1. Beyond Mendel’s Laws of Inheritance

2. Extending Mendelian genetics
Mendel worked with a simple system
peas are genetically simple
most traits are controlled by a single gene
each gene has only 2 alleles, 1 of which is completely dominant to the other
The relationship between genotype & phenotype is rarely that simple

3. 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

4. It’s like flipping 2 pennies!
Incomplete dominance X P
true-breeding
red flowers
true-breeding
white flowers
100%
100% pink flowers F1
generation
(hybrids)
It’s like flipping 2 pennies!
self-pollinate
25%
white F2
generation
red
1:2:1
50%
pink

5. 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

6. 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

7. Pleiotropy Most genes are pleiotropic
Remember
The
Foxes!
Most genes are pleiotropic
one gene affects more than one phenotypic character
1 gene affects more than 1 trait
dwarfism (achondroplasia)
gigantism (acromegaly)
The genes that we have covered so far affect only one phenotypic character, but most genes are pleiotropic

8. Acromegaly: André the Giant

9. Inheritance pattern of Achondroplasia
Aa x aa
Aa x Aa
dominant inheritance a a A a  Aa Aa AA Aa A A
dwarf
dwarf
lethal a aa aa a Aa aa
50% dwarf:50% normal or 1:1
67% dwarf:33% normal or 2:1

10. How would you know that difference wasn’t random chance?
Epistasis
One gene completely masks another gene
coat color in mice = 2 separate genes
C,c: pigment (C) or no pigment (c)
B,b: more pigment (black=B) or less (brown=b)
cc = albino, no matter B allele
9:3:3:1 becomes 9:3:4
B_C_
B_C_
bbC_
bbC_
_ _cc
_ _cc
How would you know that difference wasn’t random chance?
Chi-square test!

11. Epistasis in Labrador retrievers
2 genes: (E,e) & (B,b)
pigment (E) or no pigment (e)
pigment concentration: black (B) to brown (b)
eebb
eeB–
E–bb
E–B–

12. 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

13. Skin color: Albinism
Johnny & Edgar Winter
However albinism can be inherited as a single gene trait
aa = albino
albino Africans
melanin = universal brown color
enzyme
tyrosine
albinism
melanin

14. OCA1 albino
Bianca Knowlton

15. Sex linked traits 1910 | 1933 Genes are on sex chromosomes
Discovered by T.H. Morgan at Columbia U.
Drosophila breeding
good genetic subject
prolific breeders/2 week generations
4 pairs of chromosomes
XX=female, XY=male

16. Classes of chromosomes
autosomal chromosomes
sex chromosomes

17. Discovery of sex linkage
true-breeding
red-eye female
true-breeding
white-eye male X P
Huh! Sex matters?!
100%
red eye offspring F1
generation
(hybrids)
100%
red-eye female
50% red-eye male
50% white eye male F2
generation

18. What’s up with Morgan’s flies?x x RR rr Rr Rr  r r R r R Rr Rr R RR Rr
Doesn’t work that way! R Rr Rr r Rr rr
100% red eyes
3 red : 1 white

19. 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

20. Let’s reconsider Morgan’s flies…x x
XRXR
XrY
XRXr
XRY Xr Y XR Y  XR XR
XRXr
XRY
XRXR
XRY
BINGO! XR Xr
XRXr
XRY
XRXr
XrY
100% red females
50% red males; 50% white males
100% red eyes

21. 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.

22. 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
Sex-linked
usually means “X-linked”
more than 60 diseases traced to genes on X chromosome

23. 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)

24. 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 in each cell
patchwork trait = “mosaic”
patches of black
XH
XHXh
Xh
tricolor cats can only be female
patches of orange

25. 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
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
Color of Hydrangea flowers is influenced by soil pH

26. You Young Kids With Your Rap Musics

27. Any Questions?

28. Review Questions

29. 1. Three babies were recently mixed up in a hospital
1. Three babies were recently mixed up in a hospital. After consideration of the data below, which of the following represent the correct baby/parent combinations?
Couple #
Blood groups I
A and A II
A and B
III
B and O
Baby # 1 B 2 O 3 AB
I-3, II-1, III-2
I-1, II-3, III-2
I-2, II-3, III-1
I-2, II-1, III-3
I-3, II-2, III-1
Answer: c
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #49

30. 2. A mother with type B blood has two children, one with type A blood and one with type O blood. Her husband has type O blood. Which of the following could you conclude from this information?
The husband could not have fathered either child.
The husband could have fathered both children.
The husband must be the father of the child with type O blood and could be the father of the type A child.
The husband could be the father of the child with type O blood, but not the type A child.
Neither the mother nor the husband could be the biological parent of the type A child.
Answer: d
Source: Taylor - Student Study Guide for Biology, Seventh Edition, Test Your Knowledge Question #14

31. 3. Vermilion eyes is a sex-linked recessive characteristic in fruit flies. If a female having vermilion eyes is crossed with a wild-type male, what percentage of the F1 males will have vermilion eyes? 0%
25%
50%
75%
100%
Answer: e
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #3

32. 4. Barring in chickens is due to a sex-linked dominant gene (B)
4. Barring in chickens is due to a sex-linked dominant gene (B). The sex of chicks at hatching is difficult to determine, but barred chicks can be distinguished from nonbarred at that time. To use this trait so that at hatching all chicks of one sex are barred, what cross would you make?
barred males  barred females
barred males  nonbarred females
nonbarred males  barred females
nonbarred males  nonbarred females
Answer: b
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #21

33. 5. A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color-blind marries a color-blind male. What is the probability that this couple’s son will be color-blind?
1/4
1/2
3/4 1
Answer: c
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #29

34. 6. An achondroplastic dwarf man with normal vision marries a color-blind woman of normal height. The man's father was six feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive. How many of their female children might be expected to be color-blind dwarfs? *
all
none
half
one out of four
three out of four
Answer: b
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #32
Discussion Notes for the Instructor
There are several questions which can be asked to guide the discussion of this question, including:
Are these genes linked?
Are the phenotypes of the individual parents useful?
What are the genotypes of the individuals involved?
Using these questions as an outline, discussion of the choices might look like this:
Choice A, in order for all the female offspring to be color-blind the man would have to be color-blind
Choice B, correct
Choice C, since red-green colorblindness is an X-linked recessive the female offspring can only be color-blind if the father is also color-blind
Choice D, since red-green colorblindness is an X-linked recessive the female offspring can only be color-blind if the father is also color-blind
Choice E, since red-green colorblindness is an X-linked recessive the female offspring can only be color-blind if the father is also color-blind
This discussion could be followed by just looking at dwarfism or color-blindness in the male or female offspring.

35. 7. An achondroplastic dwarf man with normal vision marries a color-blind woman of normal height. The man's father was six feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive. How many of their male children would be color-blind and normal height?
all
none
half
one out of four
three out of four
Answer: c
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #33

36. 8. In cats, black color is caused by an X-linked allele; the other allele at this locus causes orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?
tortoiseshell female; tortoiseshell male
black female; orange male
orange female; orange male
tortoiseshell female; black male
orange female; black male
Answer: d
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #38

37. 9. Red-green color blindness is a sex-linked recessive trait in humans
9. Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?
XcXc and XcY
XcXc and XCY
XCXC and XcY
XCXC and XCY
XCXc and XCY
Answer: e
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #43

38. 10. A color-blind son inherited this trait from his
mother.
father.
mother only if she is color-blind.
father only if he is color-blind.
mother only if she is not color-blind.
Answer: a
Source: Taylor - Student Study Guide for Biology, Seventh Edition, Test Your Knowledge Question #9

39. 11. In cattle, roan coat color (mixed red and white hairs) occurs in the heterozygous (Rr) offspring of red (RR) and white (rr) homozygotes. When two roan cattle are crossed, the phenotypes of the progeny are found to be in the ratio of 1 red:2 roan:1 white. Which of the following crosses could produce the highest percentage of roan cattle? *
red  white
roan  roan
white  roan
red  roan
All of the above crosses would give the same percentage of roan.
Answer: a
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #10
Discussion Notes for the Instructor
There are several questions which can be asked to guide the discussion of this question, including:
What genotype produces a “roan” phenotype?
What cross would produce the greatest percentage of this genotype?
What type of inheritance does this show?
Using these questions as an outline, discussion of the choices might look like this:
Choice A, correct; this cross will produce 100% roan offspring
Choice B, roan X roan will produce only 50% roan offspring
Choice C, white X roan will produce only 50% roan offspring
Choice D, red X roan will produce only 50% roan offspring
Choice E, only choice A will produce 100% roan offspring

40. 12. You think that two alleles for coat color in mice show incomplete dominance. What is the best and simplest cross to perform in order to support your hypothesis?
a testcross of a homozygous recessive mouse with a mouse of unknown genotype
a cross of F1 mice to look for a 1:2:1 ratio in the offspring
a reciprocal cross in which the sex of the mice of each coat color is reversed
a cross of two true-breeding mice of different colors to look for an intermediate phenotype in the F1
a cross of F1 mice to look for a 9:7 ratio in the offspring
Answer: d
Source: Taylor - Student Study Guide for Biology, Seventh Edition, Test Your Knowledge Question #11