Genetic Lecture 2 Flashcards
Charles Darwin
Published the origin of species around the time Mendel started his work. He went on a 5 year journey on a boat and is famous for his observations for how birds of the same species have different beaks when they live on different islands, because of food availability. Thought there was natural selection to survive and for it to be possible you need variation.
When was natural selection become popular?
At the end of the 19 century, biology was dominated by the theory of evolution by natural selection (origin of modern biology).
Natural Selection
Population could change (or evolve) only if variation in traits existed among its members. Variants that enhanced survival and reproduction
would increase in frequency with each generation. Variants that did not would decrease in frequency and
might eventually be eliminated from the population.
Blending Hypothesis
Widely accepted in the 1800s. The parent’s traits were mixed. ie. A short and tall parent, will make average height kids. However, people realized that traits disappeared and came back.
Particulate Hypothesis
Demonstrated by Mendel. Different alleys are handed out but still kept in the same gnome.
Gregor Mendel
He breed peas in his garden. He succeed because he used math. Developed many theories on how genes are pasted on. He didn’t care about crossing over and traits on sex chromosomes.
Dopler
Studied with Mendel, after Mendel failed to be come a teacher. He taught Mendel the experimental method, like asking questions and making hypothesis. He created the Dopler Effect where frequency increase the closer it gets to you.
Why did Mendel use garden peas?
Easy to Grow. Some characters had easily distinguishable traits. True-breeding varieties. Possible to cross-fertilize or self-fertilize different varieties of pea. Needed to use a characteristic that had an obvious answer.
True-Breeding Varieties
A particular trait is consistently inherited from one generation to the next.
How did he perform the cross?
Cut off the sex organ that he didn’t need in the pea then took the pollen of the stamen of one plant and put it on the carpel of the other. This is the parental generation (P).
F1
First filial generation offspring
What was Mendel’s question?
When F1 hybrid plants self- pollinate, which traits appear in the F2 generation?
What’s a heritable factor?
A Gene
How do recessive traits move from one generation to the next?
Not destroyed, deleted, or blended in the F 1 generation but was merely
masked.
Hybridization
Crossing of two true-breeding
varieties
Alleles
Alternative versions of the same gene
What do genes do?
Encode proteins, these protein determines the phenotype.
How do different alleles impact the genetic sequence?
They create a change in genetic sequences.
Who do dominant and recessive alleles work?
The dominant and recessive gene encodes different things. Eg. The dominant genes results in an enzyme that helps synthesize purple pigment, while the recessive gene encodes for a nonfunctional gene.
Does it matter if you have one or two dominant alleles.
No, they produce the same thing in this case.
Punnet Square
Shows the probability of getting a genotype and phenotype from two parents.
Dominant allele
Masks the recessive allele
What were Mendel’s observations?
Alternative versions of genes account for variations in inherited characters.
For each character, an organism inherits two copies (that is, two alleles) of a gene, one from each parent. If the two alleles at a locus differ: dominant allele determines the organism’s appearance recessive allele has no noticeable effect
Mendel’s First Law?
Segregation of Alleles. Two alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes. It’s during gamete formation and is a random process.
Heterozygous
An organism with two different
alleles for a character.
Homozygous
An organism with a pair of
identical alleles.
What’s the magic ratios of hybrid crosses?
3:1 phenotypic ratio
1:2:1 genotypic ratio
Test Cross?
A genetic experiment that crosses an organism with an unknown genotype to an organism with a homozygous recessive genotype to determine the genotype of the organism with the unknown genotype.
Why did Mendel have big sample sizes?
The more you have the closer you will get to the ration you are trying to observe.
Dihybrid Cross
A dihybrid cross is a mating experiment between two organisms that have two genes and are both heterozygous in F1.
Hypothesis of Independent assortment?
That the two alleles in the dihybrid cross do not move together, result is 1/4. Mendel only looked at genes on different chromosomes since they will always be independent.
What’s the phenotypic ratio for dihybrid crosses.
9:3:3:1
Mendel’s Second Law
Independent Assortment of Genes
During gamete formation, a pair of alleles for one gene will segregate independently of a pair of alleles for another gene.
When does the Mendelian ratio land heredity work?
When both laws work.
Deviations from Mendel’s Laws?
Some traits not on nuclear chromosomes. Traits on the same chromosome. Traits carried on sex-chromosomes.
Why do mitochondria and chloroplasts have chromosomes?
The endosymbiotic theory states they were once free living organisms, but then entered a symbiotic relationship with eukaryotic cells. These genes don’t segregate. This DNA is important for their specific functions.
Where does the mitochondrial DNA come from?
The mother
Where is the DNA stored in the sperm?
The head (where the nucleus is).
Midpiece of the sperm does what?
Where they get energy to move (mitochondrion).
What happened to the flagella when the sperm makes contact with the egg?
It falls off
What can be used to traced back your paternal lineage?
The Y chromosome
How does the traits on the same chromosome deviate from Mendel’s second law?
When genes are located near each other on the same chromosome, they tend to be inherited together and they are said to be linked. However it can be known for sure because the randomness of crossing over.
Why is it that alleles closer together on the same chromosome have a higher chance of segregating together than alleys that are far apart?
Because the possibility of a cross over occurring between gene alleles increases the further away they are from each other on a chromosome.
Linkage
Genes on the same chromosome.
Synaptonemal Complex
A meiosis-specific multi-protein complex that forms between homologous chromosomes during prophase of meiosis I.
Autosomes
Chromsomes that aren’t sex chromosomes.
Do the x and y chromosomes have different genes?
Yes
Why do we have two homologous chromosomes?
So there is a backup when something goes wrong with one of them.
Are there counterparts on diseases on the x chromosome?
No
What chromosomes are the genetic diseases located on?
The x chromosome
What’s x inactivation?
After fertilization one copy of the x chromosome is inactivated randomly in each cell. So females are mosaics.
If a gene is x linked where will it appear?
In the y chromosome, but females are carriers of it.
Are sex chromosomes different in each animal?
Yes. Eg. Chickens have 76 autosomes and the ZW is the female and ZZ is male.
Other Deviations from Mendel’s Laws?
Incomplete dominance, Multiple alleles, Co-dominance, Lethal alleles
Incomplete Dominance
A genetic phenomenon where both alleles of a gene are partially expressed in a heterozygote, resulting in a phenotype that is an intermix of the two. Has different intensities of colours.
How is the pigment produced for a heterozygous cross?
It’s dependent on the number of alleles present.
How is the genotype shown as?
The characteristic and trait. CRCW
The phenotypic ratio of heterozygous incomplete cross?
1:2:1
Independent Orientation
The random order the chromosomes aline in meiosis.
Parental Gametes?
It’s when the zygote only has chromosomes from one parent.
Recombinant Gametes
Have chromosomes from both parents.
Does independent orientation and crossing over happen at the same time?
Yes
