5.1 Mendelian Inheritance Pages

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

Gregor Mendel The father of genetics ( )

Pea plants

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

True-breeding plants Plants that self-pollinate or are crossed with other true- breeding plants to produce offspring that have the same trait as the parent.

Monohybrid crosses breeding two organisms with different versions on only one traits P generation (parental) …true breeding F1 generation (filial generation)…hybrid offspring

Purple flower crossed with white flower

F2 generation Crossing members of the F1 generation lead to F2 generation offspring that were sometimes purple and sometimes white. No flowers were pink. 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 vs. Phenotype Genotype: the organism’s genes (genetic make-up) including genes that are hidden from view Phenotype: the traits that are expresse d, the physical appearance of the organism.

Dominant vs. Recessive Alleles A Dominant Allele is expressed if it is present in the gene. A Recessive Allele is expressed only if there is no dominant gene

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

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 homozygous dominant or heterozygous cross it with a homozygous recessive individual. If 100% of the offspring show the dominant trait the parent was homozygous dominant. If the offspring displays both phenotypes, the parent was heterozygous.

Is the parent PP or Pp?

Eye colour B…brown b…blue

Green pods vs. yellow pods Y…yellow (dominant) y…green (recessive) Cross between yellow heterozygous and green homozygous recessive