4.1 Early Beliefs and Mendel Pages

Trait A version of a characteristic that can be inherited. Example: eye colour

Gregor Mendel The father of genetics ( ) image: biography.com

Pea plants image: anslem.edu

Experiments Flower colour Flower position Stem length Seed shape Seed colour Pod shape Pod colour

True-breeding plants Plants produce offspring with the same trait as the parent.

hybrid Offspring of two different true-breeding plants.

Monohybrid crosses breeding two organisms with different versions of only one trait

P generation (parental) …true breeding F1 generation (filial generation)…hybrid offspring

Purple flower crossed with white flower Image: biology.iupui.org

F2 generation Crossing the F1 generation: F2 generation with some purple and some white, but no pink flowers. 3:1 ratio of purple to white flowers

Mendel’s conclusions 1.For each trait, an organism carries two genes, one from each parent. 2.Parents donate only one copy of the gene to their offspring. (sperm and eggs are haploid)

Allele A specific version of a trait or form of a gene.

Genotype Genotype: the organism’s genes (genetic make-up) including genes that are hidden from view

Phenotype: the traits that are expressed, the physical appearance of the organism.

Dominant vs. Recessive Alleles A Dominant Allele is expressed if it is present in the gene. Ex. PP, Pp, pP A Recessive Allele is expressed only if there is no dominant gene Ex. pp

Purple vs. White flowers Let P be the purple flower gene Let p be the white flower gene

Homozygous…both alleles are the same, PP or pp Heterozygous…both alleles are different, Pp

What you see … isn’t always what you get! GenotypePhenotype PP homozygous dominant purple Pp heterozygousPurple (carrier of white gene) pp homozygous recessive white

Punnett Square

A grid system for predicting the probability of inheriting certain genes Image: bio8.wikispaces.com

Probability The measure of the chance that an event will happen. Example: Toss a coin, call it. The chance of tails is 50%

Test Crosses To determine if the parent is PP or Pp, cross it with a homozygous recessive individual. If 100% of the offspring show the dominant trait the parent was PP. If the offspring displays both phenotypes, the parent was Pp.

Is the parent PP or Pp?

Eye colour B…brown b…blue Image: vannuysms.org

Green pods vs. yellow pods Y…yellow (dominant) y…green (recessive) Cross between yellow heterozygous and green homozygous recessive Image: en.wikipedia.org