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?


Gregor Mendel

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


Peas• Why were they studied?• Fertilization/Pollination

Mostly self-pollinatingMendel’s experiments

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


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


• Dominant allele• Recessive allele


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


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

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

• TT• Tt = tT• tt


Punnett Squares• Mendel’s first cross (round x

wrinkled)• True-breeding =

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


• 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.


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


• Round, yellow x wrinkled green

• Genotypes:

• What alleles?


F2• Genotype

• Alleles?


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


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


• 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


• 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.


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)


• 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


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


• 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


Meiosis II• No replication in interphase• Prophase II

– Chromosomes visible• Metaphase II

– Chromosomes line up• Anaphase II

– Chromatids separate• Telophase II• Cytokinesis


• 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


Mitosis vs. Meiosis

• Both – require DNA replication first• Mitosis

– Daughter cells diploid– Produces 2 cells

• Meiosis– Daughter cells haploid– Produces 4 cells


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


Karyotype

• Genome• Karyotype

– Definition• 23 pairs, 46

chromosomes


Sex vs. Autosome• Sex

– 2 chromosomes– Female– Y

• XY = male• Smaller• Male specific genes

• Autosomal– 44 chromosomes


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


Pedigree • Family tree• Circles vs. squares• Determine

– Dominance– Sex-linked


• 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?


Genetic Disorders

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

• Carriers• Malaria resistance


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

problems– Advantage

• Europeans• Block typhoid bacterium

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


Chromosome Disorders

• Nondisjunction• Down syndrome

– Trisomy 21

• Turner’s syndrome– X

• Klinefelter’s syndrome– XXY


Gene Linkage

• Mendel– Independent assortment of genes

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

chromosome


Gene Mapping• Alfred Sturtevant

– Fruit flies– Location of genes on

chromosome

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

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mendel slide

work of gregor mendel

work of gregor mendel

genotype slide

parent slide

mendel homozygous plants