Medelian Inheritance (notes) 4A Flashcards
Blending theory of inheritance (2)
Hereditary traits blend evenly in offspring through mixing off the parent’s blood.
Offsprings had traits intermediate to parents (traits appearing halfway btwn parents)
What type of flower Mendel used and what did he do to them?
Not true breeding one
Mendel used the garden pea because it can be grown easily. Because the flower had both male and female reproductive system, Mendel had to cut off the anthers (male organoid) to cross pollinate
Mendel wanted to disapprove —— as he did not —–
blending inheritance as he did not see blending traits with his works with mice/bees
In blending inheritance, variation will be
reduced over time (particulary rare traits).
*Dilution
All traits will quickly converge on a blended average, destroying the variation that is necessary for evolution
When Mendel started his test, he always used
true breeding
What did mendel obeserve and what was his conclusions after crosing the parental generation?
He crossed the homozygous peas and generated the first fillia.The phenotype of the first fillia were all the same and that was the dominant phenotype
after generating first fillial what did his results reject?
Rejected blending inheritance as he didnt get a blending colour between yellow or green.
How is the phenotype for a dominant allele expressed?
+use peas as example
Often the dominant allele codes for a functional protein wherease the recessive allele does not. Producing protein gives us the phenotype that we want. For ex: pea colour is determined by enyzyme that breaks down chlorophyll so in yellow pea, the allele for yellow codes for an enzyme that breaks down chlorophyll.
Dominant allele is always the allele associated with the trait we see in
Type of organism*
heterozygote
Monohybrid cross
Using true breeding (offspring with same phenotype) and crossing it with another true breeding with a different phenotype
F2 ratio
3:1
Dominant: recessive
Principle of segregation is tested by
predicting the outcome of crosses
Seeds in F2 showing recessive trait should be
*Not percentage
homozygous recessive (a/a)
What was Mendel’s 3 hypotheses?
- Adults plants carry two copies of factors (genes) that govern theinheritance of a character (e.g. wrinkled versus smooth peas). Based on the combination, you have round peas or wrinkled
- If an individual’s pair of genes consist of different alleles, one allele is dominant over the other and masks it
- The pair of alleles that control a character separate as gamestes (meiosis); half of the gamestes carry one allele and the other half carry the other allele. Each gamete receives just one gene copy, which is selected randomly. Diploid organisms get one allele form each parent.
probability of a gamete inheriting one of the two alleles during meiosis is —– bc of——-
random because of random alignment of chromosomes at the metaphase plate
Probability of a genotype in a cross is determined by
the product of the probabilities of acquiring each gamete from the mother and father
homozygous in relationship to principle of segregation
the two alleles are the same therefore produce only one type of gamete
Heterozygous in relationship to principle of segregation
The two alleles are different therefore, produces two types of gametes
How do you know if you have a heterozygote?
Perform a test cross with homozygous recessive
If you have a heterozygous and you test cross it, what is produced?
You will see a 1:1 ratio of dominant and recessive phenotype
If you have a homozygous dominant and you test cross it, what is produced?
You will see all dominant phenotype
What did Sutton notice? (3)
- Chromosomes occur in pairs (homologous chromosomes) in diploid organisms
- Chromosomes of each pair seperated in gametes
- Seperation of each pair of chromsomes is independent of other pairs
Incomplete Dominance (2)
+how this happens
- One allele is not completely dominant to the other allele
(ex: red+white=pink) - intermediate phenotype
- Happens when heterozygote plants produce some functional enzyme but not full amount
Co-dominance (3)
+what we we dont get?
- Both homozygous phenotypes expressed as dominant alleles fight for expression
- Alleles have equal effect
- We dont get an intermediate phenotype but instead 2 different phenotype expressed in the individual
Why is incomplete dominance different than blending inheritance?
Because when we generate our F2, we see the red flowers come back and so we havent lost those traits. They are still behaving as individual discrete.
polymorphic
more than 2 alleles
Complex traits are—– (3)
+what this mean+ex
- polygenic
- There are multiple genes that are responsible for contributing to that particular phenotype
- Ex: height and other similar features are controlled not by one gene but by multiple genes that make small contributions to the overall outcome (more dominant= longer)
What influences create continous distribution?
Genectic and environmental influences
For continous distributions, as we increase the ——we get ——–. Within each bar….
- number of genes
- Even finer variations
- There is variation as the environments are different
MHC (4)
Tell me about this+ codominant expression
- Group of genes that code for proteins found on the surface of cells that help immune recognize foreign substance.
- Group of genes with each having an unsually large number of alleles
- Very rare for two individuals to have the same set of MHC molecules
- Two alleles of each MHC gene are expressed codominantly in each individual- with the protein products of both the alleles at a locus being expressed in the cell
