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MCAT BIO (BCHM/ORGO/CELL/MICRO) > Genetics > Flashcards

Genetics Flashcards

1
Q

what are autosomes and allosomes?

A

autosomes = non sex chromosomes = 22 pairs

allosome = sex chromosome = XX and XY

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2
Q

what is the difference between homologous chromosomes and alleles?

A

homologous chromosomes are the non-identical (but very similar) chromosomes from each parent (e.g. one maternal chromosome 18 and one paternal chromosome 18)

each chromosome has many genes.

Alleles are two copies of the same gene which exist on separate homologues.

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3
Q

a person carrying two different alleles at a locus is called? what about the same allele?

A

heterozygote - 2 alleles one locus

homozygote - identical alleles

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4
Q

true or false, after S phase of the cell cycle, the cell has 4 copies of the genome.

A

true since we are diploids (we have two copies of the genome in each cell) after replication we have 4n.

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5
Q

If after replication we have 4n copies of the genome, what is the difference between mitosis and meiosis?

A

mitosis - splits the cell into 2 creating two cells of 2n

meiosis takes it one step further and splits each 2n cell into 1n producing four 1n cells. (haploids)

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6
Q

after meiosis one, what is the ploidy number of the cells

A

haploid!! this is because, after meiosis 1 homologous chromosomes separate meaning that although the daughter cell (before meiosis 2) has 46 chromosomes, they are 23 identical pairs not 23 homologue. (explained more soon)

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7
Q

Meiosis 1: explain what occurs in prophase 1

A
  1. chromosomes condense
  2. nuclear envelope degrades
  3. HOMOLOGOUS CHROMOSOMES LINK UP
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8
Q

true or false, homologues link up in prophase 1 for meiosis and mitosis

A

false, only meiosis prophase 1 which allows for recombination events.

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9
Q

meiosis 1: synapsis refers to what in prophase 1

A

linking of homologues: once linked they are called tetrad chromosomes (or bivalent)

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10
Q

during synapsis in prophase 1, what can occur?

A

recombination aka crossing over in which homologous chromosomes trade certain genes.

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11
Q

true or false, prophase 1 is the longest meiosis stage.

A

true, due to crossing over

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12
Q

what is the synaptonemal complex?

A

The synaptonemal complex regulates crossing over during synapsis

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13
Q

meiosis 1: what occurs during metaphase 1?

A

tetrads (i.e. homologous chromosomes) are lined up at the metaphase plate (unlike mitosis which line up the sister chromatids)

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14
Q

meiosis 1: what occurs during anaphase 1?

A

homologous chromosomes separate (keeping their sister chromatids) as spindle fibres shorten.

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15
Q

meiosis 1: what occurs during telophase 1 and cytokinesis?

A

telophase one, the nuclear envelope develops and the cells divide into 2 haploid cells. (note: the cells contain 23 identical pairs of chromosomes not 23 homologues. Therefore its considered haploid)

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16
Q

what occurs in meiosis 2?

A

the sister chromatids are split apart resulting in gametes which contain one copy of every chromosome in the body

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17
Q

true or false, in meiosis recombination occurs between the sister chromatids.

A

false, this occurs between homologues!!!

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18
Q

what is nondisjunction?

A

when homologues in meiosis one or sister chromatids in meiosis 2 fail to separate. One gamete ends up with two copies of one chromosome and the other with 0.

down syndrome: in one parent gamete this occurs with chromosome 23. After fertilization the zygote has 3 copies of X23.

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19
Q

Law of segregation and Law of independent assortment explain mendelian genetics. Explain them.

A

Law of segregation –> Two alleles of an individual are separated by meiosis and passed down to off spring singly (offspring only gets one of the two)

Law of independent assortment –> the law of segregation applies to each set of alleles independently.

in other words the combination of alleles that end up in each gamete is random.

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20
Q

What is a pure-breeding strain?

A

if crossing (mating) a specific strain (A) with the same strain (A) always produces progeny with A then A is a pure breeding strain.

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21
Q

what is a test-cross?

A

when one individual is crossed with another individual who has a homozygous (pure-breeding) recessive genotype

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22
Q

when some who is XX or Xx is crossed with xx this is called a?

A

test-cross: one individual is homozygous recessive

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23
Q

if a green plant is test-crossed with a pure breeding yellow strain, and some of the F1 generation progeny are green while others are yellow, what is the genotype of the original green plant?

A

green plant is test crossed with a strain is homozygous recessive for yellow (gg) (indicating green is the dominant colour)

therefore the original pea must be heterozygous Gg

if the original green pea was GG then no offspring would be yellow

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24
Q

Show what a punnet square would like like if you crossed

GgWW with Ggww

A

GgWW x Ggww

    GW       gW

Gw

gw

note: of the W/w gene was not homozygous then there would be more sections.

25
Q

what is the probability rule of multiplication?

A

the probability of both of two independent events occurring is the product of their probabilities alone.

the probability of A = 10^-5
the probability of B = 10^-3

for both to occur it is A x B = 10^-8

26
Q

What is the rule of addition of probability?

A

this calculates the chances of EITHER two events happening. If one where to occur, the chances one of the two occurring is given by the sum of their individual probabilities. Note: you also must subtract the probability of them occurring together (rule of multiplication)

A = 10^-5, B=10^-3
chances of them both occurring = 10^-8

chances one of them happens = A + B = C

C - 10^-8 = chances of one occuring

27
Q

what is incomplete dominance and codominance?

A

incomplete dominance –> when the phenotype displays a mixture of the genotype alleles (red and white genotypes for flower pigment make pink)

codominance –> is when both specific genotypes are displayed distinctly resulting in blotches of different phenotypes for flowers.

28
Q

t or f, ABO blood types exhibit codominance in which, regardless of the other allele genotype, both alleles express the antigen for that blood type (Giving rise AB blood types)

A

true, this is codominance (no blending)

note that the genes are IA IB and i (where i is recessive)

therefore codominance occurs between IA and IB but classical dominance occurs between IA/IB and i

ii gives rise to blood type O which expresses no antigens

29
Q

What is pleiotropism and polygenism?

A

A pleiotropic gene is a single gene with many effects on different phenotypes

A polygenic phenotype is a phenotype that relies on multiple genes such as height

30
Q

What is Penetrance?

A

The likelihood that a person with a given phenotype will express the expected phenotype. A high penetrance indicates the person is likely to express the expected phenotype.

31
Q

Epistasis is?

A

the expression of alleles of one gene depend on the expression of another such as the lac operon which depends on crp and “I” activation (CAP) and repressor proteins.

32
Q

epistasis = when one gene expression effects another.

A

epistasis

33
Q

will a recessive chromosome be expressed in the sex genes of males?

A

yes because they only contain one copy of that gene!

34
Q

What is one exception to the law of independent assortment? when and how does it occur?

A

When genes are located close together on the same chromosome, they sometime are not assorted independently but rather go together to the respective gametes. This is called Linkage

35
Q

According to linkage, most genes on the same chromosome cannot sort independently. What is the exception to linkage which may allow genes on the same Xm to separate?

A

crossing over in prophase 1!!

36
Q

in a cross between two animals observing the 2 different genes of the same chromosome will complete linkage occur?

A

no, you will observe an mixture of genotypes, mainly the linked genotype but crossing over permits other genotypes to be expressed.

37
Q

The frequency of recombination of two genes on the sam chromosome is proportional to the physical distance between the two genes.

Is the frequency of recombination increased or decreased with distance?

A

increased with distance!! while linkage will decrease with distance

38
Q

true or false,

Frequency of recombination = # of recombinations / # of offspring

A

true.

The RF is given as the total recombinant phenotypes divided by the total amount of off spring.

39
Q

If you study flowers for two genes on the same chromosome and find you get 44 big flower green plants, 40 small flower yellow plants, 8 big flower yellow plants, and 8 small flower green plants,,

Which phenotypes are likely from recombination?

A

big flower yellow plant and small flower green plant which are expressed in much fewer offspring.

additionally the cross was (BbGg x bbgg)

therefore parent two cannot perform recombination since they always make bg

parent one can recombine to make bbGg or Bbgg

40
Q

If you study flowers for two genes on the same chromosome and find you get 44 big flower green plants, 40 small flower yellow plants, 8 big flower yellow plants, and 8 small flower green plants,,

what is the RF?

A

since their was 8 recombinants with one phenotype and 8 with another this equals 16 recombinants out of 100

RF = 16/100 = 16% recombination frequency

41
Q

what is the maximum RF possible?

A

50%

this means no linkage, genes assorted independently

42
Q

what is hemizygosity ?

A

hemizygosity is when an individual only has one copy of a chromosome in a diploid organism. For example the X chromosome in males exhibits hemizygosity.

43
Q

explain Y linked inheritance

A

traits that linked to the Y chromosome can only be passed from father to son. If a father makes a girl she cannot have the Y-linked trait the dad has. Note: males cannot be carriers of Y linked traits without expressing them since they only have one allele (one Y chromosome) of the trait.

44
Q

Explain why there is X linked recessive and X linked dominant traits but no discrepancy in Y linked traits.

A

X linked traits can be diploid since females have XX. Therefore recessive and dominant alleles are possible.

Y linked traits are always expressed so dominance is not an issue.

45
Q

true or false, men are hemizygous for X linked traits

A

true, they have one X chromosome in a diploid organism.

46
Q

From which parent would a male receive an X linked trait?

A

His mother since (because he is a male) he must of gotten his Y chromosome from his dad

47
Q

Why is colour blindness more common in men then in woman?

A

since colour blindness is an X linked recessive gene. Since females have two X chromosomes they simply express the proper gene on the other chromosome. Men don not have the option.

48
Q

true or false, the Hardy-Weinberg law of population genetics states that the frequencies of alleles (how much an allele is expressed in a given population) will not change over time as long as…

  1. no mutation
  2. no migration
  3. no natural selection
  4. mating is random
  5. no genetic drift
A

true

49
Q

if 100 homozygous green plants mated with 100 homozygous yellow plants to give rise to 1000 green progeny

a. does this mean the yellow allele is gone from the population?
b. what is the allele frequency for green allele

A

no!! crossing a bunch of GG with gg produces all progeny with Gg. The allele is still in the population, just not expressed.

since there is 1000 progeny, all of which are diploid, there are 2000 allele. Since all progeny are Gg the gene frequency for G is 50%.

50
Q

Explain the population equation (involving gene frequencies)

p + q = 1

A

p represents the allele frequency of the dominant allele
q represents the allele frequency of the recessive allele

since we assume there are only two alleles for this gene in the population, the frequencies of both must equal 100% (i.e. one)

51
Q

(p + q)^2 = 1^2

p^2 + 2pq + q^2 = 1

what does each term in the equation mean?

A

If p is the frequency of dominant alleles, then p squared is the freuquency of homozygous dominant alleles

if q is the frequency of recessive alleles, then q squared is the frequency of homozygous recessive alleles

2pq is the frequency of heterozygotes

52
Q

what is Hardy-Weinberg equilibrium?

A

essentially once one generation has passed allele frequencies no longer change. Since gene frequencies can be calculated from allele frequencies, gene frequencies no longer change too.

53
Q

true or false, natural selection can create new alleles in a gene pool which drives evolution.

A

False, Natural selection can only alter pre-existing alleles. Therefore, it selects for alleles in individuals with increased fitness

54
Q

How is fitness measured in genetics?

A

the ability for an organism to pass down its alleles to offspring and for those offspring to have the ability to pass down their own alleles.

a turtle with 15 children but only 1 survives is low fitness

a bird with 4 children in which 3 survive is pretty high fitness

55
Q

If natural selection can make new alleles, only select for healthy alleles, are we stuck with all alleles ever possible?

A

no, random mutation can create brand new alleles (with NS then selects for or against)

also, new combinations of alleles can occur in meiosis which again, NS selects for or against.

these are the two ways to increase genetic diversity

56
Q

if a mutation occurs in a muscle cell of an individual who then proceeds to have many progeny, will this increase the gene pools genetic diversity?

A

no, mutations only increase genetic diversity when they occur in germ line cells (muscle cells aren’t passed to offspring)

57
Q

What is directional, divergent, and stabilizing selection?

A

polygenic traits display a bell curve for expression in a population.

directional selection –> selects for the average and one extreme of the bell curve, but selects against the other extreme. This causes the phenotype to move in one direction (Giraffes with small neck selected against)

divergent –> both extremes are selected for

stabilizing –> both extremes are selected against

58
Q 
What are the terms 
anterior
posterior 
dorsal
ventral
superior
inferior
A

anterior - front facing
posterior - back facing
dorsal - towards the back (means on top)
human spine is dorsal
ventral - towards the front (underneath)
belly button is ventral

superior - towards the head
inferior - towards the feet

59
Q

if two heterozygotes mate and produce an F1 progeny that is 9:3:3:1 then this displayed…?

A

independent assortment! that is the genotype ratio (9:3:3:1) of independent assortment

MCAT BIO (BCHM/ORGO/CELL/MICRO) (8 decks)

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