INHERITANCE PATTERNS AND HUMAN GENETICS Chapter 12

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INHERITANCE PATTERNS AND HUMAN
GENETICSChapter 12
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Quick review

• Genetics is the field of biology devoted to
  understanding how characteristics are transmitted
  form parents to offspring.

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Generations P Tall x Short F1 Tall
(tall is dominant) F2 3 Tall 1 short

• The DOMINANT factor/gene masks the effect of the
  other factor in the F1 generation.
• Use CAPS ex. T for tall
• The RECESSIVE factor/genes effect can only be
  seen in the P generation or F2 generation when
  the DOMINANT gene is absent.
• Use lower case ex. t for short

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MENDELS 2 LAWS

• 1 LAW OF SEGREGATION

• A pair of factors is segregated, or separated,
  during the formation of gametes.
• Factors for different characteristics are
  distributed to gametes independently.

• 2 LAW OF INDEPENDENT ASSORTMENT

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• PHENOTYPE is the physical appearance of that
  organism.
• Ex. Tall or short

• GENOTYPE is the genetic makeup of the organism.
• TT homozygous dominant
• Tt heterozygous
• tt homozygous recessive

MENDELIAN INHERITANCE- DOMINANCE. 2 phenotypes
only. If someone has the dominant phenotype but
you arent sure of Their genotype use a
pedigree (humans) or do a test cross.
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Other Patterns of Inheritance

• Incomplete Dominance- blending seen in
  heterozygote (ex. pink flowers, brown hair)
• Codominance- both dominant and recessive
  phenotypes seen in heterozygote. (ex. type AB
  blood, roan horse fur color)
• Polygenic- more than 1 gene determines the
  phenotype. (Ex. Eye color, Hair color aabbcc)
• Multiple alleles- more than just 2 alleles
• (Ex. Blood type A allele, B allele, O allele is
  recessive.)

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EX. Polygenic Inheritance- when the trait is
controlled by multiple genes so many phenotypes
are possible.

• AaBbCc x AaBbCc
• Huge variety in possible
• Phenotypes of the offspring
• - skin, hair, eye color
• - foot size
• - nose length
• - height

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Multiple alleles- trait controlled by three or
more alleles.

• -Ex.
• ABO blood groups
• - TYPE A
• - TYPE B
• - TYPE AB Shows Codominance!
• - TYPE O

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The process of using phenotypes to deduce
genotypes

• When someone has the DOMINANT phenotype you are
  uncertain of their genotype.
• TT or Tt

• When someone has the recessive phenotype you can
  be sure of their genotype.
• tt

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DIRECTIONS

• For each of the following single gene/ Mendelian
  traits, write your phenotype on the line.
• Write as much of your genotype as you can be
  certain.
• - both alleles if RECESSIVE (rr)
• - one allele if DOMINANT (R __)
• Repeat the process by studying two blood
  relatives (parents work the best)
• Use a pedigree.

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1. HAIR TYPEvery curly or
straightTT, Tt tt
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2. Hair ColorDark or
LightDD, Dd dd
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3. Hair LineContinuous or Widows PeakWW, Ww
ww
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4. Iris ColorPigmented or
BlueEE, Ee ee
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5. Lens of EyeAstigmatism or NormalAA,
Aa aa
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6. Nose ShapeRoman (convex) or ConcaveNN,
Nn nn
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7. Ear LobeFree/Long or AttachedLL,
Ll ll
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8. P.T.C. TasterTaster or NontasterRR,
Rr rr
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9. Tongue CurlingCan curl or Can not
curlCC, Cc cc
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10. Point of chinDimpled or NO
dimpleII, Ii ii
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11. Number of FingersPolydactylism or Normal
PP, Pp pp
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(No Transcript)
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12. Little FingerBent or StraightFF, Ff ff
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13. Hypermobility of ThumbLoose Jointed or
Not soHH, Hh hh
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14. Thumb ExtensionHitchhikers Thumb or Not
HH, Hh hh
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15. Middigital HairPresent or
AbsentMM, Mm mm
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16. Palmar MuscleNormal (2) or Long
(3)UU, Uu uu
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17. AllergiesTendency Or No tendencyAA,
Aa aa
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18. VeinsVaricose or NormalVV, Vv vv
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19. White Skin SpottingFreckles or No
frecklesSS, Ss ss
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20. White Forelock
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LIST OF STRANGE MENDELIAN TRAITS

• Ear wiggling
• Misshapen toes or teeth
• Inability to smell musk or skunk
• Lack or teeth, eyebrows, nasal bones or
  thumbnails
• Whorl in the eyebrow
• Tone Deafness
• Hairs that are triangular in cross-section or
  that have multiple hues (colors)
• Hairy knuckles, palms, soles, or elbows
• Egg-shaped pupils
• Magenta urine after eating beets
• Sneezing fits in bright sunlight.

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DNA in chromosomes contain information to make
proteins.

• Geneticists use their knowledge of DNA and the
  way chromosomes behave to study how traits are
  inherited and expressed.

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• The parents genotype can be a
• gene pair of either
• - TT homozygous dominant
• - tt homozygous recessive
• - Tt heterozygous
• The parent can make gametes (sperm or eggs),
  through the process of MEIOSIS, that have either
  one or the other of the gene pair in it.

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SEX DETERMINATION

• MORGANs Fruit fly (Drosophila)
• breeding experiments of
• the 1900s revealed the
• identity of sex chromosomes.
• In males they were different
• XY in females they were the
• same XX.
• The other chromosomes
• (22 in humans) are AUTOSOMES.

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The male determines the sex of the offspring

• lt--The FEMALE XX can only make X gametes.
• lt--The MALE XY can make either X gametes or Y
  gametes.

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SEX LINKAGE traits caused by genes found on a
sex chromosome

• X-LINKED GENES
• Genes located on the X chromosome.
• Women can be carriers.
• Ex. gene for ALD (Lorenzos Oil)
• Y-LINKED GENES
• Genes located on the Y chromosome.
• Only males show these traits.
• Ex. SRY- triggers male development of testis.

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Males exhibit X-linked traits more often than
women because they only have ONE X chromosome.

• Females have two XBXb or sex linked genes.
• Females can be carriers of the bad gene yet not
  show the disease..
• Males only have one X or sex linked gene since
  they are XbY.
• Males have a higher chance of having the
  condition than if it were on an autosome.
• THERE IS NO HETEROZYGOUS for men.

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X-linked Examples

• Eye color in Drosophila
• Red-green colorblindness
• Male Pattern Baldness
• Hemophilia
• Duchenne Muscular Dystrophy
• ALD (adreno leuko dystrophy)

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What do you see in the circle?Do your bruises
look like this?
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If a carrier (woman) for hemophilia marries a
normal man, what are the chances of having kids
who are hemophiliacs? Who are not?What if the
man is a hemophiliac???????

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LINKAGE GROUPS

• Genes located on the same chromosome are said to
  be linked.
• Linked genes tend to be inherited together.

Examples Hair color and intelligence are linked
in humans. fur color and
deafness in cats are linked.
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Im kidding about intelligence and hair color
being linked.

• But if they were linked
• What would the phenotype(s) be of children of a
  dumb,blonde smart,brunette

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smart,brunette

• If that smart,brunette had kids w/ a
• dumb,blonde
• What kinds of kids could they have?
• What is the probability of each?

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• Parental Phenotypes
• Smart, brunette
• Dumb, blonde
• Recombinant Phenotypes
• Smart, blonde
• Dumb, brunette

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Linked genes result in traits that tend to be
inherited together
If you do a test cross of your Heterozygote you
can see if the genes Are linked (5511) or not
(1111).
If the intelligence and hair color genes were
linked, wed only see smart-brunettes and
dumb-blondes. (HA HA) So, since there are smart
blondes- are these genes on separate chromosomes
or on the same chromosome yet separated by
crossing over?????
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Chromosome maps can be created by conducting
breeding experiments.

• Linked genes that separate by crossing over X
  of the time are X map units apart.
• Compare 4 phenotype inheritance to 2 phenotype
  inheritance.
• Genes can now be placed on a chromosome in some
  order.

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• Genes W and Z separate by crossing over 20 of
  the time.
• Genes W and X separate by crossing over 5 of the
  time, and
• genes Z and X are separated by crossing over 25
  of the time.
• CONSTRUCT A CHROMOSOME MAP.
• Z W X
• I----20-------I--5--I

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Mutations, Disease, Human Mendelian Traits

1. Where they occur/ significance.
2. Types Chromosome or Gene
3. Diseases Inheritance Patterns.
4. Using Phenotypes to deduce Genotypes

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• Germ cell mutation
• occurs in the gametes
• does not effect the organism
• may be passed on to offspring if fertilized
• Somatic mutation
• occurs in the organisms body cells can affect
  the organism
• ex. Skin cancer leukemia
• are not passed on to offspring
• Lethal mutation
• causes death (often before birth)
• is not passed on if death occurs before
  reproduction
• Beneficial mutation
• result in phenotypes that are beneficial.
• beneficial phenotypes lead to increased
  reproduction.

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• Mutation a change in the DNA sequence.
• A) chromosome mutations (affects many genes)
• B) gene mutations (one gene)
• A) Chromosome mutations
• Cross over errors
• Deletion- loss of a piece due to breakage.
• Inversion- a piece is attached upside down.
• Translocation- a piece reattaches to a
  non-homologous chromosome.
• Segregation Error
• Nondisjunction- failure of homologous chromosomes
  to separate during meiosis.
• ex. Down Syndrome Trisomy 21 (egg
  usually has 2 of 21)

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Chromosome Mutations
nondisjunction
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• B) Gene mutations/ point mutations-
• are nucleotide differences.
• Substitution- one nucleotide is switched for
  another.
• - ex. sickle cell anemia
• Frame shift mutations- occur when nucleotides are
  added or removed either more or fewer than 3
  nucleotides at a time.
• - addition
• - deletion

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GENE MUTATION SUBSTITUTION ex. Sickle Cell
Gene- Hemoglobin
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INHERITANCE OF GENETIC DISEASES follow different
Patterns of Inheritance

1. Single allele Dominant
2. Single allele recessive
3. X-linked
4. Sex influenced

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PEDIGREE ANALYSIS

• Humans have about 100,000 genes.
• Most studies are of disease-causing genes.
• - easy to track through generations..
• A pedigree is a family record that shows how a
  trait is inherited over several generations.

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• Single allele DOMINANT- need only one gene to
  have the disease.
• - huntingtons disease (1/10,000) Hh
• - dwarfism Dd
• - cataracts Cc
• - polydactyly Pp
• PATTERN effected individuals in every generation
  of both male and female sex.

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• Single allele recessive- The individual needs two
  genes to have the disease.
• Albinism aa
• Cystic fibrosis (1/200 whites) cc
• Phenylketonuria (1/1800) pp
• Hereditary deafness dd
• Sickle cell anemia (1/500 African-Americans) sc
  sc
• Tay-Sachs disease (1/1600 European Jews) tt

Pattern 2 healthy parents have effected child of
either sex.
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• X-Linked- women need two genes, men need only one
  gene.
• - colorblindness XcXc XcY
• -hemophilia (1/7000) XhXh XhY
• -muscular dystrophy (1/10,000) XdXd XdY
• -Icthyosis simplex
• -ALD

Pattern more common in males, Can kip
generations.