Mendelian Genetics Flashcards
Blending theory of inheritance
Hereditary traits blend evenly in offspring. An old belief
Gregor Mendel
A monk who studied genetics with pea plants in the mid 1800’s.
Mendel’s education
Farm raised, studied math, chemistry, and zoology
Character
A heritable characteristic
Trait
Variations within a character
Mendel’s conclusions
Characters are passed off in discrete hereditary factors.
Genes do not blend, they stay separate
Mendel was the first to
Study genetics quantitativly
Pea plants sperm
Is in the pollen of the anthers
Pea plant egg
Is in the carpel of the flower. Often pollenated by the sperm of the same plant
How did Mendel prevent self pollenation
Cutting off the anthers so he could cross pollenate himself
To start the experiment Mendel
Used self fertilized plants without change from 1 generation to the next. Pure bread P generation
Flower colour study
1/7 characteristics Mendel studied.
Pollen from the purple plant was placed on the white plant’s stigma and vise versa
F1 generation
1st generations offspring
P generation
Plants used in the initial cross
F2 generation
The gametes produced from the F1 generation
Flower colour study results
F1 generation-All the flowers were purple
F2 generation-3:1 ratio of purple to white flowers
Mendel’s first hypothesis
The adult plants carry a pair of factors that governs the inheritance of each factor
What is correct about hypothesis 1
The 1 character comes from the mother, and one form the father
Hypothesis 1 in modern terms
1 gene per parent is inherited on a chromosome.
2 alleles per gene that govern a trait
Dominance
A non dominant trait is still present, just weaker
Hypothesis 2
If an individuals pair of genes consists of different alleles, one is dominant over the other recessive allele
Current view of hypothesis 2
Dominant alleles do not directly inhibit recessive alleles
Hypothesis 3
Principle of segregation
Principle of segregation
Alleles that control a characteristic segregate and carry 1 allele per gamete
Homozygote (homozygous)
When a zygote has 2 of the same alleles for a gene. Both gametes they form get the same allele
Heterozygote (heterozygous)
Has 2 different alleles for 1 gene, the dominant gene is the phenotype
Gametes receive dominant of recessive gene
Monohybrid
An organism that is produced from a cross involving a single character
Monohybrid cross
A cross between 2 heterozygous individuals
Genotype
The genetic constitution of an organism
Phenotype
The outward appearance of an organism
Monohybrid crosses support
All three of Mendel’s hypothesis
Probability
The possibility an outcome will occur if it is a matter of chance
Predicting probability
Divide the probability of a given outcome by all possible outcomes
The product rule
Can be used to check if events are independent
Independent events
When 1 event has no effect on the other
P(A)P(B)=P(AnB)
The sum rule
Probability of A or B or… Z occurring. P(A)+P(B)…P(Z)
Mendel and probability
The chance of what allele will fertilize an egg is 50/50
For a zygote probability Pp Pp
1/2 (the probability of a gene from dad) X 1/2 (the probability of a gene from mom)=1/4
Purple flower and probability
Use addition rule with all the possible genotypes. PP+Pp
Punnett squares and probability
Write the probability of miosis producing the gamete on the outside and multiply to the middle for offspring probability
How did Mendel test his hypothesises
He predicted the outcomes before they happened with crosses he hadn’t tried yet
Test cross
A cross between a dominant phenotype and a homozygous recessive genotype
Test crosses usage
Determine if a dominant phenotype is homozygous or heterozygous
Heterozygous results in a test cross
2:2 (dominant: recessive)
Homozygous dominant results in a test cross
4:0 (dominant: recessive)
Mendel’s 2 question
How do different alleles interact with each other
The experiment for Mendel’s second question
He bred plants and observed seed shape and color at the same time. He crossed a RR YY with a rr yy
Results of the 2 question experiment
The traits interacted independently resulting in
F1-16:0
F2-9:3:3:1
Dihybrid
A zygote produced from a cross with 2 characters
Dihybrid cross
A cross between two individuals who are heterozygous for 2 pairs of alleles
Mendel’s 4 hypothesis
Mendel’s principle of independent assortment
Mendel’s principle of independent assortment
The alleles of the genes that govern the two characters segregate independently during gamete formation
Why does independent assortment occur
Because of random assortment of alleles in miosis I
Rr Yy X rryy expected genotypic ratio
1:1:1:1
When don’t traits segregate independently
When they are close to each other on a chromosome
Factors
What Mendel called genes
3 people who later studied genetics
Vries, Correns, Tschermak
Sutton
Connected genes and inheritance with 4 points
Sutton point 1
Alleles and chromosomes occur in pairs in sexually producing organisms
Sutton point 2
Alleles and chromosomes are seperated during gamete formation
Sutton point 3
Separation of 1 chromosome pair is separate from each other
Sutton point 4
1 chromosome comes from mom and the other from dad in exact parallel with the 2 alleles of a gene
Chromosome theory of inheritance
Genes and alleles are carried on chromosomes
Locus
The site on a chromosome where a gene is located.
The sequence that codes for a protein or RNA products responsible for a phenotype
Alleles at a microscopic level
Small differences that code for different proteins
Mendel’s genetics are true for
All studied organisms
Incomplete dominance
Recessive alleles are somewhat detected in heterozygous individuals
Incomplete dominance flower color example
Red parent and a white parent make pink offspring
Incomplete dominance notation
C^RC^W
CrCw
A pink flower because neither gene is fully dominant
CrCr and CwCw
Red (all the pigment) and white(no pigment) respectively
Sickle cell disease
Defective polypeptide in hemoglobin. DsDs
Sickle cell trait
Defective polypeptide in some of the hemoglobin DSDs
Familial hypercholesterolemia
Incomplete dominance for LDL proteins. Leads to atherosclerosis
Atheriosclerosis
Hardening of the arteries due to a build up of plaque
Familial hypercholesterolemia genotypes
DlDl-Non LDL receptors
DLDl-Have half the LDL receptors it should
Incomplete dominance presentation
Can appear dominant. Biochemical studies are needed to be done to determine if it is
Tay-Sachs disease
DTDt-Does not have symptoms
DtDt-No functional enzyme to breakdown gangliosides
Gangliosides
Membrane proteins
Codominance
When 2 alleles have equal effects and are separably visible in an individual
Inheritance works the same as for incomplete dominance
Blood types
ABO codes for glycoproteins on blood cells.
LMLN
Codominance where both M and N glycoproteins are present.
MN blood type
Not medically relevant. Crucial for human evolution and prehistoric migration and paternity
Multiple alleles
When there are more that 2 different alleles for 1 gene in a population. One individual can only have 2 alleles
Human ABO blood group
Exhibits dominance and codominance through multiple alleles
Landsteiner
The first person to mix blood and found it sometimes clumped
Clumping blood occurred because of
Antibodies in the blood
Antigen
The glucose part of a glycoprotein
Type A blood
Has the antigen A on their RBC
Antibodies against the B antigen
Type B blood
Has the antigen B on their RBC
Antibodies against the A antigen
Type O blood
Neither antigen A or B, but antibodies for both
Type AB blood
Have the antigens for A and B, but no antibodies
Genotypic symbols for blood types
A-IAIA, IAi
B-IBIB, IBi
AB-IAIB
O-ii
Epistasis
Genes interact from 1 locus, inhibiting or masking the effects of alleles at different locus’, causes unexpected phenotypes
Lab colours
Determined by the amount of melatonin pigment produced.
Lab colours normal genotypes
BB-Black
Bb-Brown (chocolate)
Lab colours epistasis
There is a different gene that will not allow melanin to enter the hair cells which produces a golden lab no matter what
Epistasis in humans
It is common and determines susceptibility to disease among other things
Polygenic ingeritance
Results in continuous distribution because many genes contribute to one character
Quantitative traits
Traits controlled by polygenic inheritance. Shows up in a bell shaped curve
Genetic phenotypes
Often influenced by the environment.
Genetic phenotypes example
Nutrition on height and weight
Pleiotrophy
A single gene affects more that 1 character of an organism.
Example of pleiotrophy
Sickle cell anemia- Cell shaped causes an array of symptoms
