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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
http://chsweb.lr.k12.nj.us/psidelsky/Chapter10(Gen).htm
RR x RRIIRRII
RRI
S-B-8-1_Non-Mendelian Heredity PowerPoint
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
Roan coloration in cows (red coat with white
blotches)
S-B-8-1_Non-Mendelian Heredity PowerPoint
http://upload.wikimedia.org/wikipedia/commons/f/f3/Co-dominance_Rhododendron.jpg
http://en.wikipedia.org/wiki/File:Light_Roan_Shorthorn_Heifer_DSCN1872b.jpg
Rhododendron coloration
THINK-PAIR-SHARE
1. Distinguish between incomplete dominance and codominance.
2. How many phenotypes are seen when codominance is possible?
3. 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 ♂ IAIB
STEP 2: i IA , IB
STEP 3:
STEP 4:
STEP 5:
STEP 6:
IA IB
IAi IBii
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
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
http://www.nature.com/nrg/journal/v10/n12/box/nrg2670_BX1.html
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
http://www.ccs.k12.in.us/chsteachers/Amayhew/Biology%20Notes/sexlinked%20notes.htm
• Genes located on a sex (X or Y) chromosome
♀XX & ♂XY – Some forms of
hemophilia– Red-green
colorblindness
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– Not found in normal
males (XY) .– Explains calico
coloring in cats.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.
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: X, X' X, Y
STEP 3:
STEP 4:
STEP 5:
STEP 6:
X Y
XX XYX
X' XX' X'Y
50% ♀ Normal
50% ♀Carriers
50% ♂Normal
50% ♂ Colorblind
S-B-8-1_Non-Mendelian Heredity PowerPoint
THINK-PAIR-SHARE
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
1 2
3 4 5 67 8
Wild Type
Homozygous
Heterozygous
S-B-8-1_Non-Mendelian Heredity PowerPoint