Understanding Genetics: Mendel's Discoveries and Allele Interactions

1. Genetics Vocabulary and Monohybrid Crosses

2. The “Father” of Genetics • Gregor Mendel began his research on inheritance of traits or characteristics while studying garden pea plants in the mid 19th century. • Mendel studied one trait or characteristic at a time. • A cross in which one trait is studied at a time is called a monohybrid cross.

3. Mendel studied 7 different characteristics or “traits” in pea plants:

4. Vocabulary pairs • 1. Chromosomes come in ____________ Humans have ____ pairs of chromosomes. • 2. Each pair of chromosomes is said to be _______________ because they have the same type of ________________ In other words, they have the information to produce the same _________________ or ___________________________. 23 homologous genes traits characteristics

5. Vocabulary • 3. One of the chromosomes in a pair of homologous chromosomes came from the_____________ the other came from the _____________ • 4. All diploid organisms have pairs of _________________ chromosomes. egg sperm/pollen homologous

6. A pair of homologous chromosomes. One member of a pair came in the sperm, the other member of a pair came in the egg. Ex: Pair #7

7. A gene is a section of a chromosomes (DNA) that has the information for a particular trait (characteristic) Examples: Genes for eye color, type of hair, seed shape, pod color. Ex: Gene for seed shape

8. Alleles are alternative forms of a gene. Alleles are the different versions of agene. Most traits have 2 alleles, one in each chromosome. Example: The gene for eye color has two alleles, brown eyes and blue eyes. The gene for seed shape has 2 alleles: round seeds or wrinkled seeds. Allele for “round” Allele for “wrinkled”

9. Dominant allele: an allele that masks, or covers another. Only the dominant allele is expressed (or shown). In pea plants, when the alleles for round and wrinkled seeds are present, only the round is expressed, and the seeds look round. Dominant alleles are shown with a capital letter: R, T, S, H Recessive allele: the allele that is not observed when the alleles are different. Recessive alleles are shown with a lower case letter: r, t, s, h Allele for “round” R Allele for “wrinkled” r Dominant Recessive

10. Homozygous Individual: an individual with alleles that are the same, both dominant or both recessive (both round - RR, or both wrinkled - rr). RR means 2 round seed alleles and rr means 2 wrinkled seed alleles. Plant 1: Homozygous Dominant R R Plant 2: Homozygous Recessive r r

11. Heterozygous Individual: an individual with alleles that are different, one dominant and one recessive. Rr means that one allele is for round seed and the other allele is for wrinkled seeds. Hybrid = Carrier = Heterozygous R r Plant 3: Heterozygous

12. Genotype: is the set of alleles of an organism. The genotype is described using the letters of the alleles. There are 3 possible genotypes for the trait “seed type”: RR, Rr, rr Plant 1 = RR Plant 2 = rr Plant 3 = Rr

13. Phenotype: the appearance of an organism, what it looks like. What you can see. The phenotype is described with words: smooth, wrinked, tall, short. Plant 1 = Round Seeds Plant 2 = Wrinkled Seeds Plant 3 = Round Seeds

14. During Meiosis (spermatogenesis and oogenesis), the number of chromosomes is cut in half. Meiosis produces haploid cells (n). Eggs and sperm will have just ONE chromosome of each pair. The egg and sperm get the chromosomes randomly. You never know which member of a pair will go into each sperm or egg. ***Only showing 2 of the four gametes made during meiosis*** EGG R R R R POLLEN (sperm) r R R r

15. R R • Can we predict what the offspring will look like? YES • Punnett Squares are used to predict possible offspring. They show all the possible outcomes of a cross. • Possible alleles in the eggs and sperm from parents go outside • Possible offspring are shown inside the square. RR RR R r Rr Rr Possible Offspring of RR x Rr: - 2 Homozygous Dominant - 2 Heterozygous

16. Now it is your turn…