Chapter 11: Introduction to Genetics 11-1 The Work of Gregor Mendel

of our parents’ sex cells. a)Describe Homozygous Heterozygous Dominant Recessive b) Show gene examples for: Homozygous dominant Homozygous recessive c) What is another term for homozygous? a) Name the male sex cell. In animals In plants b) Name the female sex cell. In plants  c) From ch 10- Meiosis: Describe the chromosomes in the sex cells: haploid or diploid d) Why? e) How many genes control a trait? f) Where do they come from? g) From ch 12 DNA: how many bases make a gene?   1. An inherited trait is determined by 2 genes    2. The combination of genes that we have come from the joining of our parents’ sex cells.

inherited from parents The scientific study of inheritance Where do we get our characteristics from? What is Genetics? Who is Gregor Mendel and what did he do? inherited from parents The scientific study of inheritance An Austrian monk known as the Father of Genetics. He experimented with pea plants.

Mendel knew that: What is fertilization? the male part of each flower produces pollen, (containing sperm). the female part of the flower produces egg cells. When pollen & egg cells join. A new cell is made

What is true-breeding? Plants that self-pollinate. Pollen fertilizes the egg cells in the SAME flower. They produce offspring identical to themselves. Mendel used true-breeding plants for his experiments TALL pollen x TALL egg = TALL offspring X

Cross pollination Mendel studied plants with two contrasting traits. He joined male and female sex cells from two different plants to see what the offspring looked like.

What were some plant traits? Seed shape Seed color Plant height

A specific characteristic that varies from one individual to another What is a trait? A specific characteristic that varies from one individual to another Some plant characteristics Seed color Plant height Some animal characteristics Eye color Hair color Traits are governed by 2 genes 1 from the male parent 1 from the female parent

Each trait had contrasting characteristics GENES & DOMINANCE What did Mendel do? Each trait had contrasting characteristics Dominant traits are always expressed And written in capital letters Recessive traits are masked by dominant genes And written in small letters He cross bred plants with contrasting traits In order to trace the genes from one generation to the next Color: YELLOW vs. green YY = yellow yy = green There are always 2 genes, called alleles, for each trait, because one comes from each parent

Parent 1: the color trait had 2 genes, each for green Parent is green Parent 2: the color trait also had 2 genes, But 1 for yellow and 1 for green Parent is Yellow Questions: Which color gene is dominant? How do you know? Why does parent 2 show up yellow?

So Mendel crossed a tall plant with a short plant Tall plant x short plant = Tall plant So Mendel crossed a tall plant with a short plant to see which trait would be sent to the next generation: tall or short. What trait was sent? F1 is the 1st generation = TT x tt = Tt What happened to the short genes? They are masked by the tall genes

Dominant genes mask the recessive ones. THE LAW OF DOMINANCE Dominant genes mask the recessive ones. An organism with a dominant gene will always exhibit that trait. An organism that is hybrid will exhibit the dominant gene An organism with the recessive gene will exhibit it only when the dominant gene is not present. Example: Eye color B = Brown b = blue BB DOMINANT BROWN Bb Hybrid Brown bb recessive blue

He crossed plants from the first generation (F1). Tt x Tt THE LAW OF SEGREGATION How did Mendel know that the short gene was just hidden and had not disappeared? He crossed plants from the first generation (F1). Tt x Tt There were 3 possibilities that could show up: All tall All short Some of each Here is what happened:

3 tall and 1 short showed How do we explain this? By The Law of Segregation

T t T t T T (tall) Tt (tall) Tt (tall) tt (short) LAW OF SEGREGATION STATES: a pair of genes will separate, or segregate, when SEX CELLS form. T t Because the short plant showed up, the short gene at some point was separated from the tall gene this way the 2 short genes could combine T t T T (tall) Tt (tall) Tt (tall) tt (short)

Homozygous vs. Heterozygous  The combination of genes that you have can be described by homozygous or heterozygous.  Homozygous means that both of your genes are the same – either both are dominant or both are recessive  AA would be Homozygous Dominant (both alleles are dominant)  aa would be Homozygous Recessive (both alleles are recessive)  Heterozygous means that you have both a dominant and a recessive copy of a gene.  Aa would be Heterozygous (one dominant allele, one recessive allele) Source: zazzle.com

Genotype vs. Phenotype  Genotype is the term for the genes that an organism has. For example, BB, Bb or bb for eye color with brown eyes being dominant over blue  Phenotype are the physical characteristics created by the combination of genes that an organism has. BB and Bb give the phenotype of brown eyes Bb gives the phenotype of blue eyes B B Bb b Bb b Bb Bb

Punnett Squares offsprings’ phenotypes and genotypes.  A Punnett Square is a tool used for determining the possible genetic outcomes of the offspring of two parents  Punnett Squares can be used to determine the parents’ or offsprings’ phenotypes and genotypes.  Punnett Squares show all of the possible combinations of offspring genotypes that a couple could have. B b Bb Bb

Homework: p. 266 # 1, 2, 4, 5, 6

HOT Questions Define fertilization. Describe what TRUE-BREEDING is. Predict where each gene for our traits come from. Compare and contrast DOMINANT genes from recessive genes. Re-write the Law of Dominance Re-write the Law of Segregation. 6. Evaluate the possible offspring between a dominant TALL plant and a recessive short plant.

11.1 The Work of Gregor Mendel