Genetics
The Science
of Heredity
It all began with
Gregor Mendel
5E
Explain
Who was Gregory Mendel?
• Gregory Mendel was an Austrian
monk.
• He lived between 1822 to 1884.
• When he was a young boy,...
Heredity
• HeredityHeredity is the passing of
traits from parents to
offspring.
• Mendel experimented with
heredity of cer...
Mendel’s Pea Experiments
• Mendel chose pea plants
because their traits were easy to
see and distinguish.
• He crossed pla...
Traits Studied by Mendel
F1 Generation
• Mendel called the parent plants the P generation.
• He called the offspring from the parents the F1 genera...
Mendel’s Amazing Discovery
Mendel did the same experiment with all traits that he studied and
discovered the same pattern ...
Heredity
• Heredity is the passing of traits from
parents to offspring.
Key Terms
Genes and Alleles
•Traits are controlled...
Understanding Mendel’s Experiments
Part I
2 alleles
for purple
PP
1 allele for purple. 1 allele for white
Pp
2 alleles
for...
ALLELES ARE EXPRESSED IN LETTERS
Dominant and Recessive Traits
• Back to Mendel and his peas. Mendel found for each
charac...
Understanding Mendel’s Experiment
Part II 1 allele for purple
1 allele for white
2 alleles for purple
PP
1 allele for purp...
Probability
• Probability is the likelihood
that a particular event will
occur.
• The laws of probability
determine what i...
PUNNETT SQUARE
To understand how all this comes together we use
a……
•Punnett square is a table that shows all the possible...
Punnett Square
• Using a Punnett
square, geneticists
can predict the
probability of
occurrence of a
particular trait.
• Th...
Genotypes and Phenotypes
• Genotype: Indicates
the alleles that the
organism has
inherited regarding a
particular trait.
•...
Homozygous and Heterozygous
• Homozygous: An
organism with two
identical alleles for a trait
(a purebred organism).
•Heter...
Incomplete Dominance
When both alleles are present, neither is
dominant, and the flower color is pink in
this case. Note a...
Co-Dominance
When both alleles are
shared. The cow and
calf are both spotted
with brown and white
color. This unique
combi...
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Genetics

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Genetics

  1. 1. Genetics The Science of Heredity It all began with Gregor Mendel 5E Explain
  2. 2. Who was Gregory Mendel? • Gregory Mendel was an Austrian monk. • He lived between 1822 to 1884. • When he was a young boy, he was interested in the plants that grew on the family farm. • Mendel was the gardener of the monastery where he lived as a monk. He did experiments on hundreds of pea plants there. • He kept careful records and used mathematics to make sense of what he observed.
  3. 3. Heredity • HeredityHeredity is the passing of traits from parents to offspring. • Mendel experimented with heredity of certain traits found in peas. • Mendel studied each trait separately and discovered certain patterns in the way traits are inherited in peas. • Mendel’s work has become the basis of genetics, the study of heredity.
  4. 4. Mendel’s Pea Experiments • Mendel chose pea plants because their traits were easy to see and distinguish. • He crossed plants with two different traits, for example purple flowers with white flowers. • He started his experiments with purebred plants. • Purebred plantsPurebred plants ALWAYS produce offspring with the same trait as the parent. For example, if the parent is tall, all offspring will be tall. If the parent is short, all offspring will be short.
  5. 5. Traits Studied by Mendel
  6. 6. F1 Generation • Mendel called the parent plants the P generation. • He called the offspring from the parents the F1 generation. • When Mendel crossed pure pea plants with purple flowers with pure pea plants with white flowers, all the F1 generation had purple flowers. P Generation F1 Generation
  7. 7. Mendel’s Amazing Discovery Mendel did the same experiment with all traits that he studied and discovered the same pattern each time: In the F1 generation, one trait was always hidden. That trait appeared in the F2 generation in about ¼ of the plants. Purebred P Generation Cross Pollination F1 Generation F1 Generation Self-Pollination Hybrid F2 Generation
  8. 8. Heredity • Heredity is the passing of traits from parents to offspring. Key Terms Genes and Alleles •Traits are controlled by factors that scientists call genes. These are inherited forms of characteristics. •You inherit your genes from your parents. •The different forms of a gene are called alleles. •You inherit a combination of two alleles from your parents.
  9. 9. Understanding Mendel’s Experiments Part I 2 alleles for purple PP 1 allele for purple. 1 allele for white Pp 2 alleles for white pp Heterozygous – Hybrid, having two different alleles for a given trait Homozygous – Pure breed, having two identical alleles for the same trait Homozygous – Pure breed, having two identical alleles for the same trait P = Dominant p = recessive
  10. 10. ALLELES ARE EXPRESSED IN LETTERS Dominant and Recessive Traits • Back to Mendel and his peas. Mendel found for each characteristic in peas, one trait was stronger than the other. • He called “ the trait that always appeared “ the dominant trait. - Represented with a capital letter PP , Pp • He called “ the trait that seemed to disappear “ the recessive trait. It is hidden when a dominant allele is not present - Represented with a lower case pp , Pp
  11. 11. Understanding Mendel’s Experiment Part II 1 allele for purple 1 allele for white 2 alleles for purple PP 1 allele for purple 1 allele for white Pp 2 alleles for white pp PpPp
  12. 12. Probability • Probability is the likelihood that a particular event will occur. • The laws of probability determine what is likely to occur, not what does occur. • Mendel was the first scientist that applied the principles of probability to genetics.
  13. 13. PUNNETT SQUARE To understand how all this comes together we use a…… •Punnett square is a table that shows all the possible combinations of alleles that can result when two organisms cross.
  14. 14. Punnett Square • Using a Punnett square, geneticists can predict the probability of occurrence of a particular trait. • The allele that each parent will pass to its offspring is based on chance, just like tossing a coin.
  15. 15. Genotypes and Phenotypes • Genotype: Indicates the alleles that the organism has inherited regarding a particular trait. • Phenotype: The actual visible trait of the organism.
  16. 16. Homozygous and Heterozygous • Homozygous: An organism with two identical alleles for a trait (a purebred organism). •Heterozygous: An organism that has two different alleles for a trait (a hybrid organism).
  17. 17. Incomplete Dominance When both alleles are present, neither is dominant, and the flower color is pink in this case. Note a true red or a true white. http://www.bio.miami.edu/~cmallery/150/mendel/c14x9incomplete-dominance.jpg
  18. 18. Co-Dominance When both alleles are shared. The cow and calf are both spotted with brown and white color. This unique combination is called a “roan cow.” The cat is neither a tan nor a black cat but a combination of both colors. We call this type of cat a “Tabby.”

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