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Biology 2 > Lecture 15 Mendelian genetics > Flashcards

Lecture 15 Mendelian genetics Flashcards

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1
Q

What two assumptions were plant breeders operating under during the early 19th century?

A
  • Each parent contributes equally to offspring (correct)

- Hereditary determinants blend in offspring (incorrect)

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2
Q

In the 1770’s, the German botanist Josef Gottlieb Kolteuter studied offspring using what method?

A

Reciprocal crosses

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3
Q

What are reciprocal crosses?

A

Plants are crossed in opposite directions

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4
Q

What did Josef Gottlieb Kolreuter’s studies using reciprocal crosses show?

A

Reciprocal crosses always gave identical results, showing both parents contribute equally to offspring

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5
Q

What does it mean that hereditary determinants are blended in offspring?

A

Hereditary determinants in egg and sperm come together and blend together

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6
Q

According to the blending theory, what happens to once heritable elements once blended?

A

They could not be separated again once combined

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7
Q

Who confirmed that each parent contributes equally to offspring but disproved the blending theory?

A

Gregor Mendel, in the 1860’s

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8
Q

What methods did gregor mendel use that led to his successful deductions?

A

Quantitative experiments- due to his studies in physics and maths

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9
Q

How many crosses and resulting characteristics did Gregor Mendel observe?

A

24,034 plants

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10
Q

When did Mendel’s discoveries burst into prominence and why?

A

1900, meiosis observed and described

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11
Q

Why did Mendel chose to study the common garden pea?

A

Ease of cultivation,
feasibility of controlled pollination
Availability of varieties with contrasting traits

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12
Q

How did Mendel control pollination and thus fertilization in the pea plants?

A

By manually moving pollen from one plant to another

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13
Q

What happens to pea plants if left untouched?

A

They self-fertilize

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14
Q

What is a character?

A

An observable physical feature such as flower color

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15
Q

What is a trait?

A

A particular form of a character such as purple flowers or white flowers

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16
Q

What is a heritable trait?

A

One that is passed from parent to offspring

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17
Q

What characters did Mendel look for?

A

Characters with well-defined contrasting alternative traits, such as purple flowers versus white flowers
True breeding traits

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18
Q

What are true breeding traits?

A

Observed trait was the only one present for many generations

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19
Q

How did Mendel isolate true-breeding strains?

A

By repeated inbreeding (by crossing sibling plants or by allowing self-fertilization)

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20
Q

What characters did Mendel focus on in his experiments?

A 
Seed shape
seed color
Flower color
Inflated/constricted pod
Pod color
Flower type
Stem length
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21
Q

What are the two traits of flower type Mendel focused on? Which was dominant?

A 
Axial flowers (dominant)
Terminal flowers
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22
Q

What did Mendel do before performing any experimental cross?

A

He made sure each potential parent was from a true-breeding strain

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23
Q

What was the first step in Mendel’s crosses?

A

Collect pollen from one parental strain and place it on the stigma of another flower whose anthers were removed.

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24
Q

Why did Mendel remove anthers of some of the plants?

A

To stop the plant self-fertilizing

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25
Q

What were the plants providing and receiving pollen called in Mendel’s experiments?

A

The parental generation, P.

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26
Q

What happened after Mendel fertilized the parental generation, P?

A

Seeds formed and were planted

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27
Q

What is the name of the generation made by the parental generation?

A

The first filial generation, F1

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28
Q

What did Mendel and his assistants do with the F1 generation?

A

Examine and recorded the number of F1 plants expressing each trait

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29
Q

What happened after the F1 generation was examined>

A

The plants self-pollinated to produce the F2 generation, which was characterized and counted.

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30
Q

What is a hybrid?

A

The offspring of crosses between organisms differing in one or more traits

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31
Q

What did Mendel do in his first experiment?

A

Mendel crossed two true breeding parental lineages, differing in just one trait

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32
Q

Mendel crossed two true breeding parental lineages, differing in just one trait. What was the F1 generation called?

A

Monohybrids

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33
Q

What happened to the F1 generation in Mendel’s first experiment?

A

They were allowed to self pollinate to produce the F2 generation

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34
Q

What is it called when the monohybrids are allowed to self-pollinate?

A

Monohybrid cross

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35
Q

On what traits did Mendel perform his first experiment?

A

All 7

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36
Q

What else did Mendel also do during his first experiment?

A

Perform a complementary cross

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37
Q

What did Mendel observe regarding traits during his first experiment?

A

Some traits were never expressed in the F1 generation but they reaapear in the F2 generation

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38
Q

What was Mendel’s conclusion when some traits were not expressed in the first generation but reappear in the second?

A

Some traits are dominant to the recessive traits

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39
Q

What did Mendel observe to do with ratio’s during his first experiment?

A

Ratio of the two traits in the F2 generation is always the same, 3:1

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40
Q

Why did Mendel perform reciprocal crosses during his first experiment?

A

To prove that it does not matter which parent contributes the pollen

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41
Q

What did Mendel’s monohybrid cross experiment show could not be the case?

A

The blending theory

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42
Q

Why was the blending theory rejected?

A
  • F1 seeds should have intermediate appearance

- Recessive traits should not reaapear in the F2 generation

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43
Q

What did Mendel instead propose, after rejecting blending theory?

A

Particulate theory- units responsible for inheritance are discrete particles that appear in pairs and separate during gamete formation

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44
Q

What is Mendel’s unit of inheritance now called?

A

A gene

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45
Q

What are different forms of a gene called?

A

Alleles

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46
Q

What must individuals who produce recessive traits be?

A

Homozygous for the recessive allele

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47
Q

What is the physical appearance of an organism called?

A

Phenotype

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48
Q

What did Mendel correctly suppose about phenotypes?

A

That they are the result of the genotype

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49
Q

How many different genotypes are there for seed shape?

A

Three: Ss, SS,ss

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50
Q

What is Mendel’s first law?

A

The law of segregation

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51
Q

What is the law of segregation?

A

Separation of alleles, or homologous chromosomes, during meiosis so each haploid daughter nuclei contains one pair found in diploid cell, not both

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52
Q

How can allele combinations resulting from a cross be predicted?

A

Using a punnet square

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53
Q

What is a gene?

A

A sequence of DNA that resides as a particular site on a chromosome, called a locus, and encodes a particular gene

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54
Q

How are most genes expressed in the phenotype?

A

Mostly as proteins with particular functions, such as enzymes

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55
Q

What can a dominant gene be thought of, given that genes are expressed as phenotypes?

A

A region of DNA that expresses a functional enzyme

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56
Q

What is a recessive gene, given that a dominant gene is a region of DNA that expresses a functional enzyme?

A

A gene that expresses a non-functional enzyme

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57
Q

How did Mendel verify his hypothesis that there are two possible allele combinations for spherical seeds (the dominant trait) in the F1 generation?

A

By performing a test cross

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58
Q

What is a test cross for?

A

It is a way of showing whether an individual is homo or heterozygous

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59
Q

How is a test cross carried out?

A

The individual in question is crossed with an individual known to be homozygous for the recessive trait

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60
Q

What are the two possible results for a test cross?

A

If tested individual is SS, offspring will all show dominant trait
If tested individual is Ss, offspring will be half dominant and half recessive.

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61
Q

What is Mendel’s second law?

A

The law of independent assortment

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62
Q

What experiments did Mendel carry out to come up with the law of independent assortment?

A

Dihybrid crosses

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63
Q

What is a dihybrid cross?

A

A cross between individuals that are identical double heterozygous

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64
Q

What happened when Mendel crossed a true breeding plant dominant for two characteristics (SSYY) with a true breeding recessive ssyy?

A

All offspring in the F1 generation were SsYy (spherical, yellow)

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65
Q

What happened to the F1 generation SsYy in Mendel’s second experiment?

A

He conducted a dihybrid cross by allowing them to self pollinate

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66
Q

What were the two possibilities for the F2 generation produced by a dihybrid cross in Mendel’s second experiment?

A

The alleles maintain their associations from the parental generation (they are linked)
Or
The segregation of S from s could be independent from the segregation of Y from y

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67
Q

What would happen if segregation of S from s was independent from the segregation of Y from y in Mendel’s second experiment? (What are the expected results?)

A

SS, Ss or ss combines with YY, Yy, yy to produce 9 phenotypes occurring in the ratio 9:3:3:1

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68
Q

What is it called when parental traits occur in new combinations?

A

Recombinant phenotypes

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69
Q

What is the law of independent assortment?

A

Alleles of different genes assort independently of one another during gamete formation

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70
Q

When is the law of independent assortment?

A

When genes are on different chromosomes

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71
Q

How do geneticists apply Mendel’s laws to humans?

A

Using pedigrees

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72
Q

What are pedigrees?

A

Family trees that show occurrence of phenotypes in several generations of related humans

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73
Q

Why are human pedigrees not as clear as Mendel’s work on pea plants?

A

Because humans do not have as many offspring

74
Q

What assumptions are made when making a human pedigree?

A

-An allele causing abnormal phenotypes is rare, so members outside of the family tree are unlikely to carry it

75
Q

What are key features of a dominant allele pedigree?

A
  • Every affected person has an affected parent
  • 1/2 of offspring with affected parent is affected
  • Phenotype occurs equally in both sexes
76
Q

What are key features of recessive allele pedigrees?

A
  • Affected people usually have unaffected parents
  • In affected families, 1/4 of children are affected
  • Occurs equally in both sexes
77
Q

Why do different alleles of a gene exist?

A

Because genes are subject to mutations

78
Q

What is the name given to an allele of a particular gene that is present in most individuals that gives rise to the expected phenotype?

A

The wild type

79
Q

What name is given to alleles that are not the wild type?

A

Mutant alleles

80
Q

What is a genetic locus with a wild type present less than 99% of the time known as?

A

Polymorphic

81
Q

How is coat colour in rabbits inherited?

A

Multiple alleles

82
Q

What are the alleles for coat color in Netherland dwarf rabbits?

A

C
c^ch
c^h
cc

83
Q

What are the possible phenotypes for Netherland dwarf rabbits?

A 
Dark gray
Chinchilla
Light gray
Point restricted
Albino
84
Q

What happens when genes have alleles that are not dominant or recessive to each other?

A

Intermediate phenotype is shown

85
Q

Give an example of intermediate phenotypes.

A

Cross of truebreeding red snapdragon with truebreeding white snapdragon gives F1 generation which is all pink

86
Q

How can it be demonstrated that pink snapdragons are the result of Mendelian inheritance and not blending?

A

Further cross: F2 generation gives rise to 1 red to 2 pink to 1 white- hereditary particles are sorted not blended

87
Q

What type of dominance gives rise to intermediate phenotypes?

A

Incomplete dominance

88
Q

What is the name given when two alleles at a locus produce two different phenotypes that both appear in heterozygotes?

A

Codominance

89
Q

Where can codominance be seen?

A

ABO blood types in humans

90
Q

Why did Karl Landsteiner find that mixing blood and serum from different individuals sometimes form clumps?

A

Anitbodies in the serum react with foreign cells because of the antigens on the surface of the foreign blood

91
Q

What three alleles determine blood compatibility?

A

I^A, I^B, i^O

92
Q

What is it called when a single allele has more than one distinguishable phenotypic effect?

A

The allele is pleitropic

93
Q

Where can pleitropy be seen?

A

Allele for coloration pattern of siamese cats, which is also responsible for cross eyedness

94
Q

When does Epistasis occur?

A

When phenotypic expression of a gene is affected by another gene

95
Q

What two genes determine coat color in labrador retrievers?

A
  • Allele B (black) dominant to b (brown)

- Allele E (pigment deposition in hair) dominant to e (no pigment deposition in hair)

96
Q

What is the result of having allele e in labrador retrievers?

A

Yellow hair

97
Q

Why do problems arise as the result of inbreeding?

A

Close relatives tend to have the same recessive alleles- some of which may be harmful

98
Q

What did G.H Shull experiment on?

A

2 existing corn varieties

99
Q

What happened when Shull crossed the two corn varieties?

A

They went from producing 20 bushels of corn per acre to 80

100
Q

What is the name given to the increase in corn yield seen by Shull when he crossed two different varieties?

A

Hybrid vigor,

Heterosis

101
Q

What is the mechanism by which heterosis works?

A

It is not known

102
Q

What is a hypothesis made to explain how heterosis works?

A

Overdominance- heterozygous condition in certain important genes is superior to the homozygote

103
Q

What is another hypothesis made to explain how heterosis works?

A

Homozygotes have alleles that inhibit growth, which is less active or absent in heterozygotes

104
Q

What else effects the phenotype of an organism, other than its genotype?

A

The environment

105
Q

What types of variables can affect gene expression?

A

Light
Temperature
Nutrition

106
Q

Give an example of a phenotype caused by interaction with the environment as well as genes.

A

Point restriction in Siamese cats and certain rabbit breeds

107
Q

How is point restriction in Siamese cats and certain rabbit breeds controlled?

A

Genotype should result in dark fur over entire body
An enzyme that produces dark fur has a mutation, rendering it inactive at temperatures above 25 degrees C
Extremities are cooler

108
Q

How can an experiment demonstrate that dark fur in Siamese cats/ certain rabbits is temperature dependent?

A

Remove a patch of white fur on point-restricted rabbits back
Apply ice pack to patch
Fur grows back dark

109
Q

What two parameters describe the effects of genes and environment on the phenotype?

A
  • Penetrance

- Expressivity

110
Q

What is penetrance?

A

The proportion of individuals in a group with a given genotype that actually show the expected genotype

111
Q

What is expressivity?

A

The degree to which a genotype is expressed in an individual

112
Q

Complex characters such as height that shows continuous variation is known as what?

A

Quantitative variation

113
Q

What is quantitative variation usually the result of?

A

both multiple genes and the environment

114
Q

What name is given to all of the genes that together determine complex characters (such as height)?

A

Quantitative trait loci

115
Q

Why is it important to determine quantitative trait loci?

A

The amount of rice grain produced is the result interacting genetic factors, deciphering these leads to higher-yield rice strains

116
Q

How was the pattern of inheritance of genes that don’t follow the law of independent assortment worked out?

A

Studies done on Drosophilia melanogaster

117
Q

Why is Drosophilia melanogaster used in experiments?

A

Small size
Ease of breeding
Short generation time

118
Q

Who and when did experiments on Drosophilia meanogaster occur to discover the relationship between genes and chromosomes?

A

Thomas Hunt Morgan

1909

119
Q

What was the hypothesis that genes assort independently disproven by Thomas Hunt Morgan?

A

Crossing Drosophilia of two known genotypes,BbVgvg and bbvgvg

120
Q

What is BbVgvg?

A

B- wild type gray body
b-mutant black body
Vg- wild type wing
vg- vestigial wing

121
Q

What is the expected phenotype of a cross between BbVgvg and bbvgvg?

A

Ratio of phenotypes 1:1:1:1

122
Q

What was the actual result of the cross performed between BbVgvg and bbvgvg?

A

The genes were not assorted independently, they were mostly inherited together

123
Q

How did Morgan explain his results?

A

The genes were linked because they were on the same chromosome

124
Q

What is a linkage group?

A

A full set of loci on a given chromosome

125
Q

Why did some flies have some recombinant phenotypes?

A

Linkage is not absolute, genes can be exchanged between chromatids

126
Q

How do genes recombine?

A

Two homologous chromosomes physically exchange corresponding segments during prophase I of meiosis by crossing over.
(reciprocal)

127
Q

What name is given to the proportions in which recombinant offspring occur?

A

Recombinant frequencies

128
Q

How are recombinant frequencies calculated?

A

By dividing the number of recombinant progeny by the total number of progeny

129
Q

When are recombinant frequencies greater?

A

When loci are further apart along the chromosome because exchange events are more likely to occur

130
Q

Who discovered that recombinant frequencies could be used to make genetic maps?

A

Alfred Sturtevant, in 1911

131
Q

What is the distance between genes measured in?

A

Map units

132
Q

How many recombination frequencies does 1 Map unit correspond to?

A

0.01, also called a centimorgan

133
Q

What human disease does the parental origin of a chromosome matter?

A

Hemophilia is inherited from the mother, not father

134
Q

What name is given to plants in which one individual produces both male and female gametes?

A

Monoecious

135
Q

Give an example of a monoecious plant.

A

Corn

136
Q

What name is given to plants in which some individuals produce only male gametes and others female gametes?

A

Dioecious

137
Q

Give an example of dioecious plants.

A

Date palms

Oak trees

138
Q

How is sex determined in dioecious organisms?

A

Chromosomes

139
Q

What type of chromosome determines sex in many animals, including humans?

A

Sex chromosomes

140
Q

What name is given to chromosomes that do not determine sex?

A

Autosomes

141
Q

How does abnormal sex chromosome constitutions occur?

A

Nondisjunction during meiosis

142
Q

What are XO individuals?

A

Individuals with just an X chromosome (aneuploid)

143
Q

What are the characteristics of XO individuals?

A

Females with physical abnormalities , usually sterile

144
Q

What is the name given to the condition of having XO chromosomes?

A

Turner syndrome

145
Q

How is Turner syndrome unusual?

A

It is the only known case where a person can survive with only one member of a chromosome pair, although most XO conceptions are spontaneously terminated

146
Q

What name is given to the condition resultant from having XXY chromosomes?

A

Klinefelter syndrome

147
Q

What is the result of Klinefelter syndrome?

A

Overlong limbs

Sterile

148
Q

What does observations regarding Turner syndrome and Klinefelter syndrome suggest?

A

The gene that determines maleness is located on the Y chromosome

149
Q

What two other chromosomal abnormalities helped researchers pinpoint the location of the gene for maleness?

A

Some individuals are XY but phenotypically female but lack a small portion of Y chromosome
Some men are genetically XX but have a small piece of Y chromosome

150
Q

What did the fragments that were missing/present from

the sex chromosomes contain?

A

Sex determining region on the Y chromosome (SRY)

151
Q

What does the SRY gene encode for?

A

The protein involved in primary sex determination

152
Q

What happens in the presence of functional SRY protein?

A

Embryo developes sperm producing testes

153
Q

What happens in the absence of the functional SRY protein?

A

Embryo develops into egg-producing ovaries

Gene on X chromosome (DAX1) produces anti-testis factor

154
Q

What is the role of the SRY protein in males?

A

Inhibit the maleness inhibitor encoded by DAX1

155
Q

What is primary sex determination not the same as?

A

Secondary sex determination

156
Q

What is the result of secondary sex determination?

A

Outward manifestations of maleness and femaleness

157
Q

What are outward characteristics determined by?

A

Genes scattered on the autosomes and X chromosome that control hormones

158
Q

In Drosophilia, what are XO individuals?

A

Sterile males, rather than females seen in mammals

159
Q

What are XXY individuals in Drosophilia?

A

Fertile females

160
Q

How is Drosophilia sex determined?

A

Ratio of X chromosomes to autosome sets.

161
Q

Do genes on sex chromosomes show Mendelian pattern of inheritance?

A

No

162
Q

On which sex chromosome are most genes that affect characters carried?

A

X

163
Q

What name is given males where there are 2 X genes present in females and only one in males?

A

Hemizygous for genes on the X chromosome

164
Q

What is the consequence of males only having one gene on the X chromosome?

A

They only have one copy, so it will be expressed.

165
Q

Name a sex linked character in Drosophilia flies.

A

Eye color

166
Q

What is the wild type eye color in Drosophilia?

A

red

167
Q

What happens when a homozygous wild type red eye female is crossed with a mutant, hemizygous white eyed male?

A

All the sons and daughters have red eyes because red is dominant and all progeny inherited their X chromosome from their mother

168
Q

What was the result of the reciprocal cross (homozygous white eyed female with hemizygous red eye male?

A

All daughters are red eyed

All sons are white eyed

169
Q

How many genes are carried on the human X chromosome?

A

2000

170
Q

What are some sex-linked characters on human X chromosomes?

A

Red-green colour blindness

171
Q

What are characteristics of a sex-linked human pedigree?

A
  • Phenotype appears more often in males (only one copy of rare allele needed)
  • Male can only pass it to his daughter
  • Daughters are carriers
  • Mutant phenotype can skip a generation
172
Q

Why are X-linked dominant phenotypes rarer than X-linked recessive phenotypes?

A

People carrying harmful mutations often fail to survive and reproduce

173
Q

Where else is genetic material found?

A

Mitochondria and plastids

174
Q

How many genes are there in the human nuclear genome?

A

24,000 genes

175
Q

How many genes are there in the human mitochondrial genome?

A

37

176
Q

How big are plastid genomes?

A

5x larger than those of mitochondria

177
Q

Why are organelle genes important?

A

For organelle assembly and function

178
Q

Why is inheritance of organelle genes different to that of nuclear genes?

A

Mitochondria/plastids are usually inherited from the mother. (eggs have lots of organelles)
There are hundreds of mitochondria/plastids in a cell, so cell is highly polyploidy
Organelle genes mutate faster than nuclear genes

179
Q

Give an example of plastid gene mutations in some plants and some photosynthetic protists.

A

Some mutations affect proteins that assemble chlorophyll molecules into photosystems, results in white phenotype instead of green

180
Q

Give an example of mitochondrial gene mutations

A

Affects one of the complexes in the electron transport chain to result in less ATP production

181
Q

Where does the mutation that affects one of the complexes in the electron transport chain to result in less ATP production have noticeable affects?

A

Tissues with high energy requirements (nervous system, muscles, kidneys)

Biology 2 (14 decks)

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