mendel s work - mrs. weisenbach's biology cabin

Mendel’s Work

Early Ideas

�  People used to believe that offspring were a blend of genetic material from both parents.

�  The genetic material mixed or blended like colors of paint.

�  This is not the case because over many generations, populations would eventually look alike.

�  Blending inheritance cannot explain why some traits skip a generation.

Gregor Mendel

� Gregor Mendel: “The Father of Genetics” ÷ Austrian priest/monk ÷ 1822 to 1884

¡ Pea plants had different physical characteristics, or traits. ÷ Ex: Tall plants and short plants.

Green seeds and yellow seeds.

Gregor Mendel

�  He also noticed that the characteristics of the pea plants resembled those of the parent plants. This passing of traits from parents to offspring is called heredity.

�  Mendel worked with thousands of pea plants to

understand the process of heredity. �  Mendel’s work formed the foundation of genetics,

the scientific study of heredity.

Why Pea Plants?

�  They are self-pollinating. ¡  They have both male and female parts ¡  This means that the pollen from one

flower lands on the pistil of the same flower.

�  He developed a method to cross-pollinate ¡  He removed the pollen from one plant

and brushed it onto a second plant.

Mendel’s Experiments

�  Mendel started his experiment with purebred plants.

�  Purebred is the offspring of many generations that have the same trait.

EX: A purebred short plants always produce short offspring.

Mendel’s First Experiment

�  Mendel first crossed a purebred short plant with a purebred tall plant. He called these two plants the parental (P) generation.

�  He called the offspring the first filial generation or the (F1) generation.

�  To Mendel’s surprise, all the offspring were tall.

Mendel’s Second Experiment

�  Mendel then took the offspring, the F1 generation, and crossed them.

�  These results also surprised Mendel.

�  The offspring in the second filial generation or (F2) were a mix of tall and short plants.

�  He found that 75% were tall and 25% were short.

Mendel concluded

�  Mendel believed that individual factors or sets of genetic “information” must control the inheritance of traits. ¡ The factors that control traits exists in pairs. ¡ Each parent (mother & father) contributes 1 of

the factors for each trait. ¡ One factor in the pair can mask or hide the other

factor.

�  Gene: the factors that control a particular trait. ¡  Ex.) eye color, height, hair color, nose shape, etc.

Allele

�  Allele: the different forms of a gene ¡  Ex.) eye color: brown, blue, green

Genes and Alleles

�  A gene is a section of DNA that has information about a trait in an organism.

�  Each form of a gene with different information is called an allele.

Video Where do your genes come from? Video Link! Genetics 101 Part III, Where do your genes come from?

http://www.youtube.com/watch?v=Om0ZvtBmSAs

Dominant & Recessive

�  Dominant Allele ¡  A genetic factor that

blocks, or masks, another genetic factor

¡  Shown with capital letter ¡  When the dominant allele

is present, the trait is always expressed.

÷ EX: B, X, W, R, Y

�  Recessive Allele ¡  A genetic factor that is

hidden by the presence of a dominant factor

¡  Shown with lower case letter

¡  The trait will only be expressed when both alleles are recessive.

÷ EX: b, x, w, r, y

�  T = Dominant

�  T = Dominant �  t = Recessive

�  T = Dominant �  t = Recessive �  TT = Two dominant

�  T = Dominant �  t = Recessive �  TT = Two dominant �  tt = Two recessive

�  T = Dominant �  t = Recessive �  TT = Two dominant �  tt = Two recessive �  Tt = One dominant, one recessive

�  T = Dominant �  t = Recessive �  TT = Two dominant (purebred) �  tt = Two recessive (purebred) �  Tt = One dominant, one recessive (hybrid)

•  T = Dominant •  t = Recessive •  TT = Two dominant (purebred) •  tt = Two recessive (purebred) •  Tt = One dominant, one recessive

(hybrid)

Understanding Mendel’s Crosses

�  Mendel’s P generation plants were purebred, meaning they had two of the same alleles. ¡  (TT) = “purebred tall” (tt)= “purebred short”

�  The F1 offspring received one allele from each parent making the allele combination: Tt.

�  These plants were hybrid, an organism that has both the dominant and the recessive allele for a trait. ¡  (Tt) = “hybrid tall”

Mendel also tested many other traits

Mendel’s breeding experiments

�  Ex.) Seed color

Parents (P)

First generation (F1)

Mendels’ breeding experiments

�  Ex. Continued.) Seed color

�  1st generation(F1)

�  2nd generation (F2)

Mendel’s Contribution

�  Many scientists thought that Mendel’s explanation of heredity was oversimplified.

�  His work was forgotten for

34 years. �  Years later, three other

scientists confirmed his findings and he became known as: “The Father of Genetics”

Video Link! Genetics 101 Part IV Phenotypes http://www.youtube.com/watch?v=jHWJqzlHl3w

Genotypes and Phenotypes

�  An organism’s phenotype is its physical appearance or its visible traits.

�  Ex: Phenotype = “short” “tall” “green” “yellow” �  An organism’s genotype is its genetic make-up or

allele combination. �  Ex: Genotype = “TT, Tt, tt, GG, Gg, gg

�  What are some of your phenotypes?

Let’s practice . . .

�  Phenotype �  Phenotype �  Genotype �  Phenotype �  Phenotype �  Genotype �  Genotype

�  Yellow �  Wrinkled �  XX �  Tall �  White �  yy �  Purebred

Homozygous and Heterozygous

Scientists use two more methods to describe an organisms genotype. �  Homozygous - an organism that has two identical

alleles for a trait is said to be homozygous for that trait.

Example: TT or tt (purebred) �  Heterozygous - an organism that has different alleles

for a trait is said to be heterozygous for that trait. Example: Tt (hybrid)

Let’s practice . . .

1.  BB 2.  Rr 3.  Aa 4.  AA 5.  tt 6.  Bb 7.  ff 8.  YY 9.  hybrid

1.  Homozygous 2.  Heterozygous 3.  Heterozygous 4.  Homozygous 5.  Homozygous 6.  Heterozygous 7.  Homozygous 8.  Homozygous 9.  Heterozygous

Vocabulary Review Which le2er below best describes a gene?

A.) Allele that is covered up when the dominant allele is with it. B.) An organisms physical appearance or visible traits. C.) Factors that control traits. D.) When the female contributes one factor, while the male contributes the other.

Vocabulary Review Which le2er below best describes heredity?

A.) When the female contributes one factor, while the male contributes the other. B.) An organisms physical appearance or visible traits. C.) When traits are passed from parents to offspring. D.) Factors that control traits. E.) Allele that is covered up when the dominant allele is with it.

Vocabulary Review Which le2er below best describes Mendel’s Law of SegregaJon?

A.) An organisms physical appearance or visible traits. B.) When allele pairs separate during gamete formaJon, and randomly unite at ferJlizaJon. C.) When traits are passed from parents to offspring. D.) An organisms geneJc makeup, or allele combinaJons. E.) Allele that is covered up when the dominant allele is with it.

Vocabulary Review Answer is… Which le2er below best describes Mendel’s Law of SegregaJon?

A.) An organisms physical appearance or visible traits. B.) When allele pairs separate during gamete formaJon, and randomly unite at ferJlizaJon. C.) When traits are passed from parents to offspring. D.) An organisms geneJc makeup, or allele combinaJons. – E.) Allele that is covered up when the dominant allele is with it.

A.) An organisms physical appearance or visible traits. B.) When allele pairs separate during gamete formaJon, and randomly unite at ferJlizaJon. C.) When traits are passed from parents to offspring. – D.) An organisms geneJc makeup, or allele combinaJons.

– E.) Allele that is covered up when the dominant allele is with it.

A.) An organisms physical appearance or visible traits. B.) When allele pairs separate during gamete formaJon, and randomly unite at ferJlizaJon. C.) When traits are passed from parents to offspring. D.) An organisms geneJc makeup, or allele combinaJons. – E.) Allele that is covered up when the dominant allele is with it.

A.) An organisms physical appearance or visible traits. B.) When allele pairs separate during gamete formaJon, and randomly unite at ferJlizaJon. C.) When traits are passed from parents to offspring. – D.) An organisms geneJc makeup, or allele combinaJons.

– E.) Allele that is covered up when the dominant allele is with it.

Vocabulary Review Which le2er below best describes an allele?

A.) An organisms geneJc make up. B.) An organisms physical appearance or visible traits. C.) When traits are passed from parents to offspring. D.) The different forms of a gene. E.) Alleles do not exist in nature.

Vocabulary Review Which two le2ers below best describes an organisms phenotype and genotype?

A.) When traits are passed from parents to offspring. B.) An organisms geneJc make up. C.) An organisms physical appearance or visible traits. D.) The different forms of a gene. E.) When an organism cannot pass on geneJc informaJon.

mendel s work - mrs. weisenbach's biology cabin

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