Chapter 9: Inheritance and DNA, Chapter 10:Structure and Function of DNA (Quiz 5)

The Showy Lady’s Slipper (Cypripedium reginae)

• Threatned/Endangered due to people picking or digging them up and Habitat loss

• Found in full sun or part shade, in wet habitats

• Pollinated by bees

• Blooms mid-May through early June in Ohio

Cardinal Flower (Labelia Cardinalis)

• Perennial Plant (lives 2 years or more)

• Blooms July-September

• Pollinated mostly by hummingbirds, although snow tails do as well (b flies)

Gregor Mendel

• Austria, mid-1800s

• First person to analyze patterns of inheritance in a scientific way

• DNA wasn’t known at the time

• “Heritable factors“ were passed from parent to offspring

What did Mendel Study?

• Pea plants

• Could Control their Reproduction through:

  • Self-Fertilization

  • Cross-Fertilization

What is a Monohybrid Cross?

Two plants that are crossed and vary only in characteristic (i.e., one is homozygous dominant, other is homozygous recessive)

Mendel’s 4 hypotheses:

1. There are alternative forms of genes (alleles)

2. For each inherited trait, an organism has two genes, one from each parent; they may be of the same or different alleles

3. A sperm or egg carries only 1 copy of that gene; after fertilization, the paired condition is restored

4. When 2 genes of a pair are of different alleles, one is fully expressed (the dominant allele) while the other is masked (recessive allele)

What does Homozygous mean?

You have 2 copies of the same allele

What does Heterozygous mean?

You have 2 different alleles for a genes

Example of Homozygous Dominant

AA

Example of Heterozygous

Aa

Example of Homozygous Recessive

aa

Are Gametes Haploid or Diploid

Gametes are haploid

What is the chance of a heterozygote allele being passed down?

50%

What is the purpose of a Punnett Square?

To calculate the probabilities of characteristics of offspring if two individuals of know genotype are mated

What is a Genotype?

The genetic composition

• Example: Expressed as “PP“ or “Pp“ or “pp“, for example, where P = Dominant allele for purple flowers, and p = recessive allele for white flowers

What is a Phenotype?

The trait that an organism expresses

• Example: “Purple“ or “White“ flowers

Test Crosses

When a geneotype of an individual expressing the dominant trait is unknown, you can do a test corss to find out

• Must be crossed with a homozygous recessive

Snowberry Clearwing (moth and caterpillar)

• Diurnal (Active during daytime)

• Moths feed on nectar from flowers like wild bergamot

• Catipillars feed on Honey suckle

• Important pollinators for many flowering plants

A cross between two individuals that are heterozygous for 2 traits will result in?

A 9:3:3:1 Ratio

Which means only

• 1 out of 16 will have recessive genes

• 9 out of 16 will have at least one gene for both dominant gene

• 3 out of 16 will have a double recessive for one trait

• 3 out of 16 will have a double recessive for other traits

Principle of Segregation (1 of 2 Mendels Observations)

Pairs of alleles separate during gamete formation; the fusion of gametes at fertilization creates allele pairs again

Principle of Independent Assortment (2 of 2 Mendels Observations)

Each Pair of alleles segregates independently of the other pairs during gamete formation

Incomplete Dominance

The heterozygotes has a phenotype that is intermediate between the two homozygotes

Example of Incomplete Dominance

Flower color in snapdragons (cross between a homozygous red flower and a homozygous white flower produces pink flowers)

Examples of How 2 alleles may be present for one trait

Blood Type

ABO Blood Group

• 3 different Alleles

• Produces four different phenotypes: A, B, AB, O

A and B blood Group

• Both Dominant to O

• also co-dominant; both are expressed; a person with both A and B alleles has type AB Blood

How do you get type O blood?

You Must have two copies of the O alleles

Blood Chart

Pleiotropy

When one gene has an effect on more than one trait

Example of Pleiotropy

Sickle-Cell Anemia

What is Sickle-Cell Anemia?

• Makes red blood cells produce abnormal hemoglobin molecules, and red blood cells become sickle-shaped

• The allele for this disease is recessive; only homozygous recessives express the disease

• Heterozygotes are protected against malaria

• Sickle cell disease (and thus the gene) is most common in Africa, where Malaria is also common

Polygenic Inheritance

When more than one gene affects one trait

• Many traits vary along a continuum (Not just two or three different phenotypes)

• It is the combination of several genes that accounts for this variation

  • Ex: Skin Color and height in humans

What role does the environment play in traits

• Different interactions influence

Sex- Linked Genes

Genes located on the sex chromosome

About how many genes does the X and Y chromosome carry?

The X chromosome carries about 1100 and the Y carries about 78, mostly affecting testes development (meaning most sex-linked genes are on the x chromosome)

Why do things like red-green color blindness and hemophilia affect Primarily affect males?

because they are only carried on the X chromosome; there is no corresponding locus on the Y chromosome, doesn’t affect women because theyX NX n have 2 chances to get a good working copy while males only have 1 due to having only 1 X chromosome

How to write alleles for sex-linked traits

Alleles for sex-linked traits are written as superscripts on the X chromosome

What is DNA?

A double--stranded polymer that consist of two strands of nucleotides that form a double helix

When was the Double Helix Structure Discovered? Who Discovered it?

Early 1950s, by James Watson and Francis Crick (With the help of earlier research by Rosalind Franklin Linus Pauling, Erwin Chargaff, and others

Linus Pauling

• “Greatest Chemist of the 20th Century”

• His work spurred Watson and Crick in their work, became interested in DNA around 1950

• Thought DNA was a triple helix with the bases pointed outward

Erwin Chargaff

• Analyzed the amount of A’s, T’s, G’s and C’s in DNA from several species

• Found out that the number of A’s always equaled number of T;s and the number of G’s always equaled the number of C’s

• Realized these bases are likely paired

Rosalind Franklin

• Used X-Ray crystallography ((using an X-ray beam to view atoms in a crystal), she observed that the sugars and phosphates were on the “outside” of the DNA molecule, and that the bases were on the “inside”

• Observed the molecule was helical in shape

DNA Structure Consist of

• Two Chaince of Nucleotides

• Sugars and Phosphates that alternate in the “backbones”
  

Base Pairs

• Pair Up in the middle using hydrogen bonds

• A’s always bond with T’s

• C’s always bond with G’s

• This make stwo starts of DNA complementray

Codons

The code of DNA which is read in groups of three nucleotide

What do codons also do?

• Codes for the addition of an amino acid to a growing chain of amino acids, which will eventually become the polypeptide/protein

• think as the words of a sentence(genes)

Amino Acids

• Proteins are just long chains of amino acids

• 20 different types

• Each codon codes for a specific amino acid

• Meaning that the sequence of nucleotides in a gene dictates the sequence of amino acids that are used to build a protein

Why are DNA read in groups of three?

• Because there are 4 diff. bases; so, if each represented an amino acid, only 4 amino acids could be used to build proteins

• 16 different combinations coding for 16 diff amino acids (not enough)

About how many amino acids are there?

20

Information about Codons

• Consist of groups of 3 bases, making (4×4×4) 64 possible codes which is more than enough to code for the 20 amino acids

What Happens to the extra Codons?

• Leads to redundancy, meaning that more than one codon can code for the same amino acid

Analogy for DNA Coding

the bases of DNA are like letters in the alphabet; codons are like words in a sentence; a string of codons that composes a gene is like a sentence; all of the genes in your genome are like the sentences in the instruction booklet that explain how to make YOU!

“Start” and “Stop” codons (Punctuation marks)

• Tell the cell where to start building a new protein, and where to stop (where the sentence start and stop)

• Start: AUG

• Stop: UAA, UAG, UGA

1st Step of Getting DNA to protein: Transcription

• Information in DNA is copied to a molecule of messenger RNA

• Takes place in the Nucleus

• Similar to DNA but T’s are replaced with U’s, and the molecule is single stranded

1st Step of Transcription: Initiation

• A nucleotide sequence called the “promoter“ signals where to begin transcribing a particular gene

  • Here is where RNA polymerase attaches

    • Separates the DNA strands and begins the process of making an RNA strand complementary to the DNA of the gene being transcribed

2nd Step of Transcription: RNA Elongation

• Nucleotides are added to the strand of RNA

• RNA peels from the DNA

  • While this is happening, the two strands of DNA come back together

3rd Step of Transcription: Termination

• When a special sequence on the DNA molecule called the “Terminator” is read, transcription stops

  • End of gene

  • RNA polymerase detaches, RNA molecule detaches, and DNA “Zips back up“

Introns

• Streches of “noncoding“ mRNA

  • Intervening sequences

  • Must be removed

Exons

“Coding” regions that are spliced back together

2nd Step of Getting DNA to protein: Translation

• Information in the mRNA molecule is read by ribosomes, and used to make proteins

• Takes place outside the nucleus

  • Transfer-RNAs bring the appropriate amino acid to the growing protein chain

tRNA

• tRNA’s are the “translators” of the message in the mRNA

• Each tRNA has an “anticodon” that is complementary to a particular codon on an mRNA molecule

• On the other end of the tRNA is an attachment site for the appropriate amino acid

What do tRNA’s do?

• Bring the correct amino acid to the attachment site on the ribosome as it builds the polypeptide chain

• Also has an attachment site for the amino acid, and one called the anti-codon for hooking up to the complementary part of the mRNA molecule

How does DNA replicate?

• 2 strands separate (“unzip“), with the assistance of special enzymes, and a new strand is added to each existing strand

What Happens if a mistake occurs during DNA Replication

• Mostly detrimental; rarely beneficial (but this leads to new genetic diversity that may be selected for in natural selection)

Nucleotide Substitutions ( replacement)

• May have no effect, AKA: silent mutation

• Example of Substitution: G in GGC replaced with an A

Nucleotide Deletion

• Everything gets pushed backword

• Example: Second U in UUG deleted

Nucleotide Insertion

• Letter put in pushing everything foward

• Example: A G inserted into the UUU codon

Why are these mutations bad?

• Because The message in mRNA must always be read in nucleotide triplets (codons, which we already said are in groups of three’s), adding or deleting a nucleotide will disrupt all codons downstream of the mutation

• Shift reading frame of DNA (deletion and insertion)

Mutagens

• Physical or chemical agents that can cause mutations

  • Common Mutations: X-ray. Cigarettes Smoke, Nitrates

Mutations

• Most mutations are either harmful or silent

  •Occasionally, however, a mutation may be beneficial

  •Mutations are the source of all new genetic diversity

  •Without mutation, natural selection and evolution could not occur; the diversity of life could not exist!