Genetic Crosses

Genetics “study of genes and heredity” “study of genes and heredity” Gene – segment of DNA that codes for a Gene – segment of DNA that codes for a particular trait particular trait Heredity – study of how traits are passed on Heredity – study of how traits are passed on from parent to offspring from parent to offspring

Gregor Mendel “Father of Genetics” “Father of Genetics” Studied garden pea plants Studied garden pea plants Experiment results  P 1 generation Experiment results  P 1 generation F 1 generation F 1 generation F 2 generation F 2 generation

Gene Expression Genotype – actual genetic makeup of an Genotype – actual genetic makeup of an organism (can’t see it) organism (can’t see it) Phenotype – physical expression of a trait Phenotype – physical expression of a trait (what you see) (what you see)

Traits Dominant – allele found in all generations Dominant – allele found in all generations because it dominates the other because it dominates the other allele allele - represented by capital letter - represented by capital letter Recessive – has no observable effect on an Recessive – has no observable effect on an organism when paired with a organism when paired with a dominant trait dominant trait - represented by lowercase letter - represented by lowercase letter

Homozygous – both alleles are the same Homozygous – both alleles are the same Heterozygous – alleles are different Heterozygous – alleles are different Monohybrid Crosses – cross using only one Monohybrid Crosses – cross using only one trait trait

Punnett Square

Steps for Solving Monohybrid Crosses Read the problem carefully Read the problem carefully Identify dominant trait and assign is a CAPTIAL letter symbol Identify dominant trait and assign is a CAPTIAL letter symbol Assign the recessive trait a lower case letter of the dominant symbol Assign the recessive trait a lower case letter of the dominant symbol Identify the genotypes of the parents Identify the genotypes of the parents Form the gametes Form the gametes Fill in the square Fill in the square Count the genotypes and phenotypes Count the genotypes and phenotypes

Example In a pea plant, tall is dominant to short. Cross a homozygous tall with a heterozygous tall plant.

Incomplete, Complete and Codominance

Incomplete v. Complete Dominance Complete Dominance – one allele is completely dominant over another Complete Dominance – one allele is completely dominant over another * PP and Pp (both dominant) * PP and Pp (both dominant) Incomplete Dominance – phenotype in F1 generation that is between that of the parents Incomplete Dominance – phenotype in F1 generation that is between that of the parents RR – dominant RR – dominant rr – recessive rr – recessive Rr – intermediate (mix between the colors) Rr – intermediate (mix between the colors)

Example of Incomplete Dominance

Codominance neither allele is dominant; both alleles for a gene are expressed in a heterozygous offspring neither allele is dominant; both alleles for a gene are expressed in a heterozygous offspring Example: R – represents red Example: R – represents red W - represents white W - represents white RW - represents roan (both colors present) RW - represents roan (both colors present)

Multiple Allele Traits “traits whose genes have more than 2 alleles” “traits whose genes have more than 2 alleles” Human Blood Types Human Blood Types 4 blood types 4 blood types 1. Type A, Type B, Type AB, Type O 1. Type A, Type B, Type AB, Type O Genotypes Genotypes 1. I A I A, I A I O Type A 1. I A I A, I A I O Type A 2. I B I B, I B I O Type B 2. I B I B, I B I O Type B 3. I A I B Type AB 3. I A I B Type AB 4. I O I O Type O 4. I O I O Type O Almost to the end Almost to the end

RH Factor in the Blood RH+ = have the protein RH+ = have the protein RH- = does not have the protein RH- = does not have the protein Genotypes Phenotypes Genotypes Phenotypes IRH+/IRH+ RH+ IRH+/IRH+ RH+ IRH+/IRH- IRH+/IRH- IRH-/IRH- RH- IRH-/IRH- RH-

Example Tommy has Type AB+ (homozygous RH+) blood. He marries Susie who is homozygous B-. Tommy has Type AB+ (homozygous RH+) blood. He marries Susie who is homozygous B-.

More Examples More Examples 1. Bob has homozygous A blood. He marries Jane who has AB blood. What are the possible blood types of the offspring?

2. Betty has type O blood. She has a child that has type A blood. She claims Jim is the father. He has type B blood. Can he be the father? Show all the work to make your determination.

Sex Determination Early 1900s – Thomas Hunt Morgan Early 1900s – Thomas Hunt Morgan Female – X-X Female – X-X Male – X-Y Male – X-Y Sex chromosomes – chromosomes which determine sex Sex chromosomes – chromosomes which determine sex

Sex-Linked Traits “traits who genes are found on the X chromosome” “traits who genes are found on the X chromosome” Genotypes example Genotypes example 1. X H X H – normal female 1. X H X H – normal female 2. X H X h – normal female who is a carrier 2. X H X h – normal female who is a carrier 3. X h X h – abnormal female 3. X h X h – abnormal female 4. X H Y – normal male 4. X H Y – normal male 5. X h Y – abnormal male 5. X h Y – abnormal male

Example 1. A mother that was normal/non carrier for hemophilia married a man that was a hemophiliac. What is the probability that they will have a child that is a hemophiliac?

Polygenic Traits “traits that have more than one gene” “traits that have more than one gene” Most common Most common Skin color, height, weight, eye color, fur color Skin color, height, weight, eye color, fur color

Human Genetic Studies

Pedigrees “a family record that shows how a trait is inherited over several generations” “a family record that shows how a trait is inherited over several generations”

Practice 1.What are the genotypes of both sets of parents? 2.What are the genotypes of each child from both sets of parents? 3.What is the relationship between offspring 8 and 9? 4.What is the relationship between offspring 13 and 1?

Genetic Disorders “diseases which are expressed on the chromosomes” “diseases which are expressed on the chromosomes” Single-Allele Traits Single-Allele Traits 1. Cystic Fibrosis – failure for the chloride ion 1. Cystic Fibrosis – failure for the chloride ion transport mechanism transport mechanism * mucus clogs the liver, lungs, and pancreas * mucus clogs the liver, lungs, and pancreas

X-Linked Traits X-Linked Traits 1. Colorblindness 1. Colorblindness 2. Hemophilia 2. Hemophilia 3. Duchenne muscular Dystrophy 3. Duchenne muscular Dystrophy More Genetic Disorders More Genetic Disorders 1. Tay-sachs 1. Tay-sachs 2. PKU 2. PKU

Gene Mutation Disorders “something changes in the genes” “something changes in the genes” Point Mutation – one nitrogenous base is replaced by a different nitrogenous base Point Mutation – one nitrogenous base is replaced by a different nitrogenous base * Sickle cell Anemia – results in defective * Sickle cell Anemia – results in defective form of the protein hemoglobin form of the protein hemoglobin

Review slide of mutations “any change in an organism’s DNA” “any change in an organism’s DNA” Change DNA  Change RNA  change protein Change DNA  Change RNA  change protein Somatic Cell Mutations Somatic Cell Mutations 1. cannot be passed to offspring 1. cannot be passed to offspring 2. ex) Cancer (human skin cancer, leukemia) 2. ex) Cancer (human skin cancer, leukemia) Germ-Cell Mutations Germ-Cell Mutations 1. occur in organism’s germ cell (gametes) 1. occur in organism’s germ cell (gametes) 2. can be passed on to offspring 2. can be passed on to offspring

Nondisjuntion Mutation “failure of chromosome to separate from it’s homologue during meiosis” “failure of chromosome to separate from it’s homologue during meiosis” One extra or one less chromosome at chromosome location One extra or one less chromosome at chromosome location Monosomy v. Trisomy Monosomy v. Trisomy

Examples of Nondisjunction Disorders Down Syndrome (Trisomy 21) Down Syndrome (Trisomy 21) 1. extra chromosome extra chromosome Symptoms – mental retardation, muscle 2. Symptoms – mental retardation, muscle weakness, large forehead, large weakness, large forehead, large tongue, heart defects, short tongue, heart defects, short stature stature

Klinefelters Syndrome Klinefelters Syndrome 1. male with extra X chromosome (XXY) 1. male with extra X chromosome (XXY) 2. Symptoms: sometimes mental retardation, 2. Symptoms: sometimes mental retardation, infertile, some feminine infertile, some feminine characteristics, undersized characteristics, undersized testicles testicles Turners Syndrome Turners Syndrome 1. single X chromosomes (XO) 1. single X chromosomes (XO) 2. female appearance, infertile 2. female appearance, infertile due to not maturing due to not maturing sexually sexually

Karyotypes of Individuals with Genetic Disorders

Detecting Genetic Disorders Genetic Screening Genetic Screening 1. examining a person’s DNA 1. examining a person’s DNA 2. Karyotype 2. Karyotype Ways to get a cell sample Ways to get a cell sample 1. amniocentesis 1. amniocentesis 2. chorionic villi sampling 2. chorionic villi sampling Finding deformities Finding deformities 1. ultrasound 1. ultrasound