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Mendel’s Laws of Heredity

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1 Mendel’s Laws of Heredity
Chapter 10.1 Mendel’s Laws of Heredity

2 Explain fertilization.
Fertilization = male gamete (sperm) + female gamete (egg) Resulting cell is now called a zygote In plants, its called pollination Self-pollination = one plant Cross-pollination = two plants


4 Compare and contrast phenotype and genotype
Phenotype = physical expression of genes Ex: Brown hair vs blonde hair Genotype = actual gene combination Ex: BB, Bb, bb Homozygous = BB (dominant), bb (recessive) Heterozygous = Bb

5 Phenotypes Genotypes

6 Punnett squares. Parent’s alleles go on side and top
Carry alleles across or down Monohybrid Cross = one trait Dihybrid Cross = two traits

7 Why is Mendel the “Father of Genetics”?
Mendel studied heredity of traits among pea plants Study of heredity = genetics He came up with the basic laws and understanding of genetics

8 Explain the results of Mendel’s Monohybrid Cross.
Some terms True breeding = many generations carrying the same trait P = parent F = filial (son or daughter)

9 Explain the results of Mendel’s Monohybrid Cross.
Mendel’s cross pollination TALL plant x short plant (P1 generation) Result: Hybrids ALL offspring TALL (F1 generation) Self pollination of F1 F1 TALL X self (TALL) Result 3/4 TALL and 1/4 short (F2 generation) We refer to this as a ratio of 3:1

10 Mendel continued to test this with each of 7 traits
Mendel continued to test this with each of 7 traits. Every time the same ratios appeared… Conclusion: Each organism has 2 factors (genes) that control each of its traits. Different versions of each factor (gene) is now called an allele Ex. Gene for height has a tall and short allele

11 Describe dominant and recessive alleles.
Rule of dominance: in F1 generations the trait that is observed in 100% of the offspring is considered to be the dominant allele. Dominant alleles (TALL) mask the other form Recessive alleles (short) get masked by the dominant form ONLY ONE dominant allele is needed for the form to be expressed! Tt = TALL

12 Dom. alleles are always written first
Dom. alleles are always given a capital letter, recessive get the lower case letter EX: for Height TALL = T or H or Z Short = t or h or z

13 Describe Mendel’s Law of Segregation.
Every individual has 2 alleles for each gene Gametes are produced to carry only 1 from you parents When fertilization occurs you now have 2 alleles, 1 from mom, 1 from dad. 4 possible combinations

14 Explain the results of Mendel’s Dihybrid Cross.
P1: Round, Yellow x Wrinkled, Green RRYY x rryy F1: 100% Round, Yellow (dihybrids) F2: 9 Round, Yellow: 3 Round, Green : 3 Wrinkled, Yellow : 1 Wrinkled, Green


16 Describe Mendel’s Law of Independent Assortment.
Genes of different traits are inherited independently when found on different C. Ex: Not all Blondes have blue eyes


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