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BIOL 1020 > Mendelian Genetics- lecture #16 & 17 > Flashcards

Mendelian Genetics- lecture #16 & 17 Flashcards

1
Q

why did mendel use garden peas for his experiments?

A

many different versions avaliable
short generation times
produce large number of offspring
self fertilizing (each flower has male and female parts)

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2
Q

why didn’t Mendel breed with humans?

A

takes a long time to reproduce
infrequent to have more than 1 offspring
we have so many traits from ancestors…

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3
Q

what are characters?

A

varied heritable features
gene for something

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4
Q

what are examples of characters?

A

flower color, hair color, eye color

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5
Q

what are traits?

A

variant of a character
we get 2 traits inherited

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6
Q

what examples of traits?

A

purple flowers and white flowers
brown eyes vs blue eyes
brown hair vs blonde hair

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7
Q

how is a pea plant self-fertilizing? what parts makes it self fertilizing?

A

egg bearing carpel
pollen producing stamen

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8
Q

what allowed Mendel to control gametes used in fertilization?

A

removed the immature stamen
dusted the carpel with pollen taken from a different stamen
used true breeding individuals

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9
Q

what is a true breeding individual?

A

produce the parent variety only (all future generations will be of the same color as the parent only)
PP or pp

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10
Q

what is hybridization?

A

cross of two different true breeding plants

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11
Q

the two true breeding individuals form what generation?

A

parent generation
P gen

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12
Q

hybrids produced from the P gen become what generation?

A

F1 generation
not true breeding

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13
Q

what comprises the F2 generation?

A

two members from the F1 generation produce F2 generation

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14
Q

what is the law of segregation?

A

blending doesnt happen, flower is either purple or white, not light purple

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15
Q

if theres a cross between a white flower and a purple why might the next generation be mostly purple?

A

because its dominant (white is still in the genes of the next generation though, even if not expressed)

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16
Q

what were mendels 4 key observations?

A
  1. alternate versions of genes account for variation in inherited characteristics
  2. an organism will have two copies of each character
  3. if two alleles at a locus differ from one another, the dominant allele will determine the organism’s appearance
  4. law of segregation
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17
Q

what are alternate versions of a character called?

A

allele

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18
Q

DNA at the same locus of homologous pairs may exhibit what?

A

slight variation in nucleotide sequence

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19
Q

what does this variation in nucleotide sequence give rise to?

A

different allele of the same character
many alternate alleles are possible

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20
Q
  1. an organism will have two copies of each character, what does that mean?
A

one gene copy will originate from the father and one will originate from the mother

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21
Q

what does homozygous mean?

A

identical alleles of a gene

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22
Q

heterozygous

A

two copies different from one another, what is that called

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23
Q

why did the white pea plant ‘disappear’ in the F1 generation?

A

recessive allele

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24
Q

what is the process to determine which gametes are used in fertilization?

A

two alleles separate during meiosis
end up in separate gametes
if the two alleles are the same, all 4 gametes produced will have the same allele for the gene (all brown eyes)
if the two alleles are different then 2 gametes will have the dominant allele (brown eyes) and two will have the recessive allele (blue eyes)

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25
Q

what is homozygous dominant and recessive?

A

dominant: PP
recessive: pp

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26
Q

are heterozygotes true breeding?

A

no, Pp

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27
Q

what is a phenotype?

A

observable traits
the flower is purple

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28
Q

what is a genotype?

A

genetic makeup
the flower is purple but its genotype is 1:2:1 therefore there is white in its genes

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29
Q

in order to determine an unknown genotype what can we do?

A

test cross the unknown with a homozygous recessive organism

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30
Q

why do we test cross with pp?

A

we know the outcome of homozygous recessive
if there are white plants in the F1 generation then the unknown must be Pp

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31
Q

what do monohybrid crosses analyze?

A

one trait at a time
Gg x Gg
4 possibilities

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32
Q

what do dihybrid crosses analyze?

A

two traits simultaneously
YyRr x YyRr
16 possibilities

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33
Q

what is dependent assortment?

A

alleles of each trait are passed along together

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34
Q

what is independent assortment?

A

alleles for each trait are passed along as individual units

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35
Q

if the alleles are passed along together than the organisms produced in the F1 generation will form ___ and ___ gametes

A

YR and yr
4 possible gamete combinations

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36
Q

if the alleles are separated independently during gamete formation than the F1 generation will produce ___, ___, ___ and ___ gametes

A

YR, Yr, yR and yr
16 possible gamete combinations

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37
Q

mendel examined the offspring and found that the F2 generation had what phenotypic ratio?

A

9:3:3:1
9 yellow, round plants (YYRR, YYRr, YyRR, YyRr, YYRr, YyRR, YyRr, YyRr, YyRr)
3 yellow, wrinkled plants (YYrr, Yyrr & Yrr)
3 green, round plants (yyRR, yyRr & yyRr)
1 green, wrinkled plant (yyrr)

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38
Q

what is the law of independent assortment?

A

each pair of alleles will segregate independently of each other allele during gamete formation

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38
Q

what is the law of independent assortment?

A

each pair of alleles will segregate independently of each other allele during gamete formation

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39
Q

what is complete dominance?

A

dominant allele has the same phenotypic effect whether it is present in one or two copies

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40
Q

Mendel’s Law only explains ________ __________

A

complete dominance

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41
Q

Mendels laws fail to explain ______________ ____________

A

incomplete dominance

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42
Q

F1 hybrids mating a homozygous dominant and a homozygous recessive produce what?

A

heterozygotes
Bb
with an intermediate phenotype

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43
Q

what is the blending hypothesis?

A

mating heterozygotes would never again lead to the appearance of red or white
it results in 1 red: 2 pink: 1 white

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44
Q

why might pink be shown in the offspring of red and white parents?

A

blending hypothesis

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45
Q

most genes in the population have how many alleles?

A

many

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46
Q

how many alleles exist for the blood type gene?

A

I^A, I^B, i

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47
Q

what are the 4 different blood types from the possible allele combinations?

A

Type A blood: I^A I^A or IA i
Type B blood: I^B I^B or IB i
Type AB blood: I^A I^B
Type O blood: ii

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48
Q

how can I^A and I^B alleles both be expressed?

A

co-dominant

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49
Q

what can the A blood type recieve?

A

A and O blood

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50
Q

what can the B blood type recieve?

A

B and O blood

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51
Q

what can the AB blood type recieve?

A

A, B and O (the universal recipient)

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52
Q

what can the O blood type recieve?

A

only O (but is the universal donor

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53
Q

what is epistasis?

A

phenotypic expression of a gene at one locus, affects phenotypic expression of a gene at a second locus

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54
Q

what is an example of epistasis?

A

E deposits black or brown pigment
ee deposits no pigment regardless if the B was B or b
9:3:4

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55
Q

what is the phenomenon called pleiotropy?

A

many genes affect more than one phenotype

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56
Q

what is an example of pleiotropy?

A

sickle-cell disease in humans

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57
Q

what does sickle- cell disease do?

A

produces abnormal hemoglobin
causes red blood cells to change shape becoming sickle-cell in shape

58
Q

the sickle-cells are quickly destroyed by the body, leads to what?

A

anemia and body weakness
because we’re losing o2 delivery

59
Q

what does the deformed shape of the red blood cells do? what does this result in? what side effects?

A

creates blockages
results in fever and pain

60
Q

how many people does sickle-cell disease kill worldwide?

A

100,000 per annum

61
Q

sickle-cell disease only results in those that are what for the allele/trait?

A

homozygous

62
Q

what happens if someone is heterozygotes and they have sickle-cells?

A

have less sickle-cells, nothing the body cant handle
normal and sickle-cell allele are both expressed

63
Q

what is the spectrum of possibility for certain traits a consequence of?

A

polygenic inheritance

64
Q

what is polygenic inheritance?

A

the added effect of two or more genes on a single character

65
Q

what is polygenic inheritance the reverse of?

A

pleiotropy

66
Q

what type of punnett square would we use for skin color?

A

dihybrid cross + 3rd trait
trihybrid punnett square

67
Q

what are many genetic factors (including skin color) affected by?

A

the environment

68
Q

what is an example of how our environment has an effect on our skin color?

A

sun exposure (tanning)

69
Q

what is another example of a trait that results from a combination of heredity and the environment?

A

effect of experience on intelligence
nutrition on height

70
Q

what is the special position of Mendelian genes on their chromosomes?

A

loci

71
Q

chromosomes exhibit what type of assortment?

A

independent

72
Q

chromosomes undergo what?

A

segregation (separation)

73
Q

what happens to meiotic behavior of homologous chromosomes?

A

accounts for the segregation (separation) of alleles at the same locus in order to form gametes

74
Q

what happens to meiotic behavior of non-homologous chromosomes?

A

account for independent assortment of alleles for 2 or more genes on different chromosomes

75
Q

what did Thomas Morgan provide evidence to?

A

associate a particular gene with a specific chromosome

76
Q

what did Thomas Morgan study?

A

Drosophila melanogaster (type of fruit fly)

77
Q

what is a Drosophila melanogaster (fruit fly)? what does it eat?

A

fruit fly that is a fungi-eating insect

78
Q

Why did Morgan decide to use fruit flies?

A

produces hundreds of offspring
reproduces fast (2 weeks)
3 autosomal, 1 sex pair (XX and XY)

79
Q

how many autosomal cells do humans have? how many sex cells do humans have?

A

22 and one sex cell

80
Q

what did Morgan initially discover?

A

male flies that had white eyes
usually flies had red eyes

81
Q

most commonly occuring phenotype is the wild type, what does an alteration of the wild type produce?

A

mutants

82
Q

if you mate a white eyed male with a red eyed female what was found in the F1 generation?

A

all have red eyes

83
Q

if all the F1 generation had red eyes, what is the main takeaway?

A

allele behavior correlates with behavior of the chromosomal pair

84
Q

A cross of the two F1 offspring produces the typical 3:1 ratio, which gender of the F2 offspring had white eyes?

A

male
all F2 females had red eyes

85
Q

why were females unable to have white eyes? why were males only able to get white eyes?

A

eye color of the flies were linked to sex

86
Q

can males carrying a recessive alle mask it by a dominant allele?

A

no, because they only have one X, therefore they can only be X^R or X^r, they cant be heterozygous (mask)

87
Q

how many possibilities do females have to determine eye color?

A

X^R X^R and X^R X^r: red eyes
X^r X^r: white eyes
therefore, eye color is determined entirely by the chromosome provided by the mother

88
Q

how many genes does the Y chromosome have? how many proteins do they encode?

A

78 genes, encode 25 different proteins
(78 is not many compared to X)

89
Q

what are the proteins encoded by the genes on the Y chromosome necessary for?

A

normal testes development
creates differences in offspring

90
Q

what is the SRY?

A

sex determining region (gene located on the Y chromosome)

91
Q

What does the SRY trigger?

A

the development of the testes
determines the sex of fertilized egg

92
Q

what happens when the SRY gene is absent?

A

ovaries develop XX

93
Q

grasshoppers and some other insects have an X-O system, what does the O symbolize?

A

the lack of a second sex chromosome
females: XX
males:XO

94
Q

what gamete determines the sex of the offspring in grasshoppers?

A

male gamete
(same as in humans)

95
Q

what animals have sex determined by the female?

A

some fish
butterflies
birds

96
Q

what is the genotype for birds sex chromosome? how is sex determined by the female?

A

male: ZZ
females: ZW
sex is determined according to whether the egg carries a Z or a W

97
Q

what organisms do not have sex chromosomes?

A

bees and ants

98
Q

how is the sex determined in organisms that dont have sex chromosomes?

A

depends on chromosome number
males develop from unfertilized eggs (haploid) (16 chromosomes)
females develop from fertilized eggs (diploid) (32 chromosomes)

99
Q

any gene on a sex chromosome is called what?

A

sex-linked gene

100
Q

what is an example of a trait that is carried on the sex chromosome (X chromosome)?

A

eye color

101
Q

how many genotypes do females have?

A

3

102
Q

how many genotypes do males have?

A

2

103
Q

what is Rr an example of?

A

heterozygous
a carrier

104
Q

why does the man (X^rY) pass r to his daughter and not his son?

A

man doesnt give the X chromosome to son so it would only go to daughter

105
Q

mating between X^R X^R and X^rY will produce what offspring in females, and what offspring in males?

A

females: all heterozygous X^R X^r (Rr)
males will all have red eyes X^R Y (RY)

106
Q

how might a white eyed female occur?

A

if the mother has white eyes
is a heterozygous carrier and the father has white eyes

107
Q

why do sex-linked disorders mostly affect the male population?

A

because males are hemizygous
if a male receives an affected X chromosome for a particular trait than he will express that allele and be affected

108
Q

what does hemizygous mean?

A

neither homozygous or heterozygous because the X and the Y chromosome are non-identical

109
Q

why are females not normally affected by sex-linked disorders?

A

because women recieve XX
if one is affected, the other X might not be and she will not express the disorder because shes just a carrier Rr
both XX would need to be recessive in order to show the disorder rr

110
Q

what are examples of sex-linked traits?

A

hemophilia
red-green colorblindness
Duchenne muscular distrophy

111
Q

what is hemophilia?

A

blood clotting (genetic based)

112
Q

what is duchenne muscular distrophy?

A

problem with muscle development and muscle strength

113
Q

each human female contains XX chromosomes, are both these chromosomes active?

A

only one chromosome is active

114
Q

in what form does the other X copy exist? what is this state called?

A

supercoiled almost totally inactive state called a Barr Body

115
Q

why is one X chromosome inactive?

A

occurs to prevent different amounts of protein production in males and females

116
Q

when does inactivatio occur?

A

randomly, very early in the stages of embryonic development

117
Q

what does each embryonic cell consist of?

A

one X chromosome
becomes a Barr body at random

118
Q

which X chromosome is activated? one one from the mother or father?

A

can be either
on a cat black fur is from father, yellow fur from mom
when black fur is active it is shown (from father) yellow fur X chromosome is condensed
when yellow fur is active it is shown (from mother) black fur X chromosome is condensed

119
Q

in a heterozygous female for an X-linked gene what allele is turned on/off?

A

one allele turned on in some cells
other cells will have the other allele turned on

120
Q

how do you tell if genes are inherited together?

A

genes that are located near to one another on the same chromosome are inherited together

121
Q

when genes are located far apart from each other what does that mean?

A

they will not be inherited together

122
Q

what does the cross of two heterozygotes result in for the F2 offspring? phenotypic ratio
Pp x Pp (P= purple, p= red)

A

3 purple
1 red

123
Q

what does the cross of two heterozygotes result in for the F2 offspring? phenotypic ratio
Ll x Ll (L=long, l=short)

A

3 long
1 short

124
Q

when the data from the two characters are combined what is the expected ratio?

A

9:3:3:1 (independent assortment)

125
Q

what was the observed ratio of the purple, red, long and short in %?

A

75% of plants were purple and long
14% of plants were red and round

126
Q

what does linked genes refer to?

A

each chromosome carries thousands of genes, those that are located near to one another tend to be inherited together

127
Q

do linked genes follow Mendels law of independent assortment?

A

no

128
Q

meiosis of unlinked genes will produce an equal amount of how many possible genotypes?

A

RR, Rr, rR, rr

129
Q

what does crossing over give rise to? what does it lead to production of?

A

new allele combinations
leads to production of 4 different alleles

130
Q

what happened when Thomas Morgan mated a wild-type fruit fly (gray body (G) and long wings (L)) with a (black fly (g) with undeveloped wings (l))

A

unlinked genes, a mating of Gg Ll and gg ll would produce equal amounts of all four genotypes

131
Q

because the genes are linked what happened to the bulk of the offspring?

A

parental phenotypes
17% were recombinant phenotypes

132
Q

what is recombinao?tion frequency equal t

A

percentage of recombinants produced

133
Q

what were the observed phenotypes a consequence of?

A

crossing over which unlinked linked alleles

134
Q

what did the new combinations involved in fertilization give rise to?

A

recombinant offspring

135
Q

what was hypothesized by one of Morgan’s students?

A

that crossing over is equally likely at all points on a chromosome

136
Q

how did the hypothesis that ‘the further apart two genes are located on a chromosome the greater the likelihood that crossing over will occur between them’ arise?

A

arose because the increased distance allowed a greater number of possibilities for crossing over to occur
allows more flexibility

137
Q

recombinant data from fruit flies was then used to map out the location of various genes, what is this called?

A

linkage map

138
Q

what is the distance between genes measured in?

A

map units

139
Q

what is 1 map unit equal to in percent recombination frequency?

A

1 map unit = 1% recombination frequency

140
Q

B+C= 5%
A+D= 4%
D+B= 3%
A+B= 7%
what is the order of these genes on the chromosome?
what is the recombination frequency of A+C?

A

A—4—-D—3—B—5—C
A——-7———-B
A————12————-C
order of the genes on the chromosome is A-D-B-C
the recombination frequency is 12
picture of this in downloads

141
Q

is the primary hypothesis that recombination frequency should be higher between genes that are farthest apart from one another true?

A

yes, in the example the recombination frequency is 12 and is therefore the highest

142
Q

is crossing over equally likely at all points on a chromosome?

A

no

BIOL 1020 (16 decks)

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