Genetics Review The chromosomal basis of inheritance provides an - - PowerPoint PPT Presentation

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Genetics Review The chromosomal basis of inheritance provides an - - PowerPoint PPT Presentation

Jul 24, 2023 243 likes •654 views

Genetics Review The chromosomal basis of inheritance provides an understanding of the pattern of passage of genes from parent to offspring Rules of Probability Rules of Multiplication Rule of Addition Mendelian Genetics Law of Segregation

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Genetics Review

The chromosomal basis of inheritance provides an understanding of the pattern of passage of genes from parent to offspring

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Rules of Probability

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Rules of Multiplication

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Rule of Addition

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Mendelian Genetics

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Law of Segregation

  • Pair of alleles for a gene will separate from one

another during the formation of gametes

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Law of Independent Assortment

  • Genes on separate chromosomes assort in

gametes independently

  • Due to the random alignment of the

chromosomes during Metaphase I of meiosis

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Monohybrid Cross

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Dihybrid Cross

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Beyond Mendel

Inheritance patterns that cannot be explained by simple Mendelian genetics

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Linked Genes

  • Genes that are adjacent and close to each
  • ther on the same chromosomes tend to be

inherited as a unit (linked)

  • Do not follow Mendel’s laws of independent

assortment (result is unpredictable ratios)

  • Probability that genes will separate as a unit is

a function of the distance between them

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Linked Genes

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Chromosome Crossover

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Linkage Map

  • Diagrams describing the relative gene

locations using recombination frequencies

  • The shorter the distance between two genes,

the less likely a cross over event will happen between them

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Multiple Genes and/or Physiological Processes

  • Many traits are the product of multiple genes

and/or physiological processes

  • Patterns of inheritance do not follow ratios

predicted by Mendel’s laws

  • These traits can be identified by quantitative

analysis where observed phenotypic ratios statistically differ from predicted ratios

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Sex-Linked Genes

  • Gene that determines a phenotype is located
  • n the X or Y chromosome
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Incomplete Dominance

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Multiple Alleles

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Polygenic Inheritance

  • Shows quantitative variation in a population
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Epistasis

  • A gene at one locus alters the phenotypic

expression of a gene at a second locus

  • Example: Labrador Retriever Coat Color

– Black (B) coat color is dominant to chocolate coat color (b) – Pigmentation gene (E/e) is epistatic to the coat color locus

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Epistasis

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Thomas Hunt Morgan – Fruit Flies (1910)

  • Discovered the sex chromosomes and

determined XX for females and XY for males

  • Discovered genes located on sex chromosomes
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Sex-Limited Genes

  • The expression of the gene depends on the

sex of the individual

  • Examples:

– Milk production in female mammals – Pattern baldness in males

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Nonnuclear Inheritance

  • Organelles are randomly assorted into

gametes and daughter cells

  • Traits determined by chloroplast and

mitochondrial DNA do not follow simple Mendelian rules

  • Animals: mitochondrial DNA is transmitted by

the egg (mitochondrial determined traits are maternally inherited)

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Maternal Mitochondrial DNA (mtDNA)

  • Contains 37 genes
  • 13 code for enzymes used in oxidative

phosphorylation

  • Others code for tRNA and rRNA molecules
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Environmental Impact on Phenotype

  • Environmental factors influence the

expression of the genotype and ultimately the phenotype

  • Examples:

– Flower color based on soil pH – Seasonal fur color in arctic animals – Density of plant hairs (trichomes) as a function of herbivory – Arabinose and the RFP protein

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Flower Color Based on Soil pH

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Seasonal Fur Color In Arctic Animals

  • Arctic fox: genes that

produce darker pigmentation are blocked by cold temperatures

  • Spring/summer – brown

fur

  • Winter – white fur
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Density of Trichomes as a Function of Herbivory

  • Trichomes may release acids making in

difficult for insects to feed on the plant

  • Increase herbivory = Plant produces more

trichomes

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Arabinose and the RFP Protein

Coming soon to a lab near you…..

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Genomes are Flexible

  • Adaptations to the local environment reflects

a flexible response of an organisms genome

  • Examples:

– Darker fur in cooler regions of the body in mammals – Alterations in timing of flowering due to climate changes

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Himalayan Rabbits

  • Cooler temperatures = dark fur
  • Warmer temperatures = white fur
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Flowering and Climate Change

  • Flowering plants have gradually begun

blooming earlier as average temperature rise

  • Longer growing seasons, but most plants rely
  • n a certain period of “cooling” temperatures

to function properly in the spring