3.C.1 Effect on Phenotype

Changes in genotype can result in changes in phenotype.

Watch the following videos •http://www.bozemanscience.com/mutations•http://www.bozemanscience.com/001-natural-selection•http://www.bozemanscience.com/034-mechanisms-that-increase-genetic-variation

Draw 5 boxes on your paper…

• On the front of your paper fill in the 5 boxes for 3C1

• On the back of your paper take your own notes on 3C2

• Turn in your notes when you finish both

A mutation is a change of the nucleotide sequence of the genome.

Alterations in a DNA sequence can lead to changes phenotype.

Changes in phenotype result from changes in the type or amount of the

protein produced.

Amount of Protein

Box #1

• How can mutations change phenotypes?

DNA mutations can be positive, negative or neutral.

Mutations

Positive

Confers Selective Advantage

Neutral

No Change in Phenotype

ORPhenotype is Selectively

Neutral

Negative

Confers Selective Disadvantage

Whether or not a mutation is detrimental, beneficial or neutral

depends on the environmental context

Heterozygote advantage: The sickle cell trait can confer a selective advantage to heterozygote

individuals in areas affected by malaria (plasmodium).

The sickle cell trait is a point mutation, which changes only one base pair.

Mutations are the primary source of genetic variation.

Box #2

• Describe how a mutation can be beneficial.

Mutations result from:

• Errors in DNA replication• Errors in DNA repair mechanisms• External factors, such as radiation and reactive

chemicals

Errors in mitosis or meiosis can result in changes in phenotype.

Box #3

• Provide a brief explanation for the 3 ways in which mutations arise.

New chromosome combinations: triploidy usually results in a sterile individual because of unequal pairing of homologous chromosomes

during meiosis.

Changes in chromosome number often result in human disorders with developmental limitations.

There only three autosomal trisomies that result in a viable fetus; the others are too devastating, and

the fetus usually dies in utero.

• Trisomy 13: Patau Syndrome• Trisomy 18: Edward’s Syndrome• Trisomy 21: Down Syndrome

Trisomy 21: Down Syndrome

XO: Turner Syndrome

Box #4

• Research one of trisomy 13, 18, or 21, and describe how this occurs

Genetic changes that enhance fitness can be selected for by environmental

conditions.

Example: Antibiotic resistance mutations

Example: Pesticide resistance mutations

Box #5

• How can mutations increase survival (fitness)?

Learning Objectives:

LO 3.24 The student is able to predict how a change in genotype, when expressed as a phenotype, provides a variation that can be subject to natural selection.[See SP 6.4, 7.2] LO 3.25 The student can create a visual representation to illustrate how changes in a DNA nucleotide sequence can result in a change in the polypeptide produced. [See SP 1.1] LO 3.26 The student is able to explain the connection between genetic variations in organisms and phenotypic variations in populations. [See SP 7.2]