chapter 9- patterns of inheritance
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Chapter 9- Patterns of Inheritance. ABO blood groups Alleles Amniocentesis Carrier Chorionic villus sampling Chromosome theory of inheritance Codominance Cross Cross-fertilization Cystic fibrosis Dihybrid cross Dominant allele F1 generation F2 generation Genetics Genotype - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 9- Patterns of Inheritance• ABO blood groups• Alleles• Amniocentesis• Carrier• Chorionic villus sampling• Chromosome theory of inheritance• Codominance• Cross• Cross-fertilization• Cystic fibrosis• Dihybrid cross• Dominant allele• F1 generation• F2 generation• Genetics• Genotype• Hemophilia• Hermaphroditic• Heterozygous• Homozygous
• Hybrids• Incomplete dominance• Linked genes• Monoecious• Monohybrid cross• P generation• Pedigree• Phenotype• Pleiotropy• Polygenic inheritance• Principle of independent assortment• Principle of segregation• Punnett square• Recessive allele• Recombination frequency• Rule of addition• Rule of multiplication• Self-fertilize • Sex chromosomes• Sex-linked genes• Testcross• Ultrasound imaging
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Genetics
• Study of heredity
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Gregor Mendel
• Monk, father of modern genetics, 1860’s
• Discovered genetic principles by meticulous breeding of pea plants
• Used peas because they were readily available, easy to grow, had many distinguishable traits, could control mating
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Pea Traits
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Genetic Cross Vocabulary
• Self-fertilize- sperm from pollen fertilizes egg containing carpel
• Cross-fertilization- fertilizing one plant from pollen of another plant– Offspring produced
are hybrids• P generation (parent)• F1 generation – offspring of
P • F2 generation- offspring of
F1, can be self- or cross- fertilized
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Genetic Cross Vocabulary con’t• Monohybrid cross- parents
differ in only one trait• Alleles- alternate forms of a
gene A (dominant) or a (recessive)
• Homozygous- alleles for a trait are identical, AA
• Heterozygous- alleles are different, Aa
• Phenotype- organism’s physical trait expressed– Ex: purple flower
• Genotype- genetic make up of trait– Ex: PP
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• Alleles for a gene are at the same locus (point) on homologous chromosomes
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Mendel’s hypotheses:
• There are alternative forms of genes (units that determine traits)
• For each characteristic- an organism has a gene from each parent, they can be the same allele or different
• Sperm and egg each have 1 allele for a trait
• Idea of dominant and recessive alleles
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Mendel’s Principle of Segregation
• Pairs of genes segregate (separate) during gamete formation (what is that process called?)– gametes fusing
during fertilization regain pairs of genes
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Mendel’s Principle of Independent Assortment
• Each pair of alleles segregates independently during gamete formation
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• Dihybrid cross- cross between parents that differ in 2 traits
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Mendel’s principles reflect probability
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How can we determine an unknown genotype?
• Testcross- mating between an unknown individual and a homozygous recessive individual
Rule of multiplication- probability that a compound event is the product of the separate probabilities of the independent events
Ex: b from mom (1/2), b from dad (1/2)
baby being bb ½ x ½ = ¼ Rule of addition- probability that an event can occur in 2 or more alternative ways is the sum of the separate probabilities of different ways
Ex: in Punnet square Bb = ¼ the other Bb is ¼probability of being Bb is ¼ + ¼ = 2/4 = ½
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What about humans?
• To find human inheritance information:– Collect as much family data as possible– Construct pedigree chart– At first heterozygotes are not known, must
determine phenotypes of offspring then could lead to information on carriers (heterozygotes)
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Chart Key
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Pedigree Chart
• Can you figure out carriers and genotypes from this pedigree?
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Many genetic disorders are a result of a single gene
– Most are recessive • family may not know of defect until offspring with two
recessive alleles is born• Ex: CF cystic fibrosis
– Dominant traits are not always prevalent just because they are dominant, usually due to lethality of disorder (death before reproduction)
• Ex: polydactyly, achondroplasia
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How can we detect genetic disorders?
• Fetal testing– Amniocentesis-
cells from amnionic fluid is tested
– CVS- chorionic villi sampling- fetal tissue from placenta is tested
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– Ultrasound/sonogram- uses sound waves to product picture of fetus
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• Genetic screening– Most test DNA but some test enzymes– Most tell risk of disorders that depend on multiple genes– Types of testing
• Carrier- determine if you are a carrier of a harmful allele• Diagnostic- confirm or rule out disorder• Prenatal- checks for disorders in fetuses• Newborn- catches inherited disorders quickly so medical attention
can be given, “heel prick”• Predictive- test at any time to determine risk for developing
disorder– Ex: BRAC1 and 2- linked to breast cancer, Huntington’s disease
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Variations of Mendel’s PrinciplesGenotype/phenotype relationship is not always
straightforward• Incomplete dominance
– produces intermediate phenotypes• Ex: hypercholesterolemia• HH= normal, Hh=slightly affected,
hh=has disease severely
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• Codominance– when both alleles are expressed in the phenotype
• Ex: ABO bloodgroups• Some genes have more than 2 alleles, each individual
can only have 2• A, B, AB or O bloodgroups –AB is codominant
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• Pleiotrophy– impact of single gene on more than one characteristic
• Ex: sickle-cell disease – abnormal hemoglobin molecules are produced
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• Polygenic inheritance– affect of 2 or more genes on a single phenotype
trait• Ex: human skin color, height
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Other genes are on sex chromosomes
• Sex chromosomes- determine sex in species– Humans- X and Y are sex chromosomes
• Each have 44 autosomes (22pairs) and 1 pair of sex chromosomes XX-female or XY- male
• Males determine sex of offspring because they can pass X or Y, females only pass X
• SRY gene on Y chromosome triggers testes development, without it, ovaries are developed
• Fruit flies- # of X’s determine male or female, however presence of Y is essential for sperm production
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Sex chromosomes con’t
– X-O system- grasshoppers, crickets, roaches• Female- XX male- XO (O=absence of
chromosome)– Z-W system- fish, butterflies, birds
• Males-ZZ females-ZW, eggs determine sex– Determination by chromosome #- ants and bees
• Females- diploid- develop from fertilized eggs• Males- haploid- develop from unfertilized eggs
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Some can produce both sperm and eggs
• Monoecious- plants that produce sperm and eggs – ex: corn
• Hermaphroditic- animals that produce sperm and eggs – ex: earthworms
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Sex- linked genes
• Genes located on sex chromosomes– Not related to sex determination– Mostly found on X– In humans X-linked recessive traits mostly affect
males– Females are carriers and pass to sons, sons have
no other X to dominate over the recessive allele• Ex: colorblindness, hemophilia
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Chromosome behavior accounts for Mendel’s principles:
• Chromosomal Theory of Inheritance– Genes are located on chromosomes, the behavior
of chromosomes (segregation and independent assortment- Mendel’s ideas) during meiosis and fertilization accounts for the inheritance patterns
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Linked Genes
• Don’t follow Mendel’s rules • If genes are located close together they tend
to be inheritted together
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Linked Genes con’t
• Data from crossing over can lead to mapping genes, farther apart they are greater chance of crossing over in between the genes
• Crossing over accounts for new gene combinations– Morgan worked with fruit flies to develop:– Recombination frequency- % of recombinants in
offspring
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Gene Map