General Biology I - Labs 12 & 13

Mendelian Genetics & DNA Isolation in Onion Cells`

Mendel

is the father of genetics and used the garden pea plant

Mendel used the garden pea plant to

explain how genes were passed down from parents to offspring

The pea plants were easy to study because

• easy to grow

• grew to maturity in one season

• and mating was easy to control

Mendel could additionally easily observe stem height

which each had one of 2 contrasting alleles, tall or dwarf

Gregor Mendel experimented thoroughly with

one-trait inheritance

Mendel argued against the

blending mechanism of inhertiance which stated that the factors that dictated heredity were all clumped together and they were passed down to the next generation

F1 generation

display characteristics that were like one of the two parents in the P generation

The dominant allele always appeared in the F1

generation

Mendel noticed that if the recessive appeared,

they would be in the F2 generation in a 3 to 1 dominant:recessive ration

Letters are used with

allelesUp

Uppercase letters are used to represent

dominant

Lowercase letters are used to represent

recessive

Phenotype

physical expression of a trait

Genotype

Genetic composition of the organism

Particulate theory of inheritance

Genetic determinants that governed traits were inherited as discrete unit factors that remain unchanged as they were passed from one generation to another generation

The particulate theory holds true because

the recessive gene appeared in the F2 generation

Homozygous

Same letters can be dominant or recessive

Heterozygous

1 letter of each - different

Two copies of a gene seperate from each other that gives rise to the gametes

Law of segregatoin

Only one copy of each allele comes from each parent

and they are transmitted to their offspring

Punnett squares

are used to visualize the genotypes and phenotypes of potential offspring from combining gametes during fertilization

Male gametes are on the top

female gametes are on the sides

The punnet square

produces every possible combination that occurs due to random fertilization

When constructing a punnett square

one should first write down the genotypes of the parents and then the possible gametes that result from the parents

It is expected that when scientists observe randomly occuring events

the observations will almost always deviate from the expectations

Chi squares

help to analyze populations in which members of a population fall into different categories which also helps to determine the goodness of fit

The researcher then creates a null hypothesis

which states that there is no real difference between the observed and expected values and any actual differences is seen due to a random sampling error

The smaller the sample size,

the larger the sampling error

Chi - Square Set-Up

1. Set up observed and expected data

2. Calculate Deviation

3. Square Deviation

4. Set up Deviation over Expected

5. Add up values to get Chi-Square value

The degrees of freedom are

Measure of the number of categories that are independent of each other

Df is calculated by n-1

with N being the data classes

If the p-value is 0.05 or lower

the null hypothesis is rejected

When the null hypothesis is rejected, it means that

the observed differences are unlikely to be due to random chance and may indicate an error in the experiment

With a p-value of 0.05,

there is a 5% chance that the results occured by chance

In most cases,

a p-value of 0.05 or less is considered statistically significant, providing evidence against the null hypothesis