Download Genetics Since Mendel

Genetics Since Mendel
Unit 9 – Lesson 2 Notes
Modern Genetics
• We know about dominant and recessive
genes, now we are going to learn about
other types of genetic traits, such as
– Incomplete dominance
– Multiple alleles
– Polygenic Inheritance
– Mutations
Incomplete Dominance
• Neither allele for a trait
is dominant.
• The phenotype
produced is
intermediate between
the two homozygous
parents.
Multiple Alleles
• More than two alleles are multiple alleles.
• Traits controlled by multiple alleles
produce more than three phenotypes.
Multiple Alleles
There are 3 alleles for the gene that determines blood type.
(Remember: You have just 2 of the 3 in your genotype --- 1 from mom
& 1 from dad).
ALLELE
IA
IB
i
CODES FOR
Type "A" Blood
Type "B" Blood
Type "O" Blood
Notice that, according to the symbols used in the table above, that the
allele for "O" (i) is recessive to the alleles for "A" & "B".
GENOTYPES
IA IA
IA i
RESULTING
PHENOTYPES
Type A
Type A
IB IB
IB i
Type B
Type B
IAIB
Type AB
ii
Type O
Polygenic Inheritance
• A group of gene pairs acts together to
produce a trait, which creates more variety
in phenotypes.
• Many human traits are controlled by
polygenic inheritance, such as hair and
eye color.
Polygenic Inheritance
Example
Mutations
• Mutations – genes that are
altered or copied incorrectly.
– A mutation can be
harmful, beneficial, or
have no effect.
– Chromosome disorders –
caused by more or fewer
chromosomes than
normal.
Mutations
– Down syndrome – caused
by an extra copy of
chromosome 21.
Recessive Genetic
Disorders
• Both parents have a recessive allele responsible
for the disorder and pass it on to their child.
• Because the parents are heterozygous, they
don’t show any symptoms.
P
p
P
p
PP
Pp
Disorder
Expressed
Pp
pp
Recessive Genetic
Disorders Examples
• Homozygous recessive
disorders.
– PKU
– Cystic Fibrosis
– Sickle-Cell Anemia
Other Genetic Disorders
• Genes that determine the sex of an organism are XX in
females and XY in males.
• Females produce eggs with an X chromosome only.
Males produce sperm with either an X or Y chromosome.
X
Y
Y
X
X
X
Y
X
X
EGGS
X
SPERMS
Other Genetic Disorders
Disorders
– Turners Syndrome XO
– Triple X Syndrome XXX
– Klinefelter syndrome XXY
– XYY XYY
Sex-linked Disorders
• An allele inherited on
an X or Y
chromosome is a sexlinked gene.
• Color blindness is a
sex-linked disorder
caused by a recessive
allele on the X
chromosome.
Pedigree
• A pedigree follows a trait through generations of a
family.
–
–
–
–
Carriers of trait are half shaded.
People with trait are fully shaded.
Squares show males.
Circles show females.
Orange Shows the Trait
Who carries the
gene? M or F
How many people
are colorblind?