Mendelian Genetics Flashcards
What is blending inheritance?
Traits in the mother and father blend together to form the traits in their offspring. Source was mixing of blood.
White and black sheep produce gray sheep.
Analogy: Mixing of paints
When did Mendel determine rules of inheritance?
1865
Not really known until 1900’s
Who were Sutton and Boveri and what did they determine?
1903, Sutton and Boveri independently linked patterns of inheritance with chromosomes and reduction in chromosome number (meiosis) restored at fertilization.
What did Thomas H. Morgan discover?
1907, T. H. Morgan and other biologists described details of sex determination by studying fruit flies.
Why was Mendel successful?
Excellent observer and record keeper
Quantitative approach
Picked a really good model organism for his research (relatively easy to manipulate)
Some luck involved
The traits he studied were relatively simple and straightforward
The traits he studied happened to be unlinked with each other
What are Mendel’s rules of inheritance?
units of inheritance are “particles of inheritance” (material elements) => genes are nucleotide sequences on DNA coding for proteins
particles of inheritance come in pairs that do not blend together => gene alleles come in pairs on homologous chromosomes and form definite traits
particles retain their character through generations => chromosomes replicate to be passed on to each following generation
particles of inheritance separate during formation of gametes => alleles on homologous chromosomes separate during meiosis I, ending in different gametes
Define Character
Qualities or attributes of an organism that are visible or discernable (height to protein primary structure)
Ex: Seed shape, seed color
Define Trait
Variations in a character
Ex: round, wrinkled, yellow, green
Define genotype
Genetic makeup that determines trait of a character will be expressed
Define phenotype
The visible or determinable expression of the genotype
Define homozygous
An organism has two identical alleles of a gene for a given character
Define heterozygous
An organism has differing alleles for a gene for a given character
Define dominant
An allele that is expressed in the heterozygous condition
Define recessive
An allele that is not expressed in the heterozygous condition
Describe Mendel’s Law of Segregation
Mendel: the particles of inheritance for green and yellow color segregate but remain unchanged during reproduction
Mendel’s Rules of Inheritance
Males and females contribute equally to the genotype of their offspring.
Some alleles are dominant to other alleles. (certain traits “recede” but are still present)
Are homozygous alleles identical genetically?
Yes, both alleles express the same phenotype
No, the alleles will differ slightly in
DNA base pair code
Both are correct, the same phenotype can be expressed even though the underlying DNA sequence can be different (remember third position changes in DNA).
How did Mendel disprove the idea of “blending” in heredity?
There was no “blending” of traits
no intermediate or transitional forms
therefore,
“particles of inheritance” that did not change
“pairs” that did not blend
“recessive” expressed only in absence of dominant
How does a Punnet square work?
If you can’t figure this out you don’t deserve to pass the class >_<
Punnet square example: a cross between Yy and Yy (monohybrid)
What is the phenotype in the next generation?
What is the genotype in the next generation?
Many more yellow than green the expected is 3:1 yellow versus green
1:2:1 ratio of homozygous yellow: heterozygous yellow and homozygous green
Why would the actual counts of pea color only be expected to approximate the 3:1 ratio?
because science is not exact
because of experimental error
according to Mendel’s laws, there would be an exact 3:1 ratio
B is correct because some peas may be lost or miscounted, some will shrivel up and won’t be counted, etc.
How does a punnet square work with dihybrid crosses?
Same as a normal punnet square but you have two variables like X and Y for the genotype
Describe what is meant by incomplete dominance
Some traits appear to blend (in this case red and white snapdragon flowers)
A cross of red and white yields a F1 generation of all pink.
The F2 generation will have a 1:2:1 ratio of red:pink:white
Genotypic and phenotypic ratios are the same for incomplete dominance
Describe what is meant by codominance.
There are A, B, AB and O blood types in humans
A means one kind of surface protein on red blood cells, B another and O means that cells lack both A and B.
AB blood has both
Both A and B are dominant to O
Presence of A and B alleles means that both proteins are expressed
An individual can only have two alleles for these blood types
Understand what is meant by multigenic (or polygenic traits)
Multigenic traits are controlled by a series of genes.
Examples in humans include skin color, height, certain diseases like susceptibility to heart disease and complex behaviors (extroversion, schizophrenia)
The phenotypes approximate a bell shaped curve and variation appears to be smooth or continuous.
Why is color blindness more prevalent in men than women?
Because it is an allele located on the X sex-chromosome. It is a recessive allele so since men only have one X chromosome it is easier to occur. Women have two X chromosomes so both would need to have the recessive allele for color blindness
