Mendelian Genetics: Monohybrid Flashcards
Define genotype
the nucleotide sequence for a trait in an organism
ex. Homozygous dominant (PP) and heterozygous (Pp) are different genotypes, even though they might appear the same
Define phenotype
The physical and physiological traits of an organism that are determined by genetic makeup
ex. homozygous dominant (PP) and heterozygous (Pp) look the same = have the same phenotype
Explain what test crosses are for and how they work
Breeding an organism with a homozygous recessive individual to determine the unknown genotype of the original organism,
The ratios of the phenotypes of the offspring reveal the unknown genotype
What organism did Mendel conduct his studies on?
Pea plant flowers
Define hybridization
the process of crossing two true-breeding varieties
T or F: Mendel’s crosses showed the blended model was correct
FALSE. He showed it was wrong.
What is Mendel’s famous ratio?
3:1
3 Purple: 3 white flowers
Define allele
variations of genes
Define true-breeding
organisms that produce offspring of the same variety over many generations of self-pollination
What does the P generation represent?
The true-breeding parental generation
What does the F1 generation represent?
The hybrid offspring of the parental generation
1st Filial
What does the F2 generation represent?
the offspring of the F1 generation from self-pollination
2nd Filial
What is the name of the table used to determine the combinations of genetics?/to solve genetic problems?
Punnett Square
What is the blended model of inheritance?
The model of inheritance that was commonly accepted before Mendel’s model.
Stated that the F1 hybrid from a cross between purple flowers and white flowers would have pale purple flowers (an intermediate trait between those of the parental generation)
Define homozygous
An organism that has two copies of the same allele
What are the two kinds of homozygous combinations?
Homozygous dominant (ex. PP)
Homozygous recessive (ex. pp)
Define heterozygous
An organism that has two different alleles for the same given gene
ex. Pp
Define heterozygous
An organism that has two different alleles for the same, given gene
ex. Pp
What are examples of human traits controlled by recessive genes?
- attached earlobes
- albinism
- cystic fibrosis
- sickle cell disease
What are examples of human traits controlled by dominant genes?
- Achondroplasia
- Widow’s peak
- Huntington’s disease
- polydactyly
Define Punnett Square
a diagram used to show the predicted genotypic results of random fertilization in genetic crosses between individuals of known genotypes
Define Punnett Square
a diagram used to show the predicted genotypic results of random fertilization in genetic crosses between individuals of known genotypes
Explain the Law of Segregation
The 2 alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes
What were the results for Mendel’s experiment for each generation?
Parental: 1 purple crossed with 1 white (both true breeding)
F1: Purple flowers
F2: 3 purple: 1 white
In Mendel’s experiment, which was the dominant allele/trait and which recessive?
Dominant: purple flower
Recessive: white flower
What are the 4 concepts included in Mendel’s model to explain the 3:1 inheritance?
- alternative versions of genes (alleles) account for variations in inherited characters
- for each character, an organism inherits 2 copies (2 alleles of a gene, one from each parent
- if the 2 alleles at a locus differ, then one, the dominant allele, determines the organism’s appearance; the recessive allele has no noticeable effect on appearance
- the law of segregation: the 2 alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes
What are the 4 concepts included in Mendel’s model to explain the 3:1 inheritance?
- alternative versions of genes (alleles) account for variations in inherited characters
- for each character, an organism inherits 2 copies (2 alleles of a gene, one from each parent
- if the 2 alleles at a locus differ, then one, the dominant allele, determines the organism’s appearance; the recessive allele has no noticeable effect on appearance
- the law of segregation: the 2 alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes
State and explain the first concept of Mendel’s model
Alternative versions of genes (alleles) account for variations in inheritable characters
The DNA at the locus (gene), can vary slightly in its nucleotide sequence, resulting in two different alleles at the same locus.
In Mendel’s experiment, the purple flower allele and the white flower allele are two DNA sequence variations possible at the flower colour locus on one of a pea plant’s chromosomes
State and explain the first concept of Mendel’s model
Alternative versions of genes (alleles) account for variations in inheritable characters
The DNA at the locus (gene), can vary slightly in its nucleotide sequence, resulting in two different alleles at the same locus.
In Mendel’s experiment, the purple flower allele and the white flower allele are two DNA sequence variations possible at the flower colour locus on one of a pea plant’s chromosomes
State and explain the second concept of Mendel’s model
For each character, an organism inherits two copies of a gene (ie, two alleles), one from each parent.
Each somatic cell in a diploid organism has 2 sets of chromosomes, one from the mother and one from the father so a genetic locus is represented twice in a diploid cell - once on each homologue of a specific pair of chromosomes
the two alleles at a particular locus might be identical (as in the true-breeding P plants) or they can differ (as in the F1 hybrid plants)
State and explain the second concept of Mendel’s model
For each character, an organism inherits two copies of a gene (ie, two alleles), one from each parent.
Each somatic cell in a diploid organism has 2 sets of chromosomes, one from the mother and one from the father so a genetic locus is represented twice in a diploid cell - once on each homologue of a specific pair of chromosomes
the two alleles at a particular locus might be identical (as in the true-breeding P plants) or they can differ (as in the F1 hybrid plants)
State and explain the third concept of Mendel’s model
If the two alleles at a locus differ, then the dominant one will determine the organism’s appearance and the recessive one will be hidden
In Mendel’s experiment, the F1 hybrid plants all displayed the dominant allele and presented a purple flower.
State and explain the fourth concept of Mendel’s model
the law of segregation: the two alleles for a heritable character separate from each other during gamete formation and end up in different gametes
So an egg or a sperm only gets one of the two alleles that are present in the somatic cells of the organism making the gamete during meiosis
If the alleles are identical, then 100% of the gametes get that allele
if the allele differs on the homologous chromosomes, then 50% of the gametes receive the dominant allele and 50% of the gametes receive the recessive allele
Define monohybrid
An organism that is heterozygous with respect to a SINGLE gene of interest
All the offspring from a cross between parents homozygous for different alleles are monohybrid
ex. parents of genotypes AA and aa produce a monohybrid of genotype Aa
Define monohybrid cross
a cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant)
Define monohybrid cross
a cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant)
What is the probability scale
0-1
0 = 0% chance of an event occurring (an event is certain not to occur)
1 = 100% chance of an event occurring (an event is certain to occur)
Are genetic probabilities dependent or independent events?
INDEPENDENT
The results of a previous offspring will not have an effect on the next offspring
Explain what the multiplication rules of probability are used for and how they work
Used to determine the probability of two or more events happening
Ie, calculate probability of x AND y occurring
Multiple the probabilities of 2 or more independent events
Explain what the addition rules of probability are used for and how they work
Used to determine the probability of any one of two or more events occurring
Ie, calculating probability of x OR y occurring
Add the probabilities of 2 or more independent events
What is the probability of getting a heterozygous offspring from a monohybrid cross?
Monohybrid = Pp x Pp
- can get dominant OR recessive allele from either parent so it can happen in two independent ways:
Probability of heterozygote with dominant allele from father = 1/4
Probability of heterozygote with dominant allele from mother = 1/4
1/4 + 1/4 = 1/2
What is the probability of getting a heterozygous offspring from a monohybrid cross?
Monohybrid = Pp x Pp
- can get dominant OR recessive allele from either parent so it can happen in two independent ways:
Probability of heterozygote with dominant allele from father = 1/4
Probability of heterozygote with dominant allele from mother = 1/4
1/4 + 1/4 = 1/2
A cross between a black guinea pig and a white guinea pig results in F1 that are all black and F2 with 3:1 black: white ratio.
List and discuss the conditions required to give these results
The trait (colour) is controlled by one gene
Black is the dominant allele and white is recessive
Black guinea pig must be homozygous dominant (BB) or all the F1 wouldn’t be black
White guinea pig must be homozygous recessive (WW) or it wouldn’t be white
A cross between a black guinea pig and a white guinea pig results in F1 that are all black and F2 with 3:1 black: white ratio.
List and discuss the conditions required to give these results
The trait (colour) is controlled by one gene
Black is the dominant allele and white is recessive
Black guinea pig must be homozygous dominant (BB) or all the F1 wouldn’t be black
White guinea pig must be homozygous recessive (WW) or it wouldn’t be white
Explain why phenotypically identical or at least very similar parents may produce very different kinds of offspring
Because genotypes can differ even if phenotypes do not.
A parent’s genotype can be heterozygous (Pp) and the other can be homozygous dominant (PP) and they will produce the same phenotypes
Explain why, in humans, many recessive traits (like albinism or blue eyes) ‘skip’ generations while dominant traits (like polydactyly) do not
Dominant traits will be present in every generation because they are dominant.
If an organism with the recessive genes mates with another organism that has dominant genes, the recessive genes will be hidden (so they do not appear in every generation)
Define character
an observable heritable feature that can vary between individuals
Define trait and give an example
Detectable variants in a genetic character
ex. hair colour, blood type
