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Patterns of InheritanceMendel
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True-bred (all offspring of same variety) Hybridization ... Testing: amniocentesis chorionic villus sampling (CVS) The Chromosomal Theory of Inheritance ... – PowerPoint PPT presentation
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Title: Patterns of InheritanceMendel
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- Chapter 12
- Patterns of Inheritance Mendel The Gene Idea
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Mendelian genetics vocab
- Character (heritable feature, i.e., fur color)
- Trait (variant for a character, i.e., brown)
- True-bred (all offspring of same
variety) - Hybridization (crossing of 2 different
true-breds) - P generation (parents)
- F1 generation (first filial generation)
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Leading to the Law of Segregation
- Alternative versions of genes (alleles) account
for variations in inherited characteristics - For each character, an organism inherits 2
alleles, one from each parent - If the two alleles differ, then one, the dominant
allele, is fully expressed in the organisms
appearance the other, the recessive allele, has
no noticeable effect on the organisms appearance - The alleles for each character segregate
(separate) during gamete production (meiosis). - Mendels Law of Segregation
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Genetic vocabulary.
- Punnett square predicts the results of a
genetic cross between individuals of known
genotype - Homozygous pair of identical alleles for a
character - Heterozygous two different alleles for a gene
- Phenotype an organisms traits
- Genotype an organisms genetic makeup
- Testcross breeding of a recessive homozygote X
dominate phenotype (but unknown genotype)
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The Law of Independent Assortment
- Law of Segregation involves 1 character. What
about 2 (or more) characters? - Monohybrid cross vs. dihybrid cross
- The two pairs of alleles segregate independently
of each other. - Mendels Law of Independent Assortment
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Non-single gene genetics, I
- Incomplete dominance appearance between the
phenotypes of the 2 parents. Ex snapdragons - Codominance two alleles affect the phenotype in
separate, distinguishable ways.
Ex Tay-Sachs disease - Multiple alleles more than 2 possible alleles
for a gene. Ex human blood types
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Non-single gene genetics, II
- Pleiotropy genes with multiple phenotypic
effect. Ex sickle-cell anemia - Epistasis a gene at one locus (chromosomal
location) affects the phenotypic expression of a
gene at a second locus. Ex mice coat color - Polygenic Inheritance an additive effect of two
or more genes on a single phenotypic character
Ex human skin pigmentation and height
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Human disorders
- The family pedigree
- Recessive disorders Cystic fibrosis Tay-Sachs
Sickle-cell - Dominant disorders Huntingtons
- Testing amniocentesis chorionic villus
sampling (CVS)
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The Chromosomal Theory of Inheritance
- Genes have specific loci on chromosomes and
chromosomes undergo segregation and independent
assortment
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Chromosomal Linkage
- Drosophilia melanogaster
- XX (female) vs. XY (male)
- Sex-linkage genes located on a sex chromosome
- Linked genes genes located on the same
chromosome that tend to be inherited together
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Genetic recombination
- Crossing over Genes that DO NOT assort
independently of each other - Genetic maps The further apart 2 genes are, the
higher the probability that a crossover will
occur between them and therefore the higher the
recombination frequency - Linkage maps Genetic map based on recombination
frequencies
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Human sex-linkage
- SRY gene gene on Y chromosome that triggers the
development of testes - Fathers pass X-linked alleles to all daughters
only (but not to sons) - Mothers pass X-linked alleles to both sons
daughters - Sex-Linked Disorders Color-blindness Duchenne
muscular dystropy (MD) hemophilia
- X-inactivation 2nd X chromosome in females
condenses into a Barr body (e.g., tortoiseshell
gene gene in cats)
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Chromosomal errors, I
- Nondisjunction members of a pair of homologous
chromosomes do not separate properly during
meiosis I or sister chromatids fail to separate
during meiosis II - Aneuploidy chromosome number is abnormal
Monosomy missing chromosome Trisomy extra
chromosome (Down syndrome) Polyploidy
extra sets of chromosomes
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Chromosomal errors, II
- Alterations of chromosomal structure
- Deletion removal of a chromosomal segment
- Duplication repeats a chromosomal segment
- Inversion segment reversal in a chromosome
- Translocation movement of a chromosomal segment
to another
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Genomic imprinting
- Def a parental effect on gene expression
- Identical alleles may have different effects on
offspring, depending on whether they arrive in
the zygote via the ovum or via the sperm. - Fragile X syndrome higher prevalence of disorder
and retardation in males
