North Carolina Biology Updated Curriculum EOC Notes

7.3 CHARACTERISTICS OF LIFE

• Driving Question: How can bacterial infections make us so sick?
• Essential Question: Do bacteria display the 6 characteristics of life?
• All living organisms display six characteristics that define life, embedded within eight life processes.

Organization

• Living organisms are built from the same atoms and elements as non-living matter, but complexity increases as they are combined into cells.
• Atoms combine to form molecules, molecules combine to form cells, cells combine to form tissues, tissues combine to form organs, organs combine to form organ systems, and organ systems make up a living organism.
• Cells are the basic units of life.
• Organisms made of one cell are unicellular, while organisms made of many cells are multicellular.

Energy Use

• Organisms either consume or produce their own food for nutrition.
• Food contains stored energy that must be broken down to release energy through cellular respiration.
• Components of food must be transported to other parts of the body to build new molecules or cells.
• Making food and using components to build new molecules is called synthesis.

Reproduction

• Organisms must replace themselves for their species to survive.
• Reproduction can be asexual (involving one source of genetic material) or sexual (involving two parents providing genetic material).

Growth and Development

• Organisms grow, or get bigger over time, by increasing the number of cells.
• There is a limit to the size of a single cell.
• Organisms also develop, or change, during their life cycle, which may involve changes in form and function.

Respond to Stimuli

• A stimulus is any condition that causes an organism to react.
• A response is the reaction to that stimulus, which is quick and not permanent. Responses may be internal or external.

Homeostasis

• Homeostasis is the regulation of an organism’s internal environment to maintain conditions suitable for life.
• Homeostasis is controlled by feedback mechanisms.
• Excreting waste materials is an example of maintaining homeostasis.

BACTERIA VS. VIRUSES (LS.Bio.1.4)

• Essential Question: How do we describe the bacteria that causes MRSA?

Bacteria

• Bacteria are living organisms.
• Bacteria are unicellular and contain DNA; they are prokaryotic cells.
• Bacteria reproduce asexually through binary fission.
• There are MANY species of bacteria, and most are beneficial.
• Some bacteria are pathogenic and cause disease.
• Pathogenic bacteria can be treated with antibiotics.

Viruses

• Viruses are not made of cells but contain either DNA or RNA.
• Viruses are surrounded by a protein coat containing surface proteins called antigens.
• Viruses require a host cell to reproduce.
• All viruses are pathogenic.
• Antibiotics do not work against viruses; however, antiviral medications can stop viral reproduction.
• When exposed to a virus, the immune response begins, and antibodies are produced to recognize specific antigens, which can destroy the virus.
• Vaccines usually contain a weakened version of the virus, causing the body to activate the immune response and produce antibodies.
  • Active Immunity: Occurs when someone has produced their own antibodies against a virus, either after infection or vaccination.
  • Passive Immunity: Occurs when antibodies are passed between individuals, usually through a mother breastfeeding her child.

WHAT IS MEANT BY BACTERIAL GROWTH? (LS.Bio.5.1)

• Essential Question: What is happening to bacterial cells in the body of someone with an infection?

Cell Growth vs. Reproduction

• There is a limit to the size of a single cell.
• Bacterial growth refers to an increase in the number of bacterial cells rather than the size of each individual cell.

Exponential Population Growth

• When the resources an organism needs are available, a population can grow very quickly in a short period of time.
• This type of population growth is called exponential growth and is represented by a J-curve.

Logistic Population Growth

• When the resources an organism needs become limited, population growth will slow down and stabilize.
• The availability of these resources under stable conditions establishes the carrying capacity for a population, which is the maximum number of individuals an environment can support.
• This type of population growth is called logistic growth and is represented by an S-curve.

Limiting Factors

• Factors that limit the size of a population and determine carrying capacity are called limiting factors.
• As the number of organisms in a population increases, there is more competition for limited resources.
• Factors such as food, water, mates, space for habitats, and disease will have a greater effect on the size of the population.
• Some limiting factors are not influenced by the size of the population; for example, natural disasters will impact population growth regardless of the population size.

HOW DOES THE BODY RESPOND TO A BACTERIAL INFECTION? (LS.Bio.3.1, LS.Bio.2.2)

• Essential Question: How can you tell that you return to homeostasis after a bacterial infection?

Homeostasis

• Homeostasis involves keeping the internal environment of an organism’s body stable, despite changing external conditions.
• Homeostasis involves maintaining a healthy range for a number of internal factors.
  • Normal human body temperature is defined as $98.6^{\circ}F$, but normal is actually a small range around that number.

Feedback Mechanisms

• During a bacterial infection, the body tries to maintain homeostasis using feedback mechanisms.
  • Positive feedback occurs as the immune response triggers the production of cells that signal other cells to produce molecules to kill bacteria. These signals also lead to the production of more immune cells.
    • The process adds to or amplifies what is already happening in the system.
    • Positive feedback does NOT have to mean a beneficial response.
  • Negative feedback occurs as signaling molecules are received by another part of the immune system, causing a decrease in the number of immune cells being produced.
    • The process turns down what is happening in the system.
    • Negative feedback does NOT have to mean a harmful response.

Cell Specialization

• DNA is the genetic material of a cell. The information in the DNA codes for different types of proteins.
• Proteins are biological molecules that carry out different functions in organisms.
• All cells in a multicellular organism contain the same DNA.
• Although all cells in an organism have the same DNA, different types of cells make different types of proteins because different parts of the DNA are activated.
  • The parts of the DNA that are activated contain the information to make specific proteins for the cell.
  • The proteins that a cell makes determines that cell’s function.
  • Therefore cells are differentiated based on the proteins that they produce, and those proteins allow the cell to be specialized to perform a specific function.
• The cells of the immune system are examples of specialized cells.
  • Some white blood cells contain a large number of lysosomes because they destroy and digest pathogens.
  • Some immune cells produce proteins to use as chemical signals to influence the activity of other cells in feedback mechanisms.

HOW CAN A BACTERIAL INFECTION BE TREATED? (LS.Bio.9.1)

• Essential Question: Why don’t antibiotics harm human cells?

Antibiotics

• Antibiotics are medications that can destroy bacteria; therefore, we can say that bacteria are susceptible to antibiotics.
• Antibiotics only work on bacterial infections, not viral infections.
• Antibiotics destroy bacteria by damaging the bacterial cell wall.
• Antibiotics don’t treat the symptoms of an infection but work to stop the infection.
• Antibiotics are prescribed for a bacterial infection to supplement the body’s immune response.

Resistance

• Bacteria, like all living organisms, have genetic variation. The DNA of a single bacterium of a species is similar to that of others of the species, but not exactly the same.
• Some bacteria may have a gene (a section of DNA that codes for a protein) that other bacteria of that species do not have.
• Certain genes may code for a protein that makes a bacterium resistant to an antibiotic. In other words, the antibiotic does not affect those bacteria that have the gene.

BACTERIA CELLS VS. OTHER CELLS (LS.Bio.1.3, LS.Bio.1.4)

• Essential Question: How do bacterial cells reproduce?

Cell Theory

• All living organisms are made of cells.
• Cells are the basic structural and functional units of life. In other words, cells build the bodies of organisms, and all life processes occur at the cellular level.
• Cells come from pre-existing cells. Cells can reproduce.
• Essential Question: In what ways are bacteria different from other cells? In what ways are they the same?

Types of Cells

• There are two main categories of cells:
  1. Prokaryotic cells
     • Bacteria
     • Smallest and simplest cells
     • Cellular materials are suspended in a fluid called cytoplasm
     • Have no membrane-bound nucleus to hold the genetic material
     • Contain a single, circular chromosome and other smaller rings of DNA called plasmids
     • Contain ribosomes to help make proteins
     • Surrounded by a cell membrane AND a cell wall
  2. Eukaryotic cells
     • Includes plant cells, animal cells, protist cells, and fungal cells–all cells except bacteria
     • Larger and more complex than prokaryotic cells; still too small to be seen without a microscope
     • Cellular materials are suspended in a fluid called cytoplasm
     • Have a membrane-bound nucleus to hold the genetic material
     • Chromosomes made of DNA are contained in the nucleus
     • Contain various organelles to perform different cellular functions
     • Always surrounded by a cell membrane; some types of eukaryotic cells are also surrounded by a cell wall

Cell Parts and Functions

• Parts found in all cells:
  1. Cell Membrane/Plasma Membrane: The structure that allows materials such as food, water, and waste into or out of the cell.
  2. Cytoplasm: A fluid material that holds the other cellular materials in place.
  3. Nucleic Acids: DNA and RNA; the genetic material of the cell.
  4. Ribosomes: The sites of protein synthesis.
• Parts found in Prokaryotic cells:
  1. Plasmids: Small rings of DNA that can be exchanged between bacterial cells.
  2. Cell wall: Surrounds the cell membrane for extra protection.
• Parts found in all Eukaryotic cells:
  1. Nucleus: Membrane-bound structure that holds and protects the genetic material.
  2. Endoplasmic Reticulum: A series of interconnected membranes that function in cellular communication.
     • Rough ER is covered with ribosomes and plays an important role in the synthesis and modification of proteins.
     • Smooth ER does not have ribosomes attached and is important for the synthesis of lipids such as cholesterol.
  3. Golgi Complex: Stacked membranes that package materials for export from the cell.
  4. Mitochondria: Membrane-bound structure that produces the cellular energy molecule ATP through the process of cellular respiration; folded membranes inside the mitochondria increase the surface area for this reaction.
  5. Vacuole: Membrane-bound structures that store materials such as food, water, or waste; the size of the vacuole is much larger in plant cells than in animal cells.
  6. Lysosomes: Membrane-bound structures that contain digestive enzymes to help the cell dispose of wastes.
  7. Centrioles: Structures that are important to the process of animal cell division.
• Parts found in Eukaryotic Animal Cells only
• Parts found in Eukaryotic Plant Cells only
  1. Chloroplasts: Membrane-bound structures that produce food for plant cells using the process of photosynthesis; contains stacked membranes inside to increase surface area for the reaction.
  2. Cell Wall: Surrounds the cell membrane and provides additional support and protection.

WHY DON’T ANTIBIOTICS WORK ON SOME BACTERIAL INFECTIONS? (LS.Bio.9.3, LS.Bio.9.4)

• Essential Question: Why might some bacteria that are susceptible to antibiotics survive the initial treatment?

Evolution of Antibiotic Resistance

• When antibiotics are prescribed for a bacterial infection, most bacteria will be susceptible to the antibiotic and will die.
• However, some bacteria in the population will have a gene that makes them resistant to the antibiotic and will survive.
• The surviving bacteria, including those with the antibiotic resistance gene will begin to reproduce asexually by binary fission.
• The newly reproduced bacteria will be clones of the original, meaning that many will also have the antibiotic resistance gene.
• Since these bacteria are resistant to the antibiotic, the antibiotic will not act as a limiting factor for bacterial population growth.
• The antibiotic resistant bacteria population will grow exponentially.
• Antibiotics are prescribed for a bacterial infection to supplement the body’s immune response.

Adaptation

• Antibiotic resistance is a favorable trait for bacteria. Those bacteria that are resistant to antibiotics will live longer and be able to reproduce better than those bacteria that are not resistant to the antibiotic. This is called differential reproductive success.
• An adaptation is a favorable trait that helps organisms survive and reproduce in a particular environment.
• Antibiotic resistance in bacteria is a physiological adaptation.
• In an antibiotic-rich environment, bacteria who are antibiotic resistant are more fit than those that are susceptible.

Natural Selection

• Natural selection is the mechanism that allows a species to adapt to changes in the environment.

• Several conditions are required for natural selection to take place.

  1. Variation - individuals in a species have genetic variation that is passed on to their offspring
  2. Overproduction of offspring - species produce more offspring than the environment can support
  3. Competition - as a species grows in number, competition for limited resources can arise
  4. Struggle to survive - individuals may have traits resulting in a competitive advantage over other individuals of the species

• Over time, the favorable trait (such as antibiotic resistance) is selected. More individuals with the trait survive and reproduce, so the trait becomes more common in the population.

• The presence of antibiotics is the selection force that led to natural selection for antibiotic resistance.

• If the environment of the bacteria changes, there will be new selection forces. Therefore different traits may be favorable and could be selected for.

WHICH MACROMOLECULES ARE RELATED TO CHOLESTEROL? (LS.Bio.1.1)

• Driving Question: Why do some people get heart disease and not others, and what can we do to prevent it?
• Essential Question: How many atoms are in the molecule $H<em>2O$? How many atoms are in the molecule $C</em>6H<em>{12}O</em>6$?
• All living and non-living matter is made of atoms. Atoms can combine with others of the same type or with others of different types to make up molecules.
• The size of a molecule is determined by the number of atoms in that molecule.
• There are four large molecules, or macromolecules, that are particularly important for the survival of living organisms.

Lipids

• Lipids are one of the four major macromolecules.
• Cholesterol, triglycerides, and phospholipids are examples of lipids.
• Lipids have many functions in the body.
  • Functions of cholesterol include building cell membranes and producing hormones.
  • The function of triglycerides is to store unused calories and provide the body with energy when it is needed.
  • The function of phospholipids is to form the cell membrane bilayer that separates the inside of a cell from its external environment.

Proteins

• Proteins are another type of major macromolecule.
  • Proteins are polymers - molecules made up of many smaller molecules connected to each other.
  • The smaller molecules that make up a polymer are called monomers. The monomers that make up proteins are called amino acids. There are 20 different amino acids that can combine in many ways to form the different proteins in the human body.
  • When many amino acids connect to form a long chain, the protein structure that is formed is called a polypeptide.
  • Polypeptide chains can fold up in different ways depending on the sequence of amino acids, giving each type of protein a unique shape.
  • The shape of a molecule relates to its function. Therefore proteins with different shapes perform different functions. Changes to the shape of a protein may cause the protein to not function correctly or to not function at all.
• Proteins have many different functions in the body.
  • Membrane proteins are associated with or attached to the cell membrane. Different types of membrane proteins have different functions.
  • The function of one type of membrane protein is to act as a receptor for other molecules.
• Lipoproteins are particles made of protein and lipids. These particles function to carry cholesterol throughout the body. LDL carries cholesterol into cells and HDL carries cholesterol out of cells. Membrane proteins must facilitate this process.

WHAT DETERMINES WHICH PROTEINS ARE MADE BY A CELL? (LS.Bio.1.1, LS.Bio.1.5)

• Essential Question:

DNA

• DNA (deoxyribonucleic acid) is an example of a nucleic acid. Nucleic acids are one of the four major macromolecules.
• DNA is the genetic material of the cell. All cells contain DNA.
• DNA is a polymer. The monomer of DNA is called a nucleotide. Each nucleotide consists of a sugar (deoxyribose), a phosphate group, and one of 4 nitrogen bases - adenine, thymine, cytosine, or guanine.
• A DNA molecule is made up of two long chains of nucleotides that run in opposite directions. The two chains of nucleotides are held together by hydrogen bonds.
  The chains of nucleotides are twisted to form a spiral-shaped structure, so the shape of the DNA molecule is called a double helix.
• The hydrogen bonds holding the two chains of nucleotides together connect two nitrogen bases, forming a base pair. The nitrogen bases in DNA always pair the same way. Adenine (A) pairs with Thymine (T), while Cytosine (C) pairs with Guanine (G).
• The sugar and phosphate components of nucleotides make up the sides, or backbone of the DNA molecule.
• DNA coils and condenses to form chromosomes.
  • In eukaryotic cells, chromosomes are enclosed by a membrane, forming a nucleus.
  • In prokaryotic cells, the single chromosome is not enclosed in a nucleus.

Genes

• A multicellular organism typically has multiple chromosomes in each cell. The number of chromosomes in each cell depends on the species. Every cell in an organism will have the same number and type of chromosomes.
• Chromosomes occur in pairs. There are two of each type of chromosome. One of each pair was inherited from the organism’s mother and the other was inherited from the organism’s father.
• The different chromosomes in an organism have different nucleotide sequences. The sequence of nucleotides varies between species and between individuals of a species.
• The sequence of nucleotides in a DNA molecule is where the genetic “code” is contained.
• A gene is a sequence of DNA nucleotides that codes for the production of a particular protein.
• Because chromosomes occur in pairs, there are two parts to each gene. One component of the gene was inherited from the organism’s mother and the other component was inherited from the organism’s father. The two components that make up a gene are called alleles.
• Since living organisms use proteins for many different structures and functions, there are many genes on a single molecule of DNA.

HOW ARE THE INSTRUCTIONS IN DNA USED TO MAKE A PROTEIN? (LS.Bio.1.5, LS.Bio.6.2)

• Essential Question: Which organelle found in all cells is the location of protein synthesis?
• DNA is a very large molecule that is contained within a nucleus in a eukaryotic organism. Because of its size, a DNA molecule can not leave the nucleus.
• Organelles needed to make proteins are in the cytoplasm. Therefore, the DNA code needs to be copied so it can leave the nucleus and go to the cytoplasm.

RNA

• RNA (Ribonucleic acid) is another nucleic acid.
• All nucleic acids are polymers made of nucleotide monomers. However there are differences in the structure of DNA and RNA.
  • An RNA nucleotide contains a different sugar (ribose), along with a phosphate group and one of 4 nitrogen bases.
  • In RNA, there is no thymine nitrogen base. Instead, Thymine is replaced with another nitrogen base called Uracil. Therefore the 4 nitrogen bases in RNA are Adenine, Uracil, Cytosine, and Guanine.
  • RNA molecules consist of a single-strand of nucleotides.
• There are several types of RNA molecules that assist in the process of protein synthesis.

Transcription

• In order to make a protein, the gene that codes for that protein must be copied from the DNA in the nucleus.
• Messenger RNA (mRNA) is the molecule that is responsible for copying the gene.
  • The weak hydrogen bonds connecting the 2 nucleotide strands in DNA are broken and the 2 strands separate.
  • One side of the DNA is used as a template to make mRNA using nitrogen base pairing.
  • Nitrogen base pairing rules are still followed: Guanine pairs with Cytosine and Adenine now pairs with Uracil. A Thymine base in DNA will still pair with an Adenine base in mRNA.
• After the gene is copied, the mRNA will break away from the DNA and the 2 DNA strands will re-connect.
• mRNA leaves the nucleus through a nuclear membrane pore and moves to the cytoplasm.

Translation

• During the process of translation the DNA code (carried by the mRNA) is “read” and used to make an amino acid sequence. Therefore the DNA code determines the sequence of amino acids that make up the protein.

• This process occurs at the ribosomes. Ribosomes are constructed of ribosomal RNA (rRNA).

• Each sequence of 3 nitrogen bases on mRNA codes for a particular amino acid. Therefore a sequence of 3 nitrogen bases on mRNA is called a codon.

• The mRNA attaches to a ribosome at the start codon. The start codon is AUG and codes for the first amino acid in the protein.

• Transfer RNA (tRNA) delivers the specific amino acid that each mRNA codon codes for.

  • The tRNA carrying a specific amino acid has a sequence of 3 nitrogen bases on one end called an anticodon.
  • The anticodon is complementary to the mRNA codon.

• The mRNA moves along the ribosome and amino acids are delivered by the tRNA until a stop codon is reached. A stop codon signals that the polypeptide chain is complete.

• The polypeptide chain will fold into a 3 dimensional structure, forming a protein with a specific function.

Mutations

• A mutation is a change in the nucleotide sequence of the DNA.
• If the sequence of the nucleotides in DNA changes, the amino acids that are coded for may also change.
• If the amino acid sequence of a protein changes, its structure may be altered. This may mean that the protein can no longer perform its intended function.
• Mutations can spontaneously occur when DNA is copied. Environmental factors such as exposure to certain chemicals or to radiation may also cause DNA mutations.
• Mutations are a source of genetic variation.
  • Not all mutations are negative or harmful.
  • Some mutations may cause a change in protein production that is beneficial to the organism.
  • Other mutations may be neutral. Either there is no change in protein production or the change in protein production does not significantly affect the function of the protein.

ARE ALL TRAITS CONNECTED TO ONLY ONE GENE? (LS.Bio.7.2)

• Essential Question:

Phenotype vs Genotype

• A phenotype is a trait or characteristic of an individual.
• The alleles an individual has for genes that are linked to that trait is called the genotype.

Polygenic Traits

• Some traits are linked to only one gene. However, most human traits are far more complex.
• A trait that is linked to many genes is called a polygenic trait.
• Polygenic traits exhibit a wide range of possible phenotypes because various genes interact with each other. The expression of the trait depends on the genotypes of multiple genes. Different individuals may have different genotypes for each gene that is linked.
• The phenotype distribution of a polygenic trait can be visualized graphically:

HOW CAN WE PREDICT WHICH TRAITS WILL BE INHERITED? (LS.Bio.7.1)

Predicting Inheritance

• Predicting inheritance of polygenic traits is difficult because of the interaction of multiple genes. For traits that are linked to only one gene, we can make predictions about inheritance if we know the genotypes of both parents.
• Remember that a genotype for a trait consists of 2 alleles.
  • These alleles are located on chromosomes.
  • One allele for a trait is carried on a chromosome that was inherited from an individual’s mother and the other allele for a trait is carried on the same type of chromosome that was inherited from an individuals’ father.
  • For a trait, there are different versions called alleles. There are various types of inheritance that determine how the versions of different traits are expressed in an individual.
  • We can use letters to represent the alleles for a trait.

Dominant / Recessive

• Cystic fibrosis is a disorder that is linked to a membrane protein.
  • One version of the membrane protein is correctly shaped to regulate the passage of certain materials through the cell membrane. This is the dominant version of the trait.
    • A capital letter is used to represent the dominant allele (F).
  • The other version of the membrane protein has a mutation that changes the shape. This protein is not able to effectively regulate the passage of those materials across the cell membrane, causing an abnormal build-up of thick mucus in the cells of the respiratory tract. This is the recessive version of the trait.
    • The same letter in lowercase is used to represent the recessive allele (f).
• The dominant version of a trait can hide or mask the recessive version of the trait when both are present.
• Since an individual has two alleles for each trait (one from the mother and one from the father), the two alleles combined make up that individual’s genotype.
  • If there are two dominant alleles, the genotype is homozygous dominant (FF). Individuals with this genotype have the normal phenotype (no Cystic fibrosis).
  • If there are two recessive alleles, the genotype is homozygous recessive (ff). Individuals with this genotype have Cystic Fibrosis.
  • If there is one dominant and one recessive allele, the genotype is heterozygous (Ff). Individuals with this genotype have the normal phenotype (no Cystic fibrosis) because the dominant allele will mask the recessive allele.
• A Punnett square is a tool that can be used to predict the inheritance of a trait such as Cystic Fibrosis when the genotypes of the parents are known.
  • Example: A couple is considering having children and they know that Cystic Fibrosis runs in both families. Neither of them have the disease, but they want to know if they could pass it to their children. They each have a blood test and find out that they both have the heterozygous genotype (Ff).
  • The Punnett Square shows the possible results of a “cross” between these two individuals.
  • The Punnett Square reveals that there is a 75% chance that a child of this couple will not have Cystic Fibrosis, but there is a 25% chance that the child will have Cystic Fibrosis.

Incomplete Dominance

• For some traits, the allele for one version can not completely mask the other allele. This type of inheritance does not follow the pattern of normal dominance.
• For these traits, there is an intermediate phenotype for a heterozygous individual. Therefore the alleles for incompletely dominant traits must be represented differently to show this intermediate phenotype.
• Tay-Sachs disease is a disorder related to the ability to break down certain lipids in the bloodstream. A specific enzyme protein is responsible for breaking down these lipids.
  • Individuals who have two normal alleles produce the normal amount of enzyme. Individuals who have two mutated alleles do not produce ANY enzyme and develop Tay-Sachs disease. However, individuals who have one of each version produce half the normal amount of enzyme.
  • The alleles to represent this trait involve using a prime symbol (‘) on one version.
    • EE - Normal enzyme production
    • E’E’ - NO enzyme production
    • EE’ - Intermediate enzyme production (half)
  • Example: A couple is considering having children and they know that Tay-Sachs runs in both families. Neither of them have the disease, but they want to know if they could pass it to their children. They each have a blood test and find out that they both have the heterozygous genotype (EE’).
    • The Punnett Square shows the possible results of a “cross” between these two individuals.
    • The Punnett Square reveals that there is a 75% chance that a child of this couple will not have Tay-Sachs. There is a 50% chance that a child will only produce 50% of the enzyme. There is a 25% chance that the child will produce no enzyme and have Tay-Sachs.

Codominance and Multiple Alleles

• For most traits, there are two different versions or alleles. However, for the human trait of blood type, there are three possible alleles.
• Blood type in humans is determined by proteins on the surface of an individual’s red blood cells.
  • Individuals with type A blood have “A” proteins.
  • Individuals with type B blood have “B” proteins.
  • Individuals with type O blood have no proteins of this type.
  • Individuals with AB blood have both “A” and “B” proteins.
• The production of these proteins is controlled by a gene. The proteins are a type of antigen called isoagglutinogens. Antigens are proteins that can be recognized by the immune system.
  • Individuals with blood types A, B, and AB have the dominant trait of antigen production (I).
  • Individuals with blood type O have the recessive trait of no antigen production (i).
• Since there are different types of antigens that are produced, we must also indicate which of those is produced by individuals with the dominant phenotype. For this, a superscript A or B (IA or IB) is used.
• Since there are two possible dominant alleles (IA or IB) and one possible recessive allele (i), blood type is referred to as multiple allelic inheritance. However, each individual will only inherit two of the three possible alleles.
• Recall that the dominant version of a trait can mask the recessive version of a trait.
  • Individuals with blood types A or B can have the homozygous dominant or heterozygous genotype.
  • Individuals with blood type O will have the homozygous recessive genotype.
  • Individuals with blood type AB have BOTH dominant alleles. Since BOTH versions are equally expressed, we can say that this trait is Codominant.

Possible Blood Type Genotypes:

• IAIA or IAi = A

• IBIB or IBi = B

• IAIB = AB

• ii = O

• A Punnett Square can be used to predict the blood type of offspring when the genotypes of the parents are known.

  • Example: Two parents, one with blood type AB and the other with blood type O have a child. They are concerned that the child has type B blood rather than a blood type of one of the parents. Can a Punnett square be used to explain this?
    • The Punnett Square shows the possible results of a “cross” between these two individuals.
    • The Punnett Square reveals that there is a 50% chance that a child of this couple will have Type A blood and a 50% chance of Type B blood. There is a 0% chance of Blood type AB or O.

Sex-Linkage

• Human cells contain 46 chromosomes. Since chromosomes occur in pairs, this means that human cells have 23 pairs of chromosomes.
  • Each chromosome pair contains genes for different traits. Remember that one allele of the gene is located on the maternal chromosome while the other allele of the gene is located on the paternal chromosome.
• A karyotype can be used to visualize the chromosome pairs.
  • The first 22 pairs are referred to as autosomes.
  • The 23rd pair are referred to as sex chromosomes.
    • Sex chromosomes determine the biological sex of an individual. Those with 2 chromosomes at the X position (XX) are biological females. Those with one chromosome at the X position and one at the Y position (XY) are biological males.
• Genes for some human traits are found on the sex chromosomes. These are called sex-linked traits. While there are genes on the Y chromosome, we are specifically interested in genes that are found on the X chromosome.
  • Since females have two X chromosomes and males have only one X chromosome, the genotypes for these traits must be represented differently.
• Hemophilia is a sex-linked disorder. Individuals with hemophilia do not produce enough proteins that act as blood clotting factors. Normal protein production is the dominant trait while the mutated version is the recessive trait.
  • Alleles for a sex-linked trait are shown as being “carried” on the X chromosome. Females will have two alleles for a sex-linked trait while males will only have one allele.

Phenotype

• Female
• Male

Normal

• XHXH or XHXh
• XHY

Hemophiliac

• XhXh

• XhY

• Example: A couple with normal blood clotting ability has a son who is diagnosed with hemophilia. There is no family history of hemophilia on the father’s side of the family, but the mother’s great-grandfather did have the disorder.

  • The Punnett Square shows the possible results of a “cross” between these two individuals.
  • The Punnett Square reveals that the mother is a “carrier” for this disorder. There is a 50% chance that a son born to this couple will inherit hemophilia.
  • Since males only have one allele for sex-linked traits, there is a higher probability of those traits being expressed in males.

HOW CAN THE INHERITANCE OF A TRAIT IN A FAMILY BE SHOWN? (LS.Bio.7.1)

• Essential Question:

• A pedigree is a chart that shows the inheritance of a trait in a family.

• Symbols are used to represent individuals on a pedigree.

• A pedigree can be interpreted to determine the pattern of inheritance of a trait and the genotypes of the individuals.

• The pedigree shown below has three generations. Neither of the parents of the siblings in generation three has the trait, yet it appears in one of their children. This is a clue that this trait is recessive. Both of the parents