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BLGY1232 > Mendelian Genetics 1 > Flashcards

Mendelian Genetics 1 Flashcards

1
Q

Genotype

Definition

A

the underlying genetic makeup of an organism

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2
Q

Phenotype

Definition

A

the physical appearance of an organism

genotype may interact with the environment in order to produce the phenotype

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3
Q

Locus

Definition

A

a particular place in a genome, a particular physical region on the chromosome

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4
Q

Allele

Definition

A

variant of a gene

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5
Q

Diploid

Definition

A

an organism that has two copies of their genetic information, one from each parent

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6
Q

Haploid

Definition

A

cells that only contain one copy of the organisms genetic information

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7
Q

Homozygous

Definition

A

two copies of identical alleles at an individual locus

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8
Q

Heterozygous

Definition

A

two different alleles at the same locus

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9
Q

Dominant

Definition

A

the dominant phenotype is that which is the same regardless of whether or not the organism is homozygous or heterozygous for that allele at that locus
DOMINANCE IS RELATIVE

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10
Q

Recessive

Definition

A

in a diploid organism, two copies of a recessive allele are required at a particular locus for the recessive phenotype

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11
Q

Wildtype

Definition

A

the wildtype phenotype or wildtype allele is that which is most common in the population

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12
Q

Mutant

Definition

A

alleles or phenotypes that are different from the wildtype, mutant simply means different or changed

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13
Q

Mendel’s First Law of Inheritance

A

the principle of segregation states that the two members of a gene pair ssegregate from each other in the formation of gametes

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14
Q

Mendel’’s Second Law of Inheritance

A

the principle o findependent assortment states that members of different gene pairs are transmitted independently of one another during gametic production

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15
Q

What is selfing?

A

self fertilisation

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16
Q

What is a cross?

A

cross fertilisation

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17
Q

Self Fertilisation

A

to produce offspring using gametes from a single organism

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18
Q

Cross Fertilisation

A

producing offspring by fusing gametes derived from different organisms

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19
Q

True-Breeding or Pure-Breeding Strains

A

strains of organisms that when mated among themselves always produce identical progeny because they are homozygous for the phenotype under study

20
Q

Pleiotropy

Definition

A

a genetic locus where consequences effect more than one phenotype

21
Q

Mendel’s Experiments

A
  • carried out experiments using true breeding strains of the garden pea which showed different phenotypes for seven different traits:
  • flower colour
  • seed colour
  • seed shape
  • pod colour
  • pod shape
  • stem height
  • flower position
22
Q

Mendel’s Experiment

Smooth/Wrinkled - Description

A
  • Mendel noted that when a true breeding smooth and wrinkled plants were crossed all of the F1 were also smooth
  • the smooth phenotype was dominant to the wrinkled phenotype
  • when the F1 plants were selfed both the original parental phenotypes reappeared in the F2
  • Mendell predicted that each plant carried two copies of a genetic determinant, a gene
23
Q

Mendel’s Experiment

Smooth/Wrinkled - Genotypes

A 
Parental Cross: SS x ss
produced F1 : Ss
F1 cross: Ss x Ss
produced F2: SS, Ss, sS, ss
3:1 ratio of smooth:wrinkled
24
Q

Important Model Organisms for Genetics

A
  • fruit flies
  • nematode worms
  • plants - Arabidopsis thaliana
  • fungi
25
Q

Arabidopsis

A
  • agamous
  • recessive mutant allele
  • causes infertility
26
Q

Drosophila

A 
Wildtype
RR, Rr - red eye colour
WW, Ww - normal wings
Mutant
rr - white eye colour
ww - vestigial wings
27
Q

Genetic Nomenclature

A
  • gene names always written in italics
  • dominant alleles always written first, Bb not bB
  • dominant alleles always written in capitals
  • recessive alleles always written in lowercase
  • wildtypes often denoted by +
28
Q

Yellow Mice

Genotypes and Phenotypes

A
  • -an example of an organism where where the recessive allele is the wildtype
  • wildtype mouse hair colour is agouti, y/y
  • Y/y mice are heterozygous an have yellow hair
  • Y/Y mice are never found because Yelllow is a lethal gene when homozygous for the Y allele, homozygous YY embryos abort early in devlopment
29
Q

Yellow Mice

Pleiotrophy

A
  • in mice, Yellow has pleiotrophic effects, lethality an coat colour
  • coat colour is a dominant trait relative to wildtype coat colour, but lethality is recessive to wildtype for embryonic survival
30
Q

What is the simplest way to represent a genetic cross?

A

a Punnett Square

31
Q

Ss x Ss

A

3:1

32
Q

Ss x ss

A

1:1

33
Q

Ss x SS

A

1:0

34
Q

Test Cross

A

a cross between an individual of unknown genotype and an individual that is true breeding for the recessive trait

  • if the F1 are all dominant phenotype then the unknown genotype must have been AA
  • if the F1 are not all the dominant phenotype then the unkown genotype must have been Aa
  • any organism with the recessive ohenotype must be aa so you don’t need a test cross
35
Q

Snapdragons -Flower Colour

Genetic Crosses

A 
R - red
r - white
parent cross: RR x rr
produces F1: Rr - pink
F1 cross: Rr x Rr
produces F2: RR, Rr, Rr, rr
2:1:1
pink:red:white
-this is an example of codominance or incomplete dominance
36
Q

Snapdragons - Flower Colour

Explanation

A
  • the gene codes for an enzyme which manufactures the colour pigment
  • RR produces twice as much pigment as Rr so appears red where as Rr appears pink
  • -rr does not produce any pigment so the flower are white
37
Q

Yellow Mouse

Genetic Cross

A

parental cross: Yy x Yy
F1 Genotypes: YY, Yy, yy
but YY is lethal so aa class of progeny is missing from the 3:1 ratio
the observed ration in the progeny is 2:1

38
Q

Mendel’s Experiment
Seed Colour & Seed Shape
Separate Traits

A

-seeds are either yellow or green
-seeds are either smooth or wrinkled
-parental cross: YY x yy
produces F1: Yy
F1 cross: Yy x Yy
produces F2: YY, Yy, Yy, yy
expect 3:1 ratio of yellow:green

parental cross: SS x ss
produces F1: Ss
F1 cross: Ss x Ss
produces F2: SS, Ss, Ss, ss
expect 3:1 ratio of smooth:wrinkled
39
Q

Mendel’s Experiment
Seed Colour & Seed Shape
Traits Together

A

parental cross: SSYY x ssyy
produces F1: SsYy
cross F1: SsYy x SsYy
produces F2: 9:3:3:1 ratio of SmoothYellow:SmoothGreen:WrinkledYellow:Wrinkled Green
-this ratio comprises a 3:1 ratio of smooth to wrinkled within which there is a further 3:1 ratio of yellow to green

40
Q

Mendel’s Experiment
Seed Colour & Seed Shape
Branch Diagram

A

trait one: seed colour
trait two: seed shape

-for the first trait 3/4 of the progeny are smooth and 1/4 are wrinkled
-for the second trait 3/4 of the progeny are yellow and 1/4 are green
-smooth yellow:
3/4 x 3/4 = 9/16
-smooth green:
3/4 x 1/4 = 3/16
-wrinkled yellow:
1/4 x 3/4 = 3/16
-wrinkled green:
1/4 x 1/4 = 1/16

41
Q

Gene Pairs, Phenotypic Class, Genotypic Class and Genotytpe

A
  • if the number of gene pairs is n, then:
  • -the number of phenotypic classes is 2^n
  • -the number of genotypic classes is 3^n
  • -the number of genotypes is 4^n
42
Q

What is the ratio for two gene segregation?

A

9:3:3:1

43
Q

Multiple Genes, Single Trait Example

A
  • Comb development in chickens
  • four phenotypes; rose, pea, walnut and single

rose x single
produces F1: all rose
F2: 3:1 rose:single
->rose is dominant to single, looks life a single-gene trait

pea x single
produces F1: all pea
F2: 3:1 pea to single
-> pea is dominant to single, also looks like a single-gene trait

rose x pea
produces F1: all walnut
F2: 9:3:3:1 ratio of walnut to rose to pea to single
-> two gene segregation

RRpp = rose
rrPP = pea
RrPp = walnut
rrpp = single
44
Q

Multiple Alleles

Example

A
  • coat colour in rabbits
  • different colour variations derive from different combinations of alleles at the coat locus C
  • -agouti rabbits carry at least one copy of the wildtype allele C+ which is dominant to all other alleles
  • -chinchilla rabbits carry at least one copy of the Cch allele, homozygotes are chinchilla but heterozygotes carrying one Ca or Ch are light grey chinchilla
  • -himilayan rabbits carry at least one Ch allele, if heterozygotes, the other allele must be albino, Ca, for the himilayan phenotype
  • albino rabbits are homozygous for the ‘most recessive’ allele, Ca
45
Q

Multiple Alleles vs Multiple Genes

A
  • if loci are allelic you don’t get wildtype phenotypes when you cross individuals homozygous for different RECESSIVE alleles
  • this cross test is called a complementation test
  • we say that complementation occurs if we obtain the wildtype from a cross between individuals homozygous for recessive alleles, e.g. with chicken comb shape
46
Q

Trihybrid Cross

A 
parental cross: AABBCCxaabbcc
produces F1: AaBbCc
F1 cross: AaBbCc x AaBbCc
produces F2: 27:9:9:9:3:3:3:1
64 genotypes and 8 phenotypes

BLGY1232 (19 decks)

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