The Work of Gregor Mendel 11-1

Every living thing has a set of characteristics inherited from its parents Every living thing has a set of characteristics inherited from its parents Scientists realize that heredity holds the key to understanding what makes us unique Scientists realize that heredity holds the key to understanding what makes us unique As a result, genetics is at the core of a revolution in understanding biology As a result, genetics is at the core of a revolution in understanding biology Genetics - scientific study of heredity Genetics - scientific study of heredity

Gregor Mendel’s Peas Gregor Mendel Gregor Mendel Austrian monk, born 1822 Austrian monk, born 1822 Studied science and math Studied science and math Worked in a monastery - in charge of the garden Worked in a monastery - in charge of the garden Taught at the high school Taught at the high school His work in the garden changed biology forever His work in the garden changed biology forever

Mendel conducted his famous genetic experiments with garden peas Mendel conducted his famous genetic experiments with garden peas Pea plants have flowers that contain both male and female parts Pea plants have flowers that contain both male and female parts Male - stamen (anthers & filament), pollen Male - stamen (anthers & filament), pollen Female - carpel( stigma, style, ovary), eggs Female - carpel( stigma, style, ovary), eggs When pollen fertilizes an egg cell, a seed for a new plant is formed When pollen fertilizes an egg cell, a seed for a new plant is formed

Pea plants normally reproduce by self- pollination Pea plants normally reproduce by self- pollination Seeds that are produced by self- pollination inherit all of their characteristics from a single plant Seeds that are produced by self- pollination inherit all of their characteristics from a single plant Known as a true breeding plant Known as a true breeding plant Produces offspring identical to parent Produces offspring identical to parent

Mendel had a supply of true-breeding pea plants Mendel had a supply of true-breeding pea plants Basis for his experiments Basis for his experiments Noted that pea plants have 7 contrasting traits Noted that pea plants have 7 contrasting traits Height, seed shape, seed color, seed coat color, flower position, pod shape, pod color Height, seed shape, seed color, seed coat color, flower position, pod shape, pod color

Plants can also cross-pollinate Plants can also cross-pollinate Mendel manipulated this concept during his experiments Mendel manipulated this concept during his experiments He removed the male plant parts from several plants, that had a contrasting traits He removed the male plant parts from several plants, that had a contrasting traits Carefully dusted pollen from one plant onto stigma of plant with contrasting trait Carefully dusted pollen from one plant onto stigma of plant with contrasting trait Studied the offspring of the crosses Studied the offspring of the crosses

Genes & Dominance In Mendel’s cross-breeding experiments, he was studying the traits of the pea plants In Mendel’s cross-breeding experiments, he was studying the traits of the pea plants Trait - a specific characteristic, like seed color, that varies from one individual to another Trait - a specific characteristic, like seed color, that varies from one individual to another

The offspring that resulted from Mendel’s cross-breeding were known as hybrids The offspring that resulted from Mendel’s cross-breeding were known as hybrids Have parents with different traits Have parents with different traits Ex: tall x short Ex: tall x short The first set of offspring are called the F 1 generation, or first filial The first set of offspring are called the F 1 generation, or first filial Offspring in the F 1 generation only showed traits from one of the parents Offspring in the F 1 generation only showed traits from one of the parents

Mendel made 2 conclusions from these experiments: Mendel made 2 conclusions from these experiments: Biological inheritance is determined by factors that are passed from one generation to the next Biological inheritance is determined by factors that are passed from one generation to the next Today, those factors are called genes Today, those factors are called genes Mendel’s studies involved genes that had two contrasting forms Mendel’s studies involved genes that had two contrasting forms The different forms of a gene are called alleles The different forms of a gene are called alleles

His second conclusion is the principle of dominance His second conclusion is the principle of dominance Some alleles are dominant and others are recessive Some alleles are dominant and others are recessive Dominant alleles are always expressed Dominant alleles are always expressed Recessive alleles are only expressed when paired up with another recessive allele Recessive alleles are only expressed when paired up with another recessive allele

Segregation Mendel wondered what happened to the recessive traits in the F 1 crosses Mendel wondered what happened to the recessive traits in the F 1 crosses Mendel allowed all of the plants of the F 1 to self-pollinate, creating the F 2 or second filial generation Mendel allowed all of the plants of the F 1 to self-pollinate, creating the F 2 or second filial generation

The F 1 Cross In the F 2 generation, the recessive trait appeared in about 1/4 of the offspring In the F 2 generation, the recessive trait appeared in about 1/4 of the offspring The remaining 3/4 still showed the dominant trait The remaining 3/4 still showed the dominant trait

Explaining the F 1 Cross Mendel assumed that at some point, the contrasting alleles were separated, or segregated Mendel assumed that at some point, the contrasting alleles were separated, or segregated He believed that this happened during the formation of gametes - sex cells He believed that this happened during the formation of gametes - sex cells

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