HEREDITY NOTES
Father of Heredity- Gregor Mendel- Austrian Monk who was a horticulturist.
He raised peas, they had distinct characteristics.(also have low chromosome #
which he didn’t know) Grew and recorded over 30,000 plants.
No one cared about his work for 100 years.
He studied the traits of these peas that had distinct characteristics, being either one way or
the other. Yellow or green peas, tall or short plants, wrinkled or smooth peas.
He hypothesized that each organism is half of each parent. That within an egg and
sperm(gamete), are factors that contribute to a trait. He called these factor alleles. You
need two alleles, one from each parent to form a trait.
He represented these alleles with letters.
He specified if the trait was dominant or recessive.
Dominant- trait most often seen, also the one found within the hybrid
Recessive- the least common trait within a population.
He used the capital letter of the dominant trait for dominant and the lower case letter of
the dominant trait to represent recessive.
Therefore if yellow is dominant and green is recessive Green would be a y and Yellow
would be a Y.
You need two alleles represented by letters to be a trait. So you could have YY, or Yy or
yy.
If the alleles are the same they are known as pure or Homozygous
IF the alleles are different they are known as hybrid or heterozygous
Pure or Homozygous dominant would be YY and be yellow
Pure or homozygous recessive would be yy and be green
Hybrid or Heterozygous would be Yy and be yellow.
Phenotype- the trait that you see or is expressed Ex. Yellow
Genotype- the combiantion of alleles. Ex—YY
Principle of Segregation- Alleles separate and go into separate gametes. They are not
tied into each other.
Principle of Independent Assortment: The alleles for one trait DO NOT affect the
inheritance of alleles for another trait—all alleles segregate independently
Gene: A segment of DNA that codes for a particular trait
Probability- The chances of an event occuring.
Using Punnet squares and mostly using hybrid crosses
Monohybrid cross is one trait Yy x Yy
Dihybrid cross is two traits YyTt x YyTt
You are responsible for phenotypic and genotypic ratios and punnet squaresfor one trait
crosses
You are also responsible for phenotypic ratios and punnet squares for dihybrid crosses.
P1 generation is the parents
F1 is first set of offspring
F2 is second set of offspring
Give the pheontypic ratio and punnet square for a cross with a pure dominant parent for
two traits and homozygous recessive for two traits. The traits are Yellow dominant green
recessive for trait one and tall dominant and short recessive for trait two.
P1= YYTT x yytt
Possible alleles YT for one and yt for the other
F1 are all YyTt
Then cross YyTt x YyTt
Allele combos = YT, Yt, yT, yt.
Ratio = 9:3:3:1
Trick to figure out ratios of hybrid crosses- 3:1
9:3:3:1
27:9:9:9:3:3:3:1
multiply each number by three and then drop down the previous numbers
3x3=9 and 1x3=3 and add a 3 and 1 so 9:3:3:1
How many sets of numbers in the ratio= # of possible alleles
How many total squares in punnet + total # in ratio= # of alleles from each parent
multiplied.
Haploid= half the number of chromosomes (found in sex cells) 23 in human
Diploid # of chromosomes found in somatic (normal cell) 46 in humans
Exceptions to Mendel’s rules:
 Multiple alleles- more than two choices for an allele.
o Examples: Blood type—allele types = A, B or O you can only have two.
Hair, skin eye color. Hard to study. Melanin
 Incomplete dominance- Neither allele is dominant over the other
o Example: red snapdragons bred with white snapdragons will produce pink
offspring
 Codominance: Both alleles of a trait are expressed
o Example: black coated horse bred with a white coated horse will produce
offspring that have a roan coat (both black and white hairs)
 Environmental Influences- Temperature and other environmental factors will
affect the appearance of traits
o Examples: snowshoe hare in summer= brown fur, snowshoe hare in
winter= white fur; arctic fox in summer= brownish red fur, arctic fox in
winter= white fur
HUMAN HERDITY
23 pair of chromosomes=46 22 are autosomes 1 pr of sex chromosomes
xx for female so 23 pair of homologous
xy for male so 22 pair homologous and 1 pair non.
Drosophila and Chickens the female decides the sex of the offspring.
Sex linkage- Traits having to do with the sex chromosomes directly.
Formation of genitals
Color blindness
Linkage groups- traits on same chromosome, closer the traits the closer the linkage
group.
Meiosis
 Prophase I: chromosomes condense, nuclear membrane breaks apart, matching
chromosomes pair up forming tetrads—crossing over occurs
 Metaphase I: tetrads of chromosomes line up at the cell’s equator
 Anaphase I: homologous chromosomes separate and move towards opposite
poles of the cell
 Telophase I: cell begins to divide
 Prophase II: chromosomes condense and nuclear membrane starts to break
apart
 Metaphase II: chromosomes line up at the equator of the cells
 Anaphase II: chromatids separate and migrate to opposite poles of the cells
 Telophase II: cells starts to divide. Product is 4 haploid cells
Crossing over- synapse
Exchange of info between chromatids, normally happens can be abnormal (weed) or
mutagens
Karyotype: A lab procedure that looks at the number of chromosomes in a cell to detect
any chromosomal abnormality
Nondysjunction-improper separation of chromosomes, supposed to have one from mom
and one from dad for each of the 23 pairs
Trisomy- 3 of 1
Monosomy-missing 1
Both usually fatal but not always
Trisomy 21- Downs syndrome
Turners syndrome (monosomy x)- female with no secondary sex characteristics (1 in
2,000)
Kleinfelters syndrome- (trisomy x)- male with female characteristics ( 1 in 800-1000)
Polyploidy- the whole set- fatal in humans but alfalfa has it.
Chromosomal mutations: Nondisjunction (trisomy or monosomy), polyploidy,
chromosomal deletion, chromosomal translocation, chromosomal inversion
Gene muations: point mutations, base deletion, and base insertion
EX. Hemophilia, cystic fibrosis, huntingtons disease, m.d., m.s., sickle cell anemia
NOT CAUSED BY INBREEDING, it can cause bad recessives to be displayed but could
cause good ones as well (purebreds)
Photosynthesis
2 phases
Light and Dark
Light – in sun and H20
Out O2
Made – ATP & NADPH
ATP – used for energy
Energy to be released by a chemical reaction (when you move = chemical
reaction)
ATP turns into ADP plus P and energy
ATP in a plant
Causes Carbon Cycle
Starts with 5 carbon combines with CO2 and makes a 6th carbon turns
into 2 three carbons – turns to carbohydrates
Stomata – pores in plant (critical for photosynthesis)
From 2 cells – guard cells
Come in to plant CO2
Leave O2 and H2O
Has H2O stomata = open
Stomata on bottom/underside of leaf. Has hair to prevent evaporation.