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Mendel and Genetics
Genetic Terminology
Dominant
Recessive
Genotype
Phenotype
Homozygous
Heterozygous
Mendel’s Work
• Austrian Monk (1822-1884)
• Worked with pea plants
• Self Pollinated and Cross Pollinated
Sexual Reproduction
Terms
• Gamete
– A reproductive cell
– Sperm or Egg
• Fertilization – joining of gametes
• Zygote- cell formed from fertilization
Discovering Dominance
• P1 Generation
X
All constricted
Pods
All round smooth
inflated pods
F1 Generation
All smooth inflated pods
offspring
• F1 Cross
• Self pollination
• Of hybrids
X
F2 Generation
3 Inflated and smooth to 1 constricted pod
(3:1) or (3/4, ¼)
Mendel’s
Conclusion!!
Purebreeding stock have
the same instructions.
• Parental group for inflated had two
instructions to be inflated ( R)
• RR – Homozygous
• Parental group for constricted pods had
two instructions for constricted pods (r )
• rr - homozygous
Only one instruction from
the parent is passed to
offspring.
• RR X rr
• All offspring receive R from one parent and r
from the other parent and are called hybrids.
• Rr (heterozygous) were all inflated and smooth
not a combination of the two.
The trait that shows up when there are two
different instructions.
Constricted is
Traits that do not show (are not expressed)
up when there is a combination
(heterozygous) Rr.
Physical Characteristics
and Genes
Phenotype – The physical appearance or
characteristic. (i.e. brown eyes,
constricted pods, red flowers, ability to
make lactose, normal.)
Genotype – Gene combination. Two genes
(alleles) for constricted pods,
heterozygous, homozygous recessive,
RR, Rr, rr.
• When both alleles are the same for the same
gene. Example RR, rr, TT, WW, EE, ee
• When the two alleles for a trait are not the same
as each other. Example Ee, Ww, Rr, Tt
• Mendel found that he could predict
genotypes and phenotypes of offspring if
he knew the genetic history of the parents.
• We can do this using a Punnett Square.
Law of Segregation
• Each parent has two alleles for the same
trait those two alleles separate
(segregate) into different gametes.
Rules crosses
• 1. Find parent genotypes (may be given
in problem)
• 2. Find gamete possibilities.
• 3. Put one set of gametes on the top of
the square, and the other on the side of
the square.
• 4. Fill in the square: one gamete from
each parent must go into the box.
• 5. Calculate the probabilities for the
genotypes or phenotypes or both.