The Work of Gregor Mendel

Transcription

1 The Work of Gregor Mendel

2 Transmission of characteristics from is parents to offspring called. heredity The SCIENCE that studies how those characteristics are passed on from one generation to the next is called Genetics

3 The Father of Genetics is Gregor Mendel, a monk whose study of genetic traits was the beginning of our understanding about. how genes work

4 Mendel designed experiments using Pea plants in the monastery garden MALE part of flower makes Pollen (sperm) FEMALE part of flower makes egg cells

5 In pea plants, the pollen normally joins with an egg from the same plant (= Self pollinating ) so seeds have ONE parent

6 MENDEL S PEA EXPERIMENTS Mendel started his experiments with peas that were true breeding = if allowed to self pollinate they would produce offspring identical to themselves.

7 MENDEL S PEA EXPERIMENTS Mendel removed pollen making parts and added pollen from another plant. This allowed him to cross-breed plants with different characteristics and study the results

8 A specific characteristic is called a trait Mendel in peas. studied 7 traits Pearson Education Inc,; Publishing as Pearson Prentice Hall

9 MENDEL S EXPERIMENTS P 1 generation ( ) F 1 generation ( = filial offspring) F 2 parental generation

10 Principles of Dominance Section 11-1 P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short Go to Section:

11 Principles of Dominance Section 11-1 P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short Go to Section:

12 Principles of Dominance Section 11-1 P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short Go to Section:

13 When Mendel crossed PURE PLANTS with 2 contrasting traits: (EX: Tall crossed with short) He always found same pattern: 1. ONLY ONE trait showed F 1 in the generation BUT... Missing 2. trait in F 2 3:1 the generation in a ratio returned

14 PATTERNS ARE THE KEY Image modified from:

15 Mendel decided that there must be a pair of FACTORS that each control trait and that one factor must be able to the other. HIDE

16 We now know that Mendel s factors are genes carried on the pair of homologous chromosomes

17 DIFFERENTgene CHOICES for a trait are called. ALLELES

18 DOMINANT = An allele HIDES that the presence of another allele RECESSIVE = An allele is hidden by that the presence of another allele

19 Why did the recessive trait disappear in the F 1 generation and reappear in the F 2? The pattern corresponds to the movement of chromosomes during MEIOSIS Image modified from:

20 WHAT DOES MEIOSIS HAVE TO DO WITH IT?

21 REMEMBER HOMOLOGOUS chromosomes SEPARATE during ANAPHASE I = SEGREGATION Image modified from:

22 offspring an allele for F 1 received tallness from their TALL parent and an allele for shortness from their SHORT parent. The F 1 plants ALL LOOK TALL carrying but are an shortness allele for Images from: BIOLOGY by Miller & Levine; Prentice Hall Publishing 2006

23 EXPLAINING the F 1 CROSS LAW OF SEGREGATION alleles are separated when the F 1 plants made gametes When these gametes recombined to make the F 2 generation, the recessive trait reappears in ¼ of the offspring Image from: BIOLOGY by Miller & Levine; Prentice Hall Publishing 2006

24 Mendel s 3 laws Law of segregation: alleles (chromosomes) are separated into gametes Law of dominance: an organism only needs 1 dominant allele to express the dominant trait Law of independent assortment: alleles are separated randomly/independent of one another