3.34 Causes of Mutation

The incidence of mutations  can be increased by exposure to ionising radiation (gamma rays, X-rays and ultraviolet rays) and some chemical mutagens (tabbaco)

1.       Radiation – such as the sun (UV-B)   which can cause skin cancer.

2.       Chemicals can also cause mutations such as the effect of tar in tabbaco causing mutations in the base sequence producing new alleles. Chemicals that cause mutations are called mutagens. Chemicals which cause mutations and cancer are called carcinogens.

3.32 Types of mutation

The mutation in a gene creating new alleles can be, beneficial, harmful or nuetral ( neither positive or negative)

An example of a beneficial mutation can be improving the efficiency of an enzyme.

An example of a harmful mutation can be production of a enzyme that doesn’t work.

An example of a nuetral mutation can be production of  that has no particular effect on an idividual, though in the long run it may due to environmental changes.

3.33  Antibiotic Resistance

How resistance to antibiotics can increase in bacterial population.

3.30 Mutation

The base sequence in which the letters are arranged constitutes the gene, the form of the gene is called the allele.

The base sequence of the DNA can be changed as shown in the diagram, producing a new allele which can produce an entirely different protien affecting the phenotype this is called mutation and this is also how the variation in the phenotypes occur.

3.29 Species variation

Variation is the differences that can be seen in the phenotype of individuals.

Every individual has a phenotype which depends on that individuals genotype which can be influenced by that particular persons living environment.

Variation in a population are the differences in the phenotypes of each individual, this is caused by variation in the species genotype and changes in the environment they live in.

1)      Variation caused by genes (discontinueos)

2)      A combination of variation caused by genes and environment ( continueos)

3)      Variation caused by environment

The third type of variation in population can be purely to do with environmental variation and has nothing to do with genetic charateristics, an example of this is the home language that an individual speaks. This cannot be inherited.

3.21 Genetic Probabilities

a) Predicting the probabilities of outcomes from monohybrid crosses

-the chance of offspring from one type of gene

Parents : red petal flower x white petal flower ( red is dominant )

Genotype : RR x rr

Through meiosis all genotypes os the offspring half of each of the parent alleles, which in this case is R and r.

Producing four heterozygotes

Genotype of offspring is all Rr

Phenotype of offspring is all red

When a homozygous red petaled flower is crossed with a homozygous white petaled flower the genotype of the offspring produced is Rr therefore the phenotype has a probability of 100% red.

b) crossing F1 offsprings

Parent phenotype : red x red

Parent genotype : Rr x Rr

Both Parents are heterozygotes

Through Meiosis all genotypes of the offspring will include half of each parents alleles.

 

Genotypes of offspring:                      RR   :  2Rr  : rr

Phenotype ratio of offspring(F2):     Red : Red : White    

                                                                         1   :   2    :    1

                                                                         3         :          1

                                                                         75%    :       25%

3.20a and b Pedigree diagrams

3.21b Genetic Probabilities