STAAR Notebook 4

Viruses

Viruses have a protein shell called a capsid. Bacterial cell Viruses have a protein shell called a capsid. Animal cell Virus Viruses are NOT made of cells, and they do NOT contain any organelles. Cells can reproduce themselves, but viruses CANNOT reproduce themselves. Viruses need a host cell to replicate. Cells and viruses BOTH contain genetic material in the form of DNA or RNA.

Viruses have surface markers that allow them to attach to host cells. Surface marker Viruses gain access to host cells so they can replicate themselves. Viruses use the host cell’s own machinery to replicate more viruses. Viruses take over and destroy cells to make more copies of viruses.

Lytic Cycle In the lytic cycle, viruses replicate quickly causing symptoms to appear soon after infection.

Lysogenic Cycle In the lysogenic cycle, viruses can remain dormant and inactive for long periods of time.

Antiviral drugs disrupt the ability of viruses to attach to cells or keep cells from replicating more viruses. Spanish flu outbreak of 1918 New viruses spread quickly because people lack immunities to new viral strains. Vaccines allow people to be immune to viruses without ever being sick! Vaccines contain weakened viruses and cause the body’s immune system to produce antibodies.

HIV HIV is a virus that destroys T cells as it replicates itself. T cells are an important part of the immune system. Because HIV destroys T cells, patients are more likely to get secondary infections from other viruses or bacteria.

A

H

B

J

J

J

Punnett Squares

Alleles are the different versions of a gene. Genotype = Gg There are different alleles for flower color in pea plants. Phenotype = Green pea pods Genotype describes the combination of alleles. Purple flowers White flowers Phenotype describes the physical appearance. Alleles are the different versions of a gene.

Bb bb BB Dominant alleles are always expressed. B = black fur b = white fur BB Bb bb Dominant alleles are always expressed. Recessive alleles are only expressed if the organism has 2 copies of the recessive allele.

gg GG Gg Homozygous Homozygous Dominant Recessive Heterozygous 2 copies of the recessive allele 2 copies of the dominant allele A combination of different alleles

Punnett squares allow scientists to predict the probability of an offspring having a specific physical trait or combination of alleles. g g G Gg Gg gg Gg g gg gg Each box in a Punnett square represents a 25% chance that the offspring will have that genotype. The probability that offspring will have a specific trait can also be expressed as a ratio. Remember that both homozygous dominant and heterozygous offspring will express the dominant trait.

X Dihybrid crosses predict the probability of offspring having TWO traits or genotypes. GGLl × ggll Green feathers/Long beak Yellow feathers/Short beak L l G G X g l Ll ll Gg Gg Ll ll g Gg Gg l When doing a dihybrid cross, be sure that you use 2 boxes. It is important to put each trait in its own box! To determine the percentage of offspring that would be expected to have two traits, you MULTIPLY the percentage from each box together!

The alleles for A and B blood are codominant over the allele or O blood. When alleles are codominant, they are both expressed when they appear together! Recessive alleles are recessive to both codominant alleles. Codominant alleles can produce a wide variety of phenotypes.

When an allele demonstrates incomplete dominance, heterozygous offspring have an intermediate phenotype.

J

C

F

D

X

C

F

Quiz Next Class!!!!!!!!!!!!!! Study STAAR 4 for Quiz next class! Will count double in the gradebook!