pure strains by allowing the plants to selfpollinate for several generations copyright cmassengale 30

Eight Pea Plant Traits Seed shape --- Round (R) or Wrinkled (r) Seed Color ---- Yellow (Y) or Green (y) Pod Shape --- Smooth (S) or wrinkled (s) Pod Color --- Green (G) or Yellow (g) Seed Coat Color ---Gray (G) or White (g) Flower position---Axial (A) or Terminal (a) Plant Height --- Tall (T) or Short (t) Flower color --- Purple (P) or white (p) copyright cmassengale 31

What Do the Peas Look Like? copyright cmassengale 32

copyright cmassengale 33

copyright cmassengale 34

Mendel and the relationship between genotype and phenotype Click on the link that appears below to see an animation about Gregor Mendel and the relationship between genotype and phenotype **Once you get to the sight, click on animation at the bottom of the page to see the animation!!** http: //www. dnaftb. org/dnaftb/2/concept/index. html

Go to the following link and see how changing the genotype of a fictional dragon will change its phenotype. https: //concord. org/teachinggenetics/dragons/ Then go to the following link and watch the video. This may help you remember what you have learned. http: //youtube. com/watch? v=Ev. R_Sdm 1 or U