Introduction to GeneticsIntroduction to Genetics

Chapter 11Chapter 11

DNA BasicsDNA Basics1.1. DNA contains the code for making proteins.DNA contains the code for making proteins.2.2. Proteins control the chemistry of life. Proteins control the chemistry of life.

Everything that occurs within a living thing Everything that occurs within a living thing is done through chemistry, thus making is done through chemistry, thus making DNA/proteins vital.DNA/proteins vital.

3.3. DNA is made of base pairs:DNA is made of base pairs:A-TA-T

C-GC-G4.4. The sequence of A, T, C, and G determines The sequence of A, T, C, and G determines

the construction of the particular protein.the construction of the particular protein.5. DNA is inheritable. It is passed on from 5. DNA is inheritable. It is passed on from

generation to generation.generation to generation.

Genes & ChromosomesGenes & Chromosomes

What is a gene?What is a gene?A segment of DNA that codes for a particular protein (trait).

Where are genes found?Where are genes found?On a particular location on a chromosome called a locus.

Genes & ChromosomesGenes & ChromosomesWhat does diploid mean?What does diploid mean?1. Chromosomes come in pairs.Chromosomes come in pairs.2. The pairs are calledThe pairs are called

homologous chromosomes.homologous chromosomes.- one chromosome - one chromosome

came came from the motherfrom the mother (maternal (maternal chromosome)chromosome)

- the other chromosome - the other chromosome came from the fathercame from the father

(paternal chromosome)(paternal chromosome)3. The symbol for diploid is The symbol for diploid is 2N 2N

oror 2n. 2n.4. Sexual reproductionSexual reproduction creates creates

diploidy.diploidy.

Genes & ChromosomesGenes & Chromosomes

What does haploid mean?What does haploid mean?

1.1. The chromosomes The chromosomes do do notnot come in pairs. come in pairs.

2.2. In humans, only the In humans, only the gametesgametes (ovum & (ovum & sperm cell) sperm cell) are haploidare haploid..

3. Meiosis creates haploid cells in a diploid organism.

MeiosisMeiosisMeiosis is also known as reduction Meiosis is also known as reduction

division.division.1.1. The daughter cells will have ½ The daughter cells will have ½

the number of mother cell the number of mother cell chromosomes.chromosomes.

2.2. How is this done?How is this done?- - Replicate the DNA onceReplicate the DNA once- - Divide twiceDivide twice

3.3. The 1The 1stst division is known as division is known as Meiosis IMeiosis I

- - crossing-over occurs crossing-over occurs herehere

4.4. The 2The 2ndnd division is known as division is known as Meiosis IIMeiosis II

- this is when the - this is when the reduction reduction occurs occurs

Meiosis IMeiosis IWhat is the coolest thing What is the coolest thing

that occurs during that occurs during Meiosis I?Meiosis I?

1.1. Homologous chromosomes Homologous chromosomes pair up in a process called pair up in a process called synapsissynapsis and form a and form a tetradtetrad..

2.2. The homologous The homologous chromosomes exchange chromosomes exchange portions of their chromatids portions of their chromatids in a process called in a process called crossing-overcrossing-over..

3.3. This creates a new This creates a new combination of genes and combination of genes and greatly increases genetic greatly increases genetic variety.variety.

chiasmachiasma

Meiosis IIMeiosis II

What occurs during Meiosis II?What occurs during Meiosis II?

1.1. No DNA replication occurs during No DNA replication occurs during Interphase II!Interphase II!

2.2. When Meiosis II is complete, When Meiosis II is complete, 4 haploid 4 haploid (n) daughter cells are produced(n) daughter cells are produced..

Meiosis Animation

MeiosisMeiosisWhat is gametogenesis?What is gametogenesis?

It is meiosis that creates gametes.It is meiosis that creates gametes.

There are two kinds of gametogenesis:There are two kinds of gametogenesis:1.1. SpermatogenesisSpermatogenesis

- creates - creates 4 viable sperm cells4 viable sperm cells2.2. OogenesisOogenesis

- creates - creates 1 viable ovum and 3 unviable 1 viable ovum and 3 unviable polar bodiespolar bodies- this process conserves cytoplasm - this process conserves cytoplasm

because the sperm cell contributes no because the sperm cell contributes no cytoplasm or organelles to the fertilized cytoplasm or organelles to the fertilized eggs.eggs.

Comparing Mitosis & MeiosisComparing Mitosis & Meiosis

Comparison of Mitosis & Meiosis

Mitosis Meiosis

Purpose

Start & End # of chromosomes

Cells genetically same/not

# Cells produced

Produce more Produce more body cellsbody cells

Produce sex Produce sex cells/gametescells/gametes

2N→2N2N→2N 2N→N2N→N

Genetically Genetically identicalidentical

Genetically Genetically different; different; crossing overcrossing over

1 makes 21 makes 2 1 makes 41 makes 4

Gregor MendelGregor Mendel

Who was Gregor Mendel?Who was Gregor Mendel?1.1. He is the father of He is the father of

genetics. genetics. 2.2. He was an Austrian He was an Austrian

monk who lived monk who lived during the 1800s.during the 1800s.

3.3. He was trained in He was trained in math & science.math & science.

4.4. While working in his While working in his peas garden, he peas garden, he noticed that the plants noticed that the plants displayed different displayed different traits.traits.

Gregor MendelGregor Mendel

What pea traits did Mendel study?

Mendelian VocabularyMendelian Vocabulary

What is a trait?What is a trait?

A characteristic of an organism.A characteristic of an organism.

What is a gene?What is a gene?

The genetic code for the trait.The genetic code for the trait.

What is an allele?What is an allele?

An alternative form of a geneAn alternative form of a geneExample: Trait = height; Alleles = tall (T) & short (t)Example: Trait = height; Alleles = tall (T) & short (t)

* Alleles come in pairs; one from dad, one from * Alleles come in pairs; one from dad, one from mommom

Mendelian VocabularyMendelian VocabularyWhat does homozygous mean?What does homozygous mean?Both parents contributed the Both parents contributed the same allelesame allele. (TT or tt). (TT or tt)

What does heterozygous mean?What does heterozygous mean?Parents contributed Parents contributed different allelesdifferent alleles. (Tt). (Tt)

What does dominant allele mean?What does dominant allele mean?This allele will always be expressed if present. This allele will always be expressed if present. (TT & Tt (TT & Tt

are tall). are tall). a.k.a. – principle of dominance a.k.a. – principle of dominance

What does recessive allele mean?What does recessive allele mean?This allele will only be expressed is homozygous. This allele will only be expressed is homozygous. (tt = (tt =

short)short)

Mendelian VocabularyMendelian Vocabulary

What does genotype mean?What does genotype mean?

The alleles an organism has.The alleles an organism has. Expressed Expressed in terms of recessive/dominant & in terms of recessive/dominant & homozygous/heterozygous. (TT, Tt, tt)homozygous/heterozygous. (TT, Tt, tt)

What does phenotype mean?What does phenotype mean?

Physical expression of the genotype. Physical expression of the genotype. What an organism actually looks like.What an organism actually looks like.

Mendelian VocabularyMendelian Vocabulary

What does true-breeding (purebred) mean?What does true-breeding (purebred) mean?The organism’s genotype is homozygous.The organism’s genotype is homozygous. (TT or tt) All of the organism’s gametes will (TT or tt) All of the organism’s gametes will have the same allele.have the same allele.

What does hybrid mean?What does hybrid mean?The organism’s genotype is heterozygous.The organism’s genotype is heterozygous. (Tt) The parents were two different (Tt) The parents were two different purebreds. The organism’s gametes could purebreds. The organism’s gametes could get either allele.get either allele.

Mendelian VocabularyMendelian Vocabulary

Putting it all together:Putting it all together:

Trait = height Alleles = tall (T), short (t)

Genotypes:Genotypes: Phenotypes:Phenotypes:

TT (homozygous dominant) Tall

Tt (heterozygous) Tall

tt (homozygous recessive) Short

TT & tt are true-breeding/purebred; Tt is a hybrid.

Mendelian LawsMendelian Laws

The Law of Segregation:The Law of Segregation:

The alleles separate during meiosis.The alleles separate during meiosis.

Probability & Punnett Squares

ProbabilityProbability - The likelihood that an event will occur:In a coin toss, there is a 1 in 2 chance of getting heads with each toss.

Punnett Square -Punnett Square - diagram to show possible gene combinations from a genetic cross.

Mendel’s LawsMendel’s Laws

The one-factor (monohybrid) cross:The one-factor (monohybrid) cross:

1.1. Only one trait is studiedOnly one trait is studied

2.2. 11stst parental generation ( parental generation (PP11) are ) are

different different true-breeding/purebred true-breeding/purebred genotypes & phenotypes.genotypes & phenotypes.

3.3. The first generation of offspring (The first generation of offspring (FF11) )

are are all hybridsall hybrids expressing the expressing the dominant phenotype. dominant phenotype. F= filial (Latin F= filial (Latin for “son.”for “son.”

Mendel’s LawsMendel’s Laws

The one-factor (monohybrid) cross:The one-factor (monohybrid) cross:

4.4. Use the FUse the F11 generation as the second set of generation as the second set of

parents (Pparents (P22).).

5.5. This cross will create a This cross will create a phenotype ratio of phenotype ratio of 3:13:1 (3 dominant phenotype: 1 recessive (3 dominant phenotype: 1 recessive phenotype).phenotype).

6.6. This cross will create a This cross will create a genotype ratio of genotype ratio of 1:2:11:2:1 (1 homozygous dominant: 2 (1 homozygous dominant: 2 heterozygous: 1 homozygous recessive).heterozygous: 1 homozygous recessive).

Mendel’s Monohybrid CrossesMendel’s Monohybrid Crosses

P Generation F1 Generation F2 Generation

Mendel’s LawsMendel’s LawsThe Law of Independent Assortment:The Law of Independent Assortment:

1.1. This law applies to two-factor This law applies to two-factor (dihybrid) crosses.(dihybrid) crosses.

2.2. Alleles for different traits segregate Alleles for different traits segregate independently of each otherindependently of each other

3.3. FOILFOIL ( (FFirst, irst, OOutside, utside, IInside, nside, LLast)ast)

4.4. Each gamete gets one allele for each Each gamete gets one allele for each trait.trait.

Mendel’s LawsMendel’s Laws

The dihybrid cross:The dihybrid cross:

1. The P2 are heterozygous for both traits

2. This will create a phenotype ratio of 9:3:3:1

9 dominant phenotype for both traits

3 dom. pheno. for 1st trait; rec. for 2nd

3 rec. pheno. for 1st trait; dom. for 2nd

1 recessive phenotype for both traits

Incomplete DominanceIncomplete Dominance

Four O’clock Plants :Four O’clock Plants :

R = red flower alleleR = red flower allele

W = white flower alleleW = white flower allele

Neither allele is Neither allele is dominant or recessive.dominant or recessive.

Genotypes & Phenotypes:Genotypes & Phenotypes:

RR = red flowersRR = red flowers

WW = white flowersWW = white flowers

RW = pink flowersRW = pink flowers

CodominanceCodominance: : bothboth allelesalleles contributecontribute toto thethe phenotypephenotype; ; 2 2 phenotypesphenotypes presentpresent atat samesame

timetimeHuman ABO Blood Types display this:Human ABO Blood Types display this:IIAA = type A codominant = type A codominantIIBB = type B codominant = type B codominanti = type O recessivei = type O recessive

Genotypes/Phenotypes:Genotypes/Phenotypes:IIAAIIA A & I& IAAO = type AO = type AIIBBIIBB & I & IBBO = type BO = type BIIAAIIBB = type AB (universal recipient) = type AB (universal recipient)ii = type O (universal donor)ii = type O (universal donor)

Multiple AllelesMultiple Alleles

More than two alleles exists for the trait.More than two alleles exists for the trait.

Rabbit fur is a good example:

Polygenic TraitsPolygenic Traits

These traits require These traits require the interaction of the interaction of several genes.several genes.

Human skin color is Human skin color is a good example.a good example.

Genes & the EnvironmentThe phenotype of an organism is only partially The phenotype of an organism is only partially determined by the genotype, determined by the genotype, the environment can the environment can play a key role.play a key role.

The western white butterfly is an example:

1. Springtime hatchlings are darker (shorter days)

2. Summertime hatchlings are lighter (longer days)

Spring HatchlingSpring Hatchling Summer HatchlingSummer Hatchling