Transcript Chap 9/11 : Fundamentals of Genetics

Chap 9 : Fundamentals of Genetics
I.
Mendel
-- Gregor Mendel – “Father of
Genetics” – worked with pea
plants. Discovered
inheritance (passing of traits
from parents to offspring)
A. Terminology
1. Pure or Strain – trait that’s always
passed to offspring.
2. P1 generation – parents
3. F1 generation – 1st filial
generation – offspring of P1
4. F2 generation – offspring of F1
B. 3 Principles of inheritance
1. Principle of Dominance and
Recessiveness – says that traits that mask
other traits are called dominant traits (R)
and those that don’t are recessive traits
(r).
2. Principle of Segregation – each trait is
expressed by 2 factors – one from each
parent
Ex. RR x rr = Rr
(mom) (dad) (offspring)
3. Principle of Independent Assortment – says
traits are independent from each other.
Ex. Eye color and hair color are independent of
each other.
C. Chromosomes and Genes
gene
chromosome
gene – piece of DNA
calling for a specific
trait – like eye color
allele – that form of a
gene. Ex. Blue, brown,
or green
II. Genetic Crosses
A.1. Genotype – genetic makeup of an
organism. Expressed with letters. (Rr)
2. Phenotype – physical appearance of an
organism (ex. Blue eyes)
3. Homozygous – when both alleles of a
pair are the same. (RR or rr)
4. Heterozygous – when the alleles of a
pair are not the same. (Rr)
Ex. B- black b - blonde
Bb (dad) x bb (mom)
Geneotype: Bb
bb
Phenotype: black
blonde
heterozygous homo. Rec.
Homozygous dominant – BB
Homozygous recessive – bb
5. Multiple alleles – when 3 or more
alleles control 1 trait.
ex. Blood type : A, B, O
6. Probability – the likelihood of something
occurring.
#of 1 kind of event / # of events
Ex. 50 tosses of coin
18 heads, 32 tails. What is the
probability of tossing a head ?
18/50 = 36 %
B. Monohybrid crosses – cross
between 1 trait
--- Punnett Square – tool used to predict the
probability from genetic crosses.
Types of Monohybrid Crosses
1.
In rats brown fur is dominant over white fur. If
a homozygous dominant and homozygous
recessive parent produced offspring, what
would be their genotypes and phenotypes ?
B- brown b-white
BB x bb
G: 100% Bb
b b
P : 100% Brown
B Bb Bb
B
Bb Bb
2. If two of the offspring from #1 were mated what
would be the outcome ?
B- brown
Bb x Bb
B
b
B BB Bb
b Bb bb
b- white
G : 1 BB
2 Bb
1 bb
P : 3 brown
1 white
3. In pea seeds round is dominant over wrinkled. If a
heterozygous seed is mated with a wrinkled one what
percentage would end up wrinkled ?
R- round
Rr x rr
r
r
R Rr Rr
r rr rr
r – wrinkled
50 % would be wrinkled
4. Test Cross – used to determine the
genotype of a dominant phenotype.
In mice red eyes are recessive to blue. A
mouse has blue eyes and you want to
know if red eyes “run in the family line”,
how can you determine this ?
--- Perform a test cross – cross the mouse
with a homozygous recessive (one with
red eyes). B? X bb = ?. If any offspring
have red eyes you would know the allele
in question was for red eyes.
4. Codominance – when one or more alleles is
considered dominant. The result produces a blend
of the alleles.
Ex. Flower petals exhibit codominance.If a
red flower was crossed with a white flower
describe the genotype and phenotype of
the offspring.
R – red
R’ – white
RR x R’R’
R’
R’
R RR’ RR’
R RR’ RR’
G: all RR’
P : all pink
C. Dihybrid Crosses – cross between individuals
that involves 2 different traits.
In Peas, round seeds are dominant to
wrinkled and yellow is dominant to green.
What would be the genotype and
phenotye of the offspring of a homo.rec.
and homo.dom. parents ?
R – round
G- yellow
r – wrinkled g – green
RRGG x rrgg
1 23 4
1234
RG(1+3) RG(1+4) RG(2+3) RG(2+4)
(1+3) rg RrGg
RrGg RrGg
RrGg
(1+4)
rg RrGg
(2+3)
rg
(2+4)
rg
G : all RrGg
P : all round and yellow
Ex. If two offspring from above were to be mated
what would be the phenotypes of the offspring ?
RrGg
x RrGg
RG(1+3) Rg(1+4)
RG RRGG RRGg
Rg RRGg
RRgg
rG RrGG
RrGg
rg RrGg
Rrgg
Phenotypes :
9 round and yellow (R_G_)
3 round and green (R_gg)
3 wrinkled and yellow (rrG_)
1 wrinkled and green (rrgg)
rG(2+3)
RrGG
RrGg
rrGG
rrGg
rg(2+4)
RrGg
Rrgg
rrGg
rrgg