bio 10 lecture 10
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BIO 10 Lecture 10. REPRODUCTION: CHROMOSOMES AND HEREDITY. An Introduction to Mendel and His Peas: 1856-1863. Research in Brno, Czech Republic - PowerPoint PPT PresentationTRANSCRIPT
BIO 10 BIO 10 Lecture 10Lecture 10BIO 10 BIO 10 Lecture 10Lecture 10
REPRODUCTION: REPRODUCTION:
CHROMOSOMES AND HEREDITYCHROMOSOMES 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 plants and 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 phenotype of 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
Mendel's First Law and Meiosis
Punnett Square predicts3:1 phenotypic ratio
YY = yellowYy = yellowyy = green
- 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?