MENDEL & HEREDITY

Are You Ready For This? Can You…  Define the term gamete.  Summarize the relationship between chromosomes and genes?  Differentiate between autosomes and sex chromosomes?  Describe how independent assortment during meiosis contributes to genetic variation?

 Heredity – the passing of traits from parent to offspring  Genetics – Branch of Biology that focuses on heredity

Gregor Mendel  Austrian monk  Bred different varieties of pea plants  Was the 1 st person to develop rules to predict the outcome, or patterns of heredity

Why Pea Plants? A. Have many different traits that have two clearly different forms that are easy to tell apart. Example ) TRAIT : Color FORM: Purple or White B. Mating can be easily controlled C. Small, grow easily, mature quickly, produce many offspring

Mendel’s Experiments  Monohybrid Cross – Involved one pair of contrasting traits  Cross Pollination – allowed him to mate two plants with different characteristics and to study the results.

Observations:  What happened to the white flowers?  All results for traits in the F 2 generation were in a 3:1 ratio.

Mendel’s Hypotheses  Inheritance is determined by factors that are passed from one generation to the next, called genes.  There are alternative versions of the genes, called alleles. Example: The gene that controls plant height comes in two forms; tall and short  Principle of Dominance – Some alleles are dominant and some are recessive. Dominant = uppercase letter Recessive = lowercase letter

Genes and Dominance  You have 2 alleles for many traits in your body (one from your mom and one from your dad)  If you have a dominant allele (capital letter), you will always show that characteristic. In order to show a recessive characteristic, the dominant allele must be missing.

Example  TRAIT = Hair Texture Dominant Allele (H) - curly hair Recessive Allele (h) - straight hair  Since you have two alleles, there are three possible combinations that you may have: HH – curly hair Hh – curly hair hh – straight hair

Terminology  Two of the same alleles (HH, hh) is called homozygous, or pure  Two different alleles (Hh) is called heterozygous, or hybrid

Phenotype & Genotype  Phenotype – physical characteristics Example – straight hair, brown eyes, tall  Genotype – genetic makeup of an individual Example – hh, Bb, TT

Mendel’s Ideas Laws of Heredity Law of Segregation – Two alleles for a trait segregate when gametes are formed during meiosis Law of Independent Assortment – The alleles of different genes separate independently from one another

Do Now  In humans, polydactyl is a recessive genetic trait that causes humans to have extra digits. Normal number of digits is represented by a (P) and polydactyl is represented by a (p)  1. What are the 3 possible combinations of alleles?  2. For each set of words, write the matching genotype:  Homozygous recessive ______  Hybrid ______  Pure dominant _______  Heterozygous _______