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BLGY1232 > Mendelian Genetics 1 > Flashcards

Mendelian Genetics 1 Flashcards

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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

Study These Flashcards
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

Study These Flashcards
A

a genetic locus where consequences effect more than one phenotype

21
Q

Mendel’s Experiments

Study These Flashcards
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

Study These Flashcards
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

Study These Flashcards
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

Study These Flashcards
A
  • fruit flies
  • nematode worms
  • plants - Arabidopsis thaliana
  • fungi
25
Arabidopsis
- agamous - recessive mutant allele - causes infertility
26
Drosophila
``` Wildtype RR, Rr - red eye colour WW, Ww - normal wings Mutant rr - white eye colour ww - vestigial wings ```
27
Genetic Nomenclature
- 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
Yellow Mice | Genotypes and Phenotypes
- -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
Yellow Mice | Pleiotrophy
- 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
What is the simplest way to represent a genetic cross?
a Punnett Square
31
Ss x Ss
3:1
32
Ss x ss
1:1
33
Ss x SS
1:0
34
Test Cross
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
Snapdragons -Flower Colour | Genetic Crosses
``` 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
Snapdragons - Flower Colour | Explanation
- 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
Yellow Mouse | Genetic Cross
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
Mendel's Experiment Seed Colour & Seed Shape Separate Traits
-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
Mendel's Experiment Seed Colour & Seed Shape Traits Together
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
Mendel's Experiment Seed Colour & Seed Shape Branch Diagram
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
Gene Pairs, Phenotypic Class, Genotypic Class and Genotytpe
- 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
What is the ratio for two gene segregation?
9:3:3:1
43
Multiple Genes, Single Trait Example
- 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
Multiple Alleles | Example
- 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
Multiple Alleles vs Multiple Genes
- 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
Trihybrid Cross
``` 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 ```

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