Transcript Mendelian Traits

**An Austrian monk who was the first person to
observe different inherited traits such as color and
height using the reproduction of pea plants
I’m a monk and I like
peas, darn it !
**In plants, fertilization is called pollination
(pollen from the male meets the female
parts)
 Self-pollination occurs when a plant is
allowed to pollinate itself
 Cross pollination – Different plants
Female
excepts
the pollen
Male Produces
Pollen
**He studied only
one trait at a time
to control the
variables
** He called these
traits factors
He would cross-pollinate plants with two variations of one
trait: For example, this dwarf plant was mated with this tall
plant
P1  Parent Generation
**tall plant mated with a
short plant
Their Offspring (F1)  Filial 1
(1st generation)
**All Tall – allowed to selfpollinate
Their offspring (F2) – Filial 2
(2nd) generation
**3 tall and 1 short
F1 Must carry
the tall AND
the short
“factors”
** Traits are inherited from generation to
generation
** Also, a hybrid is the offspring that inherited both
the tall “factor” and the short “factor”
~ Rule of Unit factors: Two factors (one from each
parent) affect one trait in an individual
~ Rule of Dominance: The observed trait is called
dominant and the trait that cannot be seen is recessive
~ We now call Mendel’s
factors genes and are
found on chromosomes
~ Remember!!! We have a
total of46 chromosomes
•½ from mom and ½ from
dad
~ 44 are called autosomal
chromosomes and 2 are
called sex chromosomes
(X’s and Y’s)
** We call the alternate forms of a gene alleles
** Alleles inherited from the mother are in red. Those
inherited from the father in blue.
Homologues;
Same
chromosome
from each
parent; Just
different forms
of alleles
“A” Alleles
aA are different,
or alternate, forms
of the “A” gene
D Alleles
T Alleles

Genotype  pair of alleles denoted by
letters
› TT = homozygous dominant (Upper Case)
› Tt = heterozygous (hybrid, carrier…the
recessive “t” is not expressed; the “T”
dominnates over the “t”; the “t”
cannot be seen
› tt = homozygous recessive

Phenotype  how the alleles are
expressed; what it “looks” like; such as tall
and short or even a genetic disease or
abnormality (like polydactyl fingers)
BB
Homozygous
Dominant
bb
Homozygous
Recessive
Remember!! Combination of alleles denoted by
using a capital letter for dominant alleles and
lower case letters for recessive traits
Codes For
Genotype
(AA, Aa,aa)
Phenotype
(Fur Color)
Principle of Segregation:
What it means: each gene has two copies (alleles)
and a parent will give only one copy to a child. The
other parent will give another copy, and thus the
child will receive two copies (alleles)
Segregation of alleles in the production
of sex cells
Principle Independent Assortment: Genes for
different traits may assort independently of one another in
gamete production  Leads to genetic diversity
What it means: different genes are inherited
separately. For example, the gene which codes
for eye color is inherited separately from the
gene which codes for nose shape.

Table that shows probability of offspring
having a particular trait

Shows a cross (mating)between a male’s
gamete with the female’s
**Cross a male with a Female – What are the
probabilities of the sexes of the babies?
X
Y
X
XX
XY
X
XX
XY
**Genotypic Ratio: 2 XY to 2 XX  1:1 (50/50 chance)
**Phenotypic Ratio: 2 Males to females  2:2  1:1
Mom’s Genotype is Rr and
her phenotype is Round
R
R
r
RR
Rr
Rr
rr
Dad’s Genotype is Rr
and his phenotype is
Round
r
**Genotypic Ratio: 1RR:2Rr:1rr 
 Write Homozygous Dominant 1st, then Heterozygous then
Homozygous Recessive.
**Phenotypic Ratio: 3Round:1Wrinkled3:1  Dominant first then
recessive

Determine the genotypes of a parent based on
offspring.

In a Test cross, cross an unknown genotype to a
known recessive (below)
T
t
t
Tt
Tt
T
T
Tt
Tt
If all offspring are tall the
unknown
Is TT, homozygous
dominant
t
t
Tt
tt
t
Tt
t t
If half of the offspring
are short and the other
half tall the unknown is
Tt, heterozygous

Cross the following and determine the
genotypic and phenotypic ratios:
› Homozygous yellow pod (YY) with
heterozygous yellow pod (Yy)
› 2 heterozygous tall plants (Tt)
› 1 plant with wrinkled seeds (rr) with a plant
that is heterozygous for round seeds (Rr)
› A homozygous dominant purple flower (PP)
with a homozygous white flower (pp)