Heredity

1
Heredity

• Non-Mendelian Genetics

2
Mendelian Heredity
S-B-8-1_Non-Mendelian Heredity PowerPoint

• Principle of Dominance 
• Law of Segregation
• Law of Independent Assortment

http//mac122.icu.ac.jp/gen-ed/mendel-gifs/01-mend
el-himself.JPG
3
Non-Mendelian Heredity

• does not fit Mendels Laws
• is not governed by one autosomal gene

4
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
5
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.

6
Codominance More Examples
Rhododendron coloration

• Roan coloration in cows (red coat with white
  blotches)

http//en.wikipedia.org/wiki/FileLight_Roan_Short
horn_Heifer_DSCN1872b.jpg
http//upload.wikimedia.org/wikipedia/commons/f/f3
/Co-dominance_Rhododendron.jpg
7
THINK-PAIR-SHARE
S-B-8-1_Non-Mendelian Heredity PowerPoint

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
8
Multiple Alleles
S-B-8-1_Non-Mendelian Heredity PowerPoint

• 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
9
Problems with Multiple Alleles
S-B-8-1_Non-Mendelian Heredity PowerPoint

• 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


IA IB
STEP 4
IAi IBi
i
STEP 5
STEP 6
Theres a 50 chance that their baby will be Type
A or Type B.
10
Polygenic Inheritance
S-B-8-1_Non-Mendelian Heredity PowerPoint

• 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//www.nature.com/nrg/journal/v10/n12/box/nrg2
670_BX1.html
http//scienceblogs.com/geneticfuture/a_ruler_beat
s_genetics_in_pred/tall_short1.jpg
11
THINK-PAIR-SHARE
S-B-8-1_Non-Mendelian Heredity PowerPoint

• 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?

12
Linked Traits
S-B-8-1_Non-Mendelian Heredity PowerPoint

• 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/FileWoman_redhead_na
tural_portrait_1.jpg
13
Sex-Linked Traits
S-B-8-1_Non-Mendelian Heredity PowerPoint

• 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/Biolo
gy20Notes/sexlinked20notes.htm
14
Red-Green Colorblindness
S-B-8-1_Non-Mendelian Heredity PowerPoint
http//upload.wikimedia.org/wikipedia/commons/e/e0
/Ishihara_9.png
15
Hemophilia
S-B-8-1_Non-Mendelian Heredity PowerPoint
16
Barr Bodies
S-B-8-1_Non-Mendelian Heredity PowerPoint

• 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.
17
Calico Cats
S-B-8-1_Non-Mendelian Heredity PowerPoint
http//waynesword.palomar.edu/biex4hnt.htm
18
Solving Sex-Linked Problems
S-B-8-1_Non-Mendelian Heredity PowerPoint

• 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 6
STEP 1 ? XX' ? XY
50 ? Normal 50 ?Carriers 50 ?Normal 50 ?
Colorblind
STEP 2 X, X' X, Y
STEP 3



X Y
STEP 4
XX XY
X X'
STEP 5
XX' X'Y
19
THINK-PAIR-SHARE
S-B-8-1_Non-Mendelian Heredity PowerPoint
Wild Type
Homozygous
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