Genetics

What is Genetics? Genetics is the field of Biology devoted to understanding how characteristics are transmitted from parents to offspring. Genes: Hereditary information passed down from parent to offspring that codes for a trait. Examples Examples Genes for eye color, hair color, dimples, flower color, seed color, seed shape, etc…

The “father of genetics” Genetics was founded with the work of Gregor Mendel an Austrian monk who worked with garden peas, Pisum sativum.

What would happen if…?

The unexpected results All of the offspring had round peas. This is called the F 1 generation.

It gets even stranger for Mendel He crosses now the plants from F 1 generation Now what do you expect?

A magic ratio arose 3 : 1 Ratio of Round : Wrinkled The F 2 generation

Other traits that had the same pattern

Why did this happen? He realized that there must be two alleles that control each trait. Allele - one alternative form of a gene. In our example there are two alleles for seed shape: one allele for round (R) and one allele for wrinkled (r). In our example there are two alleles for seed shape: one allele for round (R) and one allele for wrinkled (r). He also realized that each individual gets one allele from each parent.

So how does this explain the result Starting with the original plants Genotype - the specific allelic combination for a certain gene or set of genes RR x rr What are the possible genotypes for the offspring?

All the offspring in F 1 are Heterozygous Heterozygote - an individual which contains one of each member of the gene pair In our example this means Rr In our example this means Rr Homozygote - an individual which contains only one allele at the allelic pair In our example the parents are homozygous In our example the parents are homozygous One had an RR genotype and the other had an rr genotype Why are all the peas round?

Round is Dominant Phenotype - literally means "the form that is shown"; it is the outward, physical appearance of a particular trait and is determined by a persons genotype. What is the phenotype for the Rr genotype? What is the phenotype for the Rr genotype? Rr = This means that the Round allele is dominant over the Wrinkled allele. This means that the Round allele is dominant over the Wrinkled allele.

Dominant vs Recessive Dominance - the ability of one allele to express its phenotype at the expense of an alternate allele In our example round is dominant over wrinkled In our example round is dominant over wrinkled Recessive - an allele whose expression is suppressed in the presence of a dominant allele

Why do we a 3 : 1 ratio of Round : Wrinkled in the F 2 generation?