What do you already know about Gregor Mendel?
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What do you already know about Gregor Mendel? What do you know about genetics? PowerPoint PPT Presentation


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What do you already know about Gregor Mendel? What do you know about genetics? What questions do you have about genetics?. 1822 in Czech Republic Priest Studied math and science Taught in a monastery In charge of monastery gardens. Gregor Mendel. Peas. Why were they studied?

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What do you already know about Gregor Mendel? What do you know about genetics?

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  • What do you already know about Gregor Mendel?

  • What do you know about genetics?

  • What questions do you have about genetics?


1822 in Czech Republic

Priest

Studied math and science

Taught in a monastery

In charge of monastery gardens

Gregor Mendel


Peas

Why were they studied?

Fertilization/Pollination

Mostly self-pollinating

Mendel’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


Self-pollination of F1

Produced F2

¼ exhibited recessive traits

Conclusion

Alleles separate in sex cells (gametes)

One allele from each parent

Crossing F1 Generations


Mathematical model

Assumptions

Tall vs. short

Dominant (T)

Recessive (t)

Genotype

Phenotype

Homozygous

Heterozygous

TT

Tt = tT

tt

Inheritance of Genes


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


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