LIFE 102 Section 3

Mitosis, Meiosis, Genetics

asexual cellular reproduction

daughter cells are identical copies of mother cells

occurs in all organisms

in what organisms does asexual cellular reproduction occur?

sexual cellular reproduction

daughter cells are not identical copies of mother cells

only occurs in eukaryotes

in what organisms does sexual ceullular reproduction occur?

genome

total cellular DNA

46

how many chromosomes in human genome?

chromosomes

DNA is organized in multiple…

chromatids

condensed chromosomes in sets of two

1 duplicated chromosome =

2 sister chromatids

centromere

what connects two chromatids together?

after separation

when do chromatids become chromosomes?

Interphase

phase of cell cycle where cells grows and DNA is copied in preparation for cell division

90%

how much of the cell cycle does interphase take up?

G1, S, G2

Interphase Subphases

G1

1st phase of interphase where cell only grows

S phase

second phase of interphase where cell grows and DNA is copied

G2 phase

third phase of interphase where cell grows more and 2 centrosomes have formed by duplication of a single centrosome

Mitosis

phase of cell cycle where duplicated DNA is separated into two nuclei

prophase, prometaphase, metaphase, anaphase, telophase

Subphases of mitosis

prophase

phase of mitosis where chromatin become tightly coiled, each duplicated chromosomes appears as 2 sister chromatids, the mitotic spindle begins to form, and centrosomes move away from each other

mitotic spindle

structure made of microtubules that controls chromosome movement

centrosomes

regions that organize the microtubule of the spindle

prometaphase

phase of mitosis where the nuclear envelope fragments, the microtubules extending from each centrosome can now invade the nuclear area, each 2 chromatids now has a kinetochore

kinetochore

protein complexes associated with centromeres; spindle microtubules attach here during prometaphase

metaphase

phase of mitosis where the centrosomes are now at opposite poles and the chromosomes convene at the metaphase plate

metaphase plate

imaginary plane equidistant between the 2 poles of the spindle

anaphase

phase of mitosis where the sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell; each chromatid is now a chromosomes

telophase

phase of mitosis where genetically identical daughter nuclei form at opposite ends of the cell and the spindle eventually disassembles

cytokinesis

phase of cell cycle which results in one cell separating into two

animal cytokinesis

a cleavage furrow is formed and a contractile ring of microfilaments split cell into two; called cleavage

plant cytokinesis

a cell plate forms, turning into a cell wall which separate one cell into two

anaphase or telophase

when does cytokinesis begin?

cell cycle control system

a molecular control system that regulates the cell cycle

whether a cell with divide or not

what does the cell cycle control system determine?

G1, G2, M

cell cycle checkpoints

G1 checkpoint

seems to be the most important checkpoint for many cells; if cell receives go ahead, it will usually complete all other phases and divide

the cell receives a go ahead signal or does not recive a go ahead signal

What happens at checkpoints?

cell will exit the cycle, switching to non dividing state called G_o phase

what happens when a cell doesn’t receive a go ahead signal?

density dependent inhibition

external signal limiting division due to crowding

anchorage dependence

inhibition in animal cells where cell must be attached to a surface in order to divide

no

do cancer cells exhibit density dependent inhibition or anchorage dependence?

gene

stretch of DNA (part of a chromosome) that contains the information to make 1 protein

gametes

reproductive cells that pass on genes to next generation

half the number of other cells

how many chromosomes do gametes have?

diploid

cells with 2 copies of each chromosome (2n)

haploid

cells with 1 copy of each chromosome (n)

23

how many chromosomes do human gametes have?

somatic cells

any cell other than a gamete, have 23 pairs of homologous chromosomes

homologous chromsomes

pair of chromosomes that have one chromosome from each parent, have same length and shape, carry genes controlling the same inherited characters

fertilization

the union of sperm and egg

zygote

fertilized egg with one set of chromosomes from each parent

meiosis

type of cell division by which haploid gametes are formed from diploid body cells (1 diploid becomes 4 haploid)

homologous chromosomes are duplicated

what happens before meiosis?

meiosis 1

homologous chromosomes pair up and separate resulting in 2 haploid daughter cells with replicated chromosomes

prophase 1

longest stage of meiosis where duplicated homologous chromosomes pair and exchange segments

metaphase 1

stage of meiosis where chromosomes line up by homologous pairs

anaphase 1

stage of meiosis where each pair of homologous chromosomes separate

telophase 1 and cytokinesis

stage of meiosis where two haploid cells form, each chromosomes still consists of two sister chromatids

meiosis II

each replicated chromosomes is split up and sister chromatids distributed to daughter cells; stages follow mitosis but cell contains only one sister chromatid (now single chromosomes) at the end

more genetic variation (contributes to evolution), offspring are less vulnerable to environmental changes

Why does sexual reproduction exist?

independent assortment of chromosomes, crossing over, random fertilization

3 mechanisms of genetic variation

independent assortment of chromosomes

homologous chromosomes orient randomly and are divided randomly

crossing over

homologous portions of 2 non sister chromatids trade places

random fertilization

adds genetic variation because any sperm can fuse with any ovum

over 8 million

number of combinations when chromosomes assort independently into gametes

about 70 trillion diploid combination

how many combinations does random fusion of 2 gametes produce?

genetic traits

the physical properties of an organism determined by 1 or more genes

locus

the location of a gene on a chromosome (It’s “address”)

alleles

versions of a gene

homologous genes

gnes with the same locus on homologous chromosomes

gametes

genes are given to offspring via…

P generation; purple x white

parent generation in Mendel’s experiments

F₁ generation; purple

first generation in Mendel’s experiments

F₂ generation; 3:1 purple and white

second generation in Mendel’s experiments

dominant allele

allele that determines the organism’s appearance (creates functional protein)

recessive allele

allele that has no noticeable effect on appearance (creates non functional proteins)

homozygous

two identical alleles

heterozygous

two different alleles

phenotype

physical appearance

genotype

genetic makeup

law of segregation, law of independent assortment

Mendel’s laws of inheritance

law of segregation

law that states that alleles for a specific trait will segregate from each other during gamete formation

law of independent assortment

law that states that alleles for one trait will segregate independently of alleles for a different trait

complete dominance

occurs when phenotypes of the heterozygote and dominant homozygote are identical

incomplete dominance

the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties (an intermediate phenotype)

codominance

heterozygotes show combined (two) phenotypes

polygenic inheritance

an additive effect of two or more genes on a single phenotype

quantitative characters

characters that vary in the population along a continuum

polygenic inheritance

quantitative variation usually indicates…

epistasis

a gene at one locus alters the phenotypic expression of a gene at a second locus

recessively inherited disorders

genetic disorders that are inherited in a recessive manner

carrier

individuals that are heterozygous for a recessively inherited disorders (phenotypically normal)