IB Assessment State

• State that eukaryote chromosomes are made of DNA and proteins.

DNA and Chromosomes.

• DNA is the large molecule that makes up chromosomes in cells.

DNA and Chromosomes

• DNA and Chromosomes• In prokaryotic (i.e. bacteria) cells, DNA is

located in the cytoplasm.• Most prokaryotes have a single DNA

molecule containing nearly all of the cell’s genetic information.

• Prokaryotes’ chromosomes have NO associated proteins

DNA and Chromosomes

Chromosome

E. Coli Bacterium

Bases on the Chromosomes

DNA and Chromosomes

• Many eukaryotes (i.e. humans, fish) have 1000 times the amount of DNA as prokaryotes.

• Eukaryotic DNA is located in the cell nucleus inside chromosomes.

• The number of chromosomes varies widely from one species to the next.

DNA and Chromosomes

– Chromosome Structure

• Eukaryotic chromosomes contain DNA and protein, tightly packed together to form chromatin.

• Chromatin consists of DNA tightly coiled around proteins called histones.

DNA and Chromosomes– Eukaryotic Chromosome Structure

Chromosome

Animation

• Animation about Eukaryotic DNA COILING

• http://www.biostudio.com/demo_freeman_dna_coiling.htm

IB Assessment Statement

• Define gene, allele and genome.

Genetics – the study of inheritance and of variation of inherited characteristics that chromosomes control.

Key Vocabulary

• Gene – a heritable factor that controls a specific characteristic.

• Allele – one specific form of a gene, differing from other alleles (example blue eyes).

• Genome – the whole genetic information of the organism.

IB Assessment Statement

• Define gene mutation.

IB ASSESSMENT STATEMENT

• Explain the consequence of a base substitution mutation in relation to the processes of transcription and translation, using the example of sickle-cell anemia.

• GAG has mutated to GTG causing glutamic acid to be replaced by valine, and hence sickle-cell anemia.

•  •  

Consequence of a base substitution mutation –A point mutation is a single base substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA

• Causes of Sickle Cell Anemia– A base substitution mutation in DNA in the

gene that codes for hemoglobin

Sickle Cell Causes

• The Normal allele has a ‘A’ – adenine(a nitrogenous base in a nucleotide in DNA) and codes for the GAG = glutamic acid.

• The sickle allele has and ‘T’ –Thymine (a nitrogenous base in a nucleotide in DNA) and codes for the GTG valine amino acid

Genetic Causing of Sickle Cell

Normal Hemoglobin

The hemoglobin molecule picks up oxygen in the lungs and releases it when the red cells reach tissues, such as the muscles.

• Normal hemoglobin molecules exist as single, isolated units in the red cell, whether they have oxygen bound or not.

• Normal red cells maintain a basic disc shape, whether they are transporting oxygen or not.

Sickle cell hemoglobin

• Sickle hemoglobin exist as isolated units in the red cells when they have oxygen bound.

• .

Sickle cell hemoglobinWhen sickle hemoglobin releases oxygen

in the p tissues, the molecules tend to stick together and form long chains or polymers.

Sickle cell hemoglobin

• These rigid polymers distort the cell and cause it to bend out of shape.

• While most distorted cells are simply shaped irregularly, a few have a cresent-like appearence under the microscope.

Sickle-shaped red blood cells

• Sickle Hemoglobin deforms the shape of the red cells.

• The problem is not simply one of abnormal shape.

• The membranes of the red blood cells are rigid due to hemoglobin

• These rigid cells fail to move through the small blood vessels, blocking local blood flow to a microscopic region of tissue.

• Amplified many times, these episodes produce tissue hypoxia (low oxygen supply). The result is pain, and often damage to organs.

Consequences of Sickle Cell

• Life expectancy is shortened, with studies reporting an average life expectancy of 42 in males and 48 in females

Inheritance of the Sickle Cell trait• The gene for

sickle cell is recessive (Hbs)

• To have sickle cell anemia you have to have inherited it from both parents (HbsHbs)

Inheritance of the Sickle Cell trait• Some one who is a

heterozygote (HbAHbs)

(inherited normal gene and a sickle cell gene from parents) for sickle cell anemia is called a carrier of sickle cell anemia.

Carriers of Sickle Cell

• The gene for sickle cell is incompletely recessive,

• Carriers (heterozygoussickle cell trait) can produce a few sickled red blood cells, not enough to cause symptoms,

Why do harmful Alleles Survive over time?

• If natural selection eliminates individuals with detrimental phenotypes from a population, then why do harmful mutant alleles persist in a gene pool?

Sickle Cell Anemia and Malaria

Distribution of Malaria Case

Distribution of Sickle Cell Anemia Cases

Malaria• Malaria is a female-mosquito-

borne infectious disease caused by a eukaryotic protist of the genus Plasmodium.

• After a period of between two weeks and several months (occasionally years) spent in the liver, the malaria parasites start to multiply within red blood cells,

• GOOD ANIMATION BELOW• http://www.youtube.com/

watch?v=qvlTOhCmxvY

Life Cycle of Plasmodium• The parasite's primary

(definitive) hosts are humans and other vertebrates.

• Female mosquitoes of the Anopheles genus are secondary hosts and transmission vectors.

• Young mosquitoes first ingest the malaria parasite by feeding on an infected human carrier and the infected Anopheles mosquitoes carry Plasmodium sporozoites in their salivary glands.

• A mosquito becomes infected when it takes a blood meal from an infected human

Deaths Caused by Malaria

• It is estimates that malaria causes 250 million cases of fever and approximately one million deaths annually.

• More than all other infectious disease combined!

Heterozygote Advantage

Having some sickle cells give a resistance to malaria.

• Because of this, heterozygotes have a higher fitness than either of the homozygotes.

• This is known as heterozygote advantage.

Heterozygote Advantage

• The sickle cell gene may have been brought to Africa by people migrating from Southern Arabia and India, or it may have arisen by mutation directly in East Africa.

• People who inherited one copy of the sickle cell allele had red blood cell membranes that did not admit the parasite.

• Carriers had more children and passed the protective allele to approximately half of them.

Heterozygote Advantage

• Gradually, the frequency of the sickle cell allele in East Africa rose from 0.1 percent to a spectacular 45 percent in thirty-five generations.

• Carriers paid the price for this genetic protection, whenever two produced a child with sickle cell disease.

Why do harmful Alleles Survive over time?

• A disease can remain prevalent when heterozygotes have some other advantage over individuals who have two copies of the wild type allele.

• When carriers have advantages that allow a detrimental allele to persist in a population, balanced polymorphism is at work.

• This form of polymorphism often entails heterozygosity for an inherited illness that protects against an infectious illness.

Awesome animation about epigenetics

• http://www.youtube.com/watch?v=kp1bZEUgqVI