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
