Lecture #23 and #24 - Mendelian genetics Flashcards
Pea flower cross pollination
- Give me the 5 steps
- What did it show?
Method:
- Removed stamens from purple flower
- Transferred pollen from stamens of white flower to carpel of purple flower
- Pollinated carpel matured into pod
- Planted seeds from pod
- Examined the offspring - all were purple
* Can fertilize bc one flower has both male and female genitals - he snippedoff stamen and took pollen from another flower and cross pollination occured. He planted the peas and flower (F1 generation) all purple so somehow dominant*
This showed that inheritance isn’t al about blending - white and purple doesn’t make light purple.
Appreciate this because not much to say
What is atavism?
What’s going on here? How is info passed on? What’re alleles? How many alleles in one gamete?
Atavism is when something that seemed to be lost suddenly comes back - eg thought the wrinkled seeds had got lost in F1 generation but they came back in F2.
What’s going on?
- No signs of blending inheirtance
- Info passed on from parents to offspring if information is packaged as discrete particels. Mendel called these ‘factors’ - we call them GENES
- Also it appears that individuals have 2 copies of each gene, one inherited from the mother and the other from the father. Genes controlling a trait can differ - these different forms of a gene are called ALLELES - what explains the variation in us; we all hv genes but different vaersions (alleles)
- NOTE: only one of the two copies is present in each gamete
The genes for a partiuclar trait reside where?
The genes for a particular trait reside at a specific locus (position) on a certain chromosome…
This individual with two homologous chromosomes who is heterozygous bc two different alleles.
Locus - poisition where gene is on chromosome
Appreciate this
So every egg has R and every sperm has r and every egg/sperm of offpsring can be R or r
The punnet squre - appreicate
The only way to show whether it’s RR/Rr is……also appreicate
Do a test cross with rr
What’s the ratio in F2 generation in a monohybrid cross between PP and pp (original parents)?
3:2
Appreciate
The test cross
Appreciate
Appreciate
Where are both laws of Mendel explained?
What is Mendel’s first law?
Law of Segregation:
Genes segregate at meiosis so that each gamete (haploid) contains only one of the two possessed by the parent (diploid)
What is Mendel’s 2nd Law?
Law of Independent Assortment
Alleles of different genes assort independently during gamete formation
When investigating alleles for two different characters, each allele assorts indenpendently during gamete formation
Appreciate
What’s the ratio for SsYy x SsYy?
9:3:3:1
Appreciate
Only works if on different chromosomes - if on same then different probabilities
Appreciate
Lethal alleles
Some alleles are beneficial and some aren’t - having one dose may be okay (or even beneficial?) but two alleles will result in death
Always 2:1 ratio because one always dead
A lethal allele occurs when a mutation results in an allele that produces a non fucntional version of an essential protein. If an indivisual inherits a lethal combo of mutated allelels, it’ll die shortly after birth or before.
What does it mean to be polymorphic?
Existence of a gene in several allelic forms
Some genes have lotsa variation “lots of forms” - one gene has many phenotypes
Our immune system - 1000 different alleles in our population but it cant ____ bc we have lotsa variation too? Idek
What does this experiment appear to prove?
What does this experiment soundly disprove?
What’s this called?
Blending inheritance and blending inheritance
Incomplete dominance = inheritance where neither allele “dominates” the other. If heterozygous genotype then both will contribute to produce a phenotype that is an intermediate or blend of the genetic information
Self fertilise the F1 or breed with eachother - have 2:1:1 ratio
White flower = one allele isn’t working and other not good enough on its own
What mendel discovered were mostly the non-functioning ones.
Co-dominance
When both phenotypes exist side by side within the organism (both alleles are equally dominant). Both allels are equally and independently expressed.
One allele (homozygous) and in the middle both are side by side
Appreicate
This is polymorphc - one pattern superimposed on another so co-dominance
Not blend - just side by side
Appreicate
Co-dominance
A and B both new - almost superimposed
Epistasis
One gene affects the action of another (they have nothing to do with eachother - each independent)
Gene A needs to turn something into pigment
Gene B deposits the colour so the end
e.g. gene A and B determine whether pigmeent is produced
The term epistasis describes a certain relationship between genes, where an allele of one gene (e.g., ‘spread’) hides or masks the visible output, or phenotype, of another gene (e.g., pattern). Epistasis is entirely different from dominant and recessive, which are terms that apply to different alleles of the same gene (e.g., ‘bar’ is dominant to ‘barless’ and recessive to ‘check’).
Appreicate this
White mice = all recessive so recessive homozygous
Mice - two genes interact. One gene greates and one deposits colour
Ratio gets modified because changed something
9:3:4
Polygenic traits
(in graph - 3 doses of pigment)
Phenotype controlled by many genes that have an additive effect
Characters appear continuous or quantitative
(i. e. non-discrete steps in range of phenotypes)
e. g. skin colour, weight, milk yeild, wool length, IQ, height (controlled by groups of genes)
Additive effect - e.g. getting __ out of 6
No colour = damaged allele or some shit
The environment
Environment also affects phenotype (e.g. nutrition and height/weight; life expectancy and disease)
e.g. Hydrangea is pink in alkaline soils but blue in acidic soils
Can have two genetically identical people but have different phenotypes because environment
Environment smooths differences among phenotypes e.g. size of wheat ears (1 genes, 2 alleles; additive)
On y-axis, the frequency and on x-axis, the range of phenotypes
Pleiotropy
One gene ——> many effects
e. g.
1. Sickle cell gene produces many symptoms
2. Coloration pattern and cross eyes of siamese cats produced by same gene
3. Eye colour, wing length and body hair traits in Drosophila - affected one gene
