Download Discussion & Naming of Complex Patterns of Inheritance

Unit 4 – Lecture 7
Review
 Mendellian / Single-Gene Inheritance
 two alleles per gene = 1 dominant, 1 recessive
 ex: R = red, r = blue




RR = red
Rr = red
rr = blue
COLOR THE IMAGES
ON YOUR LECTURE NOTES
Discuss
 What does it mean to be “incomplete” ?
[don’t say – to not be complete…think about this]
Incomplete Dominance
 Incomplete Dominance
 two dominant alleles present
 BLEND of alleles is expressed when combined
 uses same letter with “prime” or
1
A
another letter as exponent
 can have a recessive allele still – which is hidden
by BOTH of the dominant alleles if present.
Incomplete Dominance – cont’d
 Incomplete Dominance
 ex: R = red, R1 = blue
 RR = red
 RR1 = PURPLE
 R1R1 = blue

COLOR THE IMAGES
ON YOUR LECTURE NOTES
Codominance
 Codominance
 two dominant alleles present
 BOTH alleles are expressed when combined
 offspring show both phenotypes at same time
 uses same letter with “prime” or
another letter as exponent
 can have a recessive allele still – which is hidden
by BOTH of the dominant alleles if present.
Codominance – cont’d
 Codominance
 ex: R = red, R1 = blue




RR = red
RR1 = red AND blue
[striped, spotted, checkered, etc]
R1R1 = blue
COLOR THE IMAGES
ON YOUR LECTURE NOTES
Multiple Alleles
 Multiple Alleles
 trait is coded for by more than 2 alleles
for the SAME gene [same letter!!]
 more combinations for the same trait
 gene can have:
 multiple dominant alleles – like
codominant or incomplete dominance
 multiple recessive alleles – all of which would
be hidden by any dominant allele present
MA Example - Discuss
 Example: three alleles for the “R” gene
 R = red
R1 = white
r = orange
 What color phenotypes would result from
each of the following genotypes? [assume co-dominance]
 RR red
RR1 red AND white
 R1R1 white Rr
red
white rr orange
 R1r
Multiple Alleles – cont’d
 Multiple Alleles
 ex: Blood Type – codominant multiple allele trait

alleles = IA, IB & io
A and B are dominant, O is recessive

caps letter “I”

lower-case letter “i”
MA – Discuss
A
B
 So…if A [I ] and B [I ] are dominant,
and O [io]is recessive …
 which genotypes will give each blood-type
phenotype? [A, B, and O]
o
 A blood: IA IA or IA i
 B blood:
IB I B
o
B
I i
or
o o
 O blood: only i i
NOTE
 You MAY NOT do blood type
as your multiple allele trait.
Your traits must ALL be able to
be seen just by looking at your creature.
Polygene Inheritance
 Polygene Inheritance
 “poly” = many
 traits are influenced by many genes
will have combinations of different letters
 ex: traits with ranges or many types
 hair/eye/skin color, height, build, etc.

Polygene Inheritance
 Polygene Inheritance
 ex: A / G / R = red


a / g / r = no red
more dominant alleles, more color
Aa Gg Rr is darker red than Aa gg rr
Naming Inheritance
 Types of Chromosomes
 Autosome = non-sex determining
chromosome [1-22]
 “autosomal” trait =
trait on a non-sex chromosome
 Sex-Chromosome = X or Y,
chromosome pair #23
 “sex-linked” trait =
trait on the X or Y [sex] chromosome
Naming Inheritance
 Autosomal Dominant
 dominant trait on a non-sex chromosome
 heterozygotes [Aa] and
dominant homozygotes [AA] have the trait
 children with trait have at least
one parent with the trait
 affects males and females equally
Naming Inheritance
 Autosomal Recessive
 recessive trait on a non-sex chromosome
 must be recessive homozygote [aa] to have the trait
 children with trait have parents who either show or
carry the trait
 carrier – heterozygote person for a recessive trait –
does not show it, but has the allele [Aa]
 if both parents have the trait,
ALL children will have the trait
Naming Inheritance
 Autosomal Recessive
 affects males and females equally
 traits often skip generations
Naming Inheritance
 Sex-linked Dominant [XA]
 dominant trait on a sex chromosome
 typically on the X-chromosome
 many are fatal [especially in males]
 if both parents have trait, most children will have it
¾ of children if heterozygous mother
 all children if homozygous mother
 affects males and females equally
 if both parents have it, all kids have it.

Naming Inheritance
 Sex-linked Recessive [Xa]
 recessive trait on a sex-chromosome
 typically on the X-chromosome
 females can be carriers; males cannot
 affects more males than females
son with trait can have parents
who don’t show trait
 no father to son transmission of trait
 traits often skip generations
