Genetics: Inherited Traits

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Genetics Inherited Traits
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Genes

• A particular segment of DNA
• Locusa genes ________________________on a
  chromosome
• ________________alternative forms of genes
• Homologous chromosomesgenes are at same location
  but may be slightly different
• ________________same allele at each locus
  (______)
• ________________different alleles at each locus
  (_____)

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A pair of homologous chromosomes, each in the
unduplicated state (most often, one from a male
parent and its partner from a female parent)
A gene locus (plural, loci), the location for a
specific gene on a chromosome. Alleles are at
corresponding loci on a pair of homologous
chromosomes
A pair of alleles may be identical or
nonidentical. They are represented in the text by
letters such as D or d
Three pairs of genes (at three loci on this pair
of homologous chromosomes) same thing as three
pairs of alleles
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Foundation of Genetics

• Gregor Mendelfather of genetics
• Monk at St. Thomas (Czech Republic)
• Prior to himblending
• Discovered that traits were a result of
  inheritance units (genes)
• Garden peasself fertilize
• Manipulated them and cross fertilized them
• Studied results one at a timeflower color, seed
  shape, stem height, seed color,

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The Garden Pea Plant

• Self-pollinating
• _________________(different alleles not normally
  introduced)
• Can be experimentally cross-pollinated

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Foundation of Genetics

• P parental generation
• F1 offspring from 1st cross
• F2 offspring from 2nd cross
• Initial studies were crosses of a single trait
  Ex.) flower color
• Monohybrid cross______________________
• Dihybrid cross_________________________

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Mendels Experiments

• Crossed true breeding plants and observed
  flower color
• Parental generation (P) was a cross between a
  purple flower and white flower
• F1 generationall offspring were purple
• Where did the white go?
• ______________________mask expression of other
  alleles
• ______________________only expressed in
  homozygotes

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F1 Results of One Monohybrid Cross
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Mendels Experiments

• Now took seeds from offspring (F1)
• Allowed them to self-fertilize
• F2 generationyielded ¾ purple and ¼ white (31
  ratio)
• Showed white flower trait ______________
• _____________________________________

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F2 Results of Monohybrid Cross
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Flower Color Mendel

• A purple
• a white
• Homozygous parent_________________
• Heterozygous parent _________________
• When A present flower will be purple (dominant
  allele)

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Mendels Conclusions

• ______________the combination of alleles carried
  by an organism (AA, Aa, aa)
• ______________observable traits of an organism
  (purple or white)
• Mendel was able to predict outcome of crosses
• _______________tool to predict outcome of
  crosses (genotype and phenotype)

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Punnett Square of a Monohybrid Cross
3 dominant 1 recessive
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Mendels Monohybrid Cross Results
F2 plants showed dominant-to-recessive ratio that
averaged 31
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Results of Mendels Experiments

• 1. Traits are determined by specific units
  (_____________)
• 2. Law of segregationalleles of genes are
  _______________ during meiosis
• 3. Assignment of alleles to gametes is random
• Dominant vs. recessive alleles
• true breeders are _______________ for the
  particular allele

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Multiple Traits

• Mendel began crossing plants that differed in two
  traits
• Flower colorpurple or white
• Purple dominant (A) white recessive (a)
• Plant Heighttall or short
• Tall dominant (B) short recessive (b)
• Crossed true breeding dominant (AABB) with true
  breeding recessive (aabb)

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Multiple Traits

• All offspring in F1 generation were AaBb (smooth
  and yellow)
• F2 generation yielded 9331 ratio of traits
• Dihybrid crossPunnett Square testing the two
  traits

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Explanation of Mendels Dihybrid Results

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Phenotypic Ratios in F2
AaBb X
AaBb

• Four Phenotypes
• Tall, purple-flowered (9/16)
• Tall, white-flowered (3/16)
• Dwarf, purple-flowered (3/16)
• Dwarf, white-flowered (1/16)

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Multiple Traits

• ______________________________multiple traits
  are inherited independently
• Alleles assort independently in meiosis
• Only genes that occur on separate chromosomes
  assort independently
• Genes that occur on ________________will not
  assort independently

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Mendels Work

• Mendels studies are good for ___________
• _____________________________________
• __________________ that all traits he studied
  occurred on different chromosomes
• All traits do not follow inheritance patterns
  observed by Mendel

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Testcross

• Individual that shows dominant phenotype is
  crossed with individual with recessive phenotype
• Examining offspring allows you to determine the
  __________________ of the dominant individual

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Dominance Relations

• ______________________ dominance
• ___________________ dominance
• Heterozygote phenotype is somewhere between that
  of two homozyotes
• _____________________
• Non-identical alleles specify two phenotypes that
  are both expressed in heterozygotes

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homozygous parent
homozygous parent
All F1 offspring heterozygous for flower color
Cross two of the F1 plants, and the F2 offspring
will show three phenotypes in a 121 ratio
Fig. 10-11, p.158
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Genes Influence Traits

• Eye color
• Polygenetic inheritancegoverned by
  ___________________________rather than by a
  single gene
• Pigment reflects color (blue to dark brown)
• 2 or more genes influence production of pigment

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Fig. 10-14, p.160
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Genetics of ABO Blood Types Three Alleles

• Gene that controls ABO type codes for enzyme that
  dictates structure of a glycolipid on blood cells
• Two alleles (IA and IB) are _________________
  when paired
• Third allele (i) is recessive to others

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ABO Blood TypeAllele Combinations

• Type A - IAIA or IAi
• Type B - IBIB or IBi
• Type AB - IAIB
• Type O - ii

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ABO Blood Type Glycolipids on Red Cells

• Type A - Glycolipid A on cell surface
• Type B - Glycolipid B on cell surface
• Type AB - Both glyocolipids A B
• Type O - Neither glyocolipid A nor B

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ABO and Transfusions

• Recipients immune system will attack blood cells
  that have an unfamiliar glycolipid on surface
• Type O is ____________________because it has
  neither type A nor type B glycolipid

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Single Gene Influence

• One gene
• _________________single gene influences several
  different traits
• ______________sex determining gene on Y
  chromosome
• Influences development of testes, sex hormones,
  reproductive structures

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Albinism

• Phenotype results ____________________
• ________________________ is completely blocked
• Genotype - Homozygous recessive at the gene locus
  that codes for tyrosinase, an enzyme in the
  melanin-synthesizing pathway

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Environmental Influence

• Environment can trigger ______________
• _____________________________ of genes
• Himalayan rabbit
• Genotype codes for black fur enzyme
• Inactive at warm (93o F) temperatures
• Black fur at extremities, white on body
• Cave fisheye development

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Environmental Influence

• Human skinsun exposure
• Heightnutrition
• Intelligence
• Sexuality
• __________________________________
• Complex interactions between genes and
  environment (cloning???)