Introduction to Mendelian Genetics Introduction to Mendelian Genetics.
12 Medelian Genetics Presentation - Rob Channell Mendelian Genetic… · Mendelian Genetics Lecture...
Transcript of 12 Medelian Genetics Presentation - Rob Channell Mendelian Genetic… · Mendelian Genetics Lecture...
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Mendelian GeneticsLecture 12
At the end of this series of lectures, you should be able to:
Define terms.
Explain how recessive and dominant disorders are inherited. Provide examples of each.
Explain the chromosomal basis of the laws of segregation and independent assortment.
Explain how family pedigrees can help determine the inheritance of many human traits.
Objectives
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Describe the inheritance patterns of incomplete dominance, multiple alleles, codominance, pleiotropy, and polygenic inheritance. Provide an example of each.
Explain how linked genes are inherited differently from nonlinked genes.
Explain how crossing over produces new combinations of alleles.
Explain why sex‐linked disorders are expressed more frequently in men than in women.
Explain how family pedigrees can help determine the inheritance of many human traits.
Objectives
Heredity
The transmission of traits from one generation to the next.
Genetics
The scientific study of heredity.
Terms
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Gregor Mendel
Monk
Father of genetics
Cheated
Discrete inheritable factors
Mendel
Short generation time. Large numbers of offspring. Many readily distinguishable varieties.
Flower color Flower position Seed color Seed shape Pod color Pod shape Stem length
Peas
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Character
Trait
Self‐fertilization
Cross‐fertilization
P
F1 F2
Terms
Genes Alleles Homozygous Heterozygous Dominant Recessive
Convention in the notation associated with dominant/recessive traits
Phenotype Genotype
Monohybrid cross
Terms
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A sperm or egg only carries one allele for each inherited character.
Homologous chromosomes separate in anaphase I and sister chromatids separate in anaphase II.
Law of Segregation
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Madprime, Public Domain, http://commons.wikimedia.org/wiki/File:Punnett_square_mendel_flowers.svg
Law of Independent Assortment
The inheritance of one character does not affect the inheritance of another character.
Dihybrid cross
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Biology by OpenStax College is licensed under a Creative Commons Attribution 3.0
Testcross
If you want to know the genotype of an organism with a dominant phenotype (could be homozygous dominant or heterozygous) what do you do.
Mate it with an individual with the recessive phenotype.
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DominantRecessive
Gideon Tsang, CC BY‐SA 2.0, http://en.wikipedia.org/wiki/Tongue_rolling#mediaviewer/File:Rolled_tongue_flikr.jpg
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DominantRecessive
Armin Kübelbeck, CC BY‐SA 3.0, http://de.wikipedia.org/wiki/Spitzer_Haaransatz#mediaviewer/Datei:Widows_peak_01.jpg
Frank Vincentz, CC BY‐SA 3.0, http://en.wikipedia.org/wiki/Forehead#mediaviewer/File:Forhead_01_ies.jpg
Pedigree
Jerome Walker, CC BY‐SA 3.0, http://commons.wikimedia.org/wiki/File:Autosomal_Dominant_Pedigree_Chart.svg
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Inherited Disorders
Can be either dominant or recessive traits Most frequently recessive traits
Recessive inheritance Two recessive alleles are needed to show disease. Heterozygous parents are carriers of the disease‐causing allele, and The probability of inheritance increases with mating between close
relatives.
Dominant inheritance One dominant allele is needed to show disease. Dominant lethal alleles are usually eliminated from the population.
Genetic testing Tay Sachs
Fetal Testing Amniocentesis
Chorionic villus sampling
Newborn screening Phenylketonuria
Ethical considerations
Genetic Legacy
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The F1 offspring are intermediate between the two parental traits.
F2 offspring show both parental traits and an intermediate trait.
Incomplete Dominance
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Multiple Alleles
Most genes have more than two alleles.
Codominance – Both alleles are expressed in a heterozygous individual.
ABO blood groups.
Anatomy and Physiology, OpenStax College, CC BY 3.0, http://commons.wikimedia.org/wiki/File:1913_ABO_Blood_Groups.jpg
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Pleiotropy
One gene influences multiple characters.
More than one gene influences a single character.
Polygenic Inheritance
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Law of Segregation and the Law of Independent Assortment are the results of chromosomal behavior in meiosis.
Chromosomal Basis of Inheritance
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Genetic Linkage
Genes that are located on the same chromosome tend to be inherited together.
Linked genes
Do not follow the Law of Independent Assortment.
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Sex Determination
XY – Mammals XX – Females
XY ‐‐Males
XO – Some insects XX – Females
XO – Males
ZW – Birds ZW – Females
ZZ ‐‐Males
Chromosome number (egg is fertilized or not) – Other insects
32 Chromosomes ‐‐ Females
16 Chromosomes ‐‐Males
Environment – Some reptiles
Incubate warm – Males
Incubate cool ‐‐ Females
In mammals, the X chromosome contains many genes and the Y chromosome contains very few genes.
In a male, which has only one copy of the X chromosome, if a gene on their X is flawed it will be expressed.
In a female, which has two copies of the X chromosome, if a gene is on one of their X is flawed it probably will not be expressed – they have another copy which is probably not flawed. Carriers.
Sex‐linked Inheritance
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