S-B-8-1_Non-Mendelian Heredity PowerPoint
Heredity
Non-Mendelian Genetics
S-B-8-1_Non-Mendelian Heredity PowerPoint
Mendelian Heredity
• Principle of
Dominance
• Law of Segregation
• Law of
Independent
Assortment
http://mac122.icu.ac.jp/gen-ed/mendel-gifs/01-mendel-himself.JPG
S-B-8-1_Non-Mendelian Heredity PowerPoint
Non-Mendelian Heredity
• does not fit Mendel’s Laws
• is not governed by one autosomal
gene
S-B-8-1_Non-Mendelian Heredity PowerPoint
Incomplete Dominance
• Heterozygotes look
different from a
homozygotes
• Blending of
phenotypes
RR x RIRI
RRI
http://chsweb.lr.k12.nj.us/psidelsky/Chapter10(Gen).htm
Codominance: Both alleles of a gene
pair are expressed.
Example: Human Blood Types
• Human blood type is determined by codominant
alleles. There are three different alleles: IA, IB, and i.
The IA and IB alleles are codominant, and the i allele
is recessive.
• The possible human phenotypes for blood group are
type A, type B, type AB, and type O.
• Type A and B individuals can be either homozygous
(IAIA or IBIB, respectively), or heterozygous (IAi or
IBi, respectively). Type O is IOIO.
S-B-8-1_Non-Mendelian Heredity
PowerPoint
Codominance: More Examples
Rhododendron
coloration
http://upload.wikimedia.org/wikipedia/commons/f/f3/Codominance_Rhododendron.jpg
Roan coloration in cows
(red coat with white
blotches)
http://en.wikipedia.org/wiki/File:Light_Roan_Shorthorn_Heifer_DSCN18
72b.jpg
S-B-8-1_Non-Mendelian Heredity
PowerPoint
S-B-8-1_Non-Mendelian Heredity PowerPoint
THINK-PAIR-SHARE
1.
2.
3.
Distinguish between incomplete dominance and
codominance.
How many phenotypes are seen when codominance
is possible?
Red color (R) in snapdragons shows incomplete
dominance to white snapdragons (RI). The
heterozygotes are pink. If pink snap dragons are
crossed with a white snapdragon, what are the
genotypic/ phenotypic ratios?
R
RI
RI
RRI RIRI
S-B-8-1_Non-Mendelian Heredity PowerPoint
Multiple Alleles
• When 4 or more possible
phenotypes exist within a
population
– Blood type
– Eye & hair color
– Fur in mammals
http://www.learner.org/interactives/dna/genetics8.html
S-B-8-1_Non-Mendelian Heredity PowerPoint
Problems with Multiple Alleles
A woman with type O blood marries a man with
type AB blood. What are the possible blood
types that a child of theirs could inherit?
STEP 1:
♀ ii
STEP 2:
STEP 3:
STEP 4:
i
STEP 5:
♂ IAIB
IA , IB
i
IA
IB
IAi
IBi
STEP 6: There’s a 50% chance that their baby will be
Type A or Type B.
S-B-8-1_Non-Mendelian Heredity PowerPoint
Polygenic Inheritance
http://www.nature.com/nrg/journal/v10/n12/box/nrg2670_BX1.html
Poly-many genic-gene
• More than one gene
on more than one loci
or on more than one
chromosome.
• Give the appearance
of gradation
– Hair & skin color
– Height
– Body size
http://scienceblogs.com/geneticfuture/a_ruler_beats_genetics_in_pred/tall_short1.jpg
S-B-8-1_Non-Mendelian Heredity PowerPoint
THINK-PAIR-SHARE
Black fur (BBl) is completely dominant to
brown fur in rabbits, but brown fur (BBr) is
dominant to white (b). A hybrid brown doe
(BBrb) is crossed with a hybrid black buck
(BBlb). What are the expected phenotypes of
the offspring? Ratios?
S-B-8-1_Non-Mendelian Heredity PowerPoint
Linked Traits
• When the loci of two
genes are located
close together on the
same chromosome
– Red hair, freckles, and
fair skin are linked.
http://en.wikipedia.org/wiki/File:Woman_redhead_natural_portrait_1.jpg
S-B-8-1_Non-Mendelian Heredity PowerPoint
Sex-Linked Traits
• Genes located on a
sex (X or Y)
chromosome
♀XX & ♂XY
– Some forms of
hemophilia
– Red-green
colorblindness
http://www.ccs.k12.in.us/chsteachers/Amayhew/Biology%20Notes/sexlinked%20notes.htm
S-B-8-1_Non-Mendelian Heredity PowerPoint
Red-Green Colorblindness
http://upload.wikimedia.org/wikipedia/commons/e/e0/Ishihara_9.png
S-B-8-1_Non-Mendelian Heredity PowerPoint
Hemophilia
http://biology.clc.uc.edu/courses/bio105/sex-link.htm
S-B-8-1_Non-Mendelian Heredity PowerPoint
Barr Bodies
• The inactive X
chromosome found
in female (XX)
somatic cells
http://www.genetics.com.au/factsheet/fs14.asp
The nucleus of a cell. The arrow is
pointing to the inactive X
chromosome, the Barr Body.
– Not found in normal
males (XY) .
– Explains calico
coloring in cats.
S-B-8-1_Non-Mendelian Heredity PowerPoint
Calico Cats
http://waynesword.palomar.edu/biex4hnt.htm
S-B-8-1_Non-Mendelian Heredity PowerPoint
Solving Sex-Linked Problems
A woman who is a carrier for red-green
colorblindness marries a man with normal sight.
What percent of the male and female children will
be red-green colorblind or carriers?
STEP 1:
♀ XX'
♂ XY
STEP 2:
STEP 3:
STEP 4:
X, X'
X, Y
STEP 5:
X
Y
X
XX
XY
X'
XX'
X'Y
STEP 6:
50% ♀ Normal
50% ♀Carriers
50% ♂Normal
50% ♂ Colorblind
S-B-8-1_Non-Mendelian Heredity PowerPoint
THINK-PAIR-SHARE
Wild Type
1
2
Homozygous
7
3
8
4
5
6
Heterozygous
1. Is the trait sex-linked? How do you know?
2. How could we tell if female #5 is heterozygous
if she never has children?
3. What are the expected phenotypic ratios from a
cross between #3 & #7?
http://upload.wikimedia.org/wikipedia/commons/c/c5/Autosomal_Recessive_Pedigree_Chart_.svg