What is the probability of rolling a 1 and 5 in two separate rolls?

Agenda for Tuesday March 30th • Mendel notes• Punnett Squares

Law of Segregation

• Chromosomes separate during meiosis and unite during fertilization

Law of Independent Assortment

• Random distribution of chromosomes occurring during meiosis– Genes on separate chromosomes sort independently

The point?

• It’s all random– Which alleles we get (genes) (traits)– Crossing over– Etc.

What is a trait?

Agenda for Thursday March 31st 1.Mendel2.Punnett Squares

Mendel• Father of genetics• Loved nature• Austrian monk

– taught natural science – worked on plant breeding experiments

using pea plants

• Developed basic understanding of genetics and inheritance

Mendel’s Work

• It took him 2 years to select the pea plant• He collected data for 10 years.• His sample sizes were large; he tabulated

results from 28,000 pea plants.• He replicated his experiments.• Published work but was dismissed

– Found later

Mendel’s Experiment

• P Generation – parent generation• F1 generation – first filial generation, offspring

of parents• F2 generation – second filial generation,

offspring of F1 generation

• Ratio of 3:1

Mendel’s ResultsP1 F1 F2 F2 ratio

smooth X wrinkled seeds

all smooth 5474 smooth1850 wrinkled

2.96:1

yellow X green seeds

all yellow 6022 yellow2001 green

3.01:1

axial X terminal flowers

all axial 651 axial207 terminal

3.14:1

red X white flowers all red 705 red224 white

3.15:1

inflated X constricted pods

all inflated 882 inflated299 constricted

2.95:1

green X yellow pods all green 428 green152 yellow

2.82:1

tall X dwarf plants all tall 787 tall277 dwarf

2.84:1

Collected 6022 yellow and 2001 green3:1 ratio

Conclusions• 2 forms of seed traits in the pea plants

– Alleles – forms of a gene passed on to each generation• Green and yellow pea seeds

– We use letters to represents alleles/genes/traits

– Individuals are diploid so we use 2 letters

**Genes are on the chromosomes

Dominant and Recessive

• Dominant – the trait we see (expressed with capital letter, A)

• Recessive – trait that is masked (expressed with lower case letter, a)

• Which is better, dominant or recessive?

Dominance

• Mendel’s experiment, green color was masked– Recessive

• Organism with two of the same allele – homozygous– AA, aa

• Organism with two different alleles – heterozygous– Aa– Dominant trait observed (notice the dominant allele)

Homozygous (pure bred)

Same

HH hh

Heterozygous (hybrid)

Different

Hh Rr

Genotype

Allele makeup of an individual

Tt T T tt

RR Rr rr

PhenotypeObservable characteristics of an individual

Punnett Squares

Let’s Practice

PracticeA Tt (tall) plant is crossed with a tt (short plant).

What percentage of the offspring will be tall?

A green pea sead (gg) is crossed with a hybrid yellow seed (Gg). What will be the genotypic and phenotypic ratios of the offspring?

PracticeA heterozygous plant (Tt) is crossed with another

heterozygous (Tt) plant. What percentage of the offspring will be tall?

In guinea pigs, rough coats are dominant over smooth coats. If an Rr guinea pig is crossed with an Rr guinea pig. What are the chances of each genotype and phenotype? Include genotypic and phenotypic ratios.

Define homozygous, heterozygous, phenotype, and genotype

Agenda for Friday April 1st 1.Quiz2. More practice with Punnett Squares

A Tt (tall) plant is crossed with a tt (short plant). What percentage of

the offspring will be tall?

• Quiz• Review Punnett Squares• Making Dragons

Making Dragons

A Rr (round) seed is crossed with a Rr (round plant). What are the

phenotypic and genotypic ratios?• Finish making dragons• Comparing ratios of Punnett squares to actual

ratios lab

What is the process of combining two gametes called?

• Finish Comparing Punnett Square ratios• Dihybrid Crosses

Dihybrid Cross

• a cross between of two individuals that differ in two traits of particular interest

For example: GGbb/ggBb or RRYY/rryy

What is a dihybrid cross?

• Dihybrid Review• Gene Linkage and Polyploidy

– Mapping Chromosomes

Genetic Recombination

• New combination of genes produced by crossing over and independent assortment

Why is genetic recombination important?

Gene Linkage

• Genes on same chromosomes are said to be linked– Travel together during Meiosis

• Not always true – crossing over occurs

• Genes close together cross over more frequently– Make chromosome maps based on that info.

Chromosome Map

• Map genes A, B, C, D

• Frequency of crossing over– AD = 25%– AB = 30%– CD = 15%– BD = 5%– BC = 20%

Polyploidy

• Most cells are Diploid (2n)• Polyploidy – one or more extra sets of

chromosomes– Triploid – 3n

• In humans polyploidy is lethal– Other organisms it is not– Roughly 1 in 3 plants are polyploidy

• Increased vigor and size