Download AdvancedGenetics2017

Beyond Mendel’s Laws
of Inheritance
AP Biology
2006-2007
Incomplete dominance
 Heterozygote shows an intermediate,
blended phenotype

example:
 RR = red flowers RR
 rr = white flowers WW
 Rr = pink flowers RW
 make 50% less color
AP Biology
RR
RW
WW
Practice…
 Wavy hair appears to be the
heterozygous expression of a pair of
alleles for straight (H) or curly hair (h).
A woman with wavy hair has a child
with a man who has straight hair. What
is the chance that the child will have
wavy hair?
Parents are Hh x HH
 Child is Hh or HH so 50% chance

AP Biology
Codominance
 2 or more alleles that are dominant in a
phenotype.
 Both alleles are expressed in heterozygous
condition.
 Spotted, striped or freckled phenotype
AP Biology
Practice…
 Parental genotypes?
 RrBB and RrBW
 F1 phenotypic ratio?
 6:6:2:2 or 3:3:1:1
 If they had 16 chicks, how many should
be a “blue rosecomb”chicken?
AP Biology
6
Multiple Alleles
 3 or more alleles for a trait
 But, individual can only carry

2 alleles
Ex: Human blood groups
A B
 I , I , i
 IA & IB alleles are codominant
 i allele recessive to both
AP Biology
Rabbit Fur Color Trait
Practice…
 A man with type O blood marries a
woman with Type AB blood. Among
their children, what is the probability
that the offspring will have type AB
blood? What are the genotypic ratio
and phenotypic ratios?
0% will have AB phenotype
 Geno 1:1 and Pheno 1:1

AP Biology
Practice…
 Cross a heterozygous himalayan with a
chinchilla colored rabbit. What are the
phenotypes and genotypes of the
offspring?
Genotypes: cchch and cchca
 Phenotypes: light grey only

AP Biology
Polygenic inheritance
 2 or more genes affecting a single trait
 Genes spread out over different locations

AP Biology
Human traits: skin color, height, eye color
Sex linked traits
1910 | 1933
 Genes are on the sex chromosomes



as opposed to autosomal chromosomes
first discovered by T.H. Morgan at Columbia U.
Drosophila breeding
 good genetic subject
 prolific
 2 week generations
 4 pairs of chromosomes
 XX=female, XY=male
AP Biology
Discovery of sex linkage
P
F1
true-breeding
red-eye female
X
true-breeding
white-eye male
100%
red eye offspring
Huh!
Sex matters?!
generation
(hybrids)
F2
generation
AP Biology
100%
red-eye female
50% red-eye male
50% white eye male
Genetics of Sex
 In humans & other mammals, there are 2
sex chromosomes: X & Y

2 X chromosomes
 develop as a female: XX
 gene redundancy,
like autosomal chromosomes

an X & Y chromosome
Which parent
decides sex
of offspring?
X
Y
X
XX
XY
X
XX
XY
 develop as a male: XY
 no redundancy
AP Biology
50% female : 50% male
Morgan’s flies…
x
XR XR
Xr
XR
XR
AP Biology
XR Xr
XR Xr
x
XrY
XR Xr
Y
XRY
XRY
100% red eyes
XR
Xr
XRY
XR
Y
XR XR
XRY
XR Xr
X rY
100% red females
50% red males; 50% white males
Genes on sex chromosomes
 Y chromosome

few genes other than SRY
 sex-determining region of Y chromosome
 master regulator for maleness
 X chromosome

traits other than sex determination
 mutations: (all are recessive)
 Hemophilia
 Duchenne muscular dystrophy
 Color-blindness
AP Biology
sex-linked recessive
Hemophilia
H Xh x X
HY
HH
XHh
female / eggs
male / sperm
XH
Xh
AP Biology
XH
Y
XH XH
XH Y
• ¼ chance that child will
be colorblind.
• ½ of the sons
• 0 chance for daughters
XH Xh
XhY
• Pay attention to what
the question is asking!
carrier
disease
X-inactivation
 Female mammals inherit 2 X chromosomes

one X becomes inactivated during
embryonic development
 condenses into compact object = Barr body
 which X becomes Barr body is random
 patchwork trait = “mosaic”
patches of black
XH 
XH Xh
tricolor cats
can only be
AP Biology
female
Xh
patches of orange
Practice…
 Coat color in cats is a codominant trait
and located on the X chromosome.
Cats can be black, orange or calico. A
calico cat has black and orange
splotches. A female calico cat is
crossed with a male black cat. What are
the phenotypes of the offspring and in
what proportion?

XBXO x XBY Parental genotypes

1(female black):1(female calico):1(male black):1(male orange)
NOTE: sex is a part of the phenotype!

AP Biology
Environmental Effects
 Phenotype is controlled by
both environment & genes
Human skin color is influenced
by both genetics &
environmental conditions
Coat color in arctic
fox influenced by
heat sensitive alleles
Color of Hydrangea flowers
APinfluenced
Biology
is
by soil pH
Pedigree Analysis
 A pedigree is a family tree that describes

the interrelationships of parents and
children across generations
Inheritance patterns of particular traits can
be traced and described using pedigrees
AP Biology
Autosomal Dominant Gene
 Determine
genotypes of
individuals: 1,
3, 7 and 11
 Could this
pedigree chart
work for an
autosomal
recessive
gene?
AP Biology
X-linked Recessive Gene
 What are the 1st
generation
genotypes?
 What are the
genotypes of
individuals: 4, 6,
9 and 12?
AP Biology