lesson overview lesson overview the work of gregor mendel what do you already know about gregor...

Lesson Overview The Work of Gregor Mendel

• What do you already know about Gregor Mendel?

• What do you know about genetics?• What questions do you have about

genetics?

Lesson Overview The Work of Gregor Mendel

Gregor Mendel

• 1822 in Czech Republic• Priest• Studied math and science• Taught in a monastery• In charge of monastery gardens

Lesson Overview The Work of Gregor Mendel

Peas• Why were they studied?• Fertilization/Pollination

Mostly self-pollinatingMendel’s experiments

• True-breeding plants• Forcibly cross-pollinated• Created hybrids• Looked at several traits

Lesson Overview The Work of Gregor Mendel

Round and Wrinkled• True-breeding parents, P generation• Offspring, F1 generation

– Only round peas• Similar results with other traits• Conclusion

– Traits passed from parents– Genes– Alleles

Lesson Overview The Work of Gregor Mendel

• Dominant allele• Recessive allele

Lesson Overview The Work of Gregor Mendel

Crossing F1 Generations

• Self-pollination of F1• Produced F2• ¼ exhibited recessive traits• Conclusion

Alleles separate in sex cells (gametes)One allele from each parent

Lesson Overview The Work of Gregor Mendel

Inheritance of Genes• Mathematical model• Assumptions• Tall vs. short

– Dominant (T)– Recessive (t)– Genotype– Phenotype– Homozygous– Heterozygous

• TT• Tt = tT• tt

Lesson Overview The Work of Gregor Mendel

Punnett Squares• Mendel’s first cross (round x

wrinkled)• True-breeding =

homozygous• 1 allele from each parent• 2 alleles in a genotype

Lesson Overview The Work of Gregor Mendel

• Mendel crossed true-breeding yellow and green peas. All the offspring were yellow.– Write the genotype for these parents and the

offspring. Use a Punnett square to help with the offspring.

– Now cross the F1 with itself and write the genotypes of possible offspring along with the phenotypes. Use a Punnett square.

Lesson Overview The Work of Gregor Mendel

What about two traits at once?

• Will one allele affect the other?– Short always yellow?– Get new combinations?

• Mendel– Homozygous plants– Round, yellow x wrinkled, green plants– Assume: independence

Lesson Overview The Work of Gregor Mendel

• Round, yellow x wrinkled green

• Genotypes:

• What alleles?

Lesson Overview The Work of Gregor Mendel

F2• Genotype

• Alleles?

Lesson Overview The Work of Gregor Mendel

Independent Assortment• Genes for different traits separate

independently during gamete formation• Not all tall plants have yellow seeds• Some genes are linked to each other

– Not in those studied by Mendel

Lesson Overview The Work of Gregor Mendel

Other Patterns of Inheritance

• Peas are simple• Incomplete

dominance– Neither dominant

nor recessive– Mixture phenotype– Plants

• Red (RR)• White (rr)• Pink (Rr)

Red flower x Pink flower

Lesson Overview The Work of Gregor Mendel

• Codominance– Both alleles expressed– Blood types– Chicken feathers

• Multiple alleles– More than 2 forms– Blood types– Rabbit coat color

• Polygenic traits– Controlled by more than 1 gene– Skin and eye color

Lesson Overview The Work of Gregor Mendel

• In Chaparral llamas, brown coat color and blue eyes are dominant to white coat color and brown eyes.

• A heterozygous (for both traits) female llama breeds with a homozygous recessive male llama. Draw a Punnett square and describe the fraction of each phenotype possible in the offspring.

Lesson Overview The Work of Gregor Mendel

Cells and Chromosomes

• Somatic cells– Most cells in the body– Reproduce through mitosis– 46 chromosomes, 23 pairs– Diploid (2n)

• Gamete cells– Reproductive cells; sperm and egg– Unite with another cell in fertilization– 23 chromosomes, no pairs– Haploid (n)

Lesson Overview The Work of Gregor Mendel

• Diploid vs. haploid– Why does there need to be a difference?– If 2N = 8, then N = – If N = 12, then 2N =

• How does this relate to genes?– DNA– Chromosomes– Homologous chromosomes

Lesson Overview The Work of Gregor Mendel

Meiosis• 2N N• 2 parts: meiosis I and

meiosis II• Meiosis I

– DNA replicates during interphase

– Diploid– Prophase I

• Similar to mitosis• Homologous chromosomes

pair tetrad• Crossing over can occur

Lesson Overview The Work of Gregor Mendel

• Metaphase I– Homologous chromosomes line up

• Anaphase I– Separate homologous

chromosomes

• Telophase I– Nuclear membrane re-forms

• Cytokinesis• Results

– 2 daughter cells– Haploid or diploid?– May not be genetically identical

Lesson Overview The Work of Gregor Mendel

Meiosis II• No replication in interphase• Prophase II

– Chromosomes visible• Metaphase II

– Chromosomes line up• Anaphase II

– Chromatids separate• Telophase II• Cytokinesis

Lesson Overview The Work of Gregor Mendel

• Results– 4 cells from original 1– Each haploid– ½ genetic information of parent

• Males – all 4 cells used• Females

– 1 out of 4 used– Meiosis II doesn’t occur until fertilization

• Fertilization– Egg and sperm unite– Diploid zygote– Goes through mitosis rapidly, repeatedly

Lesson Overview The Work of Gregor Mendel

Mitosis vs. Meiosis

• Both – require DNA replication first• Mitosis

– Daughter cells diploid– Produces 2 cells

• Meiosis– Daughter cells haploid– Produces 4 cells

Lesson Overview The Work of Gregor Mendel

Genes and the Environment

• Effect gene expression• Western white butterfly

– Wing color varies– Spring – darker– Need specific body temp. to fly– Absorb more sunlight to be warmer

Lesson Overview The Work of Gregor Mendel

Karyotype

• Genome• Karyotype

– Definition• 23 pairs, 46

chromosomes

Lesson Overview The Work of Gregor Mendel

Sex vs. Autosome• Sex

– 2 chromosomes– Female– Y

• XY = male• Smaller• Male specific genes

• Autosomal– 44 chromosomes

Lesson Overview The Work of Gregor Mendel

How are traits inherited?

• Mendelian patterns• Dominant vs. recessive• Codominant• Multiple alleles• Sex-linked

– Sex chromosomes– Y only in males– X both sexes– Recessive traits– Example

Lesson Overview The Work of Gregor Mendel

Pedigree • Family tree• Circles vs. squares• Determine

– Dominance– Sex-linked

Lesson Overview The Work of Gregor Mendel

• Define– Karyotype– Genome– Pedigree

• What is an example of a sex-linked trait and why are sex-linked traits different than other traits?

• What is the difference between sex and autosomal chromosomes?

Lesson Overview The Work of Gregor Mendel

Genetic Disorders

• Sickle cell– Recessive – Irregularly shaped RBC– Stick together– Don’t carry O2 as well– Painful– No cure– Advantages

• Carriers• Malaria resistance

Lesson Overview The Work of Gregor Mendel

• Cystic fibrosis– Recessive – Necessary protein destroyed– Digestive and respiratory

problems– Advantage

• Europeans• Block typhoid bacterium

• Huntington’s disease– Dominant allele– Different protein– Mental deterioration

Lesson Overview The Work of Gregor Mendel

Chromosome Disorders

• Nondisjunction• Down syndrome

– Trisomy 21

• Turner’s syndrome– X

• Klinefelter’s syndrome– XXY

Lesson Overview The Work of Gregor Mendel

Gene Linkage

• Mendel– Independent assortment of genes

• Thomas Hunt Morgan– Fruit fly research– Traits inherited together– Genes stay together if on same

chromosome

Lesson Overview The Work of Gregor Mendel

Gene Mapping• Alfred Sturtevant

– Fruit flies– Location of genes on

chromosome