Ch.2 Mendelian Genetics Flashcards
What is Lamarckism?
a theory of evolution based on the principle that psychical changes in organisms during their lifetime (such as greater development of an organ or a part through increases use) could be transmitted to their offspring
T/F All traits are passed on to the next generation.
FALSE. Only genetic traits (genetically determined traits) are passed on.
T/F Traits which are acquired during lifetime are passed on.
FALSE. Physical changes like the giraffe are not passed on.
Blending hypothesis (1800s)
Genetic material from 2 parents blends together like blending paint colors.
What could the blending hypothesis not explain?
Cannot explain how traits can skip generations
Gregor Mendel (Father of genetics)
Studied inherited in pea plants
1st to use an experimental approach and the scientific method to study patterns of inheritance
Why did Mendel use garden peas? (5 things)
Easy to grow Many readily distinguishable varieties Short generation time Large number of offspring Mating could be controlled; plants could be allowed to self fertilize or could be cross fertilized
What were the 7 visible traits Mendel experimented with?
Shape of seed (round or wrinkled) Color of seed (yellow or green) Color of petals (purple or white) Shape of pods (inflated or pinched) Color of pods (green or yellow) Flowers (axial or terminal) Stem length (long or short)
Phenotype
physical appearance
True breeding
usually pea plants have a system enforcing self fertilization
Female and male gametes from the same flower unite and produce seeds: inbreeding
How much variation results from true breeding?
Results in little, if any, genetic variation from one generation to the next
Cross fertilization (cross-pollination)
preventing inbreeding, artificially crossing 2 individuals Transfer antlers (male) from 1 plant onto other plant that has had its anthers removed
Reason’s for Mendel’s success
Chose a good model system (pea plants)
Restricted his experiments to one or very few pairs of contrasting traits
He kept note books with accurate quantitative records
Analyzed the collected data
Derived his postulates based on the interpretation of his data
Monohybrid Cross
crossing pea plants which different in 1 character (plant height) with 2 distinct visible traits (tall and dwarf)
Observations of monohybrid cross
Parent generation- homo dominant and homo recessive
F1 - dwarf trait disappears, all F1 are tall
F1 generation self fertilized and the two tall plants could have a dwarf offspring in the F2 gen
What was the ration that traits appeared in in the monohybrid cross?
3:1
Mendel’s Postulates
1. Unit factors exist in pairs
Genetic characters are controlled by unit factors existing in pairs in individual organisms
Each diploid individual receives one factor from each parent
Bc the factors occur in pairs, 3 combos are possible: 2 factors for dwarf, 2 for tall, or one of each
Every individual possesses 1 of these 3 combos, which determines its stem height
Mendel’s Postulates
2. Dominance/ Recessiveness
When 2 unlike unit factors responsible for a single character are present in a single individual, one unit factor is dominant to the other, which is said to be recessive Latent traits (dwarf): recessive allele Trait which get expressed (tall): dominant allele The trait expressed is controlled by the dominant factor. The trait not expressed is controlled by the recessive factor.
Mendel’s Postulates
3. Segregation
During the formation of gametes, the paired unit factors separate randomly so that each gamete receives 1 or the other with equal likelihood.
If an individual has a pair of like factors (both tall) all gametes will have the same kind of unit factor.
If an individual has a pair of unlike unit factors (tall and dwarf), each gamete has a 50% chance of receiving either one.
Unit factors
Chromosomes (the units of inheritance)
Character
gene (a heritable feature, such as stem length) the instruction for a trait, located on a chromosome, at a specific site (gene locus)
Trait
a variant of a character (tall and dwarf) an allele, a version of a gene
Phenotype
physical expression of a trait (tall, blue eyes)
Genotype
genetic makeup of an individual; alleles written in pairs (DD, Dd, or dd)
Homozygous
both alleles are the same (DD, dd)
Homozygous dominant
DD
Homozygous recessive
dd
Heterozygous
the two alleles are different (Dd)
Dihybrid Cross
a cross involving 2 pairs of contrasting pairs (seed shape and seed color)
What is the phenotypic ratio of the F2 generation for a dihybrid cross?
9:3:3:1
Mendel's Postulates #4 Independent Assortment
During gamete formation, segregating pairs of unit factors assort independently of each other.
Each gamete receives one member of every pair of unit factors.
This means the 2 different characters are inherited independently.
Walter Flemming 1879
discovers chromosomes in the cell nuclei of salamander cells
Sutton and Boveri 1902
Chromosomal Theory of inheritance: genetic material in living organisms is contained in chromosomes
Movements and behavior of chromosomes during meiosis explains what??
Mendel’s principles of segregation and independent assortment
Diploid number (2n)
The specific number of chromosomes in each somatic cell nucleus of a diploid species.
During formation of gametes via meiosis the chromosome number is precisely halved to haploid (n).
When 2 gametes combine during fertilization, the diploid number is reestablished
Rule of Segregation and chromosomes
Homologous chromosomes segregate during anaphase 1 (pairs seperate)