Genetics3.4 Inheritance

Mendel and the principles of inheritance•Gregor Mendel• http://www.biography.com/#!/people/greg

or-mendel-39282

•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