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Genetics
Think!
Recap from what we already know:
Mitosis
Chromosomes
Diploid numbers
Haploid numbers
Meiosis
Gametes
Genes
Chromosomes contain DNA.
The DNA codes instructions for
proteins. These proteins direct
our cells to do different things.
There is an instruction for every
trait.
We call them Genes.
Gregor Mendel
Czech monk, first to study
how traits are passed on.
First to claim that there was something being physically passed on from parents to offspring.
He called them factors. We
call them genes.
Mendel’s First Experiments
Mendel worked with pea plants.
He crossed purebred (“true breeding”) plants of
opposite traits and noticed that certain traits
blocked others.
Purple flowers > white flowers
Yellow peas > green peas
All of the offspring showed one dominant trait.
Pea Traits
Mendel’s method
Hand Pollination controlled which
plants were to breed.
Parents = P1
Offspring = F1
First experimental results
Parents = P1 (purebred - their parents
also had the same trait they showed)
Offspring = F1 (hybrids - the result of
parents with different traits)
All of the F1 plants show one trait.
Mendel called this trait Dominant.
The other trait was hidden, or Recessive.
P1
PP pp
Pp Pp Pp Pp
First experimental results
Mendel used symbols for each trait.
Capital letter = dominant
Lower case = recessive
Two symbols = from two parents
Purebred = two identical symbols
Hybrid = two different symbols
Second experimental results
F1 plants were left to self-fertilize.
The recessive trait reappeared in the F2 generation.
75% dominant, 25% recessive
Or, a 3:1 Ratio of traits
Second experimental results
Genotypes & Phenotypes
Genotypes = gene combinations written in symbols.
2 identical traits = Homozygous
2 different traits = Heterozygous
Phenotypes = visible traits described by our senses.
Genotype & Phenotype Examples
Yellow Pea, YY or Yy
Green Pea, yy
GenotypesP1 Purple parent: PP Homozygous Dominant
P1 White parent: pp Homozygous Recessive
F1: all Heterozygous, Pp
F2: white offspring pp
*Recessive traits must be homozygous.
F2: Purple offspring could be PP or Pp
*Dominant traits can be either HD or HR
Predicting Genetics
Using the symbols alone,
Mendel was able to predict
how traits would be
passed on.
Law 1 of Genetics:
Genes exist in different
forms, called Alleles.
Some alleles are dominant,
others are recessive.
You inherit one allele from each parent, for every gene.
Law 2 of Genetics:
Inheritance of one allele
doesn’t influence the
inheritance of any other.*
The distribution of dominant and recessive alleles is random.
*except Linked genes