Lecture7BIO155BB

Lecture7BIO155BB - BIO155 Patterns of Inheritance Dr....

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Unformatted text preview: BIO155 Patterns of Inheritance Dr. Jessica Pamment Overview Overview • • • • • • Mendel and patterns of inheritance Testcross to determine genotypes Family pedigrees Diseases controlled by a single gene Variations on Mendel’s laws Chromosomal basis of inheritance Gregor Gregor Mendel • Mendel deduced fundamental laws of genetics using garden peas in 1860s • 1866 Mendel published paper arguing that parents pass on ’heritable factors’ to their offspring, responsible for inherited traits The The Structure of a Pea Pollen is a fine to coarse powder consisting of pollen grains, which produce the male gametes (sperm cells) of seed plants. SEM of Pollen from Common Plants Mendel’s Technique Mendel’s Technique for cross­fertilizing pea plants Mendel’s Approach Mendel’s Approach • Control over self or cross­fertilization • Characteristics studied occurred in two distinct forms • Mendel started off with true­breeding plants Characteristics of Pea Plants studied by Mendel by Purple and white Pea Plant Flowers Purple Mendel’s Approach Mendel’s Approach • Control over self or cross­fertilization • Characteristics studied occurred in two distinct forms • Mendel started off with true­breeding plants Monohybrid Cross Cross Mendel’s Hypotheses Mendel’s Hypotheses 1. There are alternative forms of genes, ALLELES, that determine heritable traits 1. For each trait, an organism inherits two alleles 1. Dominant allele determines organism’s appearance. Recessive allele has no noticeable effect 1. A sperm or egg carries only one allele for each trait because the two alleles segregate during production of gametes: The Law of Segregation Monohybrid Cross Cross Explanation of monohybrid cross results cross Law of Segregation Law of Segregation • Mendel found that each of seven characteristics studied had the same inheritance pattern • The Law of Segregation applies to all the traits studied • Pairs of alleles segregate during gamete formation; fusion of gametes creates allele pairs again • The Law of Segregation applies to all sexually reproducing organisms The Relationship between Alleles and The Relationship between Alleles and homologous Chromosomes The Law of Independent The Law of Independent Assortment • Mendel observed the same 9:3:3:1 ratio for all his dihybrid crosses • These results supported the hypothesis: Each pair of alleles assorts independently of the other pairs of alleles during gamete formation A Labrador Retriever Testcross A Labrador Retriever Testcross The Rules of Probability The Rules of Probability • Apply to allele segregation and fertilization • Mendel used large samples to observe patterns of inheritance accurately • The chance of a gamete carrying either allele of a particular gene is 1/2 • The probability of two particular alleles coming together at fertilization is 1/4 Segregation of Segregation of alleles and fertilization as chance events Family Pedigrees Family Pedigrees • Mendel’s law applies to the inheritance of many human traits determined by one gene • The inheritance of human traits is studied using family trees • Mendel’s concept of dominant and recessive alleles and law of segregation apply Inherited Traits in Humans Humans Fig. 9-13 First generation (grandparents) Ff Ff ff Ff Second generation (parents, aunts, and uncles) Third generation (brother and sister) FF or Ff ff ff Ff Ff ff ff FF or Ff Female Male Attached Free Fig. 9-13b Fig. 9-13c Fig. 9-14 Parents Hearing Dd Hearing Dd Offspring D Sperm d D Eggs d DD Hearing Dd Hearing (carrier) Dd Hearing (carrier) dd Deaf Family Pedigree Showing Inheritance of Deafness Family Human disorders caused by a Human disorders caused by a single gene • Recessive disorders: most human genetic disorders are caused by recessive alleles. Range in severity from relatively harmless to deadly • Dominant disorders: range from non­lethal to lethal • Dominant alleles that are lethal are much less common than lethal recessives Predicted offspring when both parents are carriers for a recessive disorder Predicted Human disorders caused by a Human disorders caused by a single gene • Recessive disorders: most human genetic disorders are caused by recessive alleles. Range in severity from relatively harmless to deadly. Example: cystic fibrosis • Dominant disorders: range from nonlethal to • lethal Dominant alleles that are lethal are much less common than lethal recessives Dwarfism • Dwarfism can be caused by 200 different medical conditions • Achondroplasia, a bone­growth disorder, is responsible for 70% of dwarfism cases Achondroplasia Dwarfism • The most common type of dwarfism • It can be inherited in an autosomal dominant pattern • Can be inherited, but 80% of cases are due to new mutations of gene FGFR3 that can’t be explained live more than 12 months • A homozygous for achondroplasia allele will not Achondroplasia, a dominant trait dominant Molly Jo Matt Amy Zachary Jake Jeremy Fig. 9-16a Parents Normal (no achondroplasia) dd Dwarf (achondroplasia) Dd d Sperm d D Eggs d Dd Dwarf Dd Dwarf dd Normal dd Normal Autosomal Disorders in Humans Autosomal Variations on Mendel’s Laws Variations on Mendel’s Laws • Incomplete dominance: the expression of one intermediate trait • Multiple alleles and codominance: the expression of both alleles • Pleiotropy: the impact of one gene on more than one characteristic • Polygenic inheritance: the additive effect of two or more genes on a single phenotypic characteristic Incomplete Dominance in Snapdragons Snapdragons Incomplete Dominance Incomplete Dominance Incomplete Dominance in Humans Incomplete Dominance in Humans Multiple Alleles for ABO Blood Group Multiple Alleles for ABO Blood Group Blood-Typing Blood-Typing Blood-Typing Blood-Typing Pleiotropy and Sickle­cell disease Pleiotropy and Sickle­cell disease • Pleiotropy is when one gene affects more than one characteristic • Sickle cell allele makes abnormal hemoglobin • Hemoglobin crystallizes to form sickle shaped cells • Abnormal sickle cells results in series of symptoms • Sickle­cell allele codominant with normal allele Pleiotropy Pleiotropy Sickle­cell disease, multiple effects of a Sickle­cell disease, multiple effects of a single human gene Polygenic Inheritance Polygenic Inheritance • The additive effect of two or more genes on a single phenotypic characteristic • Examples: skin color and weight A model for the polygenic inheritance of skin color of Nature vs. Nurture Nature vs. Nurture • Many characteristics are determined both by genes and the environment • Height can be affected by nutrition; a tree’s leaves vary in size and shape depending on exposure to sun, wind, etc • Some traits are solely dependent on genes, such as ABO blood types Nature vs. Nurture Nurture Summary Summary • Mendel is the founder of modern genetics • Mendel came up with the Law of Segregation and the Law of Independent Assortment • Rules of probability applicable to inheritance. The chance of inheriting any particular allele from either parent is 1/2 • Family pedigrees to determine patterns of inheritance in humans Mendel’s Law of Segregation Mendel’s Summary Summary • Variations in Mendel’s laws: • Incomplete dominance results in intermediate traits • Codominance results in both alleles being expressed, e.g. ABO blood group • Pleiotropy, where one allele has an effect on several traits, e.g. sickle cell disease. One copy of allele can be beneficial to protect against malaria • Polygenic inheritance, where several genes affect one trait Pleiotropy Pleiotropy Polygenic Inheritance Polygenic Inheritance Chromosomal Theory of Inheritance Chromosomal Theory of Inheritance • Genes are located at specific positions on chromosomes • It is the chromosomes that segregate and assort independently during meiosis • The behavior of chromosomes accounts for inheritance patterns Chapter 8 $100 Question • Genes are carried on ______. – a. centrosomes – b. chiasma – c. nuclei – d. chromosomes ANSWER BACK TO GAME Chapter 8 $100 Answer • Genes are carried on ______. – a. centrosomes – b. chiasma – c. nuclei – d. chromosomes BACK TO GAME Chapter 8 1? $200 Question •Which of the following events occurs during stage – a. chromosomes line up on the midline of the cell – b. nucleoli reappear – c. the mitotic spindle begins to form – d. cytokinesis ANSWER Chapter 8 prophase? $200 Answer •Which of the following events occurs during – a. chromosomes line up on the midline of the cell – b. nucleoli reappear – c. the mitotic spindle begins to form – d. cytokinesis Chapter 8 $300 Question •Homologous chromosomes _________. – a. carry the same gene sequence – b. are a set of chromosomes that a cell receives from one parent – c. do not include the sex chromosomes – d. are formed when chromosomes separate during anaphase ANSWER Chapter 8 $300 Answer •Homologous chromosomes _________. – a. carry the same gene sequence – b. are a set of chromosomes that a cell receives from one parent – c. do not include the sex chromosomes – d. are formed when chromosomes separate during anaphase Chapter 8 _________. $400 Question • A duplicated chromosome has two sister – a. centromeres – b. centrosomes – c. chromatids – d. chromatins ANSWER Chapter 8 _________. $400 Answer • A duplicated chromosome has two sister – a. centromeres – b. centrosomes – c. chromatids – d. chromatins •Which of the following events occurs during stage 4? – a. chromosomes align on the midline of the cell – b. the cleavage furrow forms – c. tetrads form – d. centromeres divide ANSWER Chapter 8 $500 Answer •Which of the following events occurs during telophase? – a. chromosomes align on the midline of the cell – b. the cleavage furrow forms – c. tetrads form – d. centromeres divide Chapter 9 $100 Question •When is amniocentesis usually performed? – a. during the third trimester – b. between week 14 and week 20 of pregnancy – c. prior to the fourth week of pregnancy – d. after the birth of the child ANSWER Chapter 9 $100 Answer •When is amniocentesis usually performed? – a. during the third trimester – b. between week 14 and week 20 of pregnancy – c. prior to the fourth week of pregnancy – d. after the birth of the child Chapter 9 $200 Question • Who was a monk known for his work on inheritance using garden peas? – a. Carolus Linneaus – b. Charles Darwin – c. Gregor Mendel – d. Louis Pasteur ANSWER Chapter 9 $200 Answer • Who was a monk known for his work on inheritance using garden peas? – a. Carolus Linneaus – b. Charles Darwin – c. Gregor Mendel – d. Louis Pasteur Chapter 9 $300 Question • An individual heterozygous for cystic fibrosis _______. – a. is a carrier of cystic fibrosis – b. cannot reproduce – c. has cystic fibrosis – d. cannot have children with cystic fibrosis ANSWER Chapter 9 $300 Answer • An individual heterozygous for cystic fibrosis _______. – a. is a carrier of cystic fibrosis – b. cannot reproduce – c. has cystic fibrosis – d. cannot have children with cystic fibrosis Chapter 9 $400 Question •What is the genotype of an individual who is heterozygous for dimples? – – – – a. DD b. dd c. Dd d. dimples ANSWER Chapter 9 $400 Answer •What is the genotype of an individual who is heterozygous for dimples? – – – – a. DD b. dd c. Dd d. dimples Chapter 9 $500 Question •What is the name given to the specific location of a gene on a chromosome? – – – – a. phenotype b. locus c. site d. allele ANSWER Chapter 9 $500 Answer •What is the name given to the specific location of a gene on a chromosome? – – – – a. phenotype b. locus c. site d. allele BACK TO GAME • All the offspring of a white hen and a black • • • • rooster are gray. The simplest explanation for this pattern of inheritance is A. pleiotropy B. sex linkage C. codominance D. incomplete dominance • A true­breeding brown mouse is repeatedly mated with a true­breeding white mouse, and all their offspring are brown. If two of these brown offspring are mated, what fraction of the F2 mice will be brown? ...
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This note was uploaded on 04/25/2011 for the course BIO 155 taught by Professor Skoubis during the Fall '10 term at DePaul.

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