chapter 6 introduction to genetics alissa stegman period 8
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Chapter 6 Introduction to Genetics
Alissa StegmanPeriod 8
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Introduction to Genetics• Heredity is the set of
characteristics an organism recieves from its parents & genetics is the study of heredity.
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George Mendel
• George Mendel is also refered to as the father of genetics. He was born in 1822 and died in 1884 was a monk in the czeck republic. He smoked around 20 cigars a day and used pea plants for his experiments.
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Why pea plants?Why?• Small• Distinguishable traits• Quick reproductive
cycle• Produced many
offspring
Seven traits of pea plants• Seed shape• Seed color• Seed coat color• Pod shape • Pod color• Flower position• Plant heightThe traits are characteristics
that distinguish one individual from another.
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Pea plants • True breeding – plants that always pass its
characteristics to the next generation• Reproduction – pea plants use their flowers to
reproduce• Pollen = male sex cell• Egg = female sex cell• A new plant is formed when pollen fertilizes an egg• Pea plants usually reproduce by self pollination
( only have one parent).
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F1 Generation
• Mendel crossed true breeding plants that showed one form of a trait with true breeding plants that showed the other form of that trait
• Example : Trait = pod color, cross green podplant with a yellow pod plant.The offspring produced are called Hybrids
which are defined as an offspring of parents with different characteristics.
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F1 Generation continued
• Mendel called these hybrids the F1 generation, P generation refers to the parents that were crossed.
• The results? Mendel thought that the two alternate forms of a trait will blend in the F1 generation. Example, cross a tall with a small and the offspring will be medium height.
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F1 Generation continued
• This did not happen, there was no blending. Instead the traits of just one parent appeared in the offspring, the other trait seemed to vanish.
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F2 Generation
• Cross F1 generation among themselves• For each of the seven traits, the form that has
vanished in the F1 generation re appeares in the F2, they appeared in ¼ of the plants.
• Genes – the unit of heredity or unit that determines traits.
• Alleles – different forms of a gene Example : height in pea plants – 2 alleles, tall & short.
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F2 Generation Continued
• Dominant & Recesive • In pea plants that have both alleles (tall/short) only
the tall allele is expressed. This is the dominant allele, the short allele is not expressed this is recessive.
• Dominant allele are represented by capital letters• Example : T is the allele for a tall pea plant• Recessive allele are represented by lowercase letters• Example : t is the allele for a short pea plant
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F2 Generation Continued
• Phenotype – physical appearance of an organism (adjective).
• Genotype – genetic makeup of an organism ( TT, Tt, or tt)
• Pgeneration TT x tt• Homozygous – both alleles are the same TT or tt.
• Heterozygous – two different alleles, Tt
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Mendel’s principles
• Individual units, called genes, determine biological characteristics.
• For each gene, an organism receives one allele from each parent.
• If an organism inherits different alleles for the same unit, one allele may be dominant over the other.
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6-2 Meiosis
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Gamete
• Gamete is reproductive or sex cellplants humanpollen sperm egg egg
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Gamete continued
• According to Mendel’s principles, an organism has two copies of each gene, one of these copies is passed to an offspring.
• Gametes contain half the number of chromosomes found in body cells.
• 46 chromosomes per body cell, 23 per gamete• One set of chromosomes, described as haploid (n) n = 23 humans.• Body cells (somatic) cells are described as diploid,
(2n) 2n = 46 human.
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How are gametes formed?
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How are gametes formed?
• Through a process known as Melosis, ( reduction division) the # of chromosomes in a diploid cell is reduced by half, producing haploid gametes.
• Melosis has two sperate cell divisions, example prophase 1 & prophase 2.
• Provides genetic veriction because chromosomes are paired and exchange genetic info, this process is known as crossing over.
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6-3 analyzing inheritance
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Probability or likelihood
• If we flip a coin, ½ chance chance of heads• Ace of spades out of a deck – 1/52 • 2 heads in a row = ½ x ½ = ¼• 4 heads in a row = ½ x ½ x ½ x ½ = 1/16• 4 aces in a row = 1/13 x 1/13 x 1/13 x 1/13 = 1/28561