- The father of genetics
- -mid 19th C.
- -pea plants
Austrian monk & naturalist
Wasn't truely recognized for his work until decades after his death
Mendel's Main inferences
- Basic units of genetics are material elements
- These elements come in pairs
- these elements (today called genes) retain their characteristics through many generations
- these element (gene) pairs separate during gamete formation
Mendel's Experimental subjects
- PEA PLANTS:
- capable of self-pollination
therefore can be cross pollinated
peas: seeds in the ovary
Example: color, size, etc.
Technically codes for proteins
(phenotype is controlled by its genotype)
one of the alternative forms of a single gene
- P generation: parent (started with "true breeding" parents)
- F1 = first fillal generation
F1 generation self-pollination..
- 3:1 ration, yellow: green seeds
- an allele that is expressed in the heterozygous condition
- (uppercase lettter)
- heterozygous peas (Yy) the yellow was the portion that showed.
- An allele that is not expressed in the heterozygous condition
- (lower case letter)
- heterozygous peas (Yy) the green is the recessive because you cannot see it
Three Genotypes yield Two phenotypes
Chromosomes and Phenotypes
Give expected phenotypic and genotypic ratios of offspring
Law of Segregation
Differing characteristics in organisms result from two genetic elements (alleles) that separate in gamete formation
- -Each gamete only gets one of the two alleles
- -homologous chromosomes separate during Metaphase I of meiosis
- -this is how Yy could never give rise to yy
Law of independent assortment
Genes for different characters are passed on independently of each other
- Heterozygote phenotype is intermediate beetween either of the homozygous phenotypes
- (Mendel's rules do not apply to all intstances of inheritance)
EXAMPLE: the cross of a RR red snapdragon with an rr white snapdragon results in a Rr pink snap dragon...why isn't this blending?
: beause the characteristics Rr is STILL there and can be passed down to later generations. Also there isn't enough pigment of the dominant red color to color the entire flower.
- 2 alleles are equally dominant
- -Each has different phenotypic effects
- -both effects expressed in organisms heterozygous for that gene
- EXAMPLE: blood type in humans
- -3 different alleles: A, B, and O
- -A and B are codominant (think blood type AB)
- -O is recessive
(blood type is based on the surface glycolipids..)
When 3 or more alleles of the same gene exist in a population
NOTE: no single person can have more than two alleles for a gene...but a population
can have multiple variants
- Inheritance of a genetic character that is determined by the interaction of multiple genes
- -each gene has a small, additive effect on trait
- -more common than traits governed by single genes
- -display "continuous variation"
EXAMPLES: skin color, hair color, eye color, height. etc.
Effects of genes can vary greatly depending on environment.
any external influnce that is favorable or unfavorable for the development of a trait in an organism.
- EXAMPLE: Hydrangeas
- depending on the pH of the soil (acidic or basic) will determine the color of the hydrangeas
Single gene influences multiple phenotypic traits
- EXAMPLE: Fragile X Syndrome
- -break on X chromosome which can cause:
- Mental retardation, abnormally long face, large ears, large testicles.