Modeling Mendel’s Laws

Who Was Gregor Mendel? Gregor Mendel, an Austrian monk, is known as the “Father of Genetics”. He was the first person to use mathematics of probability to explain heredity and to trace one trait for several generations.

Inheriting Traits During meiosis, a pair of chromosomes separates and the alleles move into separate cells. Each chromosome now contains one gene for each trait. EXAMPLE: One chromosome may have the allele for dimples and the other may have the allele for no dimples.

What are Genotype and Phenotype? Gregor Menel recognized that an organism could pass traits on to their offspring, that were not outwardly visible in the parent. Example: Two parents might have blonde hair, but their child might have brown hair.

What are Genotype and Phenotype? Mendel had actually discovered the difference between genotype and phenotype. Genotype: the particular set of alleles or version of a gene that codes for a trait Heterozygous: An organism with two alleles for one trait that are different: Example: Tt Homozygous: An organism with two alleles for one trait that are the same. The organism can be Homozygous Dominant (TT) or Homozygous recessive (tt)

What are Genotype and Phenotype Alleles: the different forms of a trait that a gene may have: Examples: tall or short, blue eyes or brown, dimples or no dimples

What are genotype and phenotype? Phenotype: The way an organism looks and behaves as a result of its genotype.

What is Dominance? Dominant Allele: The stronger allele. It will cover up or dominate the other allele and it is always expressed in the way an organism looks. It is represented by a capital letter EXAMPLE: T for tall B for brown hair

What is Dominance? Recessive Allele: The weaker allele. It may seem to disappear if the other allele is dominant. The only way it can show up in the way an organism’s appearance is if two recessive alleles are inherited for a trait. Always represented by a lower case letter. EXAMPLE: t for short b for blond hair

What is Dominance?

Punnett Squares Probability helps you predict the chance that something will happen. To figure probability, we use a punnett square. A punnett square helps you predict the chance an organism will inherit a certain trait. a. Uppercase letters = dominant alleles, always written first. b. Lowercase letters = recessive alleles

Gregor Mendel P1 Generation: Parent Generation F1 Generation: Children of parent generation F2 Generation: Grandchildren of parent generation or

What is Dominance? EXAMPLE: Let T = tall allele t = short allele An organism gets one gene from each parent. If the organism got the following allele combinations: TT = two dominant alleles, person would be tall Tt = one dominant and one recessive, person would be tall because the dominant gene covers up the recessive one tt = two recessive alleles, person would be short

Punnett Squares Example: Let the P1 generation alleles be TT and tt. TT x tt gives the following results: 100% of offspring will be tall 0% will be short T T t T T t Tt

Punnett Squares Suppose the P1 generation was Tt x Tt T t The probabilities from this cross would be: 75 % tall 25% short TT Tt tt

Mendel’s Law of Dominance Some alleles are dominant and others are recessive. AN organism with at least one dominant allele for a gene coding for a particular trait will exhibit the dominant form of the trait. An organisms will only express the recessive trait if no dominant alleles are present

Mendel’s Law of Segregation During gamete formation, the alleles for each gene separate from each other, so that each gamete carries only one allele for each gene. NOTE: This is due to meiosis. When the cells divide in meiosis, the chromosome number is reduced from diploid to haploid, so each gamete has only one copy of the gene for a trait.

Mendel’s Law of Segregation

Mendel’s Law of Segregation If segregation of allele’s fails to happen, the chromosomes will not separate properly, and nondisjunction occurs. The result is gametes may have an extra or a missing chromosome.

Mendel’s Law of Independent Assortment Genes of different traits can segregate independently during the formation of gametes. If corn color and taste are on separate genes, this law is the reason you could have yellow corn that is sweet or purple corn that is sweet. The genes for color and taste separate independently of each other.