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Genetics: Inherited Traits

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Dihybrid cross Punnett Square testing the two traits. Explanation of Mendel's Dihybrid Results ... Only genes that occur on separate chromosomes assort independently ... – PowerPoint PPT presentation

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Title: Genetics: Inherited Traits


1
Genetics Inherited Traits
2
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
    (_____)

3
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
4
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,

5
The Garden Pea Plant
  • Self-pollinating
  • _________________(different alleles not normally
    introduced)
  • Can be experimentally cross-pollinated

6
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_________________________

7
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

8
F1 Results of One Monohybrid Cross
9
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 ______________
  • _____________________________________

10
F2 Results of Monohybrid Cross
11
Flower Color Mendel
  • A purple
  • a white
  • Homozygous parent_________________
  • Heterozygous parent _________________
  • When A present flower will be purple (dominant
    allele)

12
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)

13
Punnett Square of a Monohybrid Cross
3 dominant 1 recessive
14
Mendels Monohybrid Cross Results
F2 plants showed dominant-to-recessive ratio that
averaged 31
15
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

16
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)

17
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

18
Explanation of Mendels Dihybrid Results

19
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)

20
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

21
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

22
Testcross
  • Individual that shows dominant phenotype is
    crossed with individual with recessive phenotype
  • Examining offspring allows you to determine the
    __________________ of the dominant individual

23
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

24
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
25
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

26
Fig. 10-14, p.160
27
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

28
ABO Blood TypeAllele Combinations
  • Type A - IAIA or IAi
  • Type B - IBIB or IBi
  • Type AB - IAIB
  • Type O - ii

29
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

30
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

31
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

32
Albinism
  • Phenotype results ____________________
  • ________________________ is completely blocked
  • Genotype - Homozygous recessive at the gene locus
    that codes for tyrosinase, an enzyme in the
    melanin-synthesizing pathway

33
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34
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

35
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36
Environmental Influence
  • Human skinsun exposure
  • Heightnutrition
  • Intelligence
  • Sexuality
  • __________________________________
  • Complex interactions between genes and
    environment (cloning???)
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