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Behavior Genetics > Chapter 2: Mendelian Genetics > Flashcards

Chapter 2: Mendelian Genetics Flashcards

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1
Q

When was the first instance of a controlled experiment and what was it for?

A

1753 and to identify the cause of scurvy.

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2
Q

Who was mainly interested in heredity early on? For what reason?

A

Farmers. They wanted to improve their livestock and crops.

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3
Q

Define Generation

A

Broadly used concept in the 1800s.

It combines aspects of reproduction, heredity, and development.

Was used to explain familial resemblance.

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4
Q

Define Preformationist

A

The theory that 1 parent contributes nearly everything to produce offspring and the other either serves as (1) to initiate the process or (2) to nourish and house the offspring.

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5
Q

Define Ovists

A

Belief that the ova contained preformed embryos. Saw the mother as the one responsible for producing offspring.

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6
Q

Define Animalculists

A

Belief that the sperm cells contained preformed embryos. Saw the father as the one responsible for the producing offspring.

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7
Q

Qual. vs. Quant.

A

Qualitative Traits - Vary dimensionally (ex. height).

Quantitative Traits - Vary categorically (ex. eye color).

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8
Q

Who was Robert Bakewell?

A

He was a sheep breeder who kind of started the focus of heredity.

Breeding Strategy: bred closely related animals and did not allow breeding of “inferior” animals.

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9
Q

Who was Abbott Cyrill Napp?

A

He welcomed Gregor Mendel (a monk at the time) into the monastery.

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10
Q

How did Johann (Gregor) Mendel’s life change because of his mental health?

A

He was diagnosed with major depressive disorder in his early tweens.

Because of it, he:
- Needed extra time to graduate.
- Could not maintain a parish (priest things).
- Failed the oral component of his teaching exam (twice).

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11
Q

What was Mendel’s teaching career like?

A

1st - Became a part-time substitute secondary school teacher after losing his parish.

Then - Studied science at a university.

Then - Became a substitute teacher in natural history and physics.

Because he failed his oral exam twice, he did not become a full-time teacher. Therefore, allowing him the time to conduct the studies he did.

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12
Q

What did Mendel try to study before settling on peas?

A

The coat color in mice.

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13
Q

Mendel’s Model Criteria (for pea plants)

A
  1. Possess constantly differing characteristics.
  2. At the time of flowering, their hybrids must be protected from the action of all pollen or be easily protected.
  3. The hybrids and their progeny must not suffer any noticeable disturbance in fertility.
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14
Q

Define Varieties

A

Plants of different lines that breed true for specific phenotypes.

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15
Q

Define Bred True

A

A line that consistently produces offspring with the same trait across generations.

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16
Q

What kind of traits was Mendel looking to study?

A

Focus was on qualitative traits.

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17
Q

How many varieties did Mendel find to bred true?

A

22

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18
Q

What 7 characteristics did Mendel choose for his pea plants?

A
  1. Flower position.
  2. Flower color.
  3. Plant height.
  4. Pea shape.
  5. Pea color.
  6. Pod shape.
  7. Pod color.
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19
Q

How did Mendel perform his hybrid crosses?

A

Collected pollen from a male plant that exhibited the desired trait, then fertilized a female plant that had the other form of the trait by dusting its stigma with the pollen.

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20
Q

Define Hybrid Crosses

A

Involves controlled matings, starting with parents from lines that breed true for alternative phenotypes.

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21
Q

Define Pollen

A

Sperm containing gametes of male plants.

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22
Q

Define Stigma

A

The structure of a plant where the pollen germinates.

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23
Q

Define Reciprocal Crosses

A

Instead of mating males from P1 to females from P2, it would involve males P2 x female P1.

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24
Q

Define Monohybrid Cross

A

Design where the inheritance of 1 categorical trait is investigated.

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25
Q

Define Parental Generation (P)

A

The 1st generation in hybrid crosses. From lines that breed true for the trait(s) of interest.

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26
Q

Define First Filial Generation (F1)

A

Consists of offspring from the P line crosses.

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27
Q

Define Second Filial Generation (F2)

A

The product of F1 being mated together.

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28
Q

What was Mendel’s first experiment?

A

A monohybrid cross of pea shape.

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29
Q

Define Blended Inheritance

A

When the expression of a categorical trait in the offspring is intermediate to that of the 2 parents.

Was disproven by Mendel.

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30
Q

Mendel’s Monohybrid Cross (Pea Shape) (image)

A
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31
Q

How did Mendel disprove the idea of blended inheritance?

A

When he mated P, the F1 produced traits that resembled 1 parent. Therefore, disproving it.

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32
Q

How did Mendel disprove the idea of preformationism?

A

When he mated P, the F1 produced traits that resembled 1 parent. This only disproves blended inheritance.

However, when he did a reciprocal cross, the results when identical. Therefore, disproving it.

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33
Q

Define Dominant Traits

A

When having only 1 copy of the allele is sufficient to produce the phenotype.

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34
Q

Define Recessive Traits

A

When 2 copies of an allele are required to produce the phenotype.

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35
Q

What ratio did Mendel find in his monohybrid crosses?

A

3:1 in the F2 generation.

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36
Q

What did Mendel hypothesize about genes?

A

That 2 genes are carried by each individual for each trait.

(AA, Aa, aa, etc.)

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37
Q

Define Gene (Mendelian Genetics)

A

A hypothetical unit of inheritance responsible for the phenotype of interest.

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38
Q

Define Alleles

A

Alternative versions of a genetic variant.

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39
Q

Define Genotype (Mendelian Genetics)

A

Comprise the 2 alleles inherited from one’s parents.

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40
Q

Heterozygous vs Homozygous Genotypes

A

Heterozygous - Aa
Homozygous - AA; aa

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41
Q

Define Phenotypes

A

The observed trait of interest.

42
Q

What are gametes?

A

Sperm or the egg.

43
Q

How many alleles does a gamete receive for a single trait?

A

Each gamete receives only ONE allele. So when the parents mixes, it = 2.

44
Q

Do gametes generate alleles are equal frequencies?

A

Yes!

45
Q

Define Punnett Square

A

Way to visualize hybrid crosses to eliminate expected genotype and phenotype composition of offspring.

46
Q

Who developed the punnett square?

A

Reginald Crundall Punnett

47
Q

Parental Line Punnett Square (image)

A
48
Q

F1 Punnett Square (image)

A
49
Q

Define Law of Segregation

A

Mendel’s 1st Law.

Explained patterns of inheritance in monohybrid crosses.

States that traits are determined by 2 factors, and that each individual receives 1 from their father and 1 from their mother.

When an individual produces gametes, the 2 alleles are segregated so that each gamete receives only 1 allele.

50
Q

How to estimate the frequency of different genotypes in offspring?

A

Multiply the frequencies of each gamete.

EX. Each parent is heterozygous (Aa x Aa). 50% A-carrying gametes and 50% a carrying gametes.

Offspring estimates - 25% AA (0.5 x 0.5), 50% Aa (0.5 x 0.5 x 2), and so on.

51
Q

Define Dihybrid Crosses

A

Design where the inheritance of 2 categorical traits are investigated.

Mendel was the first to do this as well.

52
Q

Mendel’s 1st Dihybrid Cross - Pea Shape and Pea Color (image)

A
53
Q

What ratio did Mendel find in the dihybrid crosses?

A

9:3:3:1 ratio.

54
Q

Define the Law of Independent Assortment

A

Mendel’s 2nd Law.

Used to explain patterns of inheritance in dihybrid crosses.

States that alleles for each trait are distributed to gametes WITHOUT respect to alleles for other traits.

Essentially, in dihybrid crosses there are 2 monohybrid crosses occurring simultaneously.

55
Q

How is the 9:3:3:1 ratio from the dihybrid crosses associated with the 3:1 ratio from the monohybrid crosses?

A

Because the 9:3:3:1 ratio can be found by multiplying the rates of each trait when considered alone (in a monohybrid cross).

Ex.
Round x Yellow = 3/4 x 3/4 = 9/16
Round x Green = 3/4 x 1/4 = 3/16
Wrinkled x Yellow = 1/4 x 3/4 = 3/16
Wrinkled x Green = 1/4 x 1/4 = 1/16.

56
Q

When was Mendel’s contributions recognized?

A

Not until the 1900s, 30 years after its publication and 16 years after his death.

57
Q

Who was Thomas Hunt Morgan?

A

Awarded a Nobel Prize in 1933 for his work on genetics using fruit flies.

58
Q

Why use fruit flies for research?

A
  1. They adapt easily, so their easy to raise in a lab.
  2. Small and inexpensive to feed and house.
  3. A single pair can produce hundreds of offspring within a couple of weeks.
59
Q

Who was the first to identify mutations in fruit flies? (before Morgan)

A

Frank Lutz in 1908.

60
Q

How many mutant flies did they find?

A

More than 100!

61
Q

Define Chromosomes

A

Structures typically found in a cell’s nucleus comprised of DNA and packaging proteins.

62
Q

Define the Chromosomal Theory of Inheritance

A

Identified chromosomes as the location of genetic material.

63
Q

Describe the fruit flies and their chromosomes (sex differentiation)

A

They have 4 chromosomes - 3 pairs are large, 1 is small.

1 of the large pairs differs and is known as the sex chromosome.

Females carry 2 X, males carry 1 X and 1 Y.

64
Q

What determines a fruit flies sex? Difference between female and males?

A

The ratio of X to autosomes.

Females have - 2 X and 2 large autosomes (chromosomes 2 and 3, ignoring the smaller 4). Ratio of 1.0.

Males have - 1 X and 2 large autosomes, ratio of 0.5.

65
Q

Define Wild-Type

A

The most commonly occurring phenotype.

66
Q

Define Sex-Linked

A

When a phenotype is determined by a genotype found on the X chromosome.

67
Q

Morgan’s White Eye Mutation (image)

A

Believed the mutation was on the X chromosome.

68
Q

Morgan’s Dihybrid Cross - Eyes and Wings (image)

A

Conformed to Mendel’s 2nd Law. Therefore, Morgan hypothesized that the mutations are located on different chromosomes.

69
Q

Define Linkage

A

The concept that when alleles for 2 different traits are located on the same chromosome they are sometimes inherited together, thereby violating Mendel’s 2nd Law.

70
Q

Define Parental Types

A

Refers to phenotypes of offspring in hybrid crosses that are indistinguishable from the phenotypes of the parental lines.

71
Q

Define Recombinant Types

A

Refers to phenotypes of offspring in dihybrid crosses that are combinations of the phenotypes of interest that were not observed in parental lines.

72
Q

Define Backcross

A

When F1 individuals are mated to individuals from one of the parental lines.

73
Q

What happens when there are fewer than expected recombinant types?

A

It’s interpretated that the mutant genes are located on the same chromosome.

74
Q

What happens when MALE F1 were backcrossed?

A

Only parental types of offspring are observed. Therefore, recombination does not occur in male fruit flies.

They were only producing 2 types of gametes.

75
Q

Define Crossing Over

A

The exchange of chromosomal material by sister chromatids during meiosis, and the process by which recombination takes place.

76
Q

When does crossing over occur?

A

During gamete formation.

When homologous chromosomes pair up and physically exchange material.

77
Q

Define Homologous Chromosomes

A

For a given pair, 1 copy is from the father and the other from the mother.

Homologs share size, banding pattern, and sequence of genes.

78
Q

How close/far are mutations based on their recombination rate?

A

For higher rates - farther away.

For lower rates - closer together.

79
Q

Define Map Distance

A

An estimate of the distance between two loci (mutations) on a chromosome based on observed recombination rates.

80
Q

Define Recombination Rate

A

Can be estimated by calculating the percentage of recombinant types observed in backcross progeny.

81
Q

Define Centimorgan (cM)

A

A unit of measurement that indexes the recombination rate between 2 loci on a chromosome.

1 cM = 1% recombination.

82
Q

Who proposed the measurement of cM?

A

Alfred H. Sturtevant, one of Morgan’s students.

83
Q

How can you use recombinant rates to discover if there is linkage?

A

If the recombinant rate is less than 50% in backcrosses, it indicates linkage.

84
Q

2-Point vs 3-Point Crosses (images)

A

3-point are more accurate estimates of recombination rate.

85
Q

Define Double Crossovers

A

A 2nd crossover event that essentially restores the original chromosome to each sister chromatid.

Can lead to an underestimation of the recombination rate.

More common over long distances.

86
Q

Define Pedigrees

A

A diagram of a family that indicates relationships, sex, and affected status.

Can be used to determine whether a trait is inherited in Mendelian fashion.

87
Q

Is pedigree information always available?

A

Usually not.

Some family members may be deceased or may not have their phenotype information available.

Some families do not have many members or may have incomplete/inaccurate information.

88
Q

What can pedigrees differentiate?

A
  1. Dominant and recessive alleles.
  2. Autosomal and X-linked patterns of inheritance for qualitative traits (like disease).
89
Q

Define Rare Allele

A

Considered rare if they occur at a frequency less than 1%.

90
Q

Define Autosomal Dominant

A

The affected trait appears in each generation and w/o respect to sex.

Not located on the X-chromosome.

91
Q

Define X-Linked Dominant

A

Affected fathers can pass on the trait to their daughters, but not to their sons. Affected mothers can pass it on to either sex.

Located on the X-chromosome.

92
Q

What is a disease example of a X-linked dominant inheritance pattern?

A

Rett’s Syndrome

Not typical - almost all males who inherit it die in infancy.

93
Q

What is a disease example of a autosomal dominant inheritance pattern?

A

Huntington’s Disease

94
Q

What is Huntington’s Disease?

A

A rare progressive neurological disorder that impacts movement, emotion, and cognition.

Most common form has adult onset, with symptoms starting in their 30s or 40s.

95
Q

What is Rett’s Syndrome?

A

Characterized by severe deficits in language development, learning, coordination, and other areas of function, potentially including microcephaly (small head) in infancy.

96
Q

Define Autosomal Recessive

A

The affected trait appears without respect to sex, but not in each generation.

Must be homozygosis for the allele.

97
Q

What is a disease example of a autosomal recessive inheritance pattern?

A

Phenylketonuria (PKU)

98
Q

What is PKU (Phenylketonuria)?

A

A rare disorder due to a mutation that abolishes metabolism of the dietary amino acid phenylalanine.

Can produce profound intellectual disabilities.

Can test newborns; preventable.

99
Q

Define X-Linked Recessive

A

The frequency of the trait is higher in males than in females.

Affected males carry a copy of the recessive allele on their only X.

Affected females carry 2 copies.

Unaffected females carry 1 copy.

100
Q

Define Hemizygous

A

A genotype carried on 1 allele, such as seen in males for X-linked genotypes.

101
Q

What is a disease example of X-linked recessive inheritance pattern?

A

The color vision deficiency (red-green).

102
Q

What is the red-green vision defect?

A

Difficulty distinguishing between some shades of red, green, and yellow.

Found in 1 in 12 males and 1 in 200 females.

Behavior Genetics (4 decks)

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