Biology 102 Patterns of Inheritance (cont.). Lecture outline Inheritance of multiple traits...
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Transcript of Biology 102 Patterns of Inheritance (cont.). Lecture outline Inheritance of multiple traits...
Biology 102Biology 102
Patterns of Inheritance (cont.)Patterns of Inheritance (cont.)
Lecture outlineLecture outline Inheritance of multiple traitsInheritance of multiple traits
Same chromosome (linkage)Same chromosome (linkage)Sex chromosomesSex chromosomes
OverviewOverviewSex linkageSex linkage
Incomplete dominanceIncomplete dominanceCodominanceCodominanceOther variationsOther variations
Sickle cell anemia exampleSickle cell anemia examplePedigreesPedigrees
Crosses with two traitsCrosses with two traits If genes are on different chromosomes, they If genes are on different chromosomes, they
sort independentlysort independently
Genes on the same chromosome Genes on the same chromosome tend to be inherited togethertend to be inherited together
They are on the same chromosome. They are on the same chromosome. Considered to be “linked”.Considered to be “linked”.
Recombination creates new Recombination creates new combination of “linked” allelescombination of “linked” alleles
The farther away two genes are on a chromosome The farther away two genes are on a chromosome from each other, the more likely they will be from each other, the more likely they will be exchanged during crossing overexchanged during crossing over
The closer together two genes are on a The closer together two genes are on a chromosome, the more likely they will travel chromosome, the more likely they will travel together together
Sex chromosomesSex chromosomes Differ in appearanceDiffer in appearance Only small parts are Only small parts are
homologous (carrying same homologous (carrying same genes)genes)
Sex-linked genesSex-linked genes Found only on one of the sex Found only on one of the sex
chromosomeschromosomes Only 20 genes on YOnly 20 genes on Y
Related to male characteristicsRelated to male characteristics 1500 genes on X1500 genes on X
Related to a variety of traits (few Related to a variety of traits (few are gender-related)are gender-related)
Sex determinationSex determination
Male determines Male determines the gender in the gender in mammalsmammalsHow so?How so?
Birds are the Birds are the oppositeoppositeFemales XY, Females XY,
Males XXMales XX
Sex-linked inheritance: Sex-linked inheritance: Eye color in fruit fliesEye color in fruit flies
Incomplete dominanceIncomplete dominance
Snapdragon exampleSnapdragon example Heterozygote is Heterozygote is
intermediate between the intermediate between the two homozygotestwo homozygotes R codes for enzyme R codes for enzyme
catalyzing production of red catalyzing production of red pigmentpigment
R’ codes for non-functional R’ codes for non-functional enzymeenzyme
Amount of enzyme Amount of enzyme determines amount of determines amount of pigmentpigment
Human eye color:Human eye color:Polygenic, incomplete dominancePolygenic, incomplete dominance
CodominanceCodominance
Both phenotypes expressed fully.Both phenotypes expressed fully. Example: Human blood groupsExample: Human blood groups
These genes code for enzymes that These genes code for enzymes that stick sugars to cell-surface glycoproteinsstick sugars to cell-surface glycoproteins
Alleles A and B code for addition of Alleles A and B code for addition of distinct sugarsdistinct sugars
O does not code for a sugarO does not code for a sugar
Make antibodies to sugars not Make antibodies to sugars not present on own cellspresent on own cells
10%10%
40%40%
46%46%
4%4%
B or ABB or AB
A or ABA or AB
O,AB,O,AB,A,BA,B
(universal)(universal)
ABAB
B or OB or O
A or OA or O
OO
AB, A,AB, A,B, OB, O
(universal)(universal)
AA
BB
BothBoth
NeitherNeither
BB or BOBB or BO
AA or AOAA or AO
OOOO
ABAB
OO
ABAB
BB
AA
FreqFreqDonatesDonatesRe-Re-
ceivesceives
Anti-Anti-bodiesbodies
RBCsRBCsGenotypeGenotypeTypTyp
ee
Human Blood TypesHuman Blood Types
Other variationsOther variationsEnvironmental influencesEnvironmental influences
Expression of gene for black pigment in Expression of gene for black pigment in Himalayan rabbit depends upon temperatureHimalayan rabbit depends upon temperature
Most traits affected by both genes and Most traits affected by both genes and environmentenvironment
PleitropyPleitropyMultiple effects of a single geneMultiple effects of a single geneExample: Sickle cell anemiaExample: Sickle cell anemiaAlso great example from single error in a single Also great example from single error in a single
nucleotide to whole organism effectnucleotide to whole organism effect
Some human genetic diseasesSome human genetic diseases
Sickle-cell anemia: A case of Sickle-cell anemia: A case of incomplete dominanceincomplete dominanceGo from gene to whole organism effectsGo from gene to whole organism effects
Sickle cell anemia: From amino acid Sickle cell anemia: From amino acid substitution to whole body effects…substitution to whole body effects…
A A single nucleotide is substituted in 18th position of B-chain of Hb molecule (6th amino acid) GUG instead of GAG
Altered primary protein structure Valine instead of Glutamic acid
Altered tertiary structure Altered quaternary protein
structure Chains don’t fit together
correctly
Sickle cell anemia: From amino acid Sickle cell anemia: From amino acid substitution to whole body effects…substitution to whole body effects…
Hemoglobin molecules stick togetherRed blood cell shape is altered
Sickle cell anemia (cont.)Sickle cell anemia (cont.) Whole body effects (symptoms of sickle cell anemia)
Investigating human genetic disordersInvestigating human genetic disorders
Pedigrees: Use to figure out how trait is inherited Pedigrees: Use to figure out how trait is inherited (dominant, recessive, sex-linked)(dominant, recessive, sex-linked)