BIO 10 Lecture 10 REPRODUCTION: CHROMOSOMES AND HEREDITY
An Introduction to Mendel and His Peas:1856-1863 Research in Brno, Czech Republic Observed the inheritance patterns of seven inherited physical characteristics in several generations of pea plantsand applied mathematics to discover the two basic laws that govern their behavior Did his work before chromosomes (1880's) or DNA (1950's) had been discovered Was a monk who grew his pea plants in the monastery garden
-Genetic information is carried by discrete entities (genes) Complex organisms carry two copies of each gene but pass only one copy to each gamete Each gene controls a single trait (e.g. seed color) but different forms of the same gene (alleles) can confer different expressions of that trait (e.g. yellow vs. green seeds) Mendel's First Law: Law of Segregation
An individual that carries two of the same allele for a gene is homozygous. An individual that carries two different alleles for a gene is heterozygous. In a heteroygote, only one allele is physically expressed; this allele is dominant(A) over the unexpressed, recessive(a)allele. Law of Segregationcontinued...
Genotype vs. Phenotype • The phenotypeof an organism is its physical appearance or behavior • This is all Mendel could actually study • "The mature seed is yellow" = phenotype • The genotype of an organism is its genetic make-up • Mendel inferred how genes behaved based on his observations of the patterns in which phenotypes were inherited • Yy = genotype
YY = yellow Yy = yellow yy = green Punnett Square predicts 3:1 phenotypic ratio
- When two genes and their alleles are followed through a genetic cross, the alleles of the two different genes are randomly shed into the gametes without regard to one another - i.e. independently Therefore, a dihybrid will create 4 different types of gametes in equal proportions: AB, ab, Ab, and aB Mendel's Second Law: Law of Independent Assortment
Meiosis and the Law of Independent Assortment
Short Review of Lecture 10 How many gametes, and what types, can be produced by a pea plant with the genotype PP? How about Pp? pp? How many gametes, and what types, can be produced by a pea plant with the genotype PpTt? How about PPTt? How many gametes, and what types, can be produced by a pea plant with the genotype PpTtYy? How about PPTtYy?