BIOL 1610 Exam 3 Study Guide and Tips

mitosis and cell cycle!

Gene

region of DNA sequence containing information for building RNA or protein

Genome

all the DNA in a cell

23 Pairs, 20,000 genes

Histone

protein molecule around which DNA is tightly coiled in chromatin

Cell cycle phases

Interphase: G1, S (replication of DNA), G2,

orderly series of events ending in cell division

M phase (undergoing mitosis) and Interphase ( cell is growing, preparing for division)

G1 Phase

chromosomes consist of 1 DNA molecule

make proteins necessary for DNA replication

S Phase

DNA synthesis: replicates DNA so there are 2 identical copies of each DNA molecule

End of S phase

- 46 chromosomes (23 pairs)

- each chromosome has two sister chromatids

-4 copies of each gene (two are identical)

- 2 centrosomes

G2 phase

-chromosomes = 2 sister chromatids

-prepare for division

- grow

End of interphase

-extra organelles, membrane

-DNA replicated

- each chromosomes = 2 sister chromatids

-chromosomes still uncondensed

- 2 centrosome

Know the relationships between chromatids, chromosomes, kinetochores and centromeres.

A chromosome is made up of two identical sister chromatids,

which are joined together at a specific region called the centromere;

the kinetochore is a protein complex that assembles on the centromere, serving as the attachment point for spindle fibers that pull the sister chromatids apart during cell division, effectively separating the chromosomes into daughter cells.

Chromatid

-each DNA copy in a replicated chromosomes

- one copy of DNA in replicated chromosome

sister chromatids - chromatids in the same chromosomes

Chromosome

Structure containing genetic material. of one double-stranded DNA molecule

Kinetochore

Protein structure on chromosome for spindle attachment.

Centromere

Region where sister chromatids are joined.

Karyotype

Visual representation of an organism's chromosomes.

image of a full set of chromosomes from a cell

46 chromosomes total, 2 of each kind

What are the major events that happen in each phase of mitosis?

Prophase

Metaphase

Anaphase

Telophase/Cytokinesis

Prophase

chromosomes condensation starts, mitotic spindle begins to form, nuclear envelope degrades

metaphase

chromosomes line up at the metaphase plate

anaphase

chromatids pulled apart

telophase

nuclei reform, chromosomes become less condensed, mitotic spindle depolymerizes/ cleavage furrows pinches cell in two

How do plantand animal cells differ in cytokinesis?

animals have a cleavage furrow that causes both cells to separate

in plants, cell plate starts forming in between cells

Mitotic Spindle

Structure that separates chromosomes during mitosis.

microtubules and associated proteins

attach to kinetochore

spindle fibers attached to kinetochore shorten to pull chromatids apart

Centrosome

Organelle that organizes microtubules in cells.

-microtubule organizing center

How is the cell cycle controlled? What is the role of cyclin/Cdk and how is it regulated?

controlled through a series of checkpoints and through Cdks and Cyclin

when Cdk phosphorylates and activates proteins involved in mitosis, but can only phosphorylates when bound to cyclin

cyclin builds up, cyclin/cdk complex triggers M phase, activates a protein that degrades cyclin

Cyclin/Cdk

Proteins regulating the cell cycle progression.

Cell Cycle Checkpoints

Control mechanisms ensuring proper cell division.

late G1 checkpoint

G2 checkpoint

M checkpoint

late G1 checkpoint

is the cell too small?

are there enough nutrients?

what do other cells say?

is DNA damaged?

p53 protein: DNA damage triggers p53 and causes the cell cycle to shut down

late G2 checkpoint

is DNA damaged (p53)?

is cell big enough?

are chromosomes ok?

M phase checkpoint

will chromosomes separate properly

Meiosis!

Why is sexual reproduction advantageous? How does it compare with asexualreproduction?

asexual reproduction is efficient as it uses less energy than sexual reproduction and you produce more

but sexual reproduction causes variation in offspring, meaning only some of the offspring will inherit potentially damaged genes and have a genetic advantage if environmental conditions change

1. purifying selection hypothesis

2. changing environment hypothesis

How many chromosomes does a human cell have before DNA replication?

After DNA replication?

After Meiosis I? After Meiosis II?

How many individual DNA molecules are there after Meiosis I?

After Meiosis II?

Before DNA replication, we have 46 chromosomes (23 pairs)

After DNA replication, we have 46 chromosomes, now with sister chromatids

After meiosis I: we will have 23 chromosomes, 2 chromatids per each, 46 individual DNA molecules

After meiosis II: we will have 23 chromosomes, but 1 chromatid, 23 individual molecules

After meiosis I

2 cells

each cell has 1 paternal or maternal chromosomes

each chromosome has 2 sister chromatids

23 chromosomes, 46 DNA molecules

2 copies of the gene

After meiosis II

4 cells

1 paternal of 1 maternal chromosome

sister chromatids have separated

23 chromosomes, 23 individual DNA molecule

1 copy of each gene

what is ploidy?

Number of sets of chromosomes in a cell.

human somatic cells: dipiold

before DNA replication and mitosis: 2 cells

gametes are haploid:

1 chromosome set

after meiosis: 1 type of chromosome

What are the phases of meiosis, and what happens in each?

Meiosis I and II, both have prophase, metaphase, anaphase, telophase II

meiosis I - homologous chromosomes separate

meiosis II - sister chromosomes separate

Prophase I (Meiosis)

homologous chromosomes pair up and crossing over occurs within non-sister chromatids

Metaphase I

pair of homologous chromosomes line up in metaphase plate

Anaphase I

homologous chromosomes separate, and sister chromatids stay attached

When do homologous chromosomes separate?

meiosis I, anaphase I

When do sister chromatids separate?

When does crossing over occur?

Prophase 1

Exchange of genetic material between homologous chromosomes

non-sister chromatids are physically broken at same point and reattached to each other

What is recombination, and how does it result in genetic variation?

different combination of chromosomes of maternal and paternal alleles on each chromosomes

How does meiosis "shuffle" alleles?

each cell gets a random assortment of maternal and paternal chromosomes

What is the Principle of Independent Assortment?

Random distribution of alleles during gamete formation.

each pair of maternal and paternal chromosomes sort into cells independently of any pair during meiosis I

What is nondisjunction? What happens when it occurs in gametes?

Failure of chromosomes to separate properly during meiosis.

chromosomes homologs both move to one side during Anaphase I or II

results i aneuploid cells

2 many copies - trisomy

0 copies - monosomy

Why did Mendel use peas to study genetics? State Mendel's ideas using modern terminology.

peas have a short reproduction cycle, self-pollinate, have clear traits and have a large number of offspring

law of segregation: two alleles for a gene will separate from each other during meiosis

law of independent assortment: each pair of alleles segregates independently of any other pair of alleles during meiosis

3:1 ratio in phenotype, 1:2:1. ratio in genotype

genes: determinants for hereditary traits

Alleles: alternative forms of these determinants

How do recessive and dominant alleles contribute to genotype? Phenotype?

if you have two hetero crossings, then the dominant alleles cause the phenotype to have a ratio of 3:1. but regarding genotype, the ratio is 1:2:1

Why does a monohybrid cross give a 3:1 phenotypic ratio?

Because two combinations will result in a hetero, the dominant trait will be its result phenotype. And then you have your dominant homo, which will present in the dominant phenotype, and then you would only have your recessive trait that will be a different color than the rest

Tay-Sachs disease

- The HEXA gene has multiple alleles

-it's recessive, only individuals with tt will have the disease

-the absence of functional protein HEX-A enzyme that breaks downs the accumulation of ganglioside in nerve cell

Huntington's disease

-dominant

-caused by mutation in the Huntington gene (HTT)

-functions in cell communication

-large protein malfunction, causes cell death

Achondroplasia

- dominant

- short-statured phenotype

-caused by an allele of gene FGFR3, involved in triggering the transition from cartilage to bone during development (FGFR3 signals early)

autosomal recessive disorders

cystic fibrosis

sickle cell anemia

Leigh syndrome

PCD

tay sachs

What are carriers? Why aren't there carriers for dominant diseases?

individuals who are heterozygous for a recessive disease.

because you either have it or not because the dominant homo has the disease, hetro has diseases, and only recessive doesn't have the disease.

Why don't all bad alleles disappear?

-recessive alleles can be propagated by carriers

- inbreeding/closed communities

- some recessive disease-causing alleles confer a survival advantage to hetero.

-an allele's impact occur after reproductive age

-new mutations occur.

extending Mendel's rules

!!

What are sex-linked genes?

genes that reside on X or Y will have different genotypic and phenotypic ratios

red-green color blindness

sex-linked recessive trait

Hemophilia

-bleeding disorder

- causing recessive allele of clotting gene located on X chromosome

(recessive allele: nonfunctional clotting factor)

What is incomplete dominance?

incomplete dominance - heterozygotes have an intermediate phenotype

have 1:2:1 phenotypic ration than 3:1, matches genotypic ratio

Familial hypercholesterolemia

-very high levels of cholesterol in the blood increase the risk of heart disease

- mutation in the LDLR gene that removes bad cholesterol from the blood

-ll: regular cholesterol level

-Ll: high cholesterol

-LL: extremely high cholesterol starting in childhood

What is Co-dominance?

heterozygotes have a phenotype where both alleles are represented

ABO blood type

a type of co-dominance, were A and B are codominant

What is maternal mitochondrial inheritance? What does mitochondrial replacement therapy do?

mitochondria possess their own genome and are inherited from egg only

takes the nucleus from the egg with mutated mitochondrial DNA, places it into a healthy egg

results in an embryo with DNA from 3 individuals

Polygenic

multiple genes can affect one trait

Multifactorial

phenotype depends on genetics and environmental influences

Penetrance

proportion of individuals with the traits out of all individuals predicted to have trait.