inheritance patterns Flashcards
theories of inheritance
blending theory
particulate theory
blending theory
offspring phenotypes are a blend of the parental traits
particulate theory
waits are inherited as particles with an offspring receiving a particle from each parent
developed by Mendel using the scientific method
Mendels laws
law of segregation
law of independent assortment
Mendel’s law of segregation
two copies of a gene separate during gamete formation
each gamete receives only one copy
allele combinations can be predicted using a Punnett square
Mendel’s law of independent assortment
copies of different genes assort independently
chromosomes segregate independently during formation of gametes
Mendels experiements
crosses among different phenotypes of specific traits
pollination and fertilisation controlled by removing the male organs and manually pollinating the flowers
transferred pollen from one plant to another
generations in Mendel’s experiments
parental generation - P
seeds and offspring
- first filial generation - F1
F1 plants self pollinated to produce offspring
- second filial generation - F2
monohybrid crosses
cross parental varieties with contrasting traits for a single character
F1 are monohybrids
allows plants to self pollinate to produce F2 generation
ratio in monohybrid crosses
3:1
that trait that occurred in the F1 and was more abundant in the F2 was called dominant
dihybrid crosses
inheritance patterns involving 2 genes
cross pea plant differing in 2 characteristics
then cross F1 generation
if traits independant, F2 has 9 different genotypes
phenotypes - 9:3:3:1
key to Mendel’s success
true breeding lines
- Mendel self fertilised and selected peas until he got lines that consistently made offspring identical to parents
- inbred until homozygous for trait
- simplified genetic background, reduced messiness
= binary, predictable traits
large sample sizes
- able to see clear patterns
probability
if certain to happen = 1
cannot possibly happen = 0
likelihood of an event happening
multiplication rule
probability of 2 independent events happening together
= multiply probabilities of the individual events
addition rule
probability of an event that can occur in 2 different ways
= sum of the individual probabilities
what are pedigrees used for?
used to estimate disease risk
genetic chimerism
chimera = individual with cells from 2 different sources
violates typical inheritance patterns
can occur early in development
microchimerism = when only a small portion of tissues are chimeric
eg from a blood transfusion
twin chimerism = when twins exchange cells with each other in the womb, leads to a blend of their genetic material
conjugation
prokaryotic sexual process for transferring genes between cells
usually plasmids transferred
one direction from donor to recipient
why is prokaryotic inheritance different?
binary fission does not provide an opportunity for genetic recombination
how does prokaryotic inheritance work?
sex pilus extends from one cell to another and brings them together
genetic material passes through a thin cytoplasm
bridge called the conjugation tube
DNA passes from a donor cell to a recipient
there is no reciprocal transfer
donor and recipient DNA line up and crossing over occurs
- changes genetic makeup of recipient
plasmid genes
small circular chromosomes
multiple categories
- unusual metabolic functions
- antibiotic resistance genes
- genes for making sex pills
in conjugation, usually plasmid are transferred
can replicate independently of main chromosome or integrated
