Genetics & Punnett Square Notes

Transcription

1 Genetics & Punnett Square Notes

2 Essential Question What is Genetics and how are punnett squares used?

3 History of Genetics Gregor Mendel Father of modern genetics Studied pea plants Found that plants that were true-breeding (able to pollinate themselves) produced offspring identical to themselves Found that when plants reproduced (cross pollination) with other plants that offspring showed a mix of characteristics of both parents

4 Section 11-1 Figure 11-3 Mendel s Seven F 1 Crosses on Pea Plants Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall Go to Section:

5 Mendel s Principles Inheritance of biological characteristics is determined by genes. Genes are passed from parents to offspring. Some forms of a gene may be dominant and others may be recessive. Organisms have 2 alleles for each gene (1 from each parent). These alleles will segregate during gamete formation. Alleles for different genes usually segregate independently from one another.

6 Mendel s Laws of Inheritance Law of Dominance: In heterozygous genotypes, dominant alleles (capital letters) hide recessive alleles (lowercase letters) when both are inherited by an organism. (Yy means the dominant trait will show up in the phenotype)

7 Mendel s Laws of Inheritance The Law of Segregation (separation): Each organism has 2 alleles for a gene. Only one allele from each gene pair will be passed on to the offspring.

8 Polygenic Traits Traits that are controlled by more than 1 gene. Ex. Human eye color (at least 6 genes) Ex. Human skin color (at least 4 genes) Causes a wide variety of phenotypes. In the case of skin color, this is what causes the great variety of skin tones.

9 Genotype vs. Phenotype Genotype The combination of alleles for a given trait (the genetic make up) Ex. TT, Tt, tt Phenotype The physical appearance caused by the interaction of alleles In general, if a dominant allele is present then the dominant condition will be shown Ex. Tall, Short

10 Genotype vs. Phenotype Rr Red color Wavy hair bb Tall Genotype Phenotype Phenotype Genotype Phenotype

11 Alleles Homozygous = individual with 2 of the same allele for a given trait Ex. TT, RR (homozygous dominant) tt, rr (homozygous recessive) Heterozygous = individual with 2 different alleles for a given trait Ex. Tt, Rr, Ww

12 Allele Practice TT Rr Ww AA jj Homozygous dominant Heterozygous Heterozygous Homozygous dominant Homozygous recessive

13 Punnett Squares

14 Punnett Squares A Punnett square illustrates how the parents alleles might combine in offspring. The top of the Punnett Square are usually the male s alleles, the side of the Punnett square shows the female s alleles for the trait

15 Punnett Squares Examples 1. Cross a homozygous dominant tall plant with a homozygous recessive short plant. Dominant trait = tall Recessive trait = short What letters would you use to represent this cross? T = t = tall short

16 What is the genotype of a homozygous dominant tall plant? TT What is the genotype of a homozygous recessive short plant? tt T T TT x tt t Tt Tt t Tt Tt Genotype % TT % Tt % tt Phenotype % tall % short

17 2. Cross a heterozygous brown haired rabbit with a homozygous white haired rabbit. Dominant trait = brown hair Recessive trait = white hair What letters would you use to represent this cross? B = b = brown white

18 What is the genotype of a heterozygous brown haired rabbit? Bb What is the genotype of a homozygous white haired rabbit? bb B b Bb x bb b Bb bb b Bb bb Genotype % BB % Bb % bb Phenotype % brown % white

19 Now, you try this one! 3. Cross a homozygous dominant long haired guinea pig with a heterozygous guinea pig. Dominant trait = long hair Recessive trait = short hair What letters would you use to represent this cross? L = l = long short

20 What is the genotype of a homozygous dominant long haired guinea pig? LL What is the genotype of a heterozygous long haired guinea pig? Ll What is the phenotype of the heterozygous guinea pig? long hair

21 LL x Ll L L L l LL Ll Genotype 50 % LL LL Ll 50 0 % Ll % ll Phenotype % long % short

22 Summary Write 2 questions on each page of notes (relating to those notes on that page) Write a 3 sentence summary at the end over all of the notes.