1. Beyond Mendel’s Laws of Inheritance

2. Incomplete dominance
Heterozygote shows an intermediate, blended phenotype
example:
RR = red flowers
rr = white flowers
Rr = pink flowers
make 50% less color
RR
WW
RW RR RW WW

3. Co-dominance 2 alleles affect the phenotype equally & separately
not blended phenotype
human ABO blood groups
3 alleles
IA, IB, i
IA & IB alleles are co-dominant
glycoprotein antigens on RBC
IAIB = both antigens are produced
i allele recessive to both

4. Genetics of Blood type A IA IA or IA i B IB IB or IB i AB IA IB O i i
pheno-type
genotype
antigen on RBC
antibodies in blood
donation status A
IA IA or IA i
type A antigens on surface of RBC
anti-B antibodies __ B
IB IB or IB i
type B antigens on surface of RBC
anti-A antibodies AB
IA IB
both type A & type B antigens on surface of RBC
no antibodies
universal recipient O
i i
no antigens on surface of RBC
anti-A & anti-B antibodies
universal donor

5. Polygenic inheritance
Some phenotypes determined by additive effects of 2 or more genes on a single character
phenotypes on a continuum
human traits
skin color
height
weight
intelligence
behaviors

6. Sex linked traits Genes are on sex chromosomes
as opposed to autosomal chromosomes

7. Classes of chromosomes
autosomal chromosomes
sex chromosomes

8. Genetics of Sex X Y X XX XY X XX XY
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
develop as a male: XY
no redundancy X Y X XX XY X XX XY
50% female : 50% male

9. Genes on sex chromosomes
Y chromosome
few genes other than SRY
sex-determining region
master regulator for maleness
turns on genes for production of male hormones
many effects = pleiotropy!
X chromosome
other genes/traits beyond sex determination
mutations:
hemophilia
Duchenne muscular dystrophy
color-blindness
Duchenne muscular dystrophy affects one in 3,500 males born in the United States.
Affected individuals rarely live past their early 20s.
This disorder is due to the absence of an X-linked gene for a key muscle protein, called dystrophin.
The disease is characterized by a progressive weakening of the muscles and loss of coordination.

10. Human X chromosome Sex-linked usually means “X-linked”
Duchenne muscular dystrophy
Becker muscular dystrophy
Ichthyosis, X-linked
Placental steroid sulfatase deficiency
Kallmann syndrome
Chondrodysplasia punctata,
X-linked recessive
Hypophosphatemia
Aicardi syndrome
Hypomagnesemia, X-linked
Ocular albinism
Retinoschisis
Adrenal hypoplasia
Glycerol kinase deficiency
Incontinentia pigmenti
Wiskott-Aldrich syndrome
Menkes syndrome
Charcot-Marie-Tooth neuropathy
Choroideremia
Cleft palate, X-linked
Spastic paraplegia, X-linked,
uncomplicated
Deafness with stapes fixation
PRPS-related gout
Lowe syndrome
Lesch-Nyhan syndrome
HPRT-related gout
Hunter syndrome
Hemophilia B
Hemophilia A
G6PD deficiency: favism
Drug-sensitive anemia
Chronic hemolytic anemia
Manic-depressive illness, X-linked
Colorblindness, (several forms)
Dyskeratosis congenita
TKCR syndrome
Adrenoleukodystrophy
Adrenomyeloneuropathy
Emery-Dreifuss muscular dystrophy
Diabetes insipidus, renal
Myotubular myopathy, X-linked
Androgen insensitivity
Chronic granulomatous disease
Retinitis pigmentosa-3
Norrie disease
Retinitis pigmentosa-2
Sideroblastic anemia
Aarskog-Scott syndrome
PGK deficiency hemolytic anemia
Anhidrotic ectodermal dysplasia
Agammaglobulinemia
Kennedy disease
Pelizaeus-Merzbacher disease
Alport syndrome
Fabry disease
Albinism-deafness syndrome
Fragile-X syndrome
Immunodeficiency, X-linked,
with hyper IgM
Lymphoproliferative syndrome
Ornithine transcarbamylase
deficiency
Human X chromosome
Sex-linked
usually means “X-linked”
more than 60 diseases traced to genes on X chromosome

11. Map of Human Y chromosome?
< 30 genes on Y chromosome
Sex-determining Region Y (SRY)
linked
Channel Flipping (FLP)
Catching & Throwing (BLZ-1)
Self confidence (BLZ-2) note: not linked to ability gene
Devotion to sports (BUD-E)
Addiction to death & destruction movies (SAW-2)
Scratching (ITCH-E)
Spitting (P2E)
Inability to express affection over phone (ME-2)
Selective hearing loss (HUH)
Total lack of recall for dates (OOPS)
Air guitar (RIF)

12. Hemophilia XHXh XHY Hh x HH XH XHXh XH Y Xh XHXH XHXH XHY XHY XH Xh XH
sex-linked recessive
Hemophilia
XHXh
XHY
Hh x HH XH
XHXh XH Y
male / sperm Xh
XHXH
XHXH
XHY
XHY XH Xh
female / eggs XH
XHY
XHXh
XHXh
XhY
XhY Y
carrier
disease

13. Hemophilia is a sex-linked recessive trait defined by the absence of one or more clotting factors.
These proteins normally slow and then stop bleeding.
Individuals with hemophilia have prolonged bleeding because a firm clot forms slowly.
Bleeding in muscles and joints can be painful and lead to serious damage.
Individuals can be treated with intravenous injections of the missing protein.

19. X-inactivation Female mammals inherit 2 X chromosomes XH XHXh Xh
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
XHXh
Xh
tricolor cats can only be female
patches of orange

20. Environmental effects
Phenotype is controlled by both environment & genes
Human skin color is influenced by both genetics & environmental conditions
The relative importance of genes & the environment in influencing human characteristics is a very old & hotly contested debate
a single tree has leaves that vary in size, shape & color, depending on exposure to wind & sun
for humans, nutrition influences height, exercise alters build, sun-tanning darkens the skin, and experience improves performance on intelligence tests
even identical twins — genetic equals — accumulate phenotypic differences as a result of their unique experiences
Coat color in arctic fox influenced by heat sensitive alleles
Color of Hydrangea flowers is influenced by soil pH

21. What are linked genes?
There are more genes in a cell than there are chromosomes in a cell
What does that mean?
Each chromosome contains MANY genes
Genes that are close together on the same chromosome tend to be inherited TOGETHER = linked genes

22. Genetic Recombination
Independent assortment of chromosomes and crossing over produce genetic recombinants
Genetic recombination
Production of offspring with new combinations of traits different from those combinations found in parents
Results from events of meiosis and random fertilization

23. Linked Genes
Tend to be inherited together since they are located on the same chromosome
Do not assort independently

24. F1 Generation of Linked genes:
Looks normal so far...
All of F1 offspring show dominant traits

25. When F1 generation is test crossed (mated with homozygous recessive), we would expect 1:1:1:1 ratio

26. Results of Morgan’s testcross
Wild type
Double mutant
Gray body
Normal Wings
Black Body
Vestigal Wings P
b+b+ vg+vg+
bb vgvg

27. P X F1 bb vgvg b+b+ vg+vg+ Black Body Gray body Vestigal Wings
Wild type
Double mutant
bb vgvg
b+b+ vg+vg+ P
Testcross
Black Body
Vestigal Wings
Gray body
Normal wings X F1
bb vgvg
b+b vg+vg

28. F1 X F2 Expected Observed Gray body Normal wings Black Body
Testcross
Black Body
Vestigal Wings F1 X
b+b vg+vg
bb vgvg F2
Gray
Normal
Black
Vestigal
Gray
Vestigal
Black
Normal
b+b vg+vg
bb vgvg
b+b vgvg
bb vg+vg
Expected
575
575
575
575
Observed
965
944
206
185

29. F1 X Recombinants Parentals F2 Expected Observed Gray body
Normal wings
Testcross
Black Body
Vestigal Wings F1 X
b+b vg+vg
bb vgvg
Recombinants
Parentals F2
Gray
Normal
Black
Vestigal
Gray
Vestigal
Black
Normal
b+b vg+vg
bb vgvg
b+b vgvg
bb vg+vg
Expected
575
575
575
575
Observed
965
944
206
185

30. Results of testcross b b vg+ vg b+ b vg+ vg b b vg vg b+ b vg vg
Phenotypes
Genotypes
Expected results if genes are unlinked
Expected results if genes are totally linked
Actual results
Black normal
b b vg+ vg
Gray normal
b+ b vg+ vg
Black vestigial
b b vg vg
Gray vestigial
b+ b vg vg

31. Results of testcross b b vg+ vg 575 b+ b vg+ vg b b vg vg b+ b vg vg
Phenotypes
Genotypes
Expected results if genes are unlinked
Expected results if genes are totally linked
Actual results
Black normal
b b vg+ vg
575
Gray normal
b+ b vg+ vg
Black vestigial
b b vg vg
Gray vestigial
b+ b vg vg

32. Results of testcross b b vg+ vg 575 b+ b vg+ vg 1150 b b vg vg
Phenotypes
Genotypes
Expected results if genes are unlinked
Expected results if genes are totally linked
Actual results
Black normal
b b vg+ vg
575
Gray normal
b+ b vg+ vg
1150
Black vestigial
b b vg vg
Gray vestigial
b+ b vg vg

33. Results of testcross b b vg+ vg 575 206 b+ b vg+ vg 1150 965 b b vg vg
Phenotypes
Genotypes
Expected results if genes are unlinked
Expected results if genes are totally linked
Actual results
Black normal
b b vg+ vg
575
206
Gray normal
b+ b vg+ vg
1150
965
Black vestigial
b b vg vg
944
Gray vestigial
b+ b vg vg
185

34. If 50% of offspring are recombinants of parentals
2 genes are on different chromosomes (not linked)
it is expected result if 2 genes assort independently
If there is a high proportion of parental phenotypes
linkage between genes is likely

35. Recombination frequency
Total number of flies observed
= 2300
Total number of recombinant flies
= 391
Recombinant frequency
391 ÷ 2300 = .17
.17 x 100 = 17%

36. 17% of Morgan’s flies were recombinants
linkage is probably incomplete
Some mechanism occasionally breaks linkage between two genes
Crossing over during meiosis accounts for recombination of linked genes

37. Using Recombination Frequencies to construct Chromosome Map
Recombination frequencies between genes help map sequence of linked genes on particular chromosomes
Morgan’s Drosophila studies showed some genes linked more tightly than others
Recombination frequency between b and vg loci = 17%
Recombination frequency between b and cn = 9%
If crossing over occurs randomly, probability of crossing over between two genes is directly proportional to distance between them
One map unit = 1% recombination frequency
Map units are called centimorgans

38. Establish relative distance between genes farthest apart or with highest recombination frequency
Consider two possible placements of 3rd gene

39. Results of this cross are shown below: Phenotype Genotype Observed #
In Drosophila, curled wings and dark bodies are mutant traits. In a dihybrid testcross, a curled winged, dark bodied fly was crossed with a heterozygous normal bodied, normal winged fly.
Results of this cross are shown below:
Phenotype
Genotype
Observed #
Curled, dark
cucu ee
389
Normal, normal
cu+cy e+e
414
Curled, normal
cucu e+e
104
Normal, dark
cu+cu ee 93
AP Biology

40. Identify the parentals and recombinants Phenotype Genotype Observed #
Curled, dark
cucu ee
389
Normal, normal
cu+cy e+e
414
Curled, normal
cucu e+e
104
Normal, dark
cu+cu ee 93
AP Biology

41. Identify the parentals and recombinants
Calculate recombinant frequency
Phenotype
Genotype
Observed #
Curled, dark
cucu ee
389
Normal, normal
cu+cy e+e
414
Curled, normal
cucu e+e
104
Normal, dark
cu+cu ee 93
AP Biology

42. Identify the parentals and recombinants
Calculate recombinant frequency
= 197
(197÷1000) x 100 = 19.7
Calculate map units between two genes
Phenotype
Genotype
Observed #
Curled, dark
cucu ee
389
Normal, normal
cu+cy e+e
414
Curled, normal
cucu e+e
104
Normal, dark
cu+cu ee 93
AP Biology

43. Identify the parentals and recombinants
Calculate recombinant frequency
= 197
(197÷1000) x 100 = 19.7
Calculate map units between two genes
Map units = 19.7
Phenotype
Genotype
Observed #
Curled, dark
cucu ee
389
Normal, normal
cu+cy e+e
414
Curled, normal
cucu e+e
104
Normal, dark
cu+cu ee 93
AP Biology