Words to know… Heredity - the passing of traits from parent to offspring. Genetics - the study of...

Words to know…• Heredity - the passing of traits from parent to

offspring. • Genetics - the study of heredity.• Trait- a specific characteristic• Gene- chemical factor that determines a trait• Allele- A segment of a gene• Hybrid- the offspring crosses between parents

with different traits

Gregor Mendel• Father of Genetics• He lived in a monastery; He was a teacher and took

care of the garden• Mendel’s knowledge helped us understand

heredity. • He studied the pea plant most of all.

Mendel's Process• Mendel took a true-breeding (or pure) plants

that always produce offspring with the same trait when they self-pollinate and cross pollinated it with a true breeding plant with a different trait.

• The P generation is the true-breeding generation or the parent generation.

Pollination• Self pollination occurs when pollen is

transferred from the anthers (male) of one flower to the stigma (female) of the same flower.

• Cross-pollination occurs between two plants.

• The F1 generation is the offspring of the P generation.

• Mendel called the plants in the second generation the second F2

Mendel established three principles (or Laws) from his research

1. The Principle of Dominance and Recessiveness - one trait is masked or covered up by another trait

2. Principle of Segregation - the two factors (alleles) for a trait separate during gamete formation

3. Principle of Independent Assortment - factors of a trait separate independently of one another during gamete formation; another way to look at this is, whether a flower is purple has nothing to do with the length of the plants stems - each trait is independently inherited

Mendel’s LawsMendel’s Laws

copyright cmassengale 7

Results of Monohybrid CrossesResults of Monohybrid Crosses

• InheritableInheritable factors or genesfactors or genes are are responsible for all heritable responsible for all heritable characteristics characteristics

• PhenotypePhenotype is based on is based on GenotypeGenotype • Each traitEach trait is based onis based on two genestwo genes, , one one

from the mother and the other from the from the mother and the other from the fatherfather

• True-breeding individuals are True-breeding individuals are homozygous ( both alleles)homozygous ( both alleles) are the same are the same


Law of DominanceLaw of Dominance


In a cross of parents that are In a cross of parents that are pure for contrasting traitspure for contrasting traits, , only one form of the trait will only one form of the trait will appear in the next generation.appear in the next generation.

All the offspring will be All the offspring will be heterozygous and express heterozygous and express only the only the dominant trait.dominant trait.

RR x rr RR x rr yieldsyields all Rr (round all Rr (round seeds)seeds)

Law of DominanceLaw of Dominance


Law of SegregationLaw of Segregation

• During the During the formation of gametesformation of gametes (eggs or (eggs or sperm), the sperm), the two allelestwo alleles responsible for a responsible for a trait trait separateseparate from each other. from each other.

• Alleles for a trait are then Alleles for a trait are then "recombined" "recombined" at fertilizationat fertilization, producing the genotype , producing the genotype for the traits of the offspringfor the traits of the offspring.



Applying the Law of SegregationApplying the Law of Segregation

Law of Independent AssortmentLaw of Independent Assortment

• Alleles for Alleles for differentdifferent traits are traits are distributed to sex cells (& offspring) distributed to sex cells (& offspring) independently of one another.independently of one another.

• This law can be illustrated using This law can be illustrated using dihybrid crossesdihybrid crosses..


• Dominant- stronger & mask other genes; the trait that shows up more frequently– represented by a capital letter

• Recessive- “weaker” the trait that shows up less frequently– represented by a lower case letter

• A chromosome is made up of DNA. A gene is a segment of DNA on a chromosome that controls a particular hereditary trait.

• Each of two or more alternative forms of a gene is called an allele. Mendel’s factors are now called an allele.


Mendel stated that Mendel stated that physical traits are physical traits are inherited as inherited as “particles”“particles”Mendel did not know Mendel did not know that the “particles” were that the “particles” were actually actually Chromosomes & Chromosomes & DNADNA

Particulate InheritanceParticulate Inheritance

• Probability is the likelihood that a specific even will occur.

• It is the mathematical chance that something will occur.

Punnett SquarePunnett SquareUsed to help solve Used to help solve genetics problemsgenetics problems


Types of Genetic CrossesTypes of Genetic Crosses

Monohybrid cross Monohybrid cross - - cross involving a cross involving a single traitsingle traite.g. flower color e.g. flower color

Dihybrid crossDihybrid cross - - cross involving two cross involving two traits traits e.g. flower color & plant heighte.g. flower color & plant height


More TerminologyMore Terminology

GenotypeGenotype - - gene combination for a gene combination for a traittrait (e.g. RR, Rr, rr) (e.g. RR, Rr, rr)

PhenotypePhenotype - - the physical feature the physical feature resulting from a genotyperesulting from a genotype (e.g. red, (e.g. red, white) white)


GenotypesGenotypes HomozygousHomozygous genotype - gene genotype - gene

combination involving 2 dominant or 2 combination involving 2 dominant or 2 recessive genes recessive genes (e.g. RR or rr);(e.g. RR or rr); also also calledcalled pure pure

HeterozygousHeterozygous genotype - gene genotype - gene combination of one dominant & one combination of one dominant & one recessive allele (recessive allele (e.g. Rr);e.g. Rr); also called also called hybridhybrid


??????

• What is the phenotype of a heterozygous flower?

• What is the genotype of a heterozygous flower?

• What is the genotype of a homozygous dominant?

Dihybrid CrossDihybrid Cross


RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

Dihybrid CrossDihybrid Cross


RRYY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

RrYY

RrYy

rrYY

rrYy

RrYy

Rryy

rrYy

rryy

Round/Yellow: 9

Round/green: 3

wrinkled/Yellow: 3

wrinkled/green: 1

9:3:3:1 phenotypic ratio

RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

Test CrossTest Cross• A mating between an individual of A mating between an individual of unknown unknown

genotype genotype and a and a homozygous recessivehomozygous recessive individual. individual.


Its not all that easy!

• Multiple alleles- trait that is determined by more than two alleles (ex. Human blood types)

• Polygenic traits- trait influenced by several genes; genes may be on same chromosome or on different one (ex. Human eye color, weight, skin tone)

Incomplete dominance

• The phenotype is in between that of the parents. It is like a mixture (pink flower)

• Example: Snap Dragon

Codominance

• Both alleles are expressed. With Codominance you can see two dominant alleles.

CodominanceCodominance

• Two allelesTwo alleles are expressed ( are expressed (multiple allelesmultiple alleles) in ) in heterozygous individualsheterozygous individuals..

• Example:Example: blood type blood type

• 1.1. type Atype A = I= IAAIIAA or I or IAAii• 2.2. type Btype B = I= IBBIIBB or I or IBBii• 3.3. type ABtype AB = I= IAAIIBB

• 4.4. type Otype O = ii= ii


Codominance ProblemCodominance Problem

• Example: homozygous male Type B (IBIB)• x

heterozygous female Type A (IAi)


IAIB IBi

IAIB IBi

1/2 = IAIB

1/2 = IBi

IB

IA i

IB

Another Codominance ProblemAnother Codominance Problem


• Example:Example: male Type O (ii) x female type AB (IAIB)

IAi IBi

IAi IBi

1/2 = IAi1/2 = IBi

i

IA IB

i

CodominanceCodominance

• QuestionQuestion::If a boy has a blood type O and If a boy has a blood type O and his sister has blood type AB, his sister has blood type AB, what what are the genotypes and are the genotypes and phenotypes phenotypes of their parents?of their parents?

• boy - boy - type O (ii) type O (ii) X girl - X girl - type AB (Itype AB (IAAIIBB))


Thomas Hunt Morgan

• Discovered that females have XX chromosomes and males have XY by studying a fruit fly.

• Sex Chromosomes determine the sex of an organism.

• He discovered that the gene for eye color in fruit flies is a sex linked trait carried on the Y chromosome

Sex-linked TraitsSex-linked Traits• Traits (genes) located on the Traits (genes) located on the sex sex

chromosomeschromosomes• Sex chromosomes are Sex chromosomes are X and YX and Y• XXXX genotype for females genotype for females• XYXY genotype for males genotype for males• Many Many sex-linked traitssex-linked traits carried on carried on XX

chromosomechromosome• The genes interact with other genes The genes interact with other genes

scattered throughout the genomescattered throughout the genomecopyright cmassengale 34

Blood TypeBlood Type Antigen Antibody Can donate to Can receive

from

A

B

AB

O

Karyotype of Kleinfelters and Turners

Pedigree

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