10.1 Mendel’s Laws of Heredity Part 1

Heredity Why do we look the way we look?

Heredity We are all unique, but we have things in common with our family members.

Heredity Characteristics that are inherited are called traits. Bent pinky Tongue rolling Detached earlobe Hitchhiker’s thumb Widow’s peak

Heredity These are traits you got from your parents. The passing on of characteristics from parents to offspring is called heredity. Genetics is the branch of biology that studies heredity.

Mendel’s Research Austrian Gregor Mendel wanted to know why offspring look like their parents. Mendel began to breed pea plants to study the inheritance of their traits.

Mendel’s Research Garden pea plants reproduce sexually. Plants make two different sex cells, male and female Sex cells are called gametes.

Mendel’s Research A pea plant makes both male and female gametes. Male pollen Female ovule located in pistil

Mendel’s Research Pollination is the transfer of male pollen grains to the pistil.

Mendel’s Research Fertilization happens when the male and female gametes meet and develop into a seed.

Mendel’s Research Mendel could let a plant pollinate itself or he could take pollen from one and place on pistil of another

Mendel’s Research Mendel studied one trait at a time Monohybrid crosses – study breeding of plants that are the same except for one trait A hybrid is the offspring of parents that have different forms of a trait, tall or short height

Mendel’s Research Mendel started with two plants, one tall and one short. He cross-pollinated them and planted the seeds that formed.

Mendel’s Research The first generation of offspring were all tall.

Mendel’s Research He let those plants self pollinate and planted the seeds again. The second generation of offspring were mostly tall, but there were a few short ones. 3 tall : 1 short

Mendel’s Research Mendel found seven different traits that showed the same pattern, 3:1 in the second offspring generation

Mendel’s Research Mendel concluded that each plant has two factors that control each trait, one from each parent. He did not know what these factors were, we now call them alleles. Alleles are alternative forms of a gene that determine the visible trait.

Mendel’s Research So, why did the first offspring generation (F1) have all tall plants? Why did the second offspring generation have 3 tall: 1 short plant?

Mendel’s Research So, why did the first offspring generation (F1) have all tall plants? Mendel called the form that showed dominant The trait that disappeared he called recessive

Mendel’s Research Why did the second offspring generation have 3 tall: 1 short plant? The plants in F1 had one allele for tall and one for short. Since tall is dominant all were tall.

Mendel’s Research When F1 pollinated and produced seeds, some of the next generation (F2) had two short alleles. F2 generation had 3 tall plants for every 1 short plant