Unit 4 Genetics Part 1 Heredity

1. Unit 4 Genetics Part 1 Heredity M.Elizabeth Martin Luther King, Jr. JHS 2006

2. Chapter 6 Heredity 6.1 Mendel and His Peas 6.2 Meiosis Chapter 6 Review

3. 6.1 Mendel and His Peas Heredity – the passing of traits from parents to offspring; Gregor Mendel • Grew up on a farm – why he was familiar with nature • He became a priest and studied at the University • Observant and curious – what if?? Why is it so? • Chose to study pea plants

4. How Do you Like Your Peas Garden sweet peas were chosen by Mendel because: • Grow quickly • Usually self pollinating • Contain both male and female reproductive structures • Fertilization can take place within the same flower

5. Petal Stigma Anther Style Pistil Stamen Ovary Filament Ovule Sepal

6. Pollination – Sexual Reproduction There are two types of reproduction: Asexual – a single parent produces an identical offspring. Lots of organisms reproduce this way (bacteria and algae). When cells are cloned they are reproduced in this way. Sexual – requires two parents. Results in a lot better chance for genetic variation.

7. Pollination Process • Pollen containing sperm from the anthers (male) is transferred to the stigma (female). • Fertilization occurs when a sperm from the pollen travels through the stigma and enters the egg in an ovule. The transmission of characteristics/traits from one generation to another is called ____________ heredity

8. Peas be My Podner – Controlled Experiments Mendel chose to study only one characteristics (trait) at a time: • Plant height • Seed shape • Flower color • Seed color • Pod color • Pod shape • Flower position

9. Controlled Experiments True Breeding Plants – When these plants self pollinate they always produce offspring with the same trait that the parent plant has (homozygous) Mendel crossed two plants that had different forms of a single trait using cross-pollination. Cross Pollination – the anthers of one plant are removed so that the plant cannot self-pollinate Then pollen from another plant is used to fertilize the plant without anthers.

10. Mendel’s First Experiment Mendel performed crosses to study seven different characteristics (traits) Each trait was separately crossed: Example: the cross between round seeds and wrinkled seeds plants produce offspring called the first generation (F1) Mendel found that one trait always appeared and the other trait vanish??? The trait that appeared – dominant The trait that disappeared - recessive

11. Mendel’s Second Experiment • First generation plants cross by self pollination • Mendel performed this experiment and found for the two traits studied that the recessive trait shows up again • Mendel got to counting the second generation (F2) to figure out what was going on and calculated ratios to determine the dominant to recessive ratios.

12. Genes and Alleles • Mendel realized that there must be two sets of instructions for each characteristic and that each parent would donate one set of instructions to offspring • Now we know that the sets of instructions are genes and that a fertilized egg would have two forms of the same gene for every characteristics and we call these two forms alleles.

13. Mendel’s Scientific Fame • Mendel’s ideas were not immediately accepted by the scientific community when he published his results in 1865, • It was more than 30 years later that his discoveries were recognized as significant. • Once Mendel’s ideas were discovered in part by William Batson and Reginald Punnett the door to modern genetics was opened.

14. Punnett Square • To understand how Gregor Mendel came to his conclusions, a Punnett Square is used. • Punnett Square – a tool used to visualize all the possible combinations of alleles from the parents.

15. How to make a Punnett Square • Draw a square and divide it into four sections • Write the letters that represent alleles from one parent along the top of the box • Write the letters that represent alleles from the other parent along the side of the box • To make the cross bring one allele down and one over so that each of the four squares has now 2 alleles showing the genotypes that are possible with the cross

16. Probability • The mathematical chance that an event will occur – likelihood • Probability is usually expressed as a fraction (ratio) or a percent. • To express probability as a percentage, divide the fraction and multiply by 100. • 1 in 2 = ½ = 0.5 that when multiplied by 100 is 50%.

17. 6.2 Meiosis • Two types of reproduction: sexual and asexual. • Asexual • only one parent cells is needed • The parent cells copies it’s internal structures (mitosis) and then divides producing new cells that are exact copies of the parent cell

18. Sexual Reproduction • Two parents are needed • Each parent produces a sex cell (egg or sperm) which are different from ordinary cells. • Ordinary human cells contain 46 chromosomes (23 pairs). Each pair is called homologous chromosomes. • Sex cells contain 23 chromosomes (half the usual number.

19. Less is More – Meiosis to the Rescue • Because each sex cell has one-half the number of chromosomes when each sex cell is united during fertilization, the resulting zygote has a both halves of the number of chromosomes. • Meiosis is the process whereby sex cells are produced.

20. Meiosis