DNA & Genetics Review

Flashcards for a DNA and Genetics review.

Describe the structure of a DNA molecule (shape).

Double Helix

Explain the base pairing rule (what letters go together).

Adenine pairs with Thymine; Guanine pairs with Cytosine.

What are the building blocks of DNA AND what three things does it include?

Nucleotides consist of a Phosphate group, Sugar (Deoxyribose), and a Nitrogen Base (A, T, G, or C)

Where is DNA found in eukaryotic cells?

Nucleus

In prokaryotic cells, where is the DNA found?

Floating in Cytoplasm

Here is one side of the DNA strand- T T A C G A C G A. What is the complimentary strand?

A A T G C T G C T

What bond hold the bases together DNA double helix.

Hydrogen

How does DNA differ between individuals (what part of the nucleotide)?

Sequence of Nitrogen bases

List the 3 main steps of DNA replication.

1. DNA double helix unwinds and unzips 2. Free nucleotides bond with complementary bases following base pairing rules. 3. Two identical molecules of DNA are formed.

Describe the function of helicase during replication.

It’s an enzyme that separates the 2 strands of DNA

What is meant by "semi-conservative" replication?

Each molecule of DNA consists of one original strand and one “new” strand formed by free nucleotides.

Why is DNA replication necessary before cell division?

Each daughter cell needs a full copy of DNA for its structure and function.

When does DNA replication occur during the cell cycle (what phase)?

S-phase of Interphase

What happens during interphase?

G1- Cell grows S- DNA replicates G2- Checks to make sure DNA replicated properly and continues to make new organelles

Why are checkpoints important in the cell cycle?

Special proteins, cyclins, check to make sure DNA replicated with no errors. The cell cycle is halted while errors are fixed.

How do cyclins regulate the cell cycle?

They stop the cycle to check for errors and wait for errors to be fixed before allowing the cell to move forward.

What can happen if the cell cycle is not properly regulated?

Cancer may result

What are Internal regulators in the cell cycle?

proteins that respond to events inside a cell

What are External regulators of the Cell Cycle

proteins that respond to events outside the cell

How does cancer relate to the cell cycle?

Cyclins no longer function properly and the cell is allowed to continue through the cell cycle with errors. Also, the cells reproduce more often than normal.

What might happen if a cell skipped the S phase?

DNA doesn’t get replicated and new daughter cells will not be formed.

Why is it important that each daughter cell receives identical DNA?

DNA codes for proteins that provide proper functioning and structure for a cell.

How does mitosis differ from cytokinesis?

Mitosis (PMAT) is division of the nucleus; Cytokinesis is division of the cytoplasm.

Compare mitosis in animal vs. plant cells (cell plate vs cleavage furrow).

Animal cells- cleavage furrow splits the cytoplasm. Plant cells- cell plate splits the cytoplasm to form 2 daughter cells.

How is mitosis related to growth and repair?

New somatic (body) cells are made by mitosis. When cells are damaged or worn out they need to be replaced by the process of Mitosis.

What happens if a cell undergoes mitosis incorrectly?

The resulting daughter cells may have an uneven number of chromosomes. (Chromosomal mutation) or cancer can result.

Why doesn't mitosis result in genetic variation?

2 daughter cells created are identical to each other and to the original parent cell.

What is the function of mRNA?

Carry the protein code from the nucleus to the ribosome in the cytoplasm.

How does tRNA contribute to protein synthesis?

It delivers amino acids (in the cytoplasm) to the ribosome in the correct order to build a protein.

Where do transcription and translation occur in a cell?

Transcription- in the nucleus; Translation- at the ribosome in the cytoplasm

What happens during transcription?

DNA Unzips and one strand acts as a template to create mRNA

What happens during translation?

tRNA transports amino acids to the ribosome to create a protein. tRNA anticodons match up to the complementary mRNA codons to ensure the correct amino acid is delivered in the proper order.

What is a codon?

A series of 3 nucleotides on mRNA that codes for an amino acid.

T A C A A A G T C G G G A T C is the DNA. What is the amino acid sequence?

Methionine- Phenylalanine-Glutamine-Proline-STOP

What is the purpose of meiosis?

Sexual reproduction to create genetic diversity

How does meiosis increase genetic diversity?

The 4 gametes created are all unique.

Describe what happens during crossing over AND what phase does it occur?

Occurs during Prophase I; 2 homologous chromosomes pair up and exchange genes.

Why do gametes have to be haploid?

The zygote that results from fertilization (sperm and egg uniting) needs to retain the characteristic number of chromosomes.

How is meiosis different from mitosis?

Meiosis creates four genetically different haploid gametes; Mitosis creates two identical diploid daughter cells

Why is the sequence of nitrogen bases in DNA important?

Every 3 nucleotides on a strand of DNA codes for a specific amino acid. The order of amino acids and the number of them used will create a specific protein.

Explain the consequences of a mutation during protein synthesis.

A mutation may change an amino acid in the sequence, therefore, creating a different protein. It may not be a functional protein, or it may lead to a new adaptation for the organism.

What is a mutation AND what is one environmental factor that might cause it?

A change in DNA; chemicals in the environment or radiation, including UVA & UVB light from the sun, can mutate DNA.

Compare point mutations and frameshift mutations.

A point mutation may cause one amino acid to change in the sequence of amino acids that make the protein. Frameshift adds or deletes a nucleotide to the DNA strand. This causes many amino acids to change after the point of insertion or deletion. It shifts the way the code is read.

How can a mutation affect a protein?

It changes the amino acid code on DNA. A different order of amino acids may result. The order of amino acids will affect the 3-D shape of the protein and it may or may not be a functional protein.

What role do mutations play in evolution?

Proteins provide structure and function for an organism. Proteins make-up all traits. When a mutation occurs that codes for a new protein, it may help the organism to adapt to the environment in which it lives and get passed on to the next generation.

How can a mutation be inherited?

Sexual reproduction: a mutation in a gamete

What are dominant and recessive alleles?

Dominant alleles get expressed; it will “mask” a recessive allele. Recessive alleles only get expressed when there are two recessives together.

Describe the Law of Segregation.

Homologous chromosomes get separated during meiosis and go into different cells. Hence, a mother gives one allele coding for a trait to her offspring, and the father gives the other allele coding for the same trait to the offspring.

What does it mean to be homozygous or heterozygous?

Homo- both alleles are the same that code for a trait; Hetero- the two alleles coding for a trait are different (code for different proteins)

How do you use a Punnett square to predict offspring?

The father’s gametes get placed along the top of the Punnett Square; the mother’s gametes get placed along the side. The eggs are fertilized inside the Punnett Square (alleles come together showing the possible genotypes of offspring).

Use a Punnett square to predict the offspring of two heterozygous parents (Aa × Aa).

Genotypic ratio: 1 AA: 2 Aa: 1 aa Phenotypic ratio: 3 non-albino: 1 albino

Define incomplete dominance and give an example.

One allele is NOT fully dominant over another allele. In some flower species, Pink color results from a BLENDING of a red allele with a white allele.

Define codominance and give an example.

Two different alleles get equally expressed and DON’T appear blended. In Tupelo chickens, black feathers and white feathers are both expressed resulting in a checked (or speckled) chicken.

What is the genotype of a heterozygous type A individual?

Aa

Describe sex-linked traits and give an example.

A trait that is carried on the sex chromosomes (chromosome pair #23 in a human). Colorblindness, Duchenne’s Multiple Dystrophy, or Hemophilia.

Why are males more likely to express X-linked recessive traits?

They receive only one X-chromosome (from their mom). If it contains a defective gene, they will have the disorder.

The pedigree to the right shows a recessive sex-linked trait. What is the genotype of I-1?

X h Y

The pedigree to the right shows a recessive sex-linked trait. What is the genotype of II-2?

X H X h

How many biological children did generation I have?

3

What is the difference between homologous, analogous & vestigial traits?

Homologous: originate from the same group of cells in each respective organism and develop into different looking structures with different functions in each species. It shows common ancestry among the different species. Analogous- Structures that are similar looking in different species and have the same function. It doesn’t show common ancestry. Vestigial- structure is reduced in size and no longer serves a purpose. It shows evidence of evolution.

What animal did Darwin spend most of his time studying?

Finches

Compare divergent and convergent evolution.

Divergent: species can be traced back to a common ancestor but developed different traits as they migrated to different geographical areas. Convergent: Different species come to resemble each other because they live in similar environments.

A structural or internal change that betters an organism’s chance of survival is an __.

Adaptation

What is the difference between geographic, behavioral and temporal isolation?

Geographic: Two populations are separated by a geographic barrier like the ocean or mountains. Behavioral: Two populations are capable of interbreeding but have different courtship rituals. Temporal: Two or more populations breed at different times of the day or year.

What is survival of the fittest?

“Natural Selection”- the organism that possesses the adaptation(s) best suited to their environment will live long enough to reproduce and pass its genes on to its offspring.