Heredity & Reproduction

1. Heredity & Reproduction • STANDARD IV: Objective I • Recognize heritable traits that are passed from parents to offspring. • Identify physical traits that are passed from parents to offspring • Recognize how genetic traits including diseases & disorders are passed through generations - including family pedigrees and monohybrid Punnett squares • Identify what happens to DNA code when a mutation occurs and identify major causes of mutations. • Recognize and evaluate the harms and benefits that result when mutations occur.

2. STANDARD IV: Objective 2 • Explain how the DNA molecule transfers genetic information from parent to offspring. • Describe the relationships among DNA, genes, and chromosomes. • Describe in basic terms the structure and function of DNA. • Define the genetic purpose for meiosis from generation to generation. • Define and distinguish between dominant and recessive genes and know how each is expressed in parents and offspring.

3. In the 1860’s, Gregor Mendel first discovered the principles of genetics. • Genetics- the branch of biology that studies heredity. • Heredity- the passing on of characteristics from parents to offspring. • By observing pea plants, Mendel was able to successfully predict what traits would be passed on from parent to offspring. • Pollination- the transfer of the male pollen grain to the female organ. • Fertilization- the uniting of male and female gametes. • He also noticed that the pea plants inherited two forms of each gene; one from each parent plant.

4. From his studies, Mendel derived three basic principles: • Law of Segregation: when gametes(sex cells) are formed, the two alleles separate – one allele into one gamete and the other allele into a different gamete • States that during meiosis, the factors that control each trait separate, and only one factor from each pair is passed to the offspring. • Law of Independent Assortment: the alleles for different traits are inherited separately or independently of each other • States that the inheritance of alleles for one trait is not affected by the inheritance of alleles for a different trait if the genes for the traits are on separate chromosomes. • How does Mendel’s Law of Independent Assortment assure genetic diversity?

5. Genes • Your characteristics are determined by specific portions of DNA which are called genes. • Genes carry traits to be passed on from one generation to the next.

6. Alternate forms of genes are called alleles. An allele can be dominant or recessive. A dominant allele will mask (or hide) recessive gene. It is represented with a capital letter. A recessive allele is seen only when no dominant gene is present. It is represented with a lowercase letter.

7. Example of Alleles An offspring has two alleles for each trait. A mother might pass a gene for freckles (dominant - F) to her offspring, and the father might pass a gene for no freckles (recessive - f) to the offspring. Ff -- gives him freckles

8. Yellow plant Green plant YY yy Yy Yy Yy Yy • A pea plant has two alleles for seed color – yellow and green. • The gene for yellow seeds is dominant. The gene for green seeds is recessive. • Possible allele combinations are: • YY – yellow • Yy – yellow • yy – green • In order for the pea plant to produce green seeds, it must inherit two recessive alleles.

9. The combination of alleles that an individual inherits is called the The expression of the alleles is the phenotype. genotype. This is how the trait is expressed – green, tall, hairy, etc. These are the alleles actually present – yy, Tt, BB, etc.

10. If both alleles for a trait are identical the individual is If the two alleles for a trait are different the individual is homozygous heterozygous • Example: • YY • yy • Example: • Yy

11. Mother1 Mother2 Mother1/ Father1 Mother2/Father1 Father1 Mother1/Father2 Mother2/Father2 Father2 Punnett Square • The Punnett Square is a grid used to determine the possible combinations of alleles that the parents may pass to an offspring. • Predicting Genetic Combinations

12. Application In certain wasps, a hairy body is dominant over a bald body. • What would be the resulting offspring of a cross between a wasp homozygous for hairy body and a wasp homozygous for bald body? • List the genotype(s) and phenotype(s) of the possible offspring. • Specify the probabilities of each resulting genotype and each phenotypes.

13. B – hairy body b – bald body Alleles: BB Parents: bb RESULTS

14. Probabilities are determined by interpreting the # of offspring with the desired trait out of total # of offspring yellow 1 YY ; 2 Yy green 1 yy heterozygous 2 Yy How many are… ¾ or 75% are The following is an example: Y – yellow seeds y – green seeds Y y ¼ or 25% are Mother Yy – yellow Father Yy - yellow Y y ½ or 50% are

15. Monohybrid Cross Practice Problem Set www.biology.arizona.edu/mendelian_genetics/problem_sets/monohybrid_cross/01t.html • Additional Problems: • In humans, tongue rolling is dominant over non-tongue rolling. If a heterozygous roller is crossed with a non-roller, what would be the results? • Find the results of a cross between a heterozygous red tomato plant and another heterozygous red tomato plant. Red is dominant over yellow.

19. Cells containing two alleles for each trait are described as diploid. • A cell with one of each kind of chromosome is called a haploid cell. • Meiosis occurs in the specialized body cells of each parent that produce gametes. • How does meiosis maintain a constant number of chromosomes in the body cell of organisms that reproduce sexually? • Meiosis reduces the number by half and when fertilization occurs the number is restored.

20. The gamete that contains genes contributed only by the mother is an egg. • Father = sperm • Zygote- the cell produced when a male gamete fuses with a female gamete. • Explain how crossing over in meiosis results in genetic variation? • New combinations of genes leading to an increase in genetic variation in the offspring. • How does knowledge of the events of meiosis explain Mendel’s Law of Segregation? • During meiosis, the homologous chromosome pairs line up and split; then in the second division the chromotids split. This results in only one of the pair of chromosomes(containing the “factor”) in a gamete.

21. Know Fig 10.11 • When an area of chromatid is exchanged with the matching area on a chromosome, crossing over occurs. • The exchange of genetic material between homologous chromosomes. • Crossing over results in genetic recombination. • The failure of homologous chromosomes to separate properly during meiosis is called nondisjunction. • Explain how nondisjunction can result in an individual having an extra chromosome. • When this happens one gamete can receive both homologous chromosomes. If this gamete is fertilized by a normal gamete the resulting zygote will have three copies of one chromosome.