Objective: Students will apply concepts
of meiosis to heredity
Heredity- the passing
of genetic traits from
parent to offspring
What do you notice
about “heredity” from
the image to the
right?
Fertilization leading to eventually adult human
Human Male Karyotype (2n)
Human Female Karyotype (2n)
50% Chance to
donate either
one of the
homologous
chromosomes
Undergo Meiosis To Split Homologous Pairs in Each
Parent
Chromosomes have genes. Genes can be multiple variants
called alleles. Capital letters mean “dominant”.
Lowercase letters mean “recessive”.
.
A= Brown Eyes
Note!
Dominant
a= Blue Eyes
doesn’t
always
B= Weak bones
mean
“good”
b= Strong bones
G= Normal Hands
g= Sweaty Hands
Dominant alleles will show over top of recessive
alleles. A person with Bb will have “weak bones”.
B= Weak bones
b= Strong bones
Human Male Karyotype (2n)
Human Female Karyotype (2n)
50% Chance to
donate either one
of the homologous
chromosomes.
Crossing over can
still occur create
new allele combos
for Dad and for
Mom respectively.
Punnett Square- diagram used to the likelihood
of having certain traits in the offspring of a cross
Punnett Square
What are the genotypes of the offspring below?
What are the chances we get each genotype?
Genotype- The genetic
makeup of a cell
Example: BB, Bb, bb
What are the phenotypes of the offspring below?
What are the chances we get each genotype?
Phenotype- The physical characteristics or
expression of the alleles in a cell/organism
Example: Long legs, fast metabolism,
lactase enzyme production, blue eyes
b= Strong bones
B= Weak bones
Fertilization joins one chromosome of each “type”
from each parent to each a homologous pair.
One of those Punnett Square outcomes comes true.
Another example of how Punnett Squares Work
Let “T” be the trait for (T= Tall) and “t” be the trait for (t=short)
<-Father’s Alleles
Mother’s Alleles
Closure: What are the chances that a male with the
genotype Aa and a female with the genotype Aa have a
child with the dominant phenotype?
Closure Answer: What are the chances that a male with
the genotype Aa and a female with the genotype Aa
have a child with the dominant phenotype? 75%
A
a
A
AA
Aa
a
Aa
aa