Principles of Heredity

Genetics The study of heredity, how traits are passed from one generation to the next

Gregor Mendel ~ Father of Genetics Mini Biography Video

Gregor Mendel Discovered the Basic Principles of Heredity 19th century monk and teacher Predicted how traits are transferred from one generation to next

Mendel designed experiments using pea plants in the http://hus.yksd.com/distanceedcourses/YKSDbiology/lessons/FourthQuarter/Chapter11/11-1/images/MendelExperiment.gif Mendel designed experiments using pea plants in the monastery garden http://www.cedarville.edu/academics/education/resource/schools/chca/2scideb/debwebpv.htm

Male part of flower makes Female part of flower makes pollen (sperm cells) Female part of flower makes ovaries (egg cells) http://hus.yksd.com/distanceedcourses/YKSDbiology/lessons/FourthQuarter/Chapter11/11-1/images/MendelExperiment.gif http://www.cedarville.edu/academics/education/resource/schools/chca/2scideb/debwebpv.htm

In pea plants, the pollen normally joins with an egg from the same plant (= self-pollinating) so seeds have “one parent” http://hus.yksd.com/distanceedcourses/YKSDbiology/lessons/FourthQuarter/Chapter11/11-1/images/MendelExperiment.gif

MENDEL’S PEA EXPERIMENTS Mendel started his experiments with peas that were true breeding if allowed to self-pollinate they would produce offspring identical to themselves. http://hus.yksd.com/distanceedcourses/YKSDbiology/lessons/FourthQuarter/Chapter11/11-1/images/MendelExperiment.gif

MENDEL’S PEA EXPERIMENTS Mendel cross-bred plants by removing pollen making parts from one plant and adding pollen from another plant http://hus.yksd.com/distanceedcourses/YKSDbiology/lessons/FourthQuarter/Chapter11/11-1/images/MendelExperiment.gif

MENDEL’S PEA EXPERIMENTS This allowed him to experiment with plants having different characteristics and study the results http://hus.yksd.com/distanceedcourses/YKSDbiology/lessons/FourthQuarter/Chapter11/11-1/images/MendelExperiment.gif

A specific characteristic is called a trait Mendel studied 7 traits in peas Pearson Education Inc,; Publishing as Pearson Prentice Hall

Parental generation (P1) MENDEL’S EXPERIMENTS Parental generation (P1) Filial generation (F1 = offspring)

Mendel Successes Successful b/c studied only one trait at a time to control variables Analyzed his data mathematically

What’s going on? The white flower trait had reappeared. Mendel repeated for other traits and in every case he found that one trait seemed to disappear in the 1st generation only to reappear unchanged in ¼ of the 2nd generation.

one factor must be able to HIDE the other Mendel decided that there must be a pair of factors that control each trait and that one factor must be able to HIDE the other

We now know that Mendel’s “factors” are genes carried on the pair of homologous chromosomes http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif

gene (trait) are called alleles Different versions for a gene (trait) are called alleles http://sps.k12.ar.us/massengale/genetics%20tutorial.htm

Alleles = green, brown, blue Trait = eye color Alleles = green, brown, blue http://sps.k12.ar.us/massengale/genetics%20tutorial.htm

Mendel’s Law of Dominance Some alleles are dominant (trait is expressed) Other alleles are recessive (only expressed if dominant allele is absent) Ex: Purple & white flowers

All F1 plants received a purple allele for color and a white allele All F1 plants received a purple allele for color and a white allele. Which allele is dominant?

Why did the recessive trait disappear in the F1 generation and reappear in the F2?

The pattern corresponds to the movement of chromosomes during MEIOSIS Image modified from: http://www.laskerfoundation.org/rprimers/gnn/timeline/1866.html

Homologous chromosomes REMEMBER… Homologous chromosomes separate during ANAPHASE I = SEGREGRATION Image modified from: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif

EXPLAINING Mendel’s Results LAW OF SEGREGRATION: alleles are separated when the P1 plants made gametes Image from: BIOLOGY by Miller & Levine; Prentice Hall Publishing ©2006

EXPLAINING Mendel’s Results F1 offspring received an allele for purple color from their purple parent and an allele for white color from their white parent. The F1 plants ALL look purple but are carrying an allele for white color Images from: BIOLOGY by Miller & Levine; Prentice Hall Publishing ©2006

EXPLAINING Mendel’s Results When these gametes combined to make the F2 generation, the trait reappears in ¼ of the offspring Image from: BIOLOGY by Miller & Levine; Prentice Hall Publishing ©2006

How would you answer?

Which of these are genetically identical? A) Homologous chromosomes B) Sister Chromatids C) Neither

Which of these will pair up to form chromosomes during meiosis? A) Homologous chromosomes B) Sister chromatids C) Chromatids pair at random, so it’s impossible to predict

An allele is: a) another word for a gene b) a homozygous genotype c) a heterozygous genotype d) one of several possible forms of a gene

DOMINANT/RECESSIVE Dominant allele is represented by a capital letter. (usually the first letter of the trait) Recessive allele is represented by the SAME letter except in lower-case. EX: (Trait: height) Tall = T Short = t; not s for short

Misconceptions About Dominant Alleles

The genetic makeup (set of 2 alleles) of an organism is its genotype Genotype & Phenotype The genetic makeup (set of 2 alleles) of an organism is its genotype The physical appearance of an organism is its phenotype

Genotype vs. Phenotype

Talk to a Partner: Determine the genotype and phenotype of each flower

HOMOZYGOUS & HETEROZYGOUS When both alleles in the pair are the same, the organism is homozygous (purebred) EX: TT or tt When both alleles in the pair are different, the organism is heterozygous (hybrid or carrier) Ex: Tt

Which chromosome set is heterozygous?

Cornell Summary