Transmission Genetics: Mendel and beyond Flashcards
Study of how genes/traits are
passed down through generations
Transmission genetics
Traits absorbed from all over body –> sperm/eggs
Pangenesis
Kids inherit their parents acquired characteristics
Lemarckism
Little people inside if gametes (homunculus)
Preformationism
Traits of parents blend –> passed on
Blending inheritance
- Experiments with peas disproved all above
- Found discrete units of inheritance passed down
- Provide instructions for brand new organism
- No blending
- Unique combination of genes provides unique traits in offspring
Gregor Mendel
Short segments of chromosomes/DNA that
provide instructions to make a polypeptide
Genes
Different forms (variations) of the same gene that result from minor
differences in the DNA sequence
Alleles
Organism has 2 copies of the same allele for a given gene
Homozygous
Organism has 2 different alleles for a given gene
Heterozygous
both alleles are expressed (assuming no imprinting)
In a heterozygous individual
alleles that mask the effects of other alleles
DOMINANT
Those alleles that get masked
RECESSIVE
Genetic background of a trait
Genotype
Actual observable trait that we see
Phenotype
Parental generation
P
First filial generation
F1
Second generation
F2
- Each trait is controlled by one gene, each gene controls one trait
- Alleles have a clear dominant-recessive relationship
- Individuals have expected phenotype
Simple Mendelian inheritance
Two copies of the gene are segregated and packaged into separate gametes
Theory of segregation
- Done to determine if inheritance of one gene affects inheritance of another
Mendel’s original experiments
Found that when genes are on different (nonhomologous) chromosomes, they move independently during meiosis and don’t affect one another
Mendel’s original experiments
Found that when genes are on different (nonhomologous) chromosomes, they
move independently during meiosis and don’t affect one another
independent assortment
Genes located closely on the same chromosome are
inherited as one unit (NOT INDEPENDENT ASST)
when units are inherited as one unit can one be dominate and the other recessive
no
both must be dominant
or
both must be recessive
Only way to split up two genes on the same chromosome is for what to occur
crossing over
keep parental combos (non-recombinant)
No crossing over
get new combos
Crossing-over
Crossing-over – get new combos
(recombinant gametes
Frequency of crossing over between
two genes depends
on how close the two genes are
If two genes are very close on the chromosome what will
Crossing over will most likely NOT occur between them
Will almost always stay closely linked together during
gamete formation
If the genes are far apart on the chromosome what will most likely happen
More likely that crossing over will occur between them
Will NOT always stay linked together during gamete formation
genes are far apart on the chromosome
Farther apart =
more crossing over = more recombinant gametes
Scientists can increase crossing over (recombination) frequency to determine what
where genes are located on a chromosome (w/ respect to one another)
how to find Recombination frequency
(# recombinant progeny/#total progeny) x 100
Neither allele is dominant
Incomplete dominance
look like an intermediate between homozygotes
Heterozygotes
meaning neither allele (red or white) is completely dominant over the other.
Incomplete dominance
Both alleles are dominant (neither backs down)
Codominance
what does Codominance look like
combination of homozygotes
Their presence results in death of the organism
Lethal alleles
individual is never born
embryonic lethal
types of lethal alleles
1) Recessive lethal alleles
2) Dominant lethal alleles
Two copies of allele needed for lethality
Recessive lethal alleles
Only one copy needed for lethality
Dominant lethal alleles
Many genes have
more than two alleles (in the population)
