4.3: Theoretical Genetics

4.3: Theoretical Genetics ★Define genotype, phenotype, dominant allele, recessive allele, codominant alleles, locus, homozygous, heterozygous, carrier and test cross. ★Determine the genotypes and phenotypes of the offspring of a monohybrid cross using a Punnett grid. ★Predict the genotypic and phenotypic ratios of offspring of monohybrid crosses involving any of the above patterns of inheritance.

4.3: Theoretical Genetics ★State that some genes have more than two alleles (multiple alleles). ★Describe ABO blood groups as an example of codominance and multiple alleles. ★Explain how the sex chromosomes control gender by referring to the inheritance of X and Y chromosomes in humans. ★State that some genes are present on the X chromosome and absent from the shorter Y chromosome in humans.

4.3: Theoretical Genetics ★Define sex linkage. ★Describe the inheritance of color blindness and hemophilia as examples of sex linkage. ★State that a human female can be homozygous or heterozygous with respect to sex-linked genes. ★Explain that female carriers are heterozygous for X-linked recessive alleles. ★Deduce the genotypes and phenotypes of individuals in pedigree charts.

4.3: Theoretical Genetics • Theoretical Genetics is a fancy term for what you have already done before - Punnett squares and pedigrees! • Predicting traits in future generations based on parental traits. • Who is known as the father of genetics? • Gregor Mendel

4.3: Theoretical Genetics • In 1865 Gregor Mendel, an Austrian monk, published results of his experiments on how garden pea plants passed on their characteristics. • Why did he chose to work with pea plants? • Cheap, fast reproduction, no incest • At the time, the term "gene or DNA" did not exist (discovered 100 years later), so he worked with physical characteristics of pea plants - what he could see with his own 2 eyes.

4.3: Theoretical Genetics • Mendel used artificial pollination in his experiments where he carefully chose the pollen of various plants to fertilize other plants. • Pollen = gametes (sex cells) • Insects do this naturally - that is why many flowers are brightly colored, to attract insects, like bees, to pollinate, or transfer gametes from flower to flower.

4.3: Theoretical Genetics • In one cross, he fertilized short plants with tall plants and the resulting offspring were all tall. • When he took those tall offspring, and crossed them with each other, most were tall, but the short characteristic reappeared. • Mendel determined that inheritance is based on factors that can be passed on from generation to generation = genes. • Different forms of a gene = alleles

4.3: Theoretical Genetics • Genotype: symbolic representation of alleles possessed by an organism, its genetic makeup, represented by a pair of letters. • EX: AA or Aa • Phenotype: physical characteristics of an organism, can be external like flower color, or internal like sickle-cell anemia. • EX: Tall, red, color-blind

4.3: Theoretical Genetics • Dominant allele: an allele that has the same effect on the phenotype whether it's paired with the same allele or a different one. Dominant alleles are always expressed in the phenotype. Represented by a capital letter. • EX: genotype Aa (allele A is dominant) • Recessive allele: an allele that has an effect on the phenotype only when present as homozygous. Represented by a lowercase letter. • EX: genotype aa (allele a is recessive)

4.3: Theoretical Genetics • Codominant alleles: pairs of alleles that both affect the phenotype when in a heterozygous state. • EX: a blood type A parent and a blood type B parent will have a child who is type AB • Locus: the specific position of a gene on a homologous chromosome. Each gene is found at a specific place on a specific pair of chromosomes. • EX: Insulin gene always found at same position on chromosome 11 in humans

4.3: Theoretical Genetics • Homozygous: 2 identical alleles of a gene at the same locus. Alleles can be both dominant or both recessive. • EX: AA is homozygous dominant, aa is homozygous recessive. • Heterozygous: 2 different alleles of a gene at the same locus. This is because one is the parental allele, other is maternal allele. • EX: Aa is a heterozygous genotype

4.3: Theoretical Genetics • Carrier: An individual who has a recessive allele of a gene that does not have an effect on their phenotype (phenotype version of heterozygote) • EX: Aa carries the albino gene, but this person wouldn't be albino. • Test Cross: Testing a suspected heterozygote by crossing it with a known homozygous recessive. Since a recessive allele can be masked, it is often impossible to tell if an organism is AA or Aa until they produce offspring which have the recessive trait. • EX: Aa crossed with aa

4.3: Theoretical Genetics • Let's test out some of these vocab words: • Is RR the genotype or phenotype? • Is Yellow the genotype or phenotype? • If red R is dominant to yellow r, what is the phenotype of each of the following genotypes? • RR: • Rr: • rr:

4.3: Theoretical Genetics • What would be the gametes produced by a parent with each of the following genotypes? • Rr: • rr: • RR: • Label the following as either homozygous dominant, homozygous recessive, or heterozygous. • Rr: • rr: • RR:

4.3: Theoretical Genetics • Constructing a Punnett Grid: • IB calls them Punnett Grids, we are used to calling them Punnett Squares. Same thing! • A Punnett grid shows all possible combos of genetic information for a particular trait. • All the Punnett grids in IB are for monohybrid crosses, which means they show the results for one trait only. • This means we will only be doing grids with 4 squares.

4.3: Theoretical Genetics • Practice Punnett Grid 1: • Trait is for height • allele key: T=tall, t=short • Parents: TT x tt • 4 gametes: T, T, t, t • Genotype ratio: 4 Tt • Phenotype ratio: 4 tall

4.3: Theoretical Genetics • Practice Punnett Grid 2: • Trait is for color • allele key: R=red, t=white • Parents: Rr x rr • 4 gametes: R, r, r, r • Genotype ratio: • Phenotype ratio:

4.3: Theoretical Genetics • Practice Punnett Grid 3: • Trait is for albinism • allele key: A=normal, a=albino • Parents: Aa x Aa • 4 gametes: • Genotype ratio: • Phenotype ratio: • What are the chances of this couple having an albino child?

4.3: Theoretical Genetics • Practice Punnett Grid 4: • Trait is for albinism • allele key: A=normal, a=albino • Cross a heterozygote with a homozygous dominant individual. • Parents: ____ x ____ • Genotype ratio: • Phenotype ratio: • What are the chances of this couple having a normal child?

4.3: Theoretical Genetics • Practice Punnett Grid 5: • Trait is flower color • allele key: G=green, g=orange • Cross a orange plant with a homozygous green plant. • In the F2 generation, what percent chance will there be orange offspring?

4.3: Theoretical Genetics • Codominance and Multiple Alleles: • So far, we have only dealt with 2 possibilities for a gene: either dominant A, or recessive a. • With 2 alleles, 3 genotypes are possible (AA, Aa, aa) which produce 2 phenotypes. • In real life, it is not always this simple, sometimes there are 3 or more alleles for the same gene. • EX: blood type, height, skin color

4.3: Theoretical Genetics • ABO human blood type system in humans has 4 possible phenotypes: • A, B, AB, O • To create these 4 blood types there are 3 different alleles of the gene. • These 3 alleles can produce 6 different genotypes. • The gene for the ABO blood type is represented by the letter I. • To represent more than just 2 alleles, I and i are both used.

4.3: Theoretical Genetics • The 3 alleles for blood type are written as: • IA = allele for type A blood • IB = allele for type B blood • i = recessive allele for type O blood • Crossing these together in all possible combos creates 6 genotypes for 4 phenotypes.

4.3: Theoretical Genetics • Notice how the genotype IA IB clearly shows codominance. • Neither allele is masked or hidden, both show expression in the phenotype at the same time. • Rather than being either A or B blood, both are dominant together to produce AB blood. • A person's blood type depends on which combination of alleles he/she receives. With blood type, only 2 alleles can be inherited, which means one from the mom, one from the dad. • Remember, blood type is an example of a trait that is both codominant and has multiple alleles!

4.3: Theoretical Genetics • Practice Punnett Grid 6: • Cross a homozygous blood type A parent with a type O parent. • Parent cross: ____ x ____ • 4 gametes: • Genotype ratio: • Phenotype ratio: • What are the chances of this couple having a type O child?

4.3: Theoretical Genetics • Practice Punnett Grid 7: • Cross a heterozygous blood type B parent with a type AB parent. • Parent cross: ____ x ____ • 4 gametes: • Genotype ratio: • Phenotype ratio: • What are the chances of this couple having a type AB child?

4.3: Theoretical Genetics • Sex Chromosome Inheritance: • The 23rd pair of chromosomes are called sex chromosomes because they determine a person's gender. • XX = Female Xy = Male • There is a 50/50 shot of having a girl or boy baby. • WHY? Do a punnett grid for the answer: • Parent cross: XX x Xy

4.3: Theoretical Genetics • Who determines the gender of the child, the mother or father? • Explain:

4.3: Theoretical Genetics • The X chromosome is significantly larger, and thus carry more genes than the y chromosome. • For our future Punnett grids, the X chromosome will be the ONLY chromosome to carry the alleles. • The Y chromosome will carry nothing. • Any genetic trait whose allele has its locus on the X chromosome is said to be sex-linked. • Often genetic traits which show sex linkage affect one gender more than the other.

4.3: Theoretical Genetics • 2 examples of genetic traits which are this particular and we will use at length are color-blindness and hemophilia. • Colorblindness: inability to distinguish between certain colors, often green and red. To people who are color blind, these colors look the same. • Hemophilia: disorder where blood does not clot properly. These people risk bleeding to death from what most people would consider a minor injury.

4.3: Theoretical Genetics • Since the alleles for both color blindness and hemophilia are found only on the X chromosome, the letter X is used in representing them • In both cases, there is no allele on the Y chromosome, so Y is written alone without any superscript.

4.3: Theoretical Genetics

4.3: Theoretical Genetics • Practice Punnett Grid 8: • For colorblindness, cross a normal male and a heterozygous female. • Parent cross: _____ x _____ • 4 gametes: • Genotype ratio: • Phenotype ratio: • What are the chances of this couple having a normal child?

4.3: Theoretical Genetics • Practice Punnett Grid 9: • For hemophilia, cross a carrier woman with a hemophiliac male • Parent cross: _____ x _____ • 4 gametes: • Genotype ratio: • Phenotype ratio: • What are the chances of this couple having a hemophiliac male?

4.3: Theoretical Genetics • Pedigrees: • The term 'pedigree' refers to the record of an organism's ancestry. • Pedigree charts are diagrams which are constructed to show biological relationships - how a trait can pass from generation to generation. • From a pedigree, you can determine if a trait is dominant or recessive, if it is sex-linked, and probability of it affecting future generations. • To build such a chart to see the flow of genotypes, symbols and rules must be followed.

4.3: Theoretical Genetics

4.3: Theoretical Genetics • Practice Pedigree 1: • This is for color-blindness, which is sex-linked and recessive. • Color-blindness is represented with an allele b. • Determine all possible genotypes.

4.3: Theoretical Genetics • Practice Pedigree 2: • This is for hemophilia, which is sex-linked and recessive. • Hemophilia is represented with an allele h. • Determine all possible genotypes.

Topic 4: Genetics • 1. Which of the following is an inherited disease that is due to a base substitution mutation in a gene? • A. Trisomy 21 • B. Sickle cell anemia • C. AIDS • D. Type II Diabetes • Answer: A

Topic 4: Genetics • 2. Which of the following is the cause of sickle-cell anemia? • A. Tryptophan is replaced by leucine. • B. Leucine is replaced by valine. • C. Glutamic acid is replaced by valine. • D. Lysine is replaced by glutamic acid. • Answer: C

Topic 4: Genetics • 3. What is the cause of sickle-cell anemia? • A. A change to the base sequence of a hemoglobin gene. • B. Mosquitos acting as the vector for malaria. • C. Iron deficiency due to the malaria parasite. • D. Production of more white blood cells than red blood cells by bone marrow • Answer: A

Topic 4: Genetics • 4. A human cell has between 20,000-25,000 genes whereas an E. coli cell has approximately 4,000 genes. Which of the following statements is true? • A. The human genome is larger than the E. coli genome. • B. There are more genes on each human chromosome than on the E. coli chromosome. • C. The human cell and the E. coli cell produce approximately the same variety of proteins. • D. The DNA in both organisms is associated with histones (proteins). • Answer: A

Topic 4: Genetics • 5. Which of the following statements about homologous chromosomes is correct? • A. Each gene is at the same locus on both chromosomes. • B. They are two identical copies of a parent chromosome which are attached to one another at the centromere. • C. They always produce identical phenotypes. • D. They are chromosomes that have identical genes and alleles. • Answer: A

Topic 4: Genetics • 6. What happens in crossing over? • A. Exchange of genetic material between homologous chromosomes. • B. Exchange of genes during metaphase of mitosis. • C. Random distribution of chromosomes during meiosis. • D. Homologous chromosomes fail to separate during meiosis. • Answer: A

Topic 4: Genetics • 7. A cell in the testis of a male chimpanzee contains 48 chromosomes. It is about to undergo meiosis. How many molecules of DNA will be present in the nucleus of the sperm cells just after meiosis? • A. 96 • B. 48 • C. 24 • D. 12 • Answer: C

Topic 4: Genetics • 8. If the haploid number of a species is 14, how many chromatids will there be in metaphase I in a dividing diploid cell? • A. 7 • B. 14 • C. 28 • D. 56 • Answer: D

Topic 4: Genetics • 9. How many autosomes are there in a human sperm? • A. 1 • B. 22 • C. 23 • D. 46 • Answer: B

Topic 4: Genetics • 10. If the amount of DNA in a haploid gamete is represented by X, what is the net quantity of DNA in a cell from the same organism at the start of meiosis? • A. 0.5x • B. x • C. 2x • D. 4x • Answer: D

Topic 4: Genetics • 11. In the following diagram, which pair represents homologous chromosomes? • A. 1 and 2 • B. 3 and 4 • C. 2 and 5 • D. 4 and 6 • Answer: D

Topic 4: Genetics • 12. Which of the following types of information are needed to construct a karyotype? I. Size of the chromosomes II. Gene mutations of the chromosomes III. Age of the individual • A. I only • B. II only • C. I and II only • D. I, II and III • Answer: A

4.3: Theoretical Genetics