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Title: INHERITANCE PATTERNS AND HUMAN GENETICS Chapter 12


1
INHERITANCE PATTERNS AND HUMAN
GENETICSChapter 12
2
Quick review
  • Genetics is the field of biology devoted to
    understanding how characteristics are transmitted
    form parents to offspring.

3
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

4
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

5
  • 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.
6
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.)

7
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

8
Multiple alleles- trait controlled by three or
more alleles.
  • -Ex.
  • ABO blood groups
  • - TYPE A
  • - TYPE B
  • - TYPE AB Shows Codominance!
  • - TYPE O

9
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

10
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.

11
1. HAIR TYPEvery curly or
straightTT, Tt tt
12
2. Hair ColorDark or
LightDD, Dd dd
13
3. Hair LineContinuous or Widows PeakWW, Ww
ww
14
4. Iris ColorPigmented or
BlueEE, Ee ee
15
5. Lens of EyeAstigmatism or NormalAA,
Aa aa
16
6. Nose ShapeRoman (convex) or ConcaveNN,
Nn nn
17
7. Ear LobeFree/Long or AttachedLL,
Ll ll
18
8. P.T.C. TasterTaster or NontasterRR,
Rr rr
19
9. Tongue CurlingCan curl or Can not
curlCC, Cc cc
20
10. Point of chinDimpled or NO
dimpleII, Ii ii
21
11. Number of FingersPolydactylism or Normal
PP, Pp pp
22
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23
12. Little FingerBent or StraightFF, Ff ff
24
13. Hypermobility of ThumbLoose Jointed or
Not soHH, Hh hh
25
14. Thumb ExtensionHitchhikers Thumb or Not
HH, Hh hh
26
15. Middigital HairPresent or
AbsentMM, Mm mm
27
16. Palmar MuscleNormal (2) or Long
(3)UU, Uu uu
28
17. AllergiesTendency Or No tendencyAA,
Aa aa
29
18. VeinsVaricose or NormalVV, Vv vv
30
19. White Skin SpottingFreckles or No
frecklesSS, Ss ss
31
20. White Forelock
32
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.

33
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.

34
  • 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.

35
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.

36
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.

37
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.

38
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.

39
X-linked Examples
  • Eye color in Drosophila
  • Red-green colorblindness
  • Male Pattern Baldness
  • Hemophilia
  • Duchenne Muscular Dystrophy
  • ALD (adreno leuko dystrophy)

40
What do you see in the circle?Do your bruises
look like this?
41
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???????

42
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.
43
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

44
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?

45
  • Parental Phenotypes
  • Smart, brunette
  • Dumb, blonde
  • Recombinant Phenotypes
  • Smart, blonde
  • Dumb, brunette

46
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?????
47
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.

48
  • 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

49
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

50
  • 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.

51
  • 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)

52
Chromosome Mutations
nondisjunction
53
  • 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

54
GENE MUTATION SUBSTITUTION ex. Sickle Cell
Gene- Hemoglobin
55
INHERITANCE OF GENETIC DISEASES follow different
Patterns of Inheritance
  1. Single allele Dominant
  2. Single allele recessive
  3. X-linked
  4. Sex influenced

56
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.

57
  • 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.

58
  • 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.
59
  • 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.
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