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Human Genetics: Patterns of Inheritance for Human Traits

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Human Genetics: Patterns of Inheritance for Human Traits We will be discussing 5 Patterns of Inheritance for Human Traits 1. Single Allele Dominant 2. – PowerPoint PPT presentation

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Title: Human Genetics: Patterns of Inheritance for Human Traits


1
Human GeneticsPatterns of Inheritance for
Human Traits
2
We will be discussing 5 Patterns of Inheritance
for Human Traits
  • 1. Single Allele Dominant
  • 2. Single Allele Recessive
  • 3. Sex Linked (X-Linked)
  • 4. Multiple Alleles
  • 5. Polygenic Traits

3
Single Allele Genes
  • Regular traits that are either determined by a
    dominant or recessive allele on an autosome
  • Autosomal Dominant examples
  • a. Huntingtons Disease
  • b. Achondroplasia (dwarfisim)
  • c. Polydactyly (extra fingers and toes)
  • 2. Autosomal Recessive examples
  • a. Albinism
  • b. Cystic Fibrosis
  • c. Sickle Cell Anemia

4
1. Dominant Allele Disorders
  • Huntingtons Disease (HD)
  • Results in loss of muscle control and mental
    deterioration
  • No signs are shown until 30s
  • Brain degeneration
  • Treatment No cure, but drug treatments are
    available to help manage symptoms.

5
1. Dominant Allele Disorders
  • Achondroplasia
  • Dwarfism
  • Person grows no taller than 44

6
1. Dominant Allele Disorders
  • Polydactyly
  • The presence of more than the normal number of
    fingers or toes.
  • Can usually be corrected by surgery.

7
2. Recessive Allele Disorders
  • Albinism
  • Lack of pigment in skin, hair, and eyes
  • Mutation in one of several genes which provide
    the instructions for producing one of several
    proteins in charge of making melanin.

8
2. Recessive Allele Disorders
  • Cystic Fibrosis (CF)
  • Caused by recessive allele on chromosome 7
  • Small genetic change (removes one Amino Acid) ?
    changes protein
  • Results in Excess mucus in the lungs, liver and
    digestive tract, gets infection easily, and early
    death unless treated.

9
2. Recessive Allele Disorders
  • Sickle Cell Disease
  • Red blood cells are bent and twisted
  • Get stuck in capillaries ? damage tissues
  • Results in weakness, damage to brain and heart

10
3. Sex Link TraitsGenes on the X and Y
chromosomes
11
Human Chromosomes 2 Sex Chromosomes
12
Human Chromosomes44 Autosomes
13
Gender
  • We determine the gender of an individual through
    sex chromosomes
  • Sex Chromosomes X and Y
  • Female XX
  • Male XY
  • The father gives an X or Y to the gametes. The
    mother only gives an X to the gamete
  • The X chromosome is larger than the Y chromosome.

14
What are sex-linked genes? ? genes found on a
sex chromosome
  • X-linked genes are genes found on the X
    chromosome, symbolized by Xr, XR, Y0.
  • Y-linked genes are found on the Y chromosome,
    symbolized by X0, YR, Yr

15
Sex-Linked Traits
  • It is possible for a female to be a carrier of an
    X-linked trait, but not express it
  • Men will express all X-linked traits they inherit
    because they have one X chromosome

16
X-linked Genes
  • Lets do a punnett square for a female carrier of
    an x-linked gene and a recessive male
  • What will the genotypes be?
  • XRXr and XRY

17
Heres the results
  • For girls 0 have the trait
  • For boys 50 have it.
  • Probability is higher for boys because whatever X
    they get determines the trait, for girls they
    have to get 2 recessive Xs.

XR Xr
XR XR XR XR Xr
Y0 XR Y0 Xr Y0
18
Examples of X-linked traits
  • 1. Color Blindness
  • 2. Hemophilia
  • 3. Muscular Dystrophy
  • 4. Icthyosis simplex (scaly skin)

19
Colorblindness
  • A person with normal color vision sees a number
    seven in the circle above.
  • Those who are color blind usually do not see any
    number at all.

20
Colorblindness
  • RED-GREEN COLORBLINDNESS
  • People with red-green color blindness see either
    a three or nothing at all.
  • Those with normal color vision see an 8.

21
Hemophilia
  • Hemophilia- Lacking in the ability to clot blood
  • There is a gene on the X chromosome that
    control blood clotting
  • People who have hemophilia are missing the
    protein to clot blood
  • They can bleed to death by minor cut.

22
Muscular Dystrophy
  • - Results in weakening/loss of muscles
  • - Caused by defective version of gene that codes
    for muscle

23
Sex-influenced Traits
  • Sex-Influenced traits are those that are on
    autosomes, but occur because of the sex hormones
    in male and female bodies.
  • Examples Facial hair
  • Baldness

24
4. Multiple Alleles
  • Multiple Alleles any gene that has 3 or more
    alleles (not just 1 dominant and 1 recessive)
  • Example Blood type has 3 alleles
  • IA Type A blood (dominant)
  • IB Type B blood (dominant)
  • i Type O blood (recessive)

25
Check out the possible genotypes and phenotypes
of blood below
Genotypes Phenotypes
IAIA or IAi Type A
IBIB or IBi Type B
IAIB Type AB
ii Type O
26
Blood has both Multiple Alleles and is CoDominant
  • If you have IAIB as your genotype, you have both
    Type A and Type B blood,
    also known as Type AB
  • If you have IAi, i is recessive
    to IA, so you have type A blood
  • Q. When would you have Type O blood?
  • A. When you have ii as your genotype.

27
5. Polygenic Traits traits controlled by 2 or
more genes that interact, forming the trait
  • Usually show a wide range of phenotypes
  • Ex Skin color, eye color, foot size, height
  • Wide range of skin colors because there are more
    than 4 genes that control this trait.
  • These may also be influenced by the environment,
    for example height. If not given the proper
    nutrition as a child, they might not be as tall
    as their genes dictate.
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