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Genetics > Chapter 3: Mendelian Genetics > Flashcards

Chapter 3: Mendelian Genetics Flashcards

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Biology 101 flashcards
1
Q

A cross that involves only one pair of contrasting traits, such as flower color being purple vs. white, is called a __________.

A

monohybrid cross

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2
Q

This cross is made by mating true breeding parents (such as true breeding purple flowers and true breeding white flowers), then mating their offspring (Pp x Pp).

A

monohybrid cross

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3
Q

The results of a monohybrid cross for purple flowers (PP) and white flowers (pp) are:

A

PP Pp

Pp pp

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4
Q

The ratio for a monohybrid cross is:

A

1:2:1

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5
Q

What are Mendel’s three postulates?

A
  1. Unit factors in pairs
  2. Dominance/recessiveness
  3. Segregation (separate randomly)
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6
Q

This is the physical expression of a trait.

A

phenotype

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7
Q

Alternative forms of a single gene are called ______.

A

alleles

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8
Q

This type of cross is used to distinguish the genotype of an organism by crossing one with the dominant phenotype but unknown genotype against one that definitely has a homozygous recessive genotype.

A

Test cross

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9
Q

This type of cross involves two pairs of contrasting height, like plant height AND flower color.

A

Dihybrid cross

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10
Q

The ratio for a dihybrid cross is:

A

9:3:3:1

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11
Q

Suppose some plants can have either purple or white flowers and be tall or short. Purple and tall are dominant (PT), while white and short are recessive (pt). What are the true breeding parents you’d cross?

A

A true breeding tall purple plant, PPTT, and a true breeding short white plant, pptt.

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12
Q

Suppose some plants can have either purple or white flowers and be tall or short. Purple and tall are dominant (PT), while white and short are recessive (pt). What’s the genotype of the F1 generation after you cross the parents?

A

Tall and purple, PpTt.

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13
Q

Suppose some plants can have either purple or white flowers and be tall or short. Purple and tall are dominant (PT), while white and short are recessive (pt). What’s the genotypes of the F2 generation after you do a dihybrid cross?

A 
The parents would be PPTT and pptt, so the F1s are PpTt x PpTt. Offspring would be:
PPTT  PPTt  PpTT   PpTt
PPTt   PPtt   PpTt    Pptt
PpTT  PpTt  ppTT   ppTt
PpTt   Pptt   ppTt    pptt
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14
Q

Suppose some plants can have either purple or white flowers and be tall or short. Purple and tall are dominant (PT), while white and short are recessive (pt). What would the phenotypic ratio be for the F2s (as fractions)?

A

9/16 would have at least one dominant allele for both traits, so they’d have the dominant phenotype: purple and tall. 3/16 would have the dominant allele for one trait, but not the other: purple and short. 3/16 would have the dominant allele for the other trait, so it’d just be the other way around: white and tall. And 1/16 would be recessive all the way, so white and short.

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15
Q

How would you use the forked line method to predict all the genotypes for a trihybrid cross (parents are AABBCC x aabbcc)?

A

First, you figure out what gametes each parent can give: ABC and abc. Then you combine those, so the F1 generation is AaBbCc. Then you cross two of those: AaBbCc x AaBbCc. Next, you look at each trait individually. For the A’s, just focus on
Aa x Aa. That will give you 3/4 dominant guys and 1/4 recessive. Same with B’s and C’s.

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16
Q

Pretend you’re doing a trihybrid cross. The parents are AABBCC and aabbcc, so the F1’s you’re crossing are AaBbCc x AaBbCc. What fraction of F2’s will end up being ABC?

A 
Look at each trait separately. 
Aa x Aa = 3/4 DOMINANT, 1/4 recessive
Bb x Bb = 3/4 DOMINANT, 1/4 recessive
Cc x Cc = 3/4 DOMINANT, 1/4 recessive. 
3/4 x 3/4 x 3/4 = 27/64 all dominant (ABC)!
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17
Q

Pretend you’re doing a trihybrid cross. The parents are AABBCC and aabbcc, so the F1’s you’re crossing are AaBbCc x AaBbCc. What fraction of F2’s will end up being aBc?

A 
Look at each trait separately. 
Aa x Aa = 3/4 dominant, 1/4 RECESSIVE
Bb x Bb = 3/4 DOMINANT, 1/4 recessive
Cc x Cc = 3/4 dominant, 1/4 RECESSIVE
1/4 x 3/4 x 1/4 = 3/64 aBc
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18
Q

What are the steps to doing a chi square analysis?

A
  1. Make a column for each category (like gray mice and white mice), and one for the total.
  2. Write down how many you observed of each and the total.
  3. Write down how many you expected. To do this, you multiply the total number by your ratio for each one. For example, if you have 1000 mice and it’s a 3:1 ratio, it would be 3/4(1000) and 1/4(1000).
  4. Write down the deviance (subtract expected from observed).
  5. Now just calculate deviance^2.
  6. And then divide that by expected. Add the numbers you get for those together to get x^2.
  7. Calculate degrees of freedom (however many categories you have - 1). Now just look at that table thing and trace your x^2 and degrees of freedom.
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19
Q

What p values should you reject the null hypothesis for?

A

0.01 - 0.001; anything higher is ok.

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20
Q

What’s a null hypothesis?

A

It means there’s no difference between measured values and predicted values. Everything went as expected.

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21
Q

What does it mean to reject a null hypothesis?

A

It means there was a difference between measured and predicted values and you need to go back and reform your hypothesis.

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22
Q

What type of heredity does albinism have?

A

autosomal recessive

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23
Q

How can you tell from a pedigree if you’ve got an autosomal recessive trait?

A

Usually skips generations.

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24
Q

How can you tell from a pedigree if you’ve got an autosomal dominant trait?

A

It will show up in every generation.

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25
Q

What type of heredity does Huntington disease have?

A

autosomal dominant

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26
Q

What is the source of new alleles?

A

Mutation!

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27
Q

A mutation that causes the gene product to be nonfunctional is called a ___________ mutation.

A

loss of function

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28
Q

A mutation that causes a gene product to be produced more is called a ___________ mutation.

A

gain of function

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29
Q

This is when an intermediate, “mixed” phenotype, like pink flowers, is achieved.

A

Incomplete/partial dominance

30
Q

Tay-Sachs is passed down via an ________ mechanism.

A

autosomal recessive

31
Q

In Tay-Sachs, if you have one good copy of the gene, you can still make enough of the gene product (not as much as normal, but still some). This is an example of _________ dominance.

A

incomplete/partial

32
Q

Joint expression of both alleles is called _________.

A

codominance

33
Q

For red and white flowers, an example of incomplete dominance would be __________ flowers. An example of codominance would be _________ flowers.

A

pink; red and white splotched

34
Q

The MN blood group is an example of what type of dominance?

A

Codominance

35
Q

Multiple alleles can only be studied in _______.

A

populations

36
Q

The ABO blood types are an example of ________.

A

codominance

37
Q

A rare case in which a person is genetically type A, B, or AB blood, but has no antibodies added and is therefore phenotypically type O.

A

Bombay phenotype

38
Q

This type of allele means that individuals with one good copy make enough gene product to be ok, but homozygous individuals can’t produce any and will die when the gene product is needed.

A

recessive lethal allele

39
Q

This type of allele means that individuals with just one copy will die. Huntington disease is an example of this.

A

dominant lethal allele

40
Q

How do you handle a problem that’s got a combination of two gene pairs with two different modes of inheritance (for example: color, Aa x Aa, and blood type, IAIB x IAIB)?

A

First, you figure out the fractions for each trait one at a time. For Aa x Aa, you’ll get 3/4 and 1/4. For the blood types, you’ll get 1/4 IAIA, 2/4 IAIB, IAIB, and 1/4 IBIB. Now take your first category, color, and apply that to each of your blood types. For example, 3/4 are dominant. Multiply that by your 1/4, separately by your 2/4, and separately again by the last 1/4. Repeat for your 1/4 aa. Those fractions will be different from your normal ratio.

41
Q

The concept states that each step of development increases the complexity of the organ/feature being made, and is under the control of lots of genes.

A

Epigenesis

42
Q

How is hereditary deafness an example of epigenesis?

A

Over 50 genes are needed for sound in the ears, and the feature of sound is created via a cascade of developments triggered by different genes. If one gene becomes mutated, the development it’s responsible for never occurs, and the next gene is not turned on. The ear never develops fully and you end up with deafness.

43
Q

This phenomenon is when the expression of one gene pair masks or modifies the effect of another gene pair.

A

Epistasis

44
Q

A dominant gene suppressing the expression of the other loci is an example of __________.

A

epistasis

45
Q

What does complementation analysis do?

A

It allows you to see if two different mutations are on the same gene and are alleles, or if they’re on separate genes and just separate mutations.

46
Q

You’ve got some flies who have a mutation that causes them to be born without wings. It’s caused by two different mutations. How do you figure out if they’re on the same gene as alleles or not?

A

You mate two of your wingless flies, one with the one wing mutation and one with the other. Pretend the girl has the A mutation and the boy has the B mutation. The girl will give a copy of her A mutation and the boy will give his B copy. If they’re on different genes, you’ll get a bad copy from each fly and a good copy from each fly for each of the two genes, and the babies will have wings! But if it’s on the same gene, you will get two bad copies for the wing gene, and the babies will not have any wings.

47
Q

You’ve got a girl fly and a boy fly. The girl fly has red eyes and the boy has white. White is an X-linked trait. What happens when they mate?

A

The girl has red eyes and must have two red X’s for her eye color. The boy is white, so his X must be white and then he’s got a Y. The girl can only donate a red X; the boy donates his white X or his Y. So a girl will be red X white X, and a boy would be red X Y. Now the girl can give a red X or a white X, and the boy can give a red X or a Y. Make a Punnet square with the girl on the top row and the boy on the side spot. Girls can be red X red X, red, or red X white X, also red. Boys can be red X Y or white X Y, which is how you’d end up with the one white eyed fly (and it’s a boy).

48
Q

You’ve got a girl fly and a boy fly again. This time the girl has got white eyes and the boy has red. White is an X-linked trait, so what happens when they mate?

A

The girl’s got two white X’s, so that’s what she donates. The boy has a red X and a Y, so he can donate either of those. A girl baby will have a red X white X, so red eyes, and a boy will have a white X an a Y, so white. When they mate, the girl can give a red X or a white X, and the boy can give a white X or a Y. Make a Punnet square. You get 2 white Xs, so white girls, red X white X, so red girls, white X Y, so white males, and red X Y, red males.

49
Q

In this case, the expression of the phenotype is absolutely limited to one sex or the other.

A

Sex-limited inheritance

50
Q

In this case, the expression of a phenotype not limited to one sex or the other is influenced by the sex of an individual.

A

Sex-influenced inheritance

51
Q

Hens have short, straight feathers no matter what the genotype. Roosters have short, straight feathers unless they are homozygous recessive (no dominant alleles), hh. This is an example of ____________ inheritance.

A

sex-limited

52
Q

Baldness is a dominant trait. In men, just one B means they’ll get bald (so they can be homozygous dominant or heterozygous). In women, they can still have the bald phenotype, but they need both B’s (homozygous dominant) for it to happen. This is an example for ____________ inheritance.

A

sex-influenced

53
Q

This means there’s a range of expression for a mutant genotype – for example, flies could have normal eyes, smaller loserish eyes, or no eyes at all.

A

Expressivity

54
Q

The percentage of individuals that show at least some degree of expression of a mutant genotype defines the ________ of the mutation.

A

penetrance

55
Q

A disease showing a progressively earlier age of onset and an increased severity in each successive generation is an example of ________________.

A

genetic anticipation

56
Q

This is when the process of selective gene silencing occurs during early development and impacts subsequent phenotypic expression.

A

parental imprinting

57
Q

How could imprinting happen?

A

A gene or a region of a chromosome could imprint on one homolog, but not the other. Since that allele isn’t there, it’s silenced, meaning the allele that did get imprinted on the other homolog automatically wins and gets to be expressed.

58
Q

When is imprinting thought to occur?

A

Before/during gamete formation, because there are different genes in sperm-forming tissues vs. egg forming tissues.

59
Q

What happens in Prader-Willi syndrome and Angelman syndrome, and what’s the difference between the two syndromes?

A

An identical deletion occurs on one member of the chromosome 15 pair. In Prader-Willi, the paternal segment gets deleted and the maternal one is expressed automatically. Patients suffer from mental retardation and severe eating disorders. In Angelman syndrome, the maternal gets deleted and paternal is expressed, also resulting in mental retardation but severe muscle contractions too.

60
Q

This is when genetic expression is not the direct result of the information stored on the nucleotide sequence of DNA, it’s altered in a way that affects its expression.

A

Epigenetics

61
Q

An example of epigenetics is ___________.

A

imprinting

62
Q

How is imprinting/epigenetic events thought to occur?

A

DNA methylation

63
Q

What happens in Kleinfelter syndrome?

A

Extra X chromosomes are present for males. They have male genitalia but do not produce sperm and often have rounded hips and some breast tissue, so feminine sexual development is there slightly too. Caused by a nondisjunction.

64
Q

What happens in Turner syndrome?

A

Like Kleinfelter syndrome, but in females. Caused by having only one X chromosome.

65
Q

What happens in 47,XXX syndrome?

A

Usually nothing, but sometimes it can be more severe, resulting in underdeveloped secondary sex characteristics, delayed development, and mental retardation. Only in women, obviously.

66
Q

What happens in 47,XYY syndrome?

A

Men are significantly taller, tend to have personality disorders, and are of subnormal intelligence. But not all are affected by it.

67
Q

What’s the pseudoautosomal region (PAR)?

A

A spot on the ends of the Y chromosomes that share homology with the X ones. They like to meet up and recombine with the X ones because they’re so similar. This is critical for segregation of X and Y chromosomes during male gametogenesis.

68
Q

What’s the male-specific region of the Y (MSY)?

A

It has euchromatin with genes, and heterochromatin without genes. The euchromatin contains the SRY, which controls male development.

69
Q

What’s the sex-determining region (SRY)?

A

A spot in the euchromatin on the Y chromosome that tells the embryo to form testes, resulting in a male. The absence of a Y chromosome automatically leads to female development, so this gene isn’t on the X chromosome.

70
Q

What is a barr body?

A

An inactivated X chromosome.

71
Q

When is it believed that X inactivation occurs in somatic cells?

A

Very early in development; then all the cells that arise from that during mitosis already have the X inactivated.

Genetics (6 decks)

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