GENETICS: Understanding Patterns of Inheritance - PowerPoint PPT Presentation

Loading...

PPT – GENETICS: Understanding Patterns of Inheritance PowerPoint presentation | free to view - id: 75dd51-MjM1N



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

GENETICS: Understanding Patterns of Inheritance

Description:

GENETICS: Understanding Patterns of Inheritance PART III: NON-Mendelian Genetics NON-MENDELIAN GENETICS Despite the importance and power of Mendel s work, there are ... – PowerPoint PPT presentation

Number of Views:146
Avg rating:3.0/5.0
Slides: 23
Provided by: MaxG152
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: GENETICS: Understanding Patterns of Inheritance


1
GENETICSUnderstanding Patternsof Inheritance
2
PART IIINON-Mendelian Genetics
3
  • NON-MENDELIAN GENETICS 
  • Despite the importance and power of Mendels
    work, there are important exceptions to some of
    his principles.
  • Examples
  • Not all genes have only a dominant or recessive
    form.
  • A majority of genes have two or more alleles.
  • Many important traits are controlled by more than
    one gene.
  • If 2 genes are close together on the same
    chromosome, they may always move together (no
    independent assortment for 2 such alleles)

4
  • Incomplete Dominance One allele is not able to
    completely silence the other.
  • Produces intermediate outcomes
  • Example a red flower crossed with a white flower
    produces pink flowers.
  • RR red flowers WW white flowers
    RW pink flowers

5
Incomplete DominanceSnap-dragon Flower Color
No Dominant or recessive alleles
Both alleles are always expressed.
Intermediate outcomes (blending) result.
6
  • Codominance Both alleles are always expressed as
    phenotype
  • PProduces mixed outcomes
  • EExample a red flower crossed with a white
    flower produces flowers that are speckled (red
    and white)
  • RR red flowers WW white flowers
    RW flowers with pure red pure white areas
  • (True-breeding White Rooster Red Hen Dappled
    Young)

7
MULTIPLE ALLELES
  • Several alleles (variations in a gene) are
    possible for a single trait.
  • This does not mean that an individual can have
    more than two alleles, just that more than two
    alleles are available in the population.
  • Produces a spectrum of outcomes.

8
EXAMPLE (OF MULTIPLE ALLELES)
  • A A hypothetical plant population has 3 different
    alleles for color, red, white, and blue. Red is
    dominant to white red and white are both
    dominant to blue.
  • AAlleles R or rW or rb

RR  
RrW All produce red flowers
Rrb  
9
EXAMPLE (OF MULTIPLE ALLELES, contd.)
rw rw Produce white flowers rw rb
rb rb Produces blue flowers
10
(Blood Types are controlled by a gene with
multiple alleles that exhibit codominance)
MULTIPLE ALLELES PLUS CODOMINANCE The Special
Case of Human Blood Typing
Multiple Alleles usually work like this
T gt tA gt tb (that
is, the first allele is dominant to the second
and third, while the second is only dominant
to the third)
  • But in some cases (like human blood typing)
    IA IB gt i
  • Note that superscripts are both capitalized
    having either A or B form causes you to always
    make one cell surface marker and another
    antibody.
  • TWO copies of i with no dominant allele to cover
    them results in NO PROTEIN AT ALL (blood type O)

11
Blood Type Genotype(s) Description
A IA IA or IA i Makes cells with A markers only makes antibodies to B surface proteins on blood cells
B IB IB or IB i Makes cells with B markers only antibodies to A surface proteins
AB IA IB only Makes cells with both A and B surface markers makes no antibodies (universal recipient)
O i i only Makes cells with neither A nor B surface markers makes antibodies to both A and B cells
12
(No Transcript)
13
  • Polygenic traits
  • Phenotype is determined by several genes
    working together
  • Genes may be on the same chromosome or on
    separate chromosomes
  • Example height is a single trait, but determined
    by many genes
  • Length of legs Length of torso
    Length of neck, etc.

14
Human Skin Color a Polygenic Trait
3 genes are involved all work together to
determine phenotype.
Each gene has a dominant and recessive form.A or
a B or b C or c
Each human is conceived with 6 alleles for this
trait (3 from each gamete).
A wide range of graded outcomes result.
15
One unusual polygenic process is epistasis
  • One gene acts as a switch enables or inhibits
    expression of another
  • Example coloring of Labrador retrievers.

16
Epistasis One Allele acts as a Switch for
Another
Epi over stasis standingepistasis
standing over
Example Purple vs. white pea plant
flowers. C or c stands on the purple/white
allele (controls its expression).
Purple (P) is dominant but controlled by C.
So a flower can only be white if the plant is
PP or Pp and this outcome is accompanied by
cc (OR if pp combination occurs).
17
Linked Genes Genes located on the same
chromosome especially those close to
each other
  • Even closely linked genes separate sometimes (due
    to cross-over during meiosis).
  • Relative frequency of gene separation during
    meiosis may be used to map exact location of a
    specific base sequence
  • Genes located farther apart separate more
    frequently.
  • Disease genes (such as Huntingtons) are
    sometimes linked to marker genes tracked this
    way.

18
X-Linked (Sex-linked) Traits Some genetic
traits are expressed in males only (or rarely
expressed in females)
  • Example White eyes in fruit flies
  • Genetic coding for these traits is usually
    recessive Coding is carried on X chromosome
    has no counterpart on Y
  • Phenotype occasionally seen in females (if they
    receive 2 copies of allele)

19
Human Examples of Sex-linked Traits
hemophilia red-green color blindness
Huntingtons disease.
Barr-Bodies
  • The cells of all female Humans de-activate one
    X chromosome (Occurs randomly unpredictable and
    arbitrary for each cell)
  • De-activated chromosome visible as
    darkly-staining object in nucleus does not
    synthesize proteins.

20
Nondisjunction (Failure of chromosomes to
separate completely during production of
gametes)
  • Results in missing or multiple copies of genes
    (or sometimes of entire chromosome) in cells of
    offspring
  • Trisomy one gamete brings 2 copies of
    chromosome zygote has 3
  • Monosomy one gamete brings NO copy of coding
    zygote ends up with only 1

21
Examples of Nondisjunction
  • Down Syndrome trisomy in chromosome 21, results
    in developmental cognitive problems
  • XXY (Klinefelter Syndrome) incomplete sexual
    development, rangy males
  • XO (Turner Syndrome) short, undeveloped females
  • XXX Syndrome limited fertility, cognitive
    developmental deficits.

22
End of PART IIINON-Mendelian Genetics
About PowerShow.com