Mendel & the Origins of Genetics

The branch of Biology that studies heredity Heredity and Genetics What is Heredity? The passing of genetic traits from parent to offspring What is Genetics? The branch of Biology that studies heredity

Gregor Mendel The Father of Genetics Gregor Mendel studied genetics in the 1800’s. He was born in Austria to peasant parents who worked as gardeners. He studied at the University of Vienna and later became a monk. The Father of Genetics Conducted experiments in the garden studying traits in pea plants. Observed & recorded traits passed from parents to offspring.

What were Mendel’s Experiments? What characteristics did Mendel study? Mendel Brainstorm What were Mendel’s Experiments? What characteristics did Mendel study?

Mendel’s Experiments Gregor Mendel carried out a series of experiments related to how certain characteristics are inherited in pea plants. The characteristics that Mendel studied include… flower color flower position plant height pod appearance pod color seed texture seed color

So why did Mendel pick pea plants? 1. Many traits exist in two clearly different forms 2. The mating or crossing of two plants can easily be controlled 3. Pea plants are small, easy to grow, mature quickly, and produce many offspring

Mendel’s Experiments P Generation (Parental Generation) Mendel allowed two plants to self-pollinate until all offspring displayed only one characteristic (example, all purple) – this is called true breeding. A true breeding plant will only allow one trait to show through because it should be either 100% homozygous dominant (purple) or 100% homozygous recessive (white).

Mendel’s Experiments He then picked two parents, each with contrasting traits (one purple and one white) and cross-pollinated them. F1 Generation The offspring of the Parental Generation which Mendel cross-bred; this generation only expressed one trait (the dominant trait, purple)

Mendel’s Experiments Next, he allowed F1 generation plants to self-pollinate. F2 Generation The self-pollinating offspring of the F1 Generation; this generation expressed both traits again, although the dominant (purple) trait was expressed more often (3:1)

Mendel’s Experiments

Mendel’s Experiments - Hypotheses Alleles the different versions of the gene; represented by letters One allele is dominant, one is recessive… Dominant: expressed form of trait (capital allele) Recessive: not expressed form of trait (lower case allele) An individual has two copies of a gene – one from each parent. There are different versions of each gene. For example, the gene for flower color in pea plants can either be purple or white, represented by letters; P = purple and p = white.

Mendel’s Experiments - Conclusions Homozygous Having identical alleles for a trait; either two dominant alleles or two recessive alleles Homozygous Dominant = BB or TT or QQ Homozygous Recessive = bb or tt or qq Heterozygous Having two different alleles Bb or Tt or Qq Genotype the set of alleles that an individual has (the actual genes) Ex: BB, Tt, or qq Phenotype the physical appearance of a trait (how it actually appears) Ex: Brown eyes or blue eyes; tall or short

Mendel’s BIG Conclusions… The Laws of Heredity Law of Segregation Two alleles for a trait separate when gametes are formed Law of Independent Assortment The inheritance of one trait does not influence the inheritance of another trait These both occur during Meiosis!

Mendel’s Contributions On the left side of your IN, write a short paragraph about the importance of Mendel’s research.

Studying heredity

What is the genotype of parent 1? What is the genotype of parent 2? Punnett Square Simple diagram used to predict expected result of a genetic cross Genetic Cross Hh x hh What is the genotype of parent 1? What is the genotype of parent 2? Punnett Squares consider all possible combination of gametes for that particular cross Hh hh Homozygous Recessive Heterozygous Hh hh

Punnett Squares – Monohybrid Cross What is the probability that the offspring is heterozygous? 50% What is the probability that the offspring is homozygous recessive? 25% A cross that considers ONE pair of contrasting traits between two individuals Cross the following! Heterozygous Male x Heterozygous Female Gg x Gg What is the probability that the offspring is green? 75% What is the probability that the offspring is brown? 25% G g Frog Color Key G – Green g- brown GG Gg G g Gg gg

Punnett Squares – Monohybrid Cross Cross the following! Heterozygous Female x Homozygous Recessive Male Gg x gg What is the probability that the offspring is green? 50% What is the probability that the offspring is brown? G g Frog Color Key G – Green g- brown g Gg gg g gg Gg

Punnett Squares – Monohybrid Cross What is the genotype of all of the offspring? Heterozygous What is the probability the offspring’s phenotype is Round? 100% Cross the following! Homozygous Dominant Female x Homozygous Recessive Male RR x rr r r Seed of Pea Plants Key R – Round r- Wrinkled R Rr Rr Rr Rr R

Punnett Squares – Monohybrid Cross How many offspring would you expect to have the: Genotype RR 1/4 or 25% Genotype Rr 2/4 or 1/2 or 50% Genotype rr How many offspring would have the following phenotype? Round Seeds 3/4 or 75% Wrinkled Seeds 1/4 or 25% Try 1 more cross! Heterozygous Male x Heterozygous Female Rr x Rr What is the phenotypic ratio? 3:1 What is the genotypic ratio? 1:2:1 R r Seed of Pea Plants Key R – Round r- Wrinkled R RR Rr r Rr rr

Test Cross A test cross can be performed to determine whether a parent with a dominant phenotype is homozygous dominant or heterozygous. In a test cross, an individual whose phenotype is dominant, but whose genotype is unknown, is crossed with a homozygous recessive individual. One can then look at the offspring to determine the genotype of the parent.

So if we get 4 purple offspring, what must the other allele be? Test Cross - examples Pea Plant Flower Color P = purple p = white Unknown with dominant phenotype P ? P So if we get 4 purple offspring, what must the other allele be? Pp= p Pp= purple purple Homozygous recessive p Pp= Pp= purple purple