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MCAT Biology Review > Genetics and Evolution > Flashcards

Genetics and Evolution Flashcards

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1
Q

Describe the three experiments showing DNA is the macromolecule carrying hereditary information?

A
  • The Griffith Experiment (cell extracts can transform bacteria, indicating that one of the biological macromolecules is responsible for the transferring of the hereditary information)
  • The McCarty experiment (shows that DNA indeed contain cellular genetic information)
  • The Hershey-Chase experiment (Once again verify that DNA carries genetic information. Radioactively label the protein coat (S) and the DNA (P))
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2
Q

What is the fundamental unit of inheritance?

A
  • Gene. A segment/ a length of DNA that codes for particular gene products.
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3
Q

Are all gene products protein? why or why not? In the other words, are DNA only used for the translation of proteins?

A
  • not all gene products are proteins.
  • DNA to RNA, but remember there are many types of RNA. There are multiple types of non-coding RNA that are important and functional. Ex: tRNA, rRNA, inRNA, etc.
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4
Q

How many chromosomes do human have? what are chromosome?

A

The genetic information of human is stored in the form of 23 pairs of homologous chromosomes (46 chromosomes - 23 from mom and 23 from dad). Not just one or two, there are 23 different chromosomes for a person. There are specific genes associated with specific locations on these 23 chromosomes. These gene locations are the same across all humans.

  • 22 autosome and 1 sex chromosome
  • 23 pairs (in each pair, 1 chromosome from dad and 1 from mom). These two are homologous chromosomes. They are contain the same genes but differs in the DNA sequence because again they are not from the same person.
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5
Q

Is a human trait associated with a specific gene hence of locus on one the chromosome? can all physcial traits of an organism be mapped to a single locus?

A

no, a trait a phenotype arisen from multiple genes. A trait is controlled by many different genes thus it does not map to single locus but rather many.

Ex: weight is controled by hormones, your metabolism, your digestive system, etc. Thus weight does not simply map to a single locus.

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6
Q

What do you call a two different version of DNA of the same genes?

A

Alleles

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7
Q

Is it possible for there to be more than two different alleles of a specific gene?

A

yes! look at humanity! There are can be so many version of a gene, however, there can only be two alleles for a gene inside a human because there is only one sperm for one egg.

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8
Q

What do you call someone who carries two different or identical coppies of an alleles?

A

homozygote - identiy

heterozygote - different

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9
Q

on a very basic level, what is the difference between meiosis and mitosis? how many rounds of division? Do they start from the same material? what is each process for?

A
  • cell replication. cell growth and differentiation for specialized functions.
  • production of gamates (egg and sperm cells) for sexual reproduction.
  • Meiosis and Mitosis both start after repliction. 4n.
  • Meiosis have two rounds of division. Crossing over and recombination occur at the first rounds leading to genetic diversity. Meiosis II is very similar to Mitosis.
  • There is only one round of division in mitosis.
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10
Q

Is the X shape a chromosome? what are sister chromatids?

A
  • the X shape actually is the chromosome after duplication. a chromosome is duplicated and held at the centromere yield the x shape. a chromosome after replication is called sister chromatids.
  • Two sister chromatids joined at the centromere = 1 chromosome
  • Two separated sister chromatids = 2 chromosomes.
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11
Q

Where in meiosis does crossing over occur?

A

the prophase when the homologous chromosomes synapse.

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12
Q

Which stage of meiosis takes the most time and why?

A

prophase I – because of the complexity and precision required in crossing over.

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13
Q

What facillitate the synapses and crossing over of homologous chromosomes? are these processes carried out by the same machinary?

A
  • Synaptonemal complex: SYCP2 & SYCP3. They form during prophase I. Latteral elements attached to each side of the homologous pair and act like zipper to bring the two chromosomes together.
  • The two processes use two different machinary; however, they do rely on one another. When the synaptonemal complex formation is inhibited, recombination is disturbed and vice versa.
  • They do happen at approximately the same time.
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14
Q

At what stage of Meisosis do the cells become haploid? What is the purpose of the second round of division?

A
  • The cells become haploid right at Anaphase I because each cell now only have a single set of chromosome and they are duplicated. there is difference between number of copies of chromosome and its duplicated version
  • to separate the sister chromatids creating cells with one single set of unduplicated chromosomes.
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15
Q

When homologous chromosomes separate, do all peternal and maternal chromosomes stay together in the daughter cells?

A

no

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16
Q

Are the sister chromatids that separate during meiotic anaphase II identical in their DNA sequence?

A

yes except the the segment of crossing over.

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17
Q

What is called when homologous chromocomes and sister chromatids failt to separate at anaphase ?

A

Nondisjuction.

18
Q

What happen to gamates when nondisjuction occur?

A

you will gave gamates with either both copies or none coppies of the chromosome.

2+ 1(normal) = 3 (trisomy)
0 + (normal) = 1 (Monosomy)

19
Q

Provide an example of nonlethal genetic defect in human? does the condition a result of absence or excess in genetic information?

A

Down Syndrome is the caused by trisomy of Chromocome #21.

Too much genetic information–> too much available proteins which disrupts normal development.

20
Q

what is an allele again?

A

a version of a gene

21
Q

What is a polymorphic trait? provide examples. What is the difference between polymorphic and polygenic trait?

A
  • Polymorphic - a trait with many forms. Ex: eye color, hair color, etc
  • Polygenic - a trait determined by many genes.
22
Q

What is classical dominance?

A

Dominant vs recessive allele.

- Heterozygous individual with a dominant and recessive allole.

23
Q

What is incomeplete dominance?

A

heterozygous offspring of homozygous parents display a blended parental phenotype.

In other words, incomplete dominance means neither of the allele can overide the other, so they compromise and arrive at a blended phenotype.

24
Q

How do you tell if you’re working with incomeplete dominance?

A
  • blended phenotype
  • two upper case letters. (2 dominant allele?)

ex: blended color of flower or animal coat.

25
Q

What is codominance? Explain and provide example.

What is codominance different from incomplete dominance?

A
  • Both alleles are expressed, independently and simultaneously.
  • An example of this is blood type:
    I(A), I(B) and i – i is recessive, I(A) and I(B) are both dominant allele.

I(A)i - type A blood
I(B)i - type B
I(A)I(B) – Type AB (both protein A and B are expressed on the surface of the red blood cell)

In order words, there are multiple dominant alleles of the same genes that can be expressed simultaneously. In incompelete dominance, you don’t actually see parental phenotype but blending (typically seen in colors).

26
Q

What is Epistasis? how is it different from other form of non-classical dominance? Provide an example. Epi-Stasis means?

A
  • This is dominance between completely different genes and not between different alleles of the same gene.
  • The expression of one gene suppresses the expression of another gene.
  • Ex: X(bald)Y = no hair. sure you can different shapes of hair (straight, curly, etc) but if you have X(bald), you have no hair and Y is completely surpressed.
  • Epi = above. stasis = stop.
27
Q

What are different forms of non-classical dominance?

A
  • Incomplete dominance
  • Codominance
  • Epistasis
28
Q

What is a person blood type consisted of? What are the genes involved?

based on that information, can you guest what the universal blood donnor would be and why?

What is the universal blood recipient?

A
  • I(A), I(B), I and the Rf factor.
    We already know about I.

Rf however follows the classical dominance. R/r.

  • RR or Rr - Rh possitive
  • rr - Rh negative.
iiRR = Type O+ 
I(A)rr = Type A-

It would be ii rr = Type ) nagtive. Nothing is expressed on the surface of the cell thus cannot be detected but the host cell immune system. No protein to trigger reaction.

  • For the person to receive any blood, it must mean that all the proteins on the blood cells are recognized as familliar. This is only possble for AB + blood type since it has all the proteins associated with all blood type.
29
Q

How do you calculate the two even that happens at the same time?

A

multiple the two probability

30
Q

How do calculate the probability of either A or B happen?

Prop (A or B)

A

Add the two probability subject the probably of both occur at the same time.

prob A + prob B - probA*probB

31
Q

What are linked genes? what is special about the sorting of these genes?

A
  • genes that are close to one another on the same chromosome and are often not sorted indepedently
32
Q

Can you determine gene linkage by looking at F1 generation? why or why not? How do you determine gene linkage by looking at F2?

A
  • You have to know the expected ratios of the gen an phenotype. If the actual cross doesn’t match the expected cross ratio –> linked genes.
33
Q

What is the recombindation frequency?

A

recombinant/ total offspring *100.

  • Recombinant = mixed phenotype.
34
Q

What are the typical gen ratior of common single and double crosses?

A

AaBb X AaBb = 9:3:3:1
AaBb x aabb = 1:1:1:1

Aa x aa = 1:1

35
Q

What is the big overlying theme of Hardy Weinberg? What are the three things you need to know about Hardy Weinberg?

A
  • The Allele frequencies are the same for generations. Unchallenging Allele Frequencies
  • The equation, the conditions for the equation to be true & How long it takes to reach equilibrium if it’s disturbed.
36
Q

What are the equations for Hardy-Weinberg? hint: one for allele frequency and one for genotype frequency.

In which type of dominance can’t you apply this equation and why? This is reflected in one of the equations.

A

q + p = 1
- This is assuming that there is one dominant and one recessive allele, which adhere to the classical dominance.

To get the genotype equation, you basically square both sides of the equation.
(p+q)^2 = pp +2pq + qq = 1

37
Q

Example question of Hardy-Weinberg

In certain randomingly mating population, the frequency of the allele causing a dominant autosomal disorder is 0.1. What is the frequency of the affected individuals in this population?

A

p - dominant = 0.1
q - recessive = 0.9

pp = 0.1*0.1 = 0.01 = 1% 
qq = 0.9*0.9 = 0.81 = 81% 
2pq = 2*0.1*0.9 = 0.18 = 18%

1: 81:18 (Genotype frequency)
dominant: recessive = 19:81 (Phenotype frequency)

A dominant disorder - 19% affected.

38
Q

What are the five assumptions for the Hardy-Weinberg equations to work?

In other words, what are assumptions that keep the allele frequency to remain the same over generations?

Are these assumption realistic?

A
  • no mutation – mutation convert one allele to another.
  • no natural selection – because it favors certain allele
  • Totally random mating – selective breading will selectively increase the frequency or certain alleles.
  • Large population only – small population has high risk for genetic drift due to the environmental factors.
  • No migration - makes sense, nobody moves in or out of the population.
39
Q

How long to reach new equilibirum if old one is disturbed?

A

One generation. you have to calculate the new allele frequency

40
Q

Is the allele dominant or recessive? How can you tell?

A

Pick a individual with the trait and see if the generation before or after them have the trait. If they don’t, that means that it’s recessive.

41
Q

Is the allele sex-linked or autosomal? if the allele is sex-linked, is it linked to the X or the linked to the Y?

A

signigicantly more men with the disorder means sex-linked.
- X-linked disorder –> 1/2 of men is affected.

most of sex linked diseases are X-linked because Y chromosomes are a lot shorter than Y.

if a condition is passed from father to son, that is Y-linked condition.

MCAT Biology Review (13 decks)

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