Mendellian Genetics Flashcards
What were Mendel’s first 3 postulates?
1) unit factors are PAIRS
2) dominant/ recessive characteristics (called discontinuous variation)
3) separate INDEPENDENTLY
What is the basic unit of heredity?
Particulate unit factor
later called a GENE
What is an alternate form of a gene?
Allele
What is Mendel’s 4th postulate? And what does it lead to?
Independent assortment - leads to genetic variation
Why did Mendel choose peas for his experiment in the 1860’s?
- easy to grow
- true breeding
- you can control their mating (because you transfer pollen from a stamen to a pistol )
How did Mendel determine that the peas genes were NOT sex linked?
RECIPROCAL CROSS
Regardless of which breed he took the pollen from, the results were the same.
Mendel had an odd finding in which generation of his experiment with dihybrid crosses? What was the odd finding?
In the F2 generation he found a genotypic ratio of 9:3:3:1
P1: 100% purebred
P2: 100% heterozygous for both traits
P3: 9:3:3:1 ratio
When do you use the product law?
When 2 events are happening simultaneously but independent
Ex: ratio of color x ratio of shape
What are passed from generation to generation unchanged?
Particulate unit factors (aka “genes”)
Which generation undergoes “selfing”?
The F1 undergoes selfing (mating with eachother) to yield an F2 generation
What is the principle of uniformity?
The appearance of heterozygotes are uniform phenotypically because of the dominance/recessive characteristics.
What is the chromosomal theory of inheritance (Sutton & Boveri, 1900’s)
Simply that genetic material is found in chromosomes
5 characteristics of being a homologous pair?
1) same size
2) identical centromere location (except x & y)
3) form pairs and synapse during meiosis
4) identical linear order of gene loci
5) 1 from mom & 1 from dad
Who suggested that variation was a blend of parent phenotypes and what was that called?
Continuous variation, suggested by Darwin & Wallace
Where are alternative forms of a gene found?
Homologous chromosomes
(SOLVING FOR # OF DIFFERENT TYPES OF GAMETES)
*What is the formula used to solve the scenario below:
On the basis of segregation and independent assortment, how many different types of gametes can be formed from an organism that has a diploid number of 12.
of copies (for diploid that’s 2) raised to the nth power.
Where n = the haploid number of chromosomes.
(In this scenario n=6. So 2^6 is 64.)
What is the term for an intermediate phenotype where neither allele is dominant
Incomplete or partial dominance
Example of an incomplete (partial) dominance
Red x White yields pink color
Phenotype ratio is the same but the genotypes have a blended intermediate
What is an example of a human disorder with incomplete dominance?
Tay sachs disease
Homozygous recessives= fatal lipid storage disorder where hexosaminidase A is absent and can’t metabolize lipids. (Less than 50% threshold)
Normal heterozygotes: get 1/2 the enzyme activity but enough to live
What is threshold affect?
Certainty level of the gene product attained. (Ex: tay Sachs disease has <50% threshold level)
What is codominance?
When 2 alleles are expressed unblended. (Example: brown x white yields white with brown spots.)
What is blood type an example of?
Codominance
IA and IB are codominant to eachother yielding AB blood type
What are possible genotypes to yield type A blood
IA IA
and
IA i
What are all the possible genotypes yielding an AB blood type
Only IA and IB
What are all possible genotypes yielding type O blood
Only ii
Explain Bombay phenotype
Female is functionally type O blood type even though she doesn’t have ii blood type.
She is homozygous for FUT1 (fucosyl transferase) so she can’t produce H substance and she can’t make A or B antigens
Describe a recessive lethal allele
One wild type (normal) allele is enough to survive.
(Therefore, homozygous recessive will not survive.)
A lethal allele is a result of a mutation in “essential genes”
What is an essential gene?
Required to survive
What are results possible from dominant lethal alleles
One allele results in death
ie: Huntington’s
What is epistasis? What is an example?
When a gene masks the phenotype of another gene
Ex: hereditary deafness and Bombay phenotype
What predicts the number of genes determining a trait
Complementation analysis
What is the complementation group?
When all mutations are present on the same gene in a complementation analysis
What is it called when a single gene has multiple phenotypic effects?
Pleiotropy
What are 2 examples of pleiotropy in human disorders
Marian syndrome
and
Porphyria variegata
Describe pleiotropy
The expression of 1 gene has MULTIPLE phenotypic effects
Porphyria variegata is an autosomal disorder that has multiple phenotypic effects
such as abdominal pain, muscular weakness, fever, racing pulse, insomnia, vision issues.
What builds up in the body when this disorder is present?
Polyphyrins buildup in the body to toxic levels
What is the difference between sex limited and sex influenced inheritance?
Sex limited is limited to one sex only.
Whereas sex influenced is not limited to one sex. The sex of the individual influences the phenotypic expression - (aka sex influences phenotype).
Example: with male pattern baldness, the results are less pronounced in females.
What is penetrance?
The percentage that a mutant phenotype is expressed in a population
What is expressivity?
RANGE of the expression of the mutant phenotype
What is position effect?
When the physical location of the gene influences its expression.
(When the chromosome is rearranged the phenotype looks different!)
What is the temperature effect?
When the temp of the climate influences the gene.
Ex: Darker fur on cooler areas (tail, feet, ears)
Examples of organisms that undergo Temperature sensitive mutations
Viruses, bacteria, fungi and DROSPHILIA
4 examples of delayed onset disorders
Tay Sachs, lesch-nyhan, muscular dystrophy (DMD), Huntington’s
What is genetic anticipation
Early onset but it gets more severe in each succeeding generation
