Mendelian Genetics. Genetics: science of heredity and variation Blending Theory: Offspring blend of parents. 6’ father + 5’ mother 5’6” child Pangenesis (Darwin): Particles in body affected by what we do passed to sex cells by blood. Inheritance of acquired characteristics:
Genetics: science of heredity and variation
Offspring blend of parents.
6’ father + 5’ mother 5’6” child
Particles in body affected by what we do passed to sex cells by blood.
Skills you acquire offspring
Mendel 1865: “Experiments in Plant Hybridization”
Discovered in 1900
Darwin 1859: “Origin of Species”
P1 x P2 F1 Hybrid
P1 x P1 P1
What about beans?
Page 183 Figure 11.2
In the egg and sperm
Phenotype vs Genotype
Dented and Smooth Pea SeedCoat
Page 184 Figure 11.3
Heredity:transfer of traits
Trait:characteristic (green seed)
Gene:unit of heredity (G)
Locus:physical location of gene
Phenotype:physical appearance (green,
Genotype:alleles from mother and father
Allele:alternate forms of a gene
(G or g)
covers recessive allele expression
Recessive Allele: (r)
Page 185 Figure 11.4
Homozygous: identical alleles at locus.
Homozygous Dominant =RR
Homozygous Recessive =rr
Heterozygous: different alleles at locus
Punnett Square Method:
Each gamete has 50% (1/2 or .5) chance of being R or r
Assume red flower color is dominant (R) to white flower color (r). You cross a homozygous dominant red flower with a homozygous white flower. What are the offspring?
True Breeding=RR x rr
Rr = F1 generation
offspring = 100%
heterozygous red flower
R (.5)r (.5)
If 100% red flowers from RRxrr Rr
If 100% red flowers from RR xRR RR
How can you tell the genotypes of the parents?
Testcross:determines if dominant phenotype is RRorRr
Tester:homozygous recessive genotype (rr)
uncovers hidden recessive (r)
One Gene Model
3:1 = phenotypic ratio
1:2:1 = genotypic ratio
1:1 = testcross ratio for Rr
1:0 = testcross ratio for RR
Two Gene Model
9:3:3:1 = phenotypic ratio
1:1:1:1 = testcross ratio forRrTt
What is the clue that the trait is controlled by one or two genes?
Problem: Cross a red rose and a white rose. Self 6 F1 plants. Count the red and white flower offspring from each F1 selfed.
1 5 19
2 9 13
3 4 21
4 4 15
5 8 15
6 4 25
Problem: Identify the genotype of the parents for each of the following F1 offspring phenotypes (assume red flower color is dominant and white flower color is recessive):
CrossRedWhite Ratio Genotypes
Red x White 82 78 1:1
Red x Red 118 39 3:1
White x White 0 50 0:1
Red x White 74 0 1:0
Red x Red 90 0 1:0
Whatare the parental genotypes for each cross?
Parents RRTT x rrtt
F1 hybrid RrTt x RrTt
Eggs (F1 gametes)
¼ RT ¼ Rt ¼ rT ¼ rt
If you have 10 red-tall flowers, how can you tell which flowers have the genotype RrTt and which are RRTT?
A testcross will separate them using the rrtt tester.
RRTT x rrtt RrTt x rrtt
All Red-Tall 1:0
rt rt rt rt
rt rt rt rt
Autosome: Chromosomes other than sex (X & Y) chromosomes.
Caused by dominant or recessive alleles inherited from parents.
Page 192 Figure 11.11
Autosome: chromosomes other than sex (X & Y) chromosomes.
Page 192 Figure 11.10
Heterozygote has an
Dominant allele does not cover the recessive allele.
Primrose, four-o’clock and
Red Flower x White Flower
1 red flower
2 pink flowers
1 white flower
Page 196 Figure 11.14
Pitch of male voice.
H1H1 = base
H1H2 = baritone
H2H2 = tenor
Straight vs curly hair.
H1H1 = curly
H1H2 = wavy
H2H2 = straight
A = IAIA, IAi = 42% central and eastern Europe
B = IBIB, IBi = 10% highest on central Asia
AB = IAIB = 3% highest in Japan, China, Pakistan
O = ii = 45% highest Central America, South America,
Australia and Western Europe
Page 197 Figure 11.15
Blood Cellular Plasma
Type %AntigensDonate ToAntibodiesReceive From
O+ 38% None O, A, B, AB anti-A, anti-B O
A+ 34% A A & AB anti-B O & A
B+ 9% B B & AB anti-A O & B
AB+ 3% A & B AB None O, A, B, AB
Rh factor in independent of blood type.
Single dominant gene Rh+.
Rh- mother takes shots if baby is Rh+ mother’s antibodies attack baby’s blood.
Normal Distribution or Bell Curve
Polygenic Inheritance: 2 or more genes (sets of alleles)
dominant allele has additive effect on phenotype
Page 198 Figure 11.17
Human Height: Very Short = aabbcc
Short = Aabbcc
Medium Short = AaBbcc
Medium = AaBbCc
Medium Tall = AABbCc
Tall = AABBCc
Very Tall = AABBCC
Each dominant allele
increases the color
of the skin.
AABBCC = Very Dark
aabbcc = Very Light
Epistasis: gene at one locus interferes with gene at different locus.
Coat color in Labrador retrievers (eumelanin pigment).
E gene: determines if pigment present
B gene: determines how dark the pigment
lips, eye rim
lips, eye rim
brown fur, nose,
Flower color: primrose
White above 32oC
Red at 24oC
Uterus effect on fertilized egg
Health of mother
Dominant gene + modifier gene
Excessive UV light
Right or left handedness
“Everyone is born right handed, only the gifted overcome it”.
DD = Strongly right handed
Dd = Mostly right handed
dd = Either right or left handed
F1 generation will be all A1A2 and F2 generation will be 1:2:1 ratio