Homeroom
Read!
Warm-up p.11
Matching:
1. Heredity
2. Alleles
3. Phenotype
4. Genotype
5. Dominant
6. Recessive
a. various forms of the same gene
b. expressed even if only 1
copy is present
c. passing of genes from parent to
offspring
d. the genes an organism has
e. physical traits that can be
observed
f. expressed only when two copies
are present
Let’s Review
• What is an allele?
• Variations in the same
gene. Height is an example!
Punnett Square
• Illustrates how the parent’s alleles might
combine in offspring
• Each parent has two alleles for a particular
gene. An offspring receives one allele from
each parent.
Reginald Punnett
• English geneticist who discovered many
genetics basics including the determination of
sex.
Letters
• Dominant Alleles=capital letter
Ex. R
• Recessive Alleles=lower case letter
Ex. r
Punnett Square
Probability
• Punnett squares show the chance an offspring
has to get certain genes or express a certain
trait
Percent
• What percent will have black hair?________
• What percent will have blonde?__________
Homozygous vs. Heterozygous
• If we have two of the same type of allele, it is
called Homozygous (RR) or (rr)
• If we have two different alleles it is called
Heterozygous (Rr)
Giant Punnett Practice
• Raise your hand to pick an allele(classmate!)
to create the following scenarios.
Homozygous vs. Heterozygous
Let’s make a homozygous pair
• Heterozygous
• Homozygous recessive
• Homozygous dominant
• In guinea pints, the allele for short hair is
dominant.
• What genotype would a heterozygous short
haired guinea pig have?
• A TT (tall) plant is crossed with a tt (short
pant). What percentage of the offspring will
be tall?
• A Tt plant is crossed with a Tt plant. What
percentage of their offspring will be short?
• In pea plants, purple flowers are dominant to
white flowers. If two white flowered plants are
crossed, what percentage of their offspring
will be white flowers?
• A white flowered plant is crossed with a plant
that is heterozygous for the trait. What
percentage of the offspring will have purple
flowers?
Design your own scenarios
• Write four of your own punnett square scenarios
using the list below. You must also solve them!
• 1. A heterozygous pink flower and a homozygous
recessive white flower
• 2. A homozygous dominant dark-haired male and
a heterozygous dark-haired female
• 3. Two homozygous recessive green-eyed people
• 4. A homozygous dominant tall person and a
homozygous recessive short person