Download File

Mendelian Genetics
Mendel laid the
groundwork for
genetics.
 Genetics is the study of
biological inheritance patterns
and variation.
 Gregor Mendel showed that
traits are inherited as discrete
units.
 Traits are distinguishing
characteristics that are
inherited.
 Many in Mendel’s day thought
traits were blended.
How did he do this?
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.
Purple x purple = purple offspring
White x white = white offspring
Then he crossed one white and
one purple from these offspring.
Purple crossed with white = all purple
How is this possible???
He then let the purple offspring self-pollinate….
3 purple flowers : 1 white flower
Mendel observed patterns in the first
and second generations of his crosses.
Mendel drew three important
conclusions.
 Traits are inherited as discrete units,
that we call genes.
 Organisms inherit two copies of each
purple
gene, one from each parent.
 The two copies segregate
during gamete formation.
(The last two conclusions are
called the law of segregation.)
white
Now we know more about our genes….
 Both parents have 2 alleles for each gene
 An allele is a variation, or form of a gene, and is located on




the same spot on homologous chromosomes.
Meiosis: chromosomes & alleles are separated.
Each gamete gets one of the alleles.
Each parent contributes only 1 allele to their offspring.
There is a 50% chance of receiving either allele from either
parent.
Genotype vs. Phenotype
Genotype: actual alleles from parents (letters)
Phenotype: physical appearance of organism (no letters:
What does it look like? What traits does it have?)
 If 2 alleles differ, one is dominant over the
other
(this trait will be expressed).
 The other one is recessive.
(it will be masked by the dominant allele)
What would have to happen in order to see a
recessive trait expressed???
Genetic Crosses



Capital letters = dominant alleles
Lowercase letters = recessive alleles
Use the SAME letter to represent both alleles!
Example:
Flower color: purple = P
white = p
Seed color:
green = G
yellow = g
freckles: F
no freckles= f
Both alleles are same = homozygous
Both alleles are different = heterozygous
Try this: Let’s use freckles.
Having freckles is dominant= F No freckles = f
How would you show an individuals genotype if they were:
Homozygous dominant for freckles?
Homozygous recessive for freckles?
Heterozygous for freckles?
Brown eyes = B
Blue eyes = b
Write the genotype for an individual that is:
Blue eyed:________________________
Homozygous dominant for eye color:____________
Heterozygous for eye color:___________________
Homozygous recessive for eye color:________
What genotypes can a person have if they have brown
eyes?_____________
Only 1 allele
from each parent
is in each box.
Each box ends
up with 2 total
alleles, one from
the mother and
one from the
father.
Monohybrid Cross
Cross involving one contrasting trait
Use a Punnett square to predict probabilities…
(let’s use F)
Cross a heterozygous
purple flower with a
homozygous recessive
white flower.
__________X__________