BIO Exam 3

What is a chromatin?

The chemical composition of chromosomes. DNA + proteins.

What is a chromatid?

The individual copies of a chromosome.

What are sister chromatids?

Identical chromatids attached at the centromere.

What is the centromere?

Links sister chromatids together.

What are homologous chromosomes?

Different versions of the same chromosome AKA same chromosome but different DNA sequence. Humans obtain one from the mother and the father.

What is a tetrad?

A group of 4 chromatids. Two pairs of sister chromatids basically.

Where are genes located?

Genes are located in the chromosomes that are in the nucleus. Genes contain the information for protein sequence for the body’s vast proteins.

What are the major phases of the cell cycle?

1. Gap 1

2. G1 Checkpoint

3. S Phase

4. Gap 2

5. G2 Checkpoint

6. Mitosis

7. Cytokinesis

In cell cycle: what happens in Gap 1?

First part of Interphase where the cell will grow in size, produce many proteins, and copy organelles.

In cell cycle: What is G1 checkpoint?

The cell makes sure that the DNA is intact and ready for replication. Defects at this checkpoint is usually associated with cancer because the cell will pass along mutations.

In cell cycle: What is S phase, and what is it also called?

DNA replication. Also called Synthesis of DNA.

What do chromosomes look like before and after S-phase?

Before S Phase: I-shaped.

After S Phase: X-shaped; Identical copies attached at centromere > called sister chromatids.

In cell cycle: what is Gap 2?

Period of growth and biochemical activity.

In cell cycle: what is G2 checkpoint?

Cell makes sure that DNA is intact and ready for mitosis.

In cell cycle: What does mitosis do and are the daughter cells identical or not to the parent?

Separates DNA into two copies. The daughter cells are identical to parent.

In cell cycle: What is cytokinesis?

Physically separates the cell into two.

Mitosis: Prophase

• Chromosomes condense

• Nuclear envelope disintegrates

• Mitotic spindle forms

What does the mitotic spindle do?

Microtubules that catch one side of every chromosome and pulls it towards them. The poles bind to one kinetichore.

Mitosis: Metaphase

• All chromosomes are captured by each pole

• Chromosomes aligned in the center of spindles.

Mitosis: Anaphase

• Centromere connections break.

• Sister chromatids separate and move towards opposite poles.

Mitosis: Telophase

• Sister chromatids at opposite poles.

• Chromosomes de-condense.

• Nuclear envelope forms.

Mitosis: Cytokinesis:

One cell physically separates into two.

What is the mitotic spindle?

Collection of microtubules at mitotic spindle poles. The microtubules will attach to one kinetochore and pull one chromatid.

What is parental cell?

The cell that undergoes cell cycle.

What are daughter cells?

The result from cell cycle of parental cell.

What is ploidy level?

The number of sets/versions of chromosomes in a cell.

What is diploid cell?

Cell has two versions of each type of chromosome.

What is haploid cell?

Cell has one version of each type of chromosome.

What are tumor supressors genes?

Genes that encode a protein that prevents excessive cell division and monitors DNA damage.

• Having one functional copy is enough for the cell to be stable.

What would happen if an animal was born with one copy of a nonfunctional tumor suppressor gene?

The other good copy has a good chance of mutating and becoming “broken”.

What are oncogenes?

Genes that encodes a protein that normally promotes cell division. Mutation of this gene can cause cell division to happen rapidly.

Defects in G1 checkpoint usually mean:

Cancer.

Why do sister chromatids need to remained attached?

So the each spindle pole can grab only one chromatid.

Are two sister chromatids attached at the centromere considered two chromosomes?

No, the pair is considered one chromosome.

What is Meiosis and what is it also called?

Also called reductive cell division because it reduces the # of genomes by half. Meiosis creates gamete cells that have half as many chromosomes as parental cell.

How many rounds of cell division that Meiosis undergo?

Two rounds.

1st round: Diploid cell to 2 haploid daughter cells.

2nd: 2 haploid cells into 4 total halploid cells (two from each original haploid). This round does not involve DNA synthesis or replication.

Meiosis I: Prophase I

1. chromosomes condense

1. meiotic spindle forms

2. nucleus disintegrates

3. homologous chromosomes pair up (X and X, Y and Y) = tetrad

4. recombination also occurs

Meiosis I: Metaphase I

23 tetrads align in center of spindle.

Meiosis I: Anaphase I

Homologous chromosomes separate and move to opposite poles. Centromeres that attached sister chromatids will not break, spindle poles merely pull the chromatids away from each other via the kinetochore.

Meiosis I: Telophase I + Cytokinesis

1. Homologous chromosomes at opposite spindle forms are not identical.

2. Chromosomes de-condense and a nuclear envelope forms around chromosomes.

3. Forms two haploid daughter cells.

Meiosis II:

• The two N cells from Meiosis I undergo Meiosis II on their own.

• The nonidentical sister chromatids separate.

• Results in 4 daughter cells that are not identical to the original N cells or the 2N parental cell.

What do the chromosomes look like after Meiosis II?

Single chromatids (I-shaped).

Differences between mitosis and meiosis.

Mitosis:

• produces two daughter cells.

  • identical to parental cells.

• undergoes cell division once.

Meiosis:

• produces 4 daughter cells.

  • not identical to parental cells.

• undergoes cell division twice.

• homologous chromosomes line up at the spindle.

What is recombination?

Equal portions of chromatids are swapped during Prophase when homologous chromosomes pair up.

Does S-Phase occur after Meiosis I?

No because the cells already have chromosomes with 2 chromatids.

Why does Meiosis II occur?

The chromosomes formed in the 2 haploid cells contain non-identical sister chromatids, thus why these sister chromatids are separated into 4 daughter cells.

Do the centromeres connecting the sister chromatids in Meiosis II break in Anaphase II?

Yes.

What is nondisjunction?

When the chromosomes fail to separate properly during cell division.

What is required for Meiosis to occur successfully?

• Must have homologous chromosomes.

• Have an even number of chromosomes.

What is a mule and why can’t they reproduce?

Mules are horse x donkey. They are infertile because they can’t do meiosis (production of gametes) due to their chromosomes not being homologous to each other due to different arrangement of genes.

Can tetraploids (4N) and hexaploids (6N) do meiosis?

Yes.

Why are common bananas and watermelons seedless?

Because they are triploids (3N). They aren’t able to undergo meiosis properly due to an uneven amount of chromosomes, so they aren’t able to make the seeds.

In human cells, how many egg cells are produced during Meiosis?

1

What are characters/characteristics?

A category of some physical attribute.

What are traits?

Specific values of a character.

What does phenotype mean?

The physical manifestation of a genotype.

What is a genotype?

A list of alleles present for a gene in an individual.

What are alleles and what did Mendel call them?

Alleles are different versions of the same gene. Mendel called them factors.

What does true-breeding mean? What were the true-breeding plants in Mendel’s experiment?

True-breeding is when all offspring of an individual will have the same trait as the parent. Either homozygous dominant or recessive. In Mendel’s experiment, the flowers either showed up as all purple (dominant) or all white (recessive).

What does nontrue-breeding mean?

Nontrue-breeding is when not all offspring will have the same trait as the parent. They’re basically heterozygous.

What was Mendel’s experimental design?

1. Used TB purple flowers and TB white flowers as parental generation.

2. Produced (F1 generation) offspring that all had purple flowers (all heterozygous) so phenotype ratio 100% purple 0% white or 4:0. Genotype ratio would be 0:4:0,

3. Offspring self-reproduced and made (F2 generation) 75% purple and 25% white flowers or 3:1 (phenotype ratio). Has a genotype ratio of 1:2:1.

What are punnett squares?

They illustrate the possible genotypes of an offspring. Each box on the punnett square is equally likely to happen.

What is homozygous?

When the alleles are the same. Ex: BB, bb.

What is heterozygous?

When the alleles are different. Ex: Bb.

What is the dominant allele?

The allele that overpowers the recessive allele and always shows up.

What is the recessive allele?

The allele that only shows up if there is no dominant allele.

What is Mendel’s Law of Segregation?

The two alleles of a gene separate from each other during meiosis. This relates to each individual gene and two alleles in a diploid’s genome.

Is Mendel’s Law of Segregation ever broken?

Typically no. But it can be broken due to nondisjunction.

• Nondisjunction violates this law because it’s when the chromosomes fail to separate properly during meiosis, thus going against the law’s statement.

What happens to alleles/factors during meiosis?

They separate. Each individual has 2 alleles for the same gene and they get these 2 alleles from Mom and Dad. An individual only passes one allele to the next generation.

Does the inheritance of one gene affect the inheritance of another?

No.

What is the typical phenotype ratio for offspring that have parents that are heterozygous for two genes (dihybrid cross)? How many possible genotypes are there?

9:3:3:1.
16 possible genotypes.

What are gamete genotypes?

Gametes = haploid, so they have one allele for genotype.

What is Mendel's Law of Independent Assortment?

The inheritance of one gene doesn’t influence the inheritance of another gene.

Can Mendel's Law of Independent Assortment be broken?

This can only be broken if the two genes are located closely together on a chromosome or are linked AKA genetic linkage.

The further apart the genes are:

the more they will independently assort.

What is genetic linkage?

When genes are located close to each other in the same chromosome. This means that the alleles for these genes will most likely end up in the same daughter cell together.

What can break up

What are many of the recessive alleles we look at?

They’re all mostly defective alleles; they do not create functional proteins.

What is incomplete dominance example?

Red + white = pink flowers

What is codominance?

When each allele fully expresses its traits.

• Ex: ABo blood type. A and B are both dominant to o but they are codominant to each other.

What is epistasis?

When the effect of one gene can cover up the effect of another gene. Basically X-linked alleles.

What are autosomes and what are sex chromosomes?

Autosomes are human chromosomes aka homologous chromosomes while sex chromosomes are X and Y.

Who do you inherit mitochondrial genome from?

Mom.

Autosomal dominance is:

One dominant allele gives trait.

Autosomal recessive is:

Two recessive alleles give the trait.

X-linked inheritance is:

One allele in XY in male gives trait (the dominant allele is in the Y), female has recessive alleles on XX.

Since the human body only requires one X to be active, what happens to the other?

One of the X’s randomly gets inactivated, which corresponds with all the other daughter cells.

Pedigree: What does it mean if only males are affected?

X-linked recessive.

Pedigree: What does it mean if not only males are not affected and if not each affected individual has affected parents?

Autosomal recessive.

Pedigree: What does it mean if not only males are not affected but each affected individual has an affected parent?

Autosomal dominant.

In Mendel's experiments he crossed a Homozygous dominant plant to a Homozygous recessive plant. What phenotype(s) did the next generation have (F1 generation)?

100% dominant phenotype.

In Mendel's experiments, what was the ratio of dominant to recessive phenotypes in the F2 generation?

3:1

In Mendel's experiments, what percent of the F2 plants with a dominant phenotype were "True-Breeding" for the dominant phenotype?

33.3%

In Mendel's experiments, what proportion of the F2 plants with a recessive phenotype were "True-Breeding" for the recessive phenotype?

100% because recessive phenotype only shows up if it’s homozygous recessive.

True or false: For X-linked recessive traits, only females can be carriers.

True, with some exceptions.D

Discovery of DNA (Griffith): What were the virulent and nonvirulent factors?

Virulent = S-strain > causes disease

Nonvirulent = R-strain > no disease

Discovery of DNA (Griffith): Why did the mice that were injected with DEAD S-strain (virulent) and the R-strain still end up dying?

The R-strain was picking up something from the dead S-strain and causing it to be transformed to S-strain, thus causing the mice to die.

What did Avery–MacLeod–McCarty Experiment show?

It showed that purified DNA was enough for transformation.

(Hershey Chase Bacteriophage Experiment) Gene that viruses use to multiply are made of up DNA and not protein, therefore:

Showing that DNA is what was needed for viruses to spread (genetic material).

• When bacteriophages entered bacteria, the DNA entered the bacterial cells while the protein remained inside.

Subunit of DNA:

Nucleotides