study session for exam 2 from monday

Meiosis and Mendelian Genetics (know stuff from that last exam might be on next exam)
Meiosis: homologous chromosomes cross over during metaphase I.
Mendel: traits sort independently EXCEPT sometimes they don't because the genes for two different traits are close on the same chromosome and cross over together.


Meiosis: homologous chromosomes cross over in metaphase 1
Mendelian genetics say traits separate independently - independent assortment (just because plant has white flowers doesn’t mean plant will have round leaves)
Except, sometimes, traits don’t separate independently
Don’t sort independently if linked chromosomes (genes which are very close together on chromosome) are crossed over

Math version
Eye color – Brown color (dominant)
Freckles – Dominant
Dad has brown eyes but no freckles
Mom has blue eyes and freckles
Text of question tells us dad is heterozygote for eye color
Don’t know if mom is heterozygote or not, but we know her mom had freckles but not her dad
½ of babies will have brown eyes, ½ will have freckles
¼ kids will have brown eyes and freckles

Multiple answer question: which of the following are reasons why the traits don't assort independently according to Mendel law?
One answer could be that genes are close together on the chromosome.
trickier question would have math like:
freckles dominate and brown eye color dominate. based on Mendelian laws what numbers of babies would be born with these two traits.
Dad:brown eyes, Bb no freckles, ff and Mom:blue eyes, bb, freckles, Ff (dad had no freckles and mom had freckles) (know what heterozygote means….it means Bb homozygote is BB or bb) How many children with have both brown eyes AND freckles?
Answer: write out Punnett Square for both genes… 1/2 (how many with brown eyes) times 1/2 (how many with freckles) = 1/4
BUT of 20 babies 10 have brown eyes only and the 10 have freckles and brown eyes. this means that 1/2 have the trait NOT 1/4. This is not what Mendel's laws predicts. So brown eye allele and freckle allele are close together and on the same chromosome
ANY deviation from Mendel's laws will be REALLY obvious.

A good summary=key points in your own words without getting stuck in jargon

when you do you add or multiple probabilities?
combined probability of independent events happening simultaneously is the PRODUCT of those all those separate probabilities.
like blue eyes 1/2 and freckles 1/2 = 1/2 times 1/2=1/4
probability of a particular outcome, if >1 way to attain that outcome is the SUM of separate probabilities of pathways to outcome.
1/2 people get divorce if the bride was young and the 1/4 get divorced if wife has more education than husband= 2/4 plus 1/4 =3/4

The DNA replication question on the exam is going to be a set of steps and you put them in order and some steps don't apply.

Codominance: variant alleles, >1 allele makes a gene product (ie protein)
ex: blood types: what proteins are put on the outside of red blood cells (A proteins, B proteins, O doesn't make a product, A and B are codominate and both phenotypes are expressed) (positive blood type is dominate and negative blood type is recessive)
all possible types are AA, AB, AO, BA, BB, BO, OA, OB, OO

review of who is Chastity's baby daddy… this could be on the test with different names and genotypes and it is possible that multiple men could be a dad or none could be a dad
SO if two men could be the dad… REALLY possible follow up question: Describe another genetic technique to figure out who is the real dad. aka DNA finger printing from lab.

Codominance: multiple variant alleles which make a gene product (ex: functional protein)
EX blood type (what proteins person puts on the outside of his/his red blood cells)

Blood type alleles:
A: “type-A proteins” codominant (equally dominant)
B: “type-B proteins” codominant (equally dominant)
O: recessive, doesn’t make a protein product
AA (A mom, A dad) only type A proteins on outside of red blood cells
AB (A mom, B dad) have type A and type B proteins on outside of RBC (red blood cells)
OA – type A proteins on outside of RBC
OO – no protein on outside of RBC

Positive – make RH protein on outside of RBC
Negative – don’t make RH protein on outside of RBC

O- best type of donor blood.
AB+ worst kind of donor blood.
Most common kind is A-

Chastity problem from worksheet
Chastity: AB (genotype: AB)
Kevin: O (genotype: OO)
Christian: A (genotype: could be AA or AO)
Chastity’s baby: AB (genotype: AB)

Draw Punnet square for Chastity and Kevin: get babies with type A blood and type B blood, but no AB
Draw Punnet square for Chastity and Christian: If we make Christian AA first, we find ½ of the babies are AB. If we make Christian AO, ¼ of the babies are AB.

Christian is the “baby daddy.”

Will be question like this on test. Could be that no candidate is father, or multiple candidates could be “guilty”.

Lab spin off: Kevin or Christian could be baby’s father. Describe another technique we could use to discover baby daddy – DNA fingerprinting using restriction enzyme. Know what restriction enzymes do. Know about cut sites. Won’t have to interpret DNA fingerprinting, but just in case, the way to interpret the results would be is: don’t expect exact correspondence between mom and baby or dad and baby. If mom doesn’t have DNA band baby has, dad does.

Dominate Lethal: homozygotes for the dominate allele die (in utero)
ex: variant coat color in mice: red. you want to breed red mice. when you breed red with white mice, all offspring are red——> so red is dominate and all the little miceys genotypes are Rr. so you when you breed that generation together then you would get RR Rr Rr and rr in the Punnett squarte so there would be 3 red mice and 1 white mouse.
60 babies 40 are red 20 are white. this DOESNT equal the Punnett Square ratio. the reason for this is that the RR babies die.

Dominant lethal – homozygotes for dominant allele die in utero (expected Mendelian genetics don’t match actual results)

Ex: rare variant in coat color in mice: red
Want to breed red mice.
Will use male red mouse, female red mouse
Breed red mouse to white mouse, first generation (F1) contains all red mice (no matter if red mouse is male or female). Tells us that red is dominant. We know F1 generation has genotype Rr (heterozygous). Breed F1 mice (all red mice) together. Think we’ll get 3 red mice & 1 white mouse for every four mice (3 to 1 ratio). In reality, second generation (F2) results are: out of 60 mice, 40 red mice and 20 white mice (2 to 1 ratio). We should see 45 red mice, 15 white mice. RR mice die (dominant lethal).

Thanks for posting this.

Thanks for everyone that posted this. It is very helpful :)

Can anyone post what they went over in the second review session that was today, tuesday, please?

Thanks! This is very helpful!


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