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Genetics
Gregor Mendel
• 1840’s
• Austrian Monk
• Tended garden, became interested in
characteristics of plants
• “Father of Genetics”
2 laws of Heredity
• 1-Law of segregation
• 2-Law of independent assortment
Mendel and his Peas
• Analyzed 7
characteristics (traits) of
pea plants….size, color,
seed texture, flowers
present, height
• Cross-pollinated various
traits to view outcome
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Fig. 23Aa
Flower Structure
stamen
anther
filament
stigma
style
Ovules
in ovary
carpel
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Cutting away
anthers
Cross Pollination vs. Self Pollination
Fig. 23Ab
Brushing on
pollen from
another plant
All peas are yellow when
one parent produces yellow
seeds and the other parent
produces green seeds.
What he noticed…
• Tall plants mixed with short plants always produced tall plants
• However….the offspring of the above plants sometimes
produced short plants in the 2nd generation
What does this mean?
• If a tall plant mixes with a short plant and the
offspring are all tall, tall must be a DOMINANT
TRAIT and the tall parents must have been
PURE BRED
Punnet Square
• Used to show probability of trait expression
when combining 2 parents genes (F1
generation)
• T-tall
• t-short
When offspring self pollinated….why
were some short?
• The offspring of the self pollinated pea plants
produced short plants because they were not
TRUE BREEDING (pure bred), they had a
recessive short gene hidden. (F2 generation)
• T-tall
• t-short
Allele
Gene for a specific trait
*Everyone has 2 alleles for a specific trait (1
from mom and 1 from dad)
If a pea plant height is Tt, they got one T from
one parent and the t from the other parent
Dominant and Recessive Alleles
• Dominant alleles will be expressed (you will
SEE the trait) over the recessive allele
• Recessive alleles will be hidden by the
dominant allele but will still be a part of the
persons genotype (gene combination for a
specific trait)
• The only way a recessive allele will be
expressed is in the absence of a dominant
allele or when 2 recessive alleles are present.
Vocab for alleles
• Homozygous dominant, pure bred dominant,
true breeding dominant-ALL mean that the
genotype is 2 dominant genes (TT)
• Homozygous recessive, pure bred recessive,
true bred recessive-ALL mean that the
genotype is 2 recessive genes (tt)
• Heterozygous-Alleles for a genotype are
different, one recessive, one dominant (Tt)
*Can also be called HYBRID
Genotype and Phenotype
• Genotype-gene or allele combination for a
specific trait
• Phenotype-what characteristic is physically
seen from the genotype
• Can be expressed in ratios or percentages
• Ex- Tt is genotype, Tall is the phenotype
Practice Punnets
• Round seeds in pea plants are dominant to
wrinkled seeds. Self fertilize a heterozygous
pea plant. R-round, r-wrinkled
• Genotype:
• Phenotype:
• Purple are dominant flowers in pea plants
over white flowers. Cross a homozygous
dominant, with a homozygous recessive.
• Purple-P, white-p
• Genotype:
• Phenotype:
• Yellow seeds are dominant to green seeds in
pea plants. Cross a homozygous recessive
with a heterozygous. Y-yellow, y-green
• Genotype:
• Phenotype:
Mendel's Laws
• 1-Law of segregation…..Alleles split into each
offspring box
• 2-Law of independent assortment…..alleles
sort out randomly in each offspring box
completely independent of other genes (by
chance)
In humans
•
•
•
•
•
Eye color
Ears
Widows peak
Pinky fingers
Interlocking fingers??? (weird)
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Fig. 23.6
one pair
S
Cell has
two pairs of
homologues.
W
Allele Key
W = Widow’s peak
w = Straight hairline
S = Short fingers
s = Long fingers
s
w
either
S
S
Ss
s
W
W
w
w
or
one pair
S
Ss
s
w
W
w
W
MEIOSIS I
S
s
s
S
S
s
w
w
W
s
MEIOSIS II
W
W
S
w
s
S
W
w
W
s
w
S
w
S
w
W
s
w
s
W
W
3
SW
sw
Sw
sW
•
Is it possible to get a white
flowered pea plant from 2 purple
flowered plants?
Try These!!
• Cross a pure bred tall plant with a
heterozygous tall plant. List genotypes and
phenotypes
• Cross a heterozygous round seeded plant with
a wrinkled seeded plant. List genotypes and
phenotypes
Is it possible to do a punnett square
using more than one trait?
• Try this one….cross a heterozygous purple
plant, homozygous tall plant with a
homozygous white plant, heterozygous tall
plant. List genotypes and phenotypes
Co-Dominance
Try this one:
• Fur color in cats is co-dominant. Cross a Black
male with an Orange female.
• *When you are done….Cross 2 orange cats…
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Incomplete Dominance
Fig. 23.13
A person with straight hair
(H1H1)
Heterozygous
Parents (H1 H2)
A person with naturally curly
hair (H1H1)
♀
H1 H2

Straight hair
Wavy hair
Curly hair
oocytes
♀
H1
H2
H1 H1
H1 H2
sperm
H1
H2
H1 H2
Key
H1 H2
H2 H2
Phenotypic Ratio
1
2
1
Offspring
(man): © Vol. 88/PhotoDisc; (woman): © Larry Williams/Corbis
Try this one:
Hair color in mice is incompletely dominant.
Cross a Black mouse with a white mouse.
Polygenic
Number of People
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Skin Color
Genetics of Blood Type
Try this one:
• Cross an O blood male with a Heterozygous A
female
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Genes Expressed due to Environmental Factors
Fig. 23.18
© Jane Burton/Bruce Coleman, Inc.
Discovery of sex linkage
P
F1
true-breeding
red-eye female
X
true-breeding
white-eye male
100%
red eye offspring
generation
(hybrids)
F2
generation
100%
red-eye female
50% red-eye male
50% white eye male
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
• X chromosome
– other genes/traits beyond sex determination
• mutations:
– hemophilia
– Duchenne muscular dystrophy
– color-blindness
Human X chromosome
• Sex-linked
– usually means
“X-linked”
– more than
60 diseases traced
to genes on X
chromosome
Duchenne muscular dystrophy
Becker muscular dystrophy
Chronic granulomatous disease
Retinitis pigmentosa-3
Norrie disease
Retinitis pigmentosa-2
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
Ornithine transcarbamylase
deficiency
Incontinentia pigmenti
Wiskott-Aldrich syndrome
Menkes syndrome
Androgen insensitivity
Sideroblastic anemia
Aarskog-Scott syndrome
PGK deficiency hemolytic anemia
Anhidrotic ectodermal dysplasia
Agammaglobulinemia
Kennedy disease
Pelizaeus-Merzbacher disease
Alport syndrome
Fabry disease
Immunodeficiency, X-linked,
with hyper IgM
Lymphoproliferative syndrome
Albinism-deafness syndrome
Fragile-X 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
Sex Linked Traits
• Usually carried on the X
– Color blindness
– Male pattern baldness (sex-influenced trait)
– Hemophilia
Hemophilia
sex-linked recessive
H Xh x X
HY
HH
XHh
XH
female / eggs
male / sperm
XH
XH
Y
XHXH
XHY
XH Xh
Xh
XH
Xh
XHXh
carrier
XhY
XHY
Y
disease
Try this one:
• Cross a color blind male with a normal female