11-1 The Work of Mendel What does every living thing inherit from their parents? Genetics – the study of heredity Look around at your classmates and make a list of some of the traits that are inherited.

What did Mendel already know… Each flower produces pollen (sperm) and egg cells Cross fertilization (sexual) – male and female cells join Self-pollination (asexual) – pollen fertilizes eggs from same plant Mendel’s pea plants were true-breeding A tall plant with green seeds would produce a tall plant with green seeds

Genes, Alleles and Dominance Trait – specific characteristic Mendel studied 7 different pea plant traits What are some examples? Plant Height, Seed Shape, Pod Color

Genes, Alleles and Dominance Genes – the chemical factors that determine traits (the segment of DNA) ex. pea plant: height Alleles – different forms of a gene from each parent ex. pea plants: tall and short (T or t)

Principle of Dominance Principle of dominance: some alleles are dominant and others are recessive Dominant allele – the trait is always shown Capital letter (T = tall) Recessive allele – the trait that will only show if there is no dominant allele Lower case letter (t = short)

True-breeding for a particular trait Heterozygous – organisms that have 2 different alleles for the same trait Hybrid for that trait Ex: Tt Homozygous – organisms that have 2 identical alleles for a particular trait True-breeding for a particular trait Ex: TT or tt

Genes, Alleles and Dominance Phenotype – physical characteristics Ex: tall, short, yellow, green Genotype – genetic make-up Ex: TT, Tt, tt Tall plants have the same phenotype (tall), but not the same genotype (TT or Tt) Why are TT and Tt genotypes for tallness, but tt is not???

11-2 Probability and Punnett Squares Mendel realized…the principles of probability could be used to explain the results of genetic crosses.

Genetics and Probability Probability – the likelihood a particular event will occur. Ex: probability of flipping a coin to heads = ½ or 50% Probability of head 3 times in a row = ½ x ½ x ½ = 1/8 The greater the number or trials, the closer to the expected ratio Past outcomes do not affect future outcomes Alleles segregate randomly (like a coin)

Principle of Segregation Segregation = separation The alleles for tall vs. short separate during the formation of gametes – sex cells Each gamete carries one allele for each gene

The Two-factor Cross: F1 4 alleles (2 genes) at the same time Provides the hybrid plants (F2 generation) Crossed a homozygous RRYY (round yellow peas) with a homozygous rryy (wrinkled, green peas)

11.3 Beyond Dominant and Recessive Alleles Genes can act in various ways Dominant vs. Recessive – one allele completely masks another allele. Incomplete Dominance Definition : one allele is not completely dominant over another Ex: flowers – white x red flowers = pink flowers

11.3 Beyond Dominant and Recessive Codominance Definition: both alleles contribute to the phenotype of the organism Ex: chicken feather – black and white alleles = black and white feathers Colors don’t blend like incomplete dominance

11.3 Multiple Alleles Definition: more than two alleles (more than 2 alleles exist in a population not an individual) Blood Types Ex: rabbit’s coat color Ex: human’s blood type

11.3 Polygenic Traits Definition: traits that are controlled by 2 or more genes Ex: fruit fly red eyes - 3 genes involved in making pigment Diff. combo of genes produce different eye colors Ex: Human skin color – more than 4 different genes Human height – more than 50 genes

11.3 Genetics and the Environment Genes provide a plan for development, but how the plan unfolds also depends on the environment: Ex. Butterflies have different wing colors depending on when they hatch Hydrangea flowers are different colors depending on soil pH.

Mendel Questions Using tall and short pea plants and the letters T = dominant and t = recessive describe Mendel’s F1 generation and F2 generation. Provide the genotype and phenotype for each of four offspring from each generation. You do not need to use a punnett square.

Meiosis

Ttrr x ttRr

ttRr x TtRr

Questions Genetics is the study of ________. Alternate characteristics of an organism such as height, hair color, eye color, etc. are called _______. Why did pea plants make such a good subject for Mendel to study? What does “true breeding” mean?

Considering the allele related to short and tall pea plants. Plants of the P generation (tall) will produce only_____________ if not crossed with plants having other alleles. Describe the phenotype (what we can see) of Mendel’s F1 Generation. What was the genotype (use letters “T” and “t”) for Mendel’s F1 generation? How did the F2 generation suggest that genes were simply segregated, not lost?