Meiosis and Mendelian Ratios Flashcards
Example #1 – Jojo
Short Hair L_ – LL or Ll
Not Striped – aa
Orange/Black – XoXb
Intense Color – D_ – DD or Dd
Has Plaibald Spotting – Ss
Pleibald spotting genotypes
SS = NO white – melanocytes CAN migrate
***s allele = can’t spread melanocytes
Ss (Heterozygous) – Less than 50% white BUT not no whiete (Has some white – mostly around feet
- Only have 1 allele for migration
What controls Coat Color in cats
Controlled by a gene on the X chromsome
Coat Color in cats
Only come in orange or black – reast are midifications
White = absence of color
***Get different colors in fancy cats = by selection –> picking rare mutants
Example cat #2 (Willow)
Hair length – short –> L_ –> LL or Ll
Has striping – A_ –> Aa or AA
Coat color – Black –> XbY or XbXb (is grey but that means that it is really a mutaed black = coat color is black)
Coat intesity – diluted –> dd
Pleibald spotting – has no white = ss
Example cat #3 (Gertrude)
Coat color – Black –> XbY or XbXb
Pleibald –> Ss
Black and orange in cats
Co-dominet – at the organismal level they are codominant – see BOTH colors
See both orange and black NOT mix of the two = co-dominant
Example cat #4 (Marisa)
WHITE cat – SS (all white –> Means no malanocyte movement)
- White = absence of pigment –> melanocyltes can’t move = no pgment
***Has a grey tail –> means not really white cat – she is REALLY a black cat with a large white spot
White cat coat
Absence of pigment –> SS because the melanocytes can’t move = have no pigment
Where is there usually dark places in cat
Can have dark head + the rest is white because the melanocytes start in the brain stem
What did dad look like?
Pleibald:
Kittens = have less than 50% white – have Ss + some mostly white = ss
- Mom = Ss
- Means dad = Ss or ss (needs to have one s to give to kittens)
Hair length:
Mom – Short hair
All cats = short hair
Dad = Short hair OR long hair –> bevause mom has short hair + all kittens have short hair MEANS that mom + Kittens = L_ ==> means the kittens can be L_ (already can get L from mom so dad can be anything)
Stripes:
Dad = can have stripes or NOT (Aa or aa) –> Because mom has striped
- Mom = A_
- Some kittens have stripes and some do not – kittens = have aa
- Means mom is Aa (need a a to give aa cats)
- Dad is Aa or aa (striped or not) BUT needs 1 a to give aa cats
Color:
Dad = needs to be XbY because have cats that are XoXb and mom is XoXo = dad need to have Xb to give cats
Dilute:
Mom = dilute – dd
Cats – some not dilute
Dad = NOT dilute – needs to have D to give not dilute cats – Makes him DD or Dd
- No kittens are dillute = none are dd = dad doesn’t HAVE to be Dd BUT he can be
Two less tahn 50% white cates
Answer: 25%
Work through – both cats are Ss (both less tahn 50% white) –> means that when do punent square have 25% ss –> 25% are solid white
Test Cross
Test a dominent individuals (A_) that you do not know if they are homozygous domineant or heterozygous and want to figure out their genotype –> CROSS them with a recessive individual and look at offspring
0% of cats will have long hair
50%
Galton
Statistician – described correlations and regressions towards the mean
- Firgured out finger prints ate unique to indivual -- this was right - Decribed weather patterns - Vocal to sat traits are blended -- "traits are blended through generations -- wrong" - Considered the father of Eugentioccs -- wrong about this ***Came up with idea of nature Vs. Nurture -- is it envirnment or genetocs
Eugentics
The idea that we can improve humanity by controlled breeding
Mendelian genetics (History)
Look at peas
1865 – mendle published explanation on plant hybrids
- People know that offspring look like theor parents –> was thought that it was belnding of traits
THEN have mendle –> mendle comes and says that blenidng is NOT true
Mendle = father of genetics
1900 – Mendle’s work was rediscivered – becayse Galton his work was ignored for 40 years BUT was then rediscovered
Idea of inheritance before mende
People knew that offspring look like their parents BUT thought it was blend of traits
Mendle BIG idea
Said that blending of traits is not true – said that traits are discrete and hide + reappear
- Not blend
- He said that there are versions of genes (alleles)
Mendle experimntes
Established true breeding lines – showed that F1 and F2 offspring had predicatibel phenotypes
F1 = all green
F2 = 3:1 ration of green:yellow
True breeding line
Means that green = only makes Green
Yellow - only makes yellow
BUT means that they are homozygous – So green is homozygous for green and yellow is homozygous for yellow
Crossing true breeding lines
True bree + True breed –> F1
F1 X F1 –> F2
***In F1 X F1 – get predicatble genotypes
What did mendles F1 show
F1 phenotypes show dominent vs recesisbve relationships
What did mendles F2 genetration show
F2 phenotypes showed the recrance of recessive traits
Overall Mednles experinments showed…
Mendle Showed that F1 and F2 offspring had predictable ratios and phenotypes
Mendle Luck
He got lucky in the traits that he looked at
- his traits were all controlled by a single gene = follwoed a relationships
- All of his traits were on different chromosomes = no linkage
How did mendle support his work
Mendle used math + Distrubutions + probabailities to suport his work
***He did not know anything about chromosomes or DNA or genes or meisosis
Mendle expermnets (Dihybrid)
True X true
F1 X F1 –> 9:3:3:1 ratio
Mendel’s discoveries
- There are heretidatu determinats of a particular nature (there are genes)
- Genes come in pairs
- Alternate phenotypes of a single charachter are dtermined by different forms of these genes – there are aleles (Dominent vs. recessive alleles)
- Gametes contain one member of ecah gene pair (ploidy) – gametes have 1.2 of what non-gametes have
- Random fertalization – Law of segragation
- Genes controlling different traits are inheruted independley – Law of independt assortment
Mendle’s law of heretidaty
- Law of dominance
- Law of segraegation
- Law of Independent assortment
Low of Dominance
Some allels are dominent while others are recessive –> a heterozygous individual will display the dominant from
Law of segregation
Only 1 allele is carried in a gamete
Law of Independent Assortment
Genes of different Traits segregate independently to the gametes
Where can you see miosis
Can watch miosis with a microscope
Miosis stages
interphase –> miosis 1 (Promphase 1 –> metaphase 1 –> Anaphase 1 –> telephase 1) –> Meiososis 2 (P2 –> M2 –> A2 –> T2)
***Chromosome from mom + dad –> Double = now 2M + 2D –> P –> M –> A –> T –> Meiosis 2
Breaking down stages within meisosis
Each stage in meiosis can be broken down into additional phases
Example – porphase can consists of Leptotene + Zygotene + Pachytene + Diplotene + Diakinesis
Interphase
G1 phase (cell growth) –> followed by S phase (DNA synthesis) –> followed by G2 phase (cell growth)
***DNA replicates during interphase
Prophase 1
Chromsomes find each other and recombine – crossover happens here
Metaphase 1
Chiasma align at metaohase plate
Turning Meiosis into punnet square
Top row + down the outside of cloum = have each possible gamete (4 gametes)
Meiosis
Going from somatic cell –> Sperm/Egg (Going from diploid to haploid)
Overall: How do we pass down information to the next generation
Why do we get 1:2:1 genotypic ratio from 4 gametes by 4 gametes
because real ratio is 2:4:2 –> that can be simplified into 1:2:1
4 X 4 (because get 4 gametes from miosis)
Dihybrid Cross
When both parents are heterozygous at two different loci
Example dihybrid Cross – LlAa X LlAa
Get 9:3:3:1 ratio
How do you find possible gametes for ONE individual
Can make a square with Gene BY Gene
Does One meiosis event produce all 4 gametes?
NO
Law of idnepent assortment in action
Predicted genotype ratios for mono and dihybird corsses
WILL ALWAYS BE THE SAME
Mono – Aa X Aa
1 AA:2 Aa: 1 aa
AaBb X AaBb
9A_B_: 3A_bb :3 aaB_ : 1aabb
Predicted phenotypic ratios for mono and dihybird corsses
Might not always be the same – depends on the relationships of the alleles
Chromosomes during Prophase 1
Always find eachother
Mieosis schematic
What is the point of mioeiss vs. mitosis
Mitosis = Make 2 identical cells
vs.
Mieosis = make 4 genetocally different cells that are destined to be sperm/egg (destined to be gametes)
What is the point of sex
Want the next generation to be different than the current generation
Set up of meiosis (chromosomes)
- Have homologous chromomes (one from mom and one from dada) BUT both are considered 1 chromosmes
Mom + dad chromsome = one chromsomes
- Each chromsome has many genes –> get 2 copies of all of the genes
- Centrosome
Chromosme in human cells
23 pairs of chromosmes – each chromsomes has many genes – get two copes of all of the genes
What is needed before meiosis
Need DNA replication – forms sister chromsatids
Sister chromatids
Product of DNA replication – they are exact copies
Centrosome
Organizes spindle
Made up of – Centrioles in the middle + microtubules around the outside
Spindle
Divides nucleus
First stage of meiosis
Interphase
Interphase
Occurs just as the cell has been formed
At start = unreplicated chromsomes + 1 centrosome
Normal cell
2 centrosomes (in interphase gets duplicated centrosomes)
DNA is loose – as go through interphase = DNA condences into chromsomes + during S phase of interphase the DNA is copies
End of interphase
Have 2 centromeres + Condensed and duplicated chromsomes
What happens during interphase
Centersome duplicates (1 –> 2 centrosomes)
DNA condesned into chromsomes + DNA is replicated during S phase
Prophase 1
Overall: Chromosomes undergo Synapsis
Homokogous chromsomes come together + Wrap aroun each other very tightly – chromosomes swap patrts of chromsoes (undergo crossing over)
- Sections of mom switch with dad – in corssing over = combining chromsome that you get from both parents – making new chromsome to kids
- If doesn’t occur = give kids exact chromosome of mom or dad
Homologous chromsomes = identical excpet for conetnts of genes = cross over between homolgous chromsomes
Where does crossing over occur
Prophase 1
Metaphase 1
All chromsomes line up – meet in the middle of the cell at metaphase plate
- has indepent assortment
Other things that happen: Spindle attaches – centrosomes go to both sides of cells and spindle attaches to centromere at each pair of Homolgous chromosomes
Chromsomes orineting at Metaphase 1
Align via indepent assortment – for 4 chromsomes –> There are 4 ways that they can align
***THIS IS A SOURCE OF VARIATION
Sources of variation in Mieosis
Crossing over (Prophase 1)
Independent Assortment (Metaphase 1)
Counting ways that chromsomes can arrange in independent assortment
2^pairs – gives you the number of ways that chromsomes can arrange in indepent orientation in metaohase 1
Example – 3 Homolgous Chromsomes –> 2^3 = 8 ways
Anaphase 1
Pull Homlogous chromsomes apart – Homolgous chromes go to either cell
Telephase 1
Reform new nuceli
Cytokenesis
Divide rest of cell
Meiosis = technically dividing of nucelus
Prophase 2
No more crossing over
Metaphase 2
Chromsomes line uo again in teh middle and spindle attaches to centromeres
Anaphase 2
Each chromsomes is pulled to either side
Telephase 2 + cytokenesis
Create 4 daughter cells
Meiosis (overall)
Start = 4 chromomsomes (2 Homologous chromsomes)
END = 4 cells – each with 2 cheromsomes
***ALL OF THE DAUGHTER CELLS ARE DIFFERENT THAN ORIGINAL CELL + HAVE 1/2 THE AMOUNT OF DNA THAN THE ORGINAL CELL DID
- Daughter cells will fertlize the egg or will be the egg (Start again and get a new organism thorugh mitosis)
Complete domninace/recessive relationships
Means that homozygotes and heterozygots for comepltley dominent allels will show the same phenotypes
Aa or AA = same phenotype IF A is completley dominent over a
***Dominent allele = usually uppercase; recessive allele = lower case
Deducing genotype (dominent vs recessive) in complete recesisve/dominent relationships
Can easily deduce the genotype for receissive trait because it must be homozygous recessive (must be aa) BUT can only partially deduce the geotype for dominenat (because it can be AA or Aa)
***can write as A_ to show uncertainty
Sex chromosomes
X and Y – contrubute to sex determineration pathways of an organisms
- They contain genes that contrubute to sex determinaton pathways
***They are always considered to be a set BUT they can be non-homogous
XX = homolgous
XY = non-homologous (BUT the still follow the rules of homolgous chromsomes during mitosis + considered to be a set
XX = Female
XY = Male
Genes on sex chromsomes
They contain genes that contribute to sex deterimination pathways BUT they also have genes for other pathays
***Different genes are found on sex chromsomes
Autosomes
All other cgromsomes that are not sex chromsomes
Sex Chromosomes Examples
Coat color in Cats
Xb –> Black
Xo –> orange
O/B = 2 alleles for the same gene
XoXo OR xoY –> Organe
XbXb OR XbY –> Black
Unique in trait = XbXo -> mix of orange and black
***NOTE all Mix black and orange cats = female
Male Sex chromosome traits
Males = only have 1 X chromsome = if the trait is controled by the X chromsome then only need 1 allele to have the trait
Example – only nee 1 Xb or 1 Xo for coat color
Co-dominence
When both alleles are present in heterozygote = leads to both phenotypes
- Both phenotypes are present in a heterozygote
Example
XoXb –> get a cat with BOTH orange and BLACK (NOT a blend of teh two colors see each one sperateley)
Incomplete dominance
Incomplete dominant alleles lead to a phenotyope that is somewhere in the middle between either allele
(in heterozygote when both alleles are present = get a phenotype that is in between the two)
- Phenotype of teh heterozygote = somewhere in the middle
***relationship vteween alleles is neither completely dominent vs. recessive
Melanocytes
Cells that produce pigment in fur
***Absense of melanocytes in skin = means no pigment in fur
***During fetal development – melanocytes orginate in brainstem and then migrate down gead and spinal cord –> THEN go around acros the skin
- Wrap around from back to stomach
Incomplete Dominence example
Melanocyte migrate in cats (pleibald spotting)
S allele = inhibits cell migartion – is incompletley dominent over the s allele
- s allele = promotes full cell migration
SS = mostly white –> because have NO melanocyte migration = no pigments
- Have large patches in skin that are white because thete is no pigemnt
Ss – 50% of less is which
- because S is incompletley domeinet to s – means that Ss = have some melanocyte migration BUT not the the full extent as ss BUT is more than SS
- Hetero cats = have patches of white – often in stomach + lower extremities because these are the last regions that receive melanocytes during fetal developments
- Example – Tuxedo cat –> have white paws + some white on the chest
ss – no white –> have full melanocyte migration – all of skin areas can have/produce pigment
Co-dominence vs. Incomplete dominece
Co-dominence – Heterozygotes show the phenotyoes of both alleles
Example – if have a white flower + red flower = heterzygote has red and white spots
- Phenotype will have BOTH red and white
Incomplete Dominance – Heterozygotes have phenotypes that are mid-way between each homozygous alleles
Example – Red + white flower –> the heterzygous would be pink
- Phenotyoe will be neither red nor white
What happns if have more than two alllels per gene
While a gene can have more than two alleles per gene –> any diplopid organisms can only have 2 alkelles corresponding to the two homolgous chromsomes
Relationships between alles
Is context specific
Ex. A1 and A2 = Co-dominnet BUT A1 and A3 are incomplete dominance
A1 to A2 gives no information about A1 and A3
Epistatsis interaction
The supression of the effect of one gene by another gene – describes when alleles at one locus mask the affects of an alelle at a different locus
- Type of genetic interaction that contributes to complexity if many traits
Example – The W allele in cats prevents the deposition of pigmnet and is dominent to the w allele
- Creates lack of pigment – without pigment being depsited into skin/fur -
- cat with W = might also have a dominat A for striping OR might be homozygous for non-striping (aa) –> BUT that might not show if have a W allele
- means that a cat withoiut strping might be because aa OR might be because of dominnabt W alelle
- Can can be white AND have XoY or XbY BUT shows white because it also has the dominant W gene = W masks the phenotypes of teh other genes
***Means that you can’t deddeuce these genotypes from yhe phenotypes
***The phenotyes cointrolled by some of other coloration genes are masked
-
Pleitropy
The phenomona where 1 gene affects more than one trait
- One allele of of gene leads to multiple phenotypes
Example – W allele causes All white Fur + Often deaf + Often have differentley colored eyes
- The W allele leads to multiple different phenotypes
- The dominent whirte allele creates additional phenotypes
Modifer genes
Some loci have major affects on phenotypes and otehrs have minor affects
Example – Agouti gene has main affect on whether a cat is striped or not
- These stripes can occur in a striaght line or in swirls –> This is a gene at a seperate locus than Agoutu that controls whether the stripes will be staight or swriled
(In exmaple the modfier gene midfies the type of stripes)
–> If have two cats – BOTH are AA or Aa (SO both are already dominent for agouti striping)
- modified Gene = TM or Tb
- TMTM OR TMTb –> Stright lines
- TbTb = swirls
Where are rare alleles common?
Common in fancy breed – common due to inbreeding + Selection
Rare alelles
Example – cs – temperature sensitive alleles
- Tyronsinase = involved in melanin production
cs allel = producsed different phenotypes at diffreent temperatures that is recessive to teh W-T allel
Cs = WT – produces melananin – dominent to temperature senistive allele
cs = produces melanin at low temperature NOT high
Number of alleles possible for a gene
A gene can have more than 2 allleles – multiple alleles on a single gene can oproduce different phenotypes
Lethal Alleles
Type of relationship between alleles
Example:
S = dominenet
s = recessive
***S allele = considered lethal!!!
SS = emoryonic lethal – affects spinal development to such a degree that the embyrp dies in uetero
Ss = Tailess
ss = tailed
