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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