1. Genetics & The Work of Mendel

2. Gregor Mendel
Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas
used good experimental design
used mathematical analysis
collected data & counted them
excellent example of scientific method
He studied at the University of Vienna from 1851 to 1853 where he was influenced by a physicist who encouraged experimentation and the application of mathematics to science and a botanist who aroused Mendel’s interest in the causes of variation in plants. After the university, Mendel taught at the Brunn Modern School and lived in the local monastery.
The monks at this monastery had a long tradition of interest in the breeding of plants, including peas. Around 1857, Mendel began breeding garden peas to study inheritance.

3. Mendel’s work Bred pea plants ? cross-pollinate true breeding parents
Pollen transferred from white flower to stigma of purple flower
Bred pea plants
cross-pollinate true breeding parents
raised seed & then observed traits
allowed offspring to self-pollinate & observed next generation
all purple flowers result
P = parents
F = filial generation
self-pollinate ?

4. Mendel collected data for 7 pea traits

5. Looking closer at Mendel’s work
true-breeding
purple-flower peas
true-breeding
white-flower peas X
Parents
100%
1st
generation
(hybrids)
purple-flower peas
In a typical breeding experiment, Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties.
The true-breeding parents are the P generation and their hybrid offspring are the F1 generation.
Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 generation.
self-pollinate
2nd
generation
3:1
75%
purple-flower peas
25%
white-flower peas

6. What did Mendel’s findings mean?
Some traits mask others
purple & white flower colors are separate traits that do not blend
purple x white ≠ light purple
purple masked white
dominant allele
functional protein
affects characteristic
masks other alleles
recessive allele
no noticeable effect
allele makes a non-functioning protein
I’ll speak for both of us!
allele producing functional protein
mutant allele malfunctioning protein
homologous chromosomes

7. Genotype vs. phenotype
Difference between how an organism “looks” & its genetics
phenotype
description of an organism’s trait
genotype
description of an organism’s genetic makeup F1 P X
purple
white
all purple
Explain Mendel’s results using
…dominant & recessive
…phenotype & genotype

8. PP pp Pp x Making crosses Can represent alleles as letters
flower color alleles  P or p
true-breeding purple-flower peas  PP
true-breeding white-flower peas  pp F1 P X
purple
white
all purple PP x pp Pp

9. phenotype & genotype can have different ratios
Aaaaah,
phenotype & genotype can have different ratios
Punnett squares
Pp x Pp
1st
generation
(hybrids) %
genotype %
phenotype P p
male / sperm PP
25%
75% Pp
50% P p
female / eggs PP Pp Pp Pp pp
25%
25% pp
1:2:1
3:1

10. Any Questions??

11. Beyond Mendel’s Laws of Inheritance

12. Extending Mendelian genetics
Mendel worked with a simple system
peas are genetically simple
most traits are controlled by single gene
each gene has only 2 version
1 completely dominant (A)
1 recessive (a)
But its usually not that simple!

13. Incomplete dominance Hybrids have “in-between” appearance RR WW RW
RR = red flowers
rr = white flowers
Rr = pink flowers
make 50% less color
RR
WW
RW RR Rr rr

14. Incomplete dominance P 1st 100% 1:2:1 2nd X true-breeding red flowers
white flowers
100%
100% pink flowers
1st
generation
(hybrids)
self-pollinate
25%
white
2nd
generation
25%
red
1:2:1
50%
pink

15. Incomplete dominance RW x RW RR R W RW RR RW R W RW WW RW WW 25% 25%
genotype %
phenotype RR
25%
25% R W
male / sperm
50%
50% RW RR RW R W
female / eggs RW WW
25%
25% RW WW
1:2:1
1:2:1

16. Codominance Equal dominance human ABO blood groups 3 version
A, B, i
A & B alleles are codominant
both A & B alleles are dominant over i allele
the genes code for different sugars on the surface of red blood cells
“name tag” of red blood cell

17. Genetics of Blood type A A A or A i B BB or B i AB O i i pheno-type
genotype
antigen on RBC
antibodies in blood
donation status A
A A or A i
type A antigens on surface of RBC
anti-B antibodies __ B
BB or B i
type B antigens on surface of RBC
anti-A antibodies AB
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

18. Blood donation clotting clotting clotting clotting clotting clotting

19. One gene: many effects
The genes that we have covered so far affect only one trait
But most genes are affect many traits
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

20. Acromegaly: André the Giant

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

22. Many genes: one trait Polygenic inheritance
additive effects of many genes
humans
skin color
height
weight
eye color
intelligence
behaviors

23. Human skin color AaBbCc x AaBbCc can produce a wide range of shades
most children = intermediate skin color
some can be very light & very dark

24. Albinism Johnny & Edgar Winter albino Africans
melanin = universal brown color

25. OCA1 albino
Bianca Knowlton

26. Coat color in other animals
2 genes: E,e and B,b
color (E) or no color (e)
how dark color will be: black (B) or brown (b)
eebb
eeB–
E–bb
E–B–

27. Environment effect on genes
Phenotype is controlled by both environment & genes
Coat color in arctic fox influenced by heat sensitive alleles
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
Color of Hydrangea flowers is influenced by soil pH

28. Genetics of sex
Women & men are very different, but just a few genes create that difference
In mammals = 2 sex chromosomes
X & Y
2 X chromosomes = female: XX
X & Y chromosome = male: XY X X X Y

29. Sex chromosomes

30. Sex-linked traits Sex chromosomes have other genes on them, too X X X
especially the X chromosome
hemophilia in humans
blood doesn’t clot
Duchenne muscular dystrophy in humans
loss of muscle control
red-green color blindness
see green & red as shades of grey X X
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. X Y

31. Sex-linked traits HH XHY XHXh Hh x XHY Y XH XH Y XHXH XHXH XHY XHY XH
sex-linked recessive HH
XHY
XHXh Hh
2 normal parents,
but mother is carrier x
XHY Y XH XH Y
male / sperm
XHXH
XHXH
XHY
XHY XH Xh
female / eggs
XHXh XH Xh
XHXh
XHXh
XhY
XhY

33. 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.

34. Dominant ≠ most common allele
Because an allele is dominant does not mean…
it is better, or
it is more common
Polydactyly
dominant allele

35. Polydactyly recessive allele far more common than dominant
individuals are born with extra fingers or toes
the allele for >5 fingers/toes is DOMINANT & the allele for 5 digits is recessive
recessive allele far more common than dominant
 only 1 individual out of 500
has more than 5 fingers/toes
 so 499 out of 500 people are homozygous recessive (aa)

36. Hound Dog Taylor

37. Any Questions?