Genetics 3.4 Inheritance

Mendel and the principles of inheritance Gregor Mendel mendel-39282http:// mendel Worked with pea plants. Carefully crossed varieties of peas by transferring pollen. Grew the resulting pea seeds. Repeated with many plants. Examined 7 different pairs of characters.

Mendel and the principles of inheritance Pioneer of research methods in biology Nature of science: What aspects of his research were “good science”? Model organism: clear characteristics that can be easily followed. And multiple characteristics allowed the conclusion that his results were not isolated to one characteristic. Quantitative: permits statistical tests of significance Large number of replicates ▫Multiple samples during individual experiments ▫And whole experiments Reliability

Blended inheritance Many early theories involved blended inheritance: See page text 170 for Mendel’s results

Mendel's Laws of Inheritance Law of Segregation: During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene. Law of Independent Assortment: Genes for different traits can segregate independently during the formation of gametes. Law of Dominance: Some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the effect of the dominant allele.

Segregation of Alleles During meiosis, a diploid nucleus divides twice to produce 4 haploid nuclei. Segregation: The separation of alleles into different nuclei. If 2 copies of one allele of a gene were present (ie PP), each haploid nuclei will receive a copy of this gene. ▫Every gamete gets a P. If two different alleles were present (ie Pp), each haploid nucleus will receive either one of the alleles or the other. ▫50% of the haploid cells will receive P & 50% will receive p

Dominant, recessive and co-dominant Dominant vs recessive: one allele is expressed over the other at the same locus. Co-dominant: pairs of alleles both have an effect.

Genotype vs Phenotype Genotype: the genetic makeup of a cell, an organism, or an individual usually with reference to a specific characteristic under consideration. Phenotype: The outward appearance of an organism; the expression of a genotype. Depends on which genes are dominant and on the interaction between genes and environment., such as hair or eye color.

Homozygous vs Heterozygous Homozygous: describes a genotype consisting of two identical alleles at a given locus Heterozygous: describes a genotype consisting of two different alleles at a locus

Punnett Grids