Download 5.2- Studying Genetic Crosses

5.2- Studying
Genetic Crosses
SBI 3U1- Ferrari
Punnett Squares
• Punnett Square- A grid
used to illustrate all
possible genotypes
and phenotypes of
offspring from genetic
crosses
• Shows probability
• Each square represents
a 25% chance of
occurrence for that
trait
Using Punnett Squares
This is a
monohybrid
cross
Possible F1 outcomes from a cross between two heterozygous
parents.
The phenotype ratio is 3:1 for flower colour (purple to white)
Test Crosses
A cross between an individual of unknown genotype and
homozygous recessive for that trait.
Analyzing the phenotype should provide insight into the
unknown genotype.
Mendel’s Dihybrid Crosses
He crossed yellow, round seeds with green, wrinkled seeds
YYRR
x
yyrr
All F1 generation displayed both dominant traits- yellow and round
The Law of Independent
Assortment
• Mendel found a 9:3:3:1 ratio for every
dihybrid cross he performed.
• This law states that the alleles for one gene
segregate or assort independently of the alleles
for other genes during gamete formation.
The Chromosome Theory of
Inheritance
By early 1900s
scientists finally
began to see the link
between meiosis &
inheritance
Walter Sutton ( 1902)
proposed that genes
located on
chromosomes and
this provides the
basis for the
segregation and
independent
assortment of alleles.
Homework
• 1) Please read and review 5.2 ( Pgs.208-217)
• 2) Punnett Square Practice Problems & Worksheets