Week 04: Mitosis, Meiosis, and Chromosome Numbers

why does chromosomes carry mendel's hereditary units?

- every cell contains 2 copies of each kind of chromosome, 2 copies of each kind of gene - meiosis- homologus chromosomes pair and then seperate to diff genes, like how alleles of a gene segregate to diff gametes - maternal and patern copies of each chromosome pair move to opposite spindle poles withour regard - fertilization- an egg's set of chromosomes unites with random encourntered sperm set of chromosomes - all cells derived from the fertilized egg

what are the 2 features that distinguish metaphase 2 from mitosis?

- haploid chromosome count - 2 sister chromatids are no longer identical

aneuploids

- not an exqact multiple of the haploid number

how do meiosis contribute to genetic diversity?

- paternal and maternal homologs migrate to 2 poles- different patterns 2^23 combinations - crossing over

The synaptonemal complex dissociates during the ________ stage of meiotic prophase I, and it completely disappears by the ____________ stage.

-diplotene -diakinesis

does age of women contribute to birth defects?

0.05% trisomy 21 mid 20s at age 45 its 3%

In comparison to a normal diploid cell, a cell that is trisomic would produce up to ______ of the protein product of the gene found in three copies. Therefore, an imbalance occurs between the level of expression of this gene versus the ones that are normally found in pairs.

150%

What happens in leptotene

1st prophase 1 chromosomes begin to condense centrosomes begin to move towards opposite poles

How many meiosis are there?

2 meiosis meiosis 1 is to seperate homologs meiosis 2 is just mitosis

Consider an animal with a normal diploid chromosome number of 20. A tetrasomic cell would have ______ chromosomes.

22

trisomic

2n + 1 additional chromosome

Which of the following best describes the outcome of mitosis and cytokinesis in human somatic cells?

2n → 2n

During mitosis of a particular diploid cell, a chromosome loss event occurs. What will be the chromosome number in the resulting daughter cells?

2n, 2n - 1

What happens in Zygotene

2nd prophase 1 homologous chromosomes enter synapsis synaptonemal complex forms zipper

what happens during interphase in a cell?

3 parts gap 1 synthesis gap 2 G1 lasts from birth of a new cell- onset of chromosome replication G0- arressted mature brain cell- do not DIVIDE S- DNA duplication - cruicial G2- interval between chromosomes duplication- beginning of mitosis microtubules become visible- from centrosome. centrioles

What happens in pachytene

3rd substage of prophase I synapsis is complete crossing over genetic exchange between nonsister chromatids of a homolohous pair occurs bivalent

what happens in diplotene?

4th stage in prophase 1 synaptonemal complex dissolves tetrad of 4 chromatids is visible crossover points appear as chiasmata- hold nonsister chromatids together meiotic arrest occurs at this time in many specieis

monosomic

A chromosomal condition in which a particular cell has only one copy of a chromosome, instead of the normal two. 2n-1

triploid

A chromosomal mutation where an organism has three sets of chromosomes (3n) instead of two (2n)

barr body

A dense body formed from a deactivated X chromosome.

hemizygous

A gene present on the X chromosome that is expressed in males in both the recessive and dominant condition

crisscross inheritance

A pattern in which an X chromosome present in a male in one generation is transmitted to a female in the next generation, and in the generation after that can be transmitted back to a male.

kinetochore

A specialized region on the centromere that links each sister chromatid to the mitotic spindle.

What is nondisjunction?

An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell

mosaic organism

An organism whose phenotype depends on which tissues bear the aneuploidy

In 1903, Walter Sutton suggested that chromosomes carry Mendel's hereditary units. Select the reasons he gave for this proposal.

Both chromosomes and alleles of unrelated genes assort independently. Every cell has two copies of each chromosome, and there are two copies of each kind of gene. In all cells derived from a fertilized egg, half of the chromosomes and genes have maternal origin, and half have paternal origin. During meiosis, homologous chromosomes and alternative alleles of a gene pair then separate to different gametes.

what happens with polyploid with even number of chromosomes

CREATE NEW SPECIES I.E. SALMON

Which species achieves dosage compensation by decreasing the level of expression on both X chromosomes in XX hermaphrodites to 50% relative to the single X of XO males?

Caenorhabditis elegans

On rare occasions, a new tetraploid species of plant may form. What factors allow the species to form and propagate?

Chromosome nondisjunction Joining of two diploid gametes Self-fertilization

Select the events that occur during prometaphase.

Chromosomes attach to the microtubules through the kinetochore. The nuclear envelope completely breaks down.

Where are microtubules found?

Cilia Flagella Mitotic spindle Neurons Centrioles

kinetochore microtubules

Connects the centrosome with the kinetochore in the centromere region of the chromosome. It allows chromosomes to slide along microtubules.

what does each thread of chromatin composed of?

DNA

Which species achieves dosage compensation by increasing the expression of genes on the X chromosome in males by twofold?

Drosophila melanogaster

Color blindness is inherited with an X-linked recessive allele. Which term describes the genotype for a color-blind male?

Hemizygous

Choose all correct statements about the basic chromosome number (x) and the number of chromosomes in gametes (n).

In polyploid species, x < n. In diploid species, x = n.

what are the 5 stages of prophase in meiosis 1

Leptotene Zygotene Pachytene Diplotene Diakinesis

Nucleolus

Makes ribosomes

dosage compensation

Mechanism in which X chromosome inactivation equalizes gene expression between males and females. bc has like 850 genes per x except its not 1 x gene being deleted but its more of a 50% 50% patchwork

Which of the following best describes how chromosomes are attached to microtubules during metaphase I of meiosis?

One pair of sister chromatids is linked to one pole, and the homologous pair is linked to the other

Interkinesis

Period of time between meiosis I and meiosis II during which no DNA replication takes place.

Which genes on the X chromosome are able to escape the effects of X chromosome inactivation in female mammalian cells?

Pseudoautosomal (PAR) genes

what are germ cells?

Reproductive cells that give rise to sperm and ovum

Based on how it is written, which of he following is a dominant mutant allele in Drosophila?

Ser

what happens in metaphase 1?

Tetrads line up at the equator of the cell- metaphase plate sister chromatids attach to the fibers from same pole

Select the events that occur during prophase of mitosis.

The centrosomes move apart. The chromatin condenses into more compact structures. The nucleolus becomes less visible.

Prometaphase

The second stage of mitosis, in which the nuclear envelope fragments and the spindle microtubules attach to the kinetochores of the chromosomes. break down nuclear envolope kinetochore form mitotic spindle from 3 different types of microtubules

Which of the following individuals will have the most trouble in producing functional gametes during meiosis?

Triploid with 30 total chromosomes

chiasmata

X-shaped regions where crossing over occurred.

Chromosome loss during mitosis of a diploid cell produces

a diploid and a monosomic daughter cell

mitotic nondisjunction

an event in which chromosomes do not segregate equally during mitosis

how does cytokinesis occur?

animal cells- contratile ring- pinches cell into approx 2 equal halves plant cells- cell plates

What are somatic cells?

any cell of a living organism other than the reproductive cells.

In polyploid organisms the number of different chromosomes that make up a single complete set (usually denoted as x) is known as the ______.

basic chromosome number

what does the symbole x means

basic chromosome number

The primary oocytes of a human female are formed ______, but are arrested in ______.

before birth; prophase I of meiosis

are regulatory checkpoints based on extrrinsic or intrsic factors

both intrinsic- i.e. cell size or external signals

metaphase

chromosome move towards equator- METAPHASE PLATE balanced equilibrium tension

chromatin

chromosomes often resemble mass of extremely fine tangled string

During prophase of mitosis, chromosomes______into discrete structures. Furthermore, the two_________separate moving towards the poles and the mitotic_______begins to form.

condense centrosome spindle

polyploid

condition in which an organism has extra sets of chromosomes

Euploid

contain only complete sets of chromosomes

Oogonia are

diploid cells

oogonia

diploid cells that produce primary oocytes by mitotic division

cytokinesis

division of the cytoplasm

what are regulatory checkpoints?

ensure correct chromosome seperation is a decision to divide

what are aneuploidies?

extra or missing chromosomes i.e. down syndrom- caused by extra copy of 21

A XXY fruit fly can make ____ types of gametes in terms of sex chromosome content.

four

What happens in prophase of mitosis?

gradual condensation of individual chromosome ascaris cells- 4 chromosomes exist with a total of 8 chromatids 3-4cm condence into chromosomes nucleoli break down and disappear microtubule grow from centrosomal organizing centers

what are triploid organisms usually?

infertile

Diakinesis

last stage of prophase chromatids thicken and shorten nuclear envelope fragments, chromosomes complete condensing, tetrads ready for metaphase.

nuclear envelope

layer of two membranes that surrounds the nucleus of a cell

non disjunction on sex chromosomes

make white eyed female i.e. gamete w 2 XX- and pass the Y (3 x - dies)

Compare and contrast mitosis and meiosis

mitosis is preceded by s phase chromosome duplicated prior to meiosis 1 but not 2 mitosis- sister chromatids attach to spindle fibers meiosis 1- homologous chromosomes attach to spingle fibers

An organism that has a single set of chromosomes (for example, 3 different chromosomes) is a(n)____organism

monoploid or haploid

what proved the chromsomal theory of inheritance

morgan's fly experiments i.e. red eye is wild allele and white eyed is mutation all f1 generation had red eyes and red allele is dominant most white eyed were males but if mixed with heterozygous female- with white eyed male, can make white eyed female

If a pair of homologous chromosomes undergoes nondisjunction during anaphase I of meiosis, what will be the chromosome number of the four resulting gametes? Assume meiosis II is normal.

n + 1, n + 1, n - 1, n - 1

is sex chromosomes aneuploidy lethal

not all i.e. triple X

telophase 1

nuclear envolope reforms resulting cells- half the number of chromosomes, 2 sister chromatids cyotkinesis- seperate daughter cells

monoploid

of a cell or organism having a single set of chromosomes

Chromatid

one of two identical "sister" parts of a duplicated chromosome

astral microtubules

position spindle in cell Extend from the centrosome toward the cell's periphery

gametogensis

production of gametes

During ______, pairs of sister chromatids become attached to kinetochore microtubules which emanate from opposite poles of the cell.

prometaphase

telophase

prophase in reverse spindle fibers dispears- nuclear envelope forms around the group of chromatids at each pole one nucleas into 2 nuclei- mitosis is over

What is the synaptonemal complex?

protein structure that temp forms between homologous chromosomes and gives rise to tetrad

pars region

pseudoautosomal regions

polar microtubules

push the poles of the cell away from each other during mitosis Originate at centrosomes and interdigitate near the cell's equator

what happens between non sister chromatids

recombination -c rosing over - produce new combinations of alleles of different genes

X-linked

referring to a gene located on the X chromosome

cell cycle

series of events that cells go through as they grow and divide M phase- mitosis

anaphase

simulataneous severing of centromeric connections - anaphase - pulled towards spingle pole, linked by kinetochore microtubules

what happens in anaphase 1?

sister centromeres remain connected to each other chiasmata dissolve homologus chromosomes move to the opposite poles

what happens in meiosis 2

sister chromatids separate

Polyploid plants that have an odd number of chromosome sets are usually ______, and those with an even number of chromosome sets are usually ______.

sterile ; fertile

meiotic nondisjunction

the event in which chromosomes do not segregate equally during meiosis make unbalanced gametes

spermatogensis stages

the formation of haploid sperm through meiosis, occurs in the seminiferous tubules. 1) spermatogonia (diploid cells) 2) primary spermatocytes (post S phase duplication) 3) secondary spermatocytes (After meiosis I, haploids) 4) spermatids (post meiosis II, haploids) 5) spermatozoa- post maturation

In Drosophila, genes are typically named based on _____.

the mutant phenotype that revealed their existence

Oogenesis

the production, growth, and maturation of an egg, or ovum oocyte- receives a lot of cytoplasm to live polar bodys- genetic components but no cytoplasam

A human male with Klinefelter syndrome (XXY) has _____.

three doses of the genes in the PAR regions

An organism that has three sets of chromosomes is called a(n)_____while one with four sets is called a(n)____

triploid tetraploid

is autosomal aneuploidy lethal

yea trisomy 18 - edwards syndrom trisomy 13- patau syndrome

do mitosis maintain chromosome number

yes, maintain chromosome number