L2 - cell cycle

why does cell cycle need to occur?

• for organism growth

• repair: repair tissues and organs

• maintenance: repair old/dead cells

what are the 3 main stages in interphase + explain them

1. G1: where the cell grows and synthesizes new molecules to prep for the next phase

2. S: DNA replication occurs and DNA exists as uncondensed fibers called chromatin

3. G2: the cell produces new molecules to prep for mitosis

what are the stages of mitosis?

1. prophase

2. metaphase

3. anaphase

4. telophase

what happens in prophase?

• chromatin condenses to become chromosomes (becomes visible to microscope)

• nuclear membrane breaks down

• pair of centrioles move to opposite poles

• spindle fibres begin to form (spindle fibres made from microtubules)

what happens in metaphase?

• chromosomes align to the middle (vertically)

• the spindle fibres attach to the centromere of the chromosomes to keep it in place

what happens in anaphase?

• chromosomes are being pulled away the opposite sides

• spindle fibres pull them away

what happens in telophase?

• new nuclei forms on both ends and it surrounds the chromosomes

• it’s the step before the final step of the cell dividing

• 46 chromosomes each in the nuclei

what happens in cytokinesis?

• it’s the final division of the 2 cells but dividing the cytoplasm

advantages of asexual reproduction?

• more offspring can be produced

• overall process will take less time since you don’t need to wait for a partner to mate with

disadvantages of asexual reproduction?

• less genetic diversity since DNA is coming from one parent

• if something were to happen, entire population will die

advantages of sexual reproduction?

• more genetic diversity since 2 diff. parents, creating more variation

disadvantages of sexual reproduction?

• more energy required

• whole process takes longer in general since you would have to wait for a partner for reproduction to occur

what are homologous chromosomes?

• they have similar characteristics

how many pairs of homologous chromosomes do humans have?

23 pairs

define “paternal”

in your homologous chromosomes, one set comes from a male (which is referred as paternal)

define “maternal”

in your homologous chromosomes, one pair comes for a female (referred as maternal)

define “diploid”

it’s when an organism or cell has homologous pairs of chromosomes (23 pairs = 46 in total)

define “haploid”

it’s when an organism or cell has one set of chromosomes (23 in total)

what are somatic cells? are they diploid or haploid?

• body cells

• 22 pairs for a human

• diploid since they exist in pairs

what are gametes? are the diploid or haploid?

• reproductive/sex cell

• found in reproductive tissue of an organism

• produce sperm and egg/ovum

• haploid since there’s only 1 set of these chromosomes

what is the male gamete called and where is it produced?

• it’s called the sperm

• it’s produced in the testes

what’s the female gamete called and where is it produced?

• it’s called ovum/egg

• it’s produced in the ovaries

what is fertilization?

• it’s the joining of the sperm + egg (ovum)

what is a zygote?

it’s what’s produced after the sperm and egg (ovum) join together

where does fertilization happen in humans?

fallopian tube

what’s ANOTHER WORD for homologous chromosomes?

tetrad

what are homologous chromosomes responsible for?

• carrying genes

• each pair are responsible for controlling the same inherited traits

describe the overall process of meiosis?

• it’s where gametes (sex cells) are being reduced by half

• diploid becomes haploid

define “oogenisis”

• it’s meiosis in female

• it produces egg (ovum)

define “spermatogenisis”

• meiosis in male

• it produces sperm

what’s the OVERALL OVERVIEW of the stages/phases of meiosis

• meiosis I - P1, M1, A1, T1

• meiosis II - P2, M2, A2, T2

what happens right before meiosis 1 can start?

interphase (G1, S, G2)

describe process of prophase 1 in meiosis 1

• homologous chromosomes pair up

• synapsis occurs (the pairing up of homologous chromosomes)

• crossing over occurs (when the homologous chromosomes join together, they transfer genetic information with each other)

describe process of metaphase 1 in meiosis 1

• chromosomes align in the middle

• this time, the chromosomes align in pairs in the middle

• this random alignment with pairs is called “independent assortment”

• spindle fibres keep them aligned in the middle

describe process of anaphase 1 in meiosis 1

• chromosomes are being split away to opposite sides

• nuclei will form on both ends

• ready to split

cytokinesis (in meiosis 1)

• 2 new cells will be created due to the division of the cytoplasm

• 23 chromosomes each with 46 chromatids

describe process of prophase 2 in meiosis 2

• similar to what happens in mitosis

• nuclear membrane breaks apart

• spindle fibres form

• pairs of centrioles move to opposite poles

describe process of metaphase 2 in meiosis 2

• chromosomes align in the middle with the help of the spindle fibres

describe process of anahase 2 in meiosis 2

• chromatids are being split away with the help of spindle fibres

describe process of telophase 2 in meiosis 2

• nuclei forms around the chromosomes

• ready to be split into 2 cells

cytokinesis after meiosis 2?

• 4 cells

• they all have 23 chromosomes and 23 chromatids

what is non-disjunction?

• it’s when chromosomes don’t divide correctly in meiosis

• this results with an incorrect # of chromosomes in gametes

euploidy?

having the correct # of chromosomes

aneuploidy?

have incorrect # of chromosomes (caused by non-disjunction)

monosomy?

missing a chromosome

polysomy?

having an additional chromosome

explain the process of nondisjunction in meiosis 1

• it’s when homologous chromosomes don’t separate properly

• occurs in anaphase 1

explain the process of nondisjunction in meiosis 2

• when the sister chromatid doesn’t separate properly

• happens in anaphase 2

what “mathematical terms” can we use to rep. monosomy

n-1 (haploid - 1)

what “mathematical terms” can we use to rep. polysomy

n+1 (haploid + 1)

how do chromosome abnormalities affect organisms (be specific to humans separately as well)?

• it affects the survival of the offspring of organisms

• for humans, it can lead to disorders in the offspring

what are the names of chromosomal abnormalities for AUTOSOMES? (just list them)

• down syndrome (trisomy 21)

• edward syndrome (trisomy 18)

• patau syndrome (trisomy 13)

explain down syndrome

• chromosomal abnormality that occurs on chromosome 21

• effects: short arms, short legs, flattened face, almond shaped eyes, intellectual disability

explain edward syndrome

• chromosomal abnormality that occurs on chromosome 18

• effects: severe intellectual disabilities, physical abnormalities (include extreme muscle tone)

• life expectancy is only for 10 weeks

explain patau syndrome

• includes abnormalities such as small and non-functioning eyes

• life expectancy is only a few weeks after birth

list the chromosomal abnormalities that happen on sex chromosomes

• klinefelter’s syndrome (XXY)

• turner’s syndrome (XO)

• jacob syndorme (XYY)

• triple x (XXX)

explain klinefelter syndrome

• it’s when a male has an extra X chromosome

• effects: sterile male (can’t produce sperm), breast swelling, feminine characteristics

• XXY

explain turner’s syndrome

• XO

• it’s when a female is missing an X chromosome

• effects: sterile female (can’t produce egg), undeveloped feminine characteristics, short neck

explain jacob’s syndrome

• XYY

• when a male has an extra y chromosome

• they may be taller than average

• typically NO unusual symptoms

explain triple X

• XXX

• it’s when a female has an extra X chromosome

• effects: menstrual irregularity, they can appear as tall and thin

list out the prenatal genetic testing options

• amniocentesis

• genetic counselling

• chronic villus sampling

• nuchal translucency screening

explain genetic counselling

• genetic counsellors help you understand the likelihood of your children attaining a certain genetic condition

• they will explain risks of having offspring

• they will let you know whether or not you should have children

• they can do punnet squares to help understand the genotypical rations/phenotypical ratios of your children inheriting a condition

explain nuchal translucency screening

• screening for baby size, heart rate and fluid behind neck (nuchal translucency)

explain chronic villus sampling

• when doctor takes sample of pregnant women’s placenta (placenta = temporary organ that grows in women’s uterus)

explain amniocentesis

• when doctors take sample of amniotic fluid of the baby (amniotic fluid = a type of fluid that’s around the baby to provide support for the baby)

describe a dominant allele

• expressed as AA or Aa

• capital letter is present

describe recessive allele

• expressed as aa

• lowercase letters (expressed in the absence of a dominant allele)

describe “genotype”

• genetic makeup of an organism

describe “phenotype”

• when a genotype is physically expressed

what is a pedigree chart?

• it’s a flow chart to demonstrate the inheritance patterns of a genetic condition in a family

define “heterozygous”

• it’s when there’s 1 capital and 1 lowercase

define “homozygous”

• aa or AA

difference between recessive homozygous and dominant homozygous?

recessive homozygous:

• aa

• they have the condition for sure

• Aa will mean that they are carriers of the condition but not actually show it

dominant homozygous:

• AA

• they have the condition for sure

• Aa will mean they still have the condition

• aa means they don’t have it as well

*overall depends on if a condition is recessive or dominant

how is pedigree chart organized by age?

• arranged from eldest to youngest child

draw symbol for normal female

circle

draw symbol for normal male

square

draw symbol for affected male

coloured in square

draw symbol for affected female

coloured in circle

draw symbol for mating

circle and square with a straight horizontal line between it attaching to both

draw symbol for identical twins

• cherry looking structure with a horizontal line at the top

• horizontal line connecting circle/square to circle/square

draw symbol for non-identical twins

cherry looking structure with a horizontal line at the top

draw symbol for deceased individual

draw square/circle with a line crossed out on it

draw symbol for unknown sex

diamond

list out the autosomal genetic conditions

• hungry = huntington’s disease

• campers = cystic fibrosis

• slept = sickle-cell anemia

• peacefully - PKU

• reading = retinoblastoma

• magazines = marfan syndrome

• tired = tay-sachs disease

• neighbors = nie-mann pick disease

• made = maple syrup disease

• apples = adenosine deaminase

describe huntington’s disease

• autosomal dominant

• chromosome 4

• loss of muscle control, decline in mental ability, decreased life expectancy

describe cystic fibrosis

• autosomal recessive

• chromosome 7

• thick mucus produced in lungs making it difficult to breathe and can lead to a lung infection

• blocks pancreas, preventing enzymes to go into intestines

describe sickle cell anemia

• chromosome 11

• autosomal recessive

• it’s when red blood cells are irregularly shaped

• caused by abnormal hemoglobin protein

• decreased life expectancy

describe PKU

• chromosome 12

• autosomal recessive

• prevents the breakdown of phenylaline, which leads to delays in brain function

• needs to be treated immediately to prevent aggravation of symptoms

describe retinoblastoma

• chromosome 13

• autosomal dominant

• it’s when tumours develop in the retina of young children

• needs to be treated immediately, otherwise it can be pretty fatal

describe marfan syndrome

• chromosome 15

• autosomal dominant

• it affects the connective tissue, leading to weakness in your heart, blood vessels and skeleton

• causes long limbs

• increased risk of develop blood vessel conditions and heart conditions

describe tay-sachs disease

• chromosome 15

• autosomal recessive

• destruction of nervous system caused by the lack of an enzyme called “hexosaminidase A” leading to the accumulation of lipids (fats)

• can be fatal in early childhood

describe niemann-pick disease

• autosomal recessive

• chromosome 18

• nervous system and brain impairment due to the accumulation of lipids in cells

• type A can be fatal

• decreased life expectancy