Mendelian Genetics and Probabilities (Lecture 4) Flashcards
Mendel’s peas were highly inbred, what does this mean?
They are, therefore “bred true or true-breeding or pure bred”
e.g. when two tall plants were crossed, they only produced tall progeny
What does the flower structure of the pea plant promote?
The flower structure promoted self-fertilization
Mendel’s experiments were designed so that he could study what?
One trait at a time
What is a gene?
An inherited factor (encoded in the DNA) that helps determine a characteristic
What is an allele?
One of two or more alternative forms of a gene
What is a locus?
A specific place on a chromosome occupied by an allele
What is a genotype?
Set of alleles possessed by an individual organism
What does it mean to be heterozygote?
An individual organism possessing two different alleles at a locus
What does it mean to be homozygote?
An individual organism possessing two of the same alleles at a locus
What is a phenotype or a trait?The appearance or manifestation of a characteristic
The appearance or manifestation of a characteristic
What is a characteristic or character?
An attribute or feature possessed by an organism
In alleles, what does an upper case letter refer to?
Refers to the dominant (expressed factor) allele
In alleles, what does a lower case letter refer to?
Refers to the recessive (latent factor) allele.
Alleles can be designated after the recessive trait, give an example of this.
example: a fly with a genetic mutation causes a white eye, whereas the wild type eye is red. The alleles would be w=white eye; W=red eye.
In some cases the alleles are designated after the dominant phenotype, give an example of this.
For example, the allele R for round seeds; r for wrinkled seeds.
RR or Rr for round seeds; rr for wrinkled seeds
The allelic combination is called what?
The genotype
The physical appearance is called what?
The phenotype
Genes exist in different versions called alleles. What do the different alleles code for?
One allele encodes round seeds
A different allele encodes for wrinkled seeds
Different alleles for a particular gene occupy the same…
Different alleles for a particular gene occupy the same locus on homologous chromosomes
Mendel started with purebred lines. What were these two purebreds and what was their phenotype?
One was purebred for the round seed; the other was purebred for the wrinkled seed. So they were each homozygous for the different alleles!
(1 & 2) How did Mendel cross varieties of peas?
To cross different varieties of peas, Mendel removed the anthers from flowers to prevent self-fertilization and dusted the stigma with pollen from a different plant
(3 & 4) What did the pollen fertilize, and what did it develop into?
The pollen fertilized ova, which developed into seeds. The seeds grew into plants.
(5) What is P and what happened at this stage?
P is the parental generation. At this stage Mendel crossed two homozygous varieties of peas.
Homozygous round seeds x Homogyzous wrinkled seeds
(6) What is F1 and what happens at this stage?
F1 is the First Filial Generation. All the F1 seeds were round. Mendel allowed plants grown from these seeds to self-fertilize
(7) What is F2 and what happens at this stage?
F2 is the Second Filial Generation. This is the result of self-fertilization. 3/4 of F2 seeds were round and 1/4 were wrinkled a 3:1 ratio.
What is the conclusion of the traits of the parent plants?
The traits of the parent plants do not blend. Although F1 plants display the phenotype of one parent, both traits are passed to F2 progeny in a 3:1 ratio.
After the F2 generation, the fraction of progeny seeds is 3/4 round and 1/4 wrinkled. Provide information for:
- Phenotype or Trait
- Characteristic
- Dominant Phenotype
- Recessive Phenotype
- Allele Designation
- Dominant Genotype
- Recessive Genotype
- Homozygote
- Heterozygote
- Phenotype or Trait: seed texture
- Characteristic: round or wrinkled
- Dominant Phenotype: Round
- Recessive Phenotype: Wrinkled
- Allele Designation: R for round; r for wrinkled
- Dominant Genotype: RR or Rr
- Recessive Genotype: rr
- Homozygote: RR or rr
- Heterozygote: Rr
One of the haploid gametes from Anther will be combined with what?
One of these haploid gametes from the Anther will be combined with one of the haploid gametes from the Stigma to produce a diploid seed.
(1 & 2) In the parent generation, Mendel crossed a plant homozygous for round seeds (RR) with a plant homozygous for wrinkled seeds (rr). What happens in the gamete formation process in the p generation?
The two alleles in each plant separated when gametes were formed; one allele went into each gamete
(3) In the F1 generation after the fertilization of the P gametes, the gametes fused to produce what plants?
Gametes fused to produce heterozygous F1 plants that had round seeds because round is dominant over wrinkles.
(4 & 5) Mendel self-fertilized the F1 to produce the F2 which appeared in what ratio of round to wrinkled?
3:1
(6 & 7) Mendel also self-fertilized the F2 seeds to produce the F3 seeds.
- Homozygous round peas produced plants with only _______
- Heterozygous plants produced round seeds and wrinkled seeds in a __________
- Homozygous wrinkled peas produced plants with only ______
- Homozygous round peas produced plants with only round peas
- Heterozygous plants produced round seeds and wrinkled seeds in a 3:1 ratio
- Homozygous wrinkled peas produced plants with only wrinkled peas
What is Segregation? (Mendel’s first law)
Which state of meiosis is each observation?
1. Each individual organism possesses two alleles encoding a trait (Before meiosis)
- Alleles separate/segregate when gametes are formed (Anaphase I)
- Alleles separate/segregate in equal proportions (Anaphase I)
What is independent assortment? (Mendel’s second law)
Which state of meiosis is each observation?
Alleles at different loci Anaphase I assortment separate independently.
(Anaphase I)
Info slide
Create a punnet square using the following information:
What is the genotypic and phenotypic ratio from the following F1 generation?
Genotypic ratio: 1 Tt : 1 tt
Phenotypic ratio 1 tall : 1 short
What is the multiplication rule?
If you roll a die, in a large number of sample rolls, on average 1 of 6 times you will obtain a 4, so the probability of obtaining a 4 in any roll is 1/6. If you roll the die again the probability of getting a 4 again is 1/6. So the probability of getting a 4 on the first roll AND the second roll is 1/6x1/6 = 1/36.
*The operative word here is “AND”
*Getting a four on the first AND second roll
The rules of probability - the multiplicative rule
If the events A and B are independent, the probability (P) that they occur TOGETHER is what?
If the events A and B are independent, the probability (P) that they occur TOGETHER** is the **PRODUCT of their individual probabilities of occurrence.
What is the addition rule?
If you roll a die, on average, one out of six times you’ll get a 3, and one out of six times you’ll get a four. That is, the probability of getting either a 3 or 4 is 1/6 + 1/6 = 1/3.
* The operative word here is EITHER** or **OR
*At three OR four
The rules of probability - the additive rule (using or)
If the events A and B are independent and do not overlap, the probability that at least one of them occurs is the sum of their individual probabilities.
Recall Mendel’s peas. What genotype gives rise to Round peas?
RR = Round
Rr = Round
rr= Wrinkled
What is the probability of a pea being Round?
It is the probability that the genotype is either RR OR Rr.
Therefore, the probability of RR is 1⁄4 or 0.25
The probability of being Rr is 1⁄2 or 0.5
1/4 + 1/2 = 3/4 will be round
In cats black fur is recessive to brown fur. If you cross a black cat with a heterozygous brown cat, what is the probability that a kitten would be black?
