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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:

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mendelian genetics
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:

Skills you acquire  offspring

Modern genetics:

Mendel 1865: “Experiments in Plant Hybridization”

Discovered in 1900

Darwin 1859: “Origin of Species”

mendelian genetics2
Mendelian Genetics

Garden Pea

  • Different
  • True-breeding
  • Easy to grow.
  • Monoecious

Cross-fertilization:

P1 x P2 F1 Hybrid

Self-fertilization:

P1 x P1 P1

What about beans?

Page 183 Figure 11.2

mendel s results
Mendel’s Results
  • Parents factors  offspring

Genes

  • Offspring receive two factors

Alleles

  • Not all factors identical

Fertilization

Crossing Over

Independent Assortment

  • One allele from each parent

In the egg and sperm

  • Presence of allele does not mean trait expressed.

Phenotype vs Genotype

Dented and Smooth Pea SeedCoat

DD

Page 184 Figure 11.3

DD

modern genetics
Modern Genetics

Heredity:transfer of traits

parent  offspring

Trait:characteristic (green seed)

Gene:unit of heredity (G)

Locus:physical location of gene

Phenotype:physical appearance (green,

yellow)

Genotype:alleles from mother and father

(Gg)

Allele:alternate forms of a gene

(G or g)

Dominant Allele:(R)

covers recessive allele expression

Recessive Allele: (r)

Page 185 Figure 11.4

modern genetics5
Modern Genetics

Homozygous: identical alleles at locus.

Homozygous Dominant =RR

Homozygous Recessive =rr

Heterozygous: different alleles at locus

Rr

solving genetic problems
Solving Genetic Problems

Punnett Square Method:

  • Determine dominant characteristic (Red Flower)
  • Code alleles (R&r)
  • Determine parental genotype and gametes

Genotypes=RR,Rrorrr, gametes=Rorr

  • Assign gamete frequency

Each gamete has 50% (1/2 or .5) chance of being R or r

  • Draw and fill in Punnett Square
    • List all possible sperm on one axis
    • List all possible eggs on other axis
    • List all offspring in the squares

Female Eggs

r

R

Sperm

RR

Rr

R

r

rR

rr

monohybrid cross 1 gene complete dominance
Monohybrid Cross (1 gene): Complete Dominance

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

Parents

Rr = F1 generation

offspring = 100%

heterozygous red flower

r r

R

Rr Rr

Rr Rr

R

monohybrid cross complete dominance example
Monohybrid Cross: Complete DominanceExample
  • Cross two heterozygous red (Rr) F1 offspring.
  • What is the genotype and phenotype of their F2 offspring?
  • Parental genotypes = Rrx Rr
  • Assign gametes
  • Assign offspring
    • genotypes
  • Assign phenotypes
  • Results:
    • 1 RR = 25%
    • 2 Rr = 50%
    • 1 rr = 25%
  • Genotypic Ratio = 1:2:1
  • Phenotypic Ratio = 3:1

Eggs

R (.5)r (.5)

Sperm

100%

R(.5)

Rr (.25)

RR (.25)

Heterozygous

Red Flower

Homozygous Dominant

Red Flower

Rr (.25)

rr (.25)

r(.5)

Heterozygous

Red Flower

Homozygous Recessive

White Flower

one gene testcross complete dominance example
One Gene Testcross: Complete DominanceExample

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)

Rrxrr

RRxrr

Phenotypic Ratio

1:0

Phenotypic Ratio

1:1

r

r

Rr

Red

Rr

Red

R

R

rr

White

r

single gene complete dominant ratios
Single Gene Complete Dominant Ratios

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?

single gene example 1
Single Gene: Example 1

Problem: Cross a red rose and a white rose. Self 6 F1 plants. Count the red and white flower offspring from each F1 selfed.

F1 SelfedRedWhite

1 5 19

2 9 13

3 4 21

4 4 15

5 8 15

6 4 25

34 108

  • What is the inheritance of white flower color?
  • Which color is dominant?
  • What are the genotypes of the parents and F1?
single gene example 2
Single Gene: Example 2

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):

OffspringParental

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?

dihybrid example complete dominance
Dihybrid Example: Complete Dominance

Parents RRTT x rrtt

(gametes) (RT)(rt)

F1 hybrid RrTt x RrTt

Eggs (F1 gametes)

¼ RT ¼ Rt ¼ rT ¼ rt

Sperm

(F1 gametes)

Phenotypic Ratio

9 Red-Tall

3 Red-Short

3 White-Tall

1 White-Short

16

¼ RT

RRTT

Red-Tall

RRTt

Red-Tall

RrTT

Red-Tall

RrTt

Red-Tall

¼ Rt

RRTt

Red-Tall

RRtt

Red-Short

RrTt

Red-Tall

Rrtt

Red-Short

F2 hybrids

RrTT

Red-Tall

RrTt

Red-Tall

rrTT

Wht-Tall

rrTt

Wht-Tall

¼ rT

Rrtt

Red-Short

rrtt

Wht-Short

RrTt

Red-Tall

rrTt

Wht-Tall

¼ rt

dihybrid testcross
Dihybrid Testcross

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

1:1:1:1

rt rt rt rt

rt rt rt rt

RT

RT

RrTt

RrTt

Red-Tall

RT

Rrtt

Red-Short

Rt

RT

rT

rrTt

White-Tall

RT

rt

rrtt

White-Short

autosomal dominant complete dominance
Autosomal Dominant: Complete Dominance

Autosome: Chromosomes other than sex (X & Y) chromosomes.

Caused by dominant or recessive alleles inherited from parents.

Page 192 Figure 11.11

autosomal recessive complete dominance
Autosomal Recessive: Complete Dominance

Autosome: chromosomes other than sex (X & Y) chromosomes.

Page 192 Figure 11.10

autosomal disorders in humans
Autosomal Disorders in Humans

Recessive

  • Tay-Sachs Disease (1/3,600)
    • Deterioration of psychomotor functions.
    • Lack enzyme.
  • Cystic Fibrosis (1/3,000)
    • Mucus in bronchial tubes.
    • Cl- can’t pass plasma membrane.
  • Phenylketonuria (1/5,000)
    • Lack enzyme for metabolism of phenylalanine.

Dominant

  • Neurofibromatosis (1/3,500)
    • Tan or dark spots on skin, small benign tumors.
    • Chromosome 17 gene.
  • Huntington Disease (1/20,000)
    • Degeneration of brain cells, muscle spasms and personality disorders.
    • Chromosome 4.
incomplete dominance
Incomplete Dominance

Heterozygote has an

intermediate phenotype.

Dominant allele does not cover the recessive allele.

Example:

Primrose, four-o’clock and

snapdragon flowers

Red Flower x White Flower

1 red flower

2 pink flowers

1 white flower

Page 196 Figure 11.14

incomplete dominance in humans
Incomplete Dominance in Humans
  • Sickle-Cell
    • Irregular red blood cells vs biconcave.
    • Glutamate (GAG) vsValine (GUG)
      • HbAHbA = normal
      • HbSHbS = sickle-cell
      • HbAHbS = sickle cell trait
      • (little or no disease
      • symptoms)

Pitch of male voice.

H1H1 = base

H1H2 = baritone

H2H2 = tenor

Straight vs curly hair.

H1H1 = curly

H1H2 = wavy

H2H2 = straight

multiple alleles human blood type
Multiple Alleles: Human Blood Type

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

  • Multiple Alleles:
  • More than 2 alleles of a gene.
  • Codominance:
  • More than 1
  • allele expressed at
  • once.

Page 197 Figure 11.15

human blood type
Human Blood Type

Blood Cellular Plasma

Type %AntigensDonate ToAntibodiesReceive From

O+ 38% None O, A, B, AB anti-A, anti-B O

O- 7%

A+ 34% A A & AB anti-B O & A

A- 6%

B+ 9% B B & AB anti-A O & B

B- 2%

AB+ 3% A & B AB None O, A, B, AB

AB- 1%

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.

one locus vs two loci vs many loci
One Locus vs Two Loci vs Many Loci

Two Loci

One Locus

Normal Distribution or Bell Curve

Many Loci

polygenic inheritance human height
Polygenic Inheritance: Human Height

Polygenic Inheritance: 2 or more genes (sets of alleles)

dominant allele has additive effect on phenotype

Page 198 Figure 11.17

_

X

Short

Tall

Human Height: Very Short = aabbcc

Short = Aabbcc

Medium Short = AaBbcc

Medium = AaBbCc

Medium Tall = AABbCc

Tall = AABBCc

Very Tall = AABBCC

polygenic inheritance
Polygenic Inheritance

Human Traits:

Height

Stature

Body shape

Hair color

Skin color:

Each dominant allele

increases the color

of the skin.

AABBCC = Very Dark

aabbcc = Very Light

epistasis
Epistasis

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

E_

ee

eebb

yellow fur

brown nose,

lips, eye rim

eeB_

yellow fur

black nose,

lips, eye rim

E_bb

chocolate Lab

brown fur, nose,

eye rim

E_B_

Black fur,

Nose, lips,

Eye rim

environmental effect on phenotype
Environmental Effect on Phenotype

Flower color: primrose

White above 32oC

Red at 24oC

Uterus effect on fertilized egg

Health of mother

Oxygen

Hormones

Medication

Cataracts

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

biochemical genotypes and phenotypes dna markers
Biochemical Genotypes and PhenotypesDNA Markers

F1 generation will be all A1A2 and F2 generation will be 1:2:1 ratio

summary
Summary
  • Complete Dominance: (R dominant overr)
    • Monohybrid (Rr)
    • Dihybrid (RrTt)
    • Autosomal Dominant (RR or Rr)
    • Autosomal Recessive (rr)
  • Incomplete Dominance: (Rrdiffers RR&rr)
  • Co-dominance: (blood type: IA and IB) both

genes expressed

  • Multiple Alleles: (blood type A,B,and O)
  • Polygenic: alleles are additive (A,B,C,D,E,etc.)
  • Environmental Effect: