Chapter 11: Intro to Genetics

Work of Gregor Mendel

Who is Gregor Mendel

• Gregor Mendel (1822-1884)– Austrian– Augustinian Monk (Catholic)– “Father of Modern Genetics”– Worked with pea plants (Why?)

• Considered true breeding plants• Could control their pollination• Design of flower made it safer

– Ideas did not catch on right away

What is Genetics?

• The study of biological inheritance• What are true breeding plants?– Plants that are self-pollinating– Create specific traits in the plant– Offspring will be identical

• What is cross breeding?– Producing plants from different parents– Ex: Crossing a yellow plant and green plant

Genes and Alleles

What are genes?Factors that are passed from one parent to

offspringEach gene controls a specific trait

What are alleles?Variations on a geneEach parents has 2 alleles

What is the Principle of Dominance?

• Principle of Dominance– Some alleles are dominant– Some alleles are recessive– When both are present, the dominant allele will always

show over the recessive allele– The only time the recessive shows is when no dominant

allele is there

What is Segregation?

• Segregation– Separating alleles– 25% of all plants showed recessive traits– Recessive traits appear in 2nd generation– Separation of alleles occurred during gamete formation– Gametes: the sperm and egg cells (sex cells)

Chapter 11: Intro to Genetics

Applying Mendel’s Principles

Probability• What is Probability?– Likelihood a particular event will happen– All genetics can be determined based off of probability

• How does segregation tie into probability?– Each gene has 2 alleles– Homozygous: Both alleles for a gene are the same (TT)– Heterozygous: The alleles for a gene are different (Tt)– This can lead to the difference between genotype and

phenotype

What is the difference between genotype and phenotype?

• What is phenotype?– The physical traits/characteristics of an organism– This can show if a plant is tall or short (Ex.)

• What is genotype?– The genetic makeup of an organism– This shows up as TT or Tt or tt (Letters not traits)

• What is the connection between them?– Organisms can have different genotypes but still have the

same phenotype– TT and Tt will still produce the same physical trait

Punnett Squares: A way to predict outcome of a genetic cross

What is Independent Assortment?

• This is all based off of the idea that one trait can be affected by the alleles for another trait

• What he found:– Genes for different traits can segregate independently– These traits have no effect on other traits

Summary of Mendel’s Work

• What he learned:– 1. Biological characteristics are inherited through genes

which are passed from parent to offspring– 2. A dominant and recessive gene occur when two or more

alleles are present– 3. Each adult has two copies of a gene– 4. Alleles for different genes segregate independently

Chapter 11: Intro to Genetics

Other Patterns of Inheritance

Co-dominance

• The idea that one allele is equal to another• Neither has dominance over the other• Both characteristics will show up in the trait• Cow has both brown and white visible

Incomplete Dominance• Similar to co-dominance• One allele is stronger than the other• However both alleles will show up in the trait• Can be mixed together• White and red colors mix to make pink appear

Multiple Alleles

• Appears within a population and not just an individual• Having more than 2 possible alleles for a gene• Allows for multiple dominance• Many different eye colors within a population

Polygenic Traits

• Trait controlled by 2 or more genes• Example: Skin color

Chapter 11: Intro to Genetics

Meiosis

Chromosome Numbers

• Diploid Cells– Human Cells– 2 sets of chromosomes– Designated as “2N”

• Haploid Cells– Gametes (Sex Cells)– Sperm and Egg Cells– Designated as “N”

What is Meiosis?

• What is meiosis?– Cell division for sex cells– Half the number of chromosome• Allows for fusion during fertilization

– Diploid cells are separated which creates the haploid cells

– Meiosis can be divided into 2 different stages

Stages of Meiosis I

• Prophase I – Copied chromosome matches up with its

homologous (identical) chromosome– Tetrads cross over creating new combos

Stages of Meiosis I

• Metaphase I– Spindle fibers attach to chromosomes

Stages of Meiosis I

• Anaphase I– Chromosomes pull apart to opposite ends

Stages of Meiosis I

• Telophase I and Cytokinesis– Nuclear membrane forms– Cell separates into haploid cells

Stages of Meiosis II

• Prophase II– 2 Connected daughter cells are created

Stages of Meiosis II

• Metaphase II– Chromosomes line up

Stages of Meiosis II

• Anaphase II– Separate and move to end of the cell

Stages of Meiosis II

• Telophase II and Cytokinesis– Nuclear membrane forms– 4 haploid cells created