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Reproduction and Genetics
Chapter 16 Section 4
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DNA and Genes• Parents pass their characteristics on to their offspring• Heredity- process in which characteristics pass from
parents to offspring• Genetics- scientific study of heredity• Traits- organism’s physical characteristics• Traits are controlled by the genetic materials in an
organisms chromosomes (rodlike structures located in the nucleus of the cell)
• Chromosomes also control an organism’s inherited characteristics
• Chromosomes are made partly of long-chain molecules called DNA
• DNA contains segments called genes• Gene- a segment of DNA molecule that contains
information that governs a specific trait
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Sexual Reproduction
• Sexual reproduction- reproduction involving 2 parents whose combined genetic material produces a new organism
• Male sperm cell joins with a female egg cell to produce offspring
• Egg an sperm cells contain half the number of chromosomes that are in the other cells
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Asexual Reproduction• Asexual reproduction- the reproductive process in
which the offspring have only one parent• Offspring of asexually reproducing organisms
inherit genes from only that parent; therefore they are genetically identical to the parent
• Sexual reproduction results in offspring that are not exactly like either parent.
• Offspring of sexually reproducing organisms are more diverse than the offspring of those that reproduce asexually
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Alleles
• Traits are controlled by genes• Chromosomes exist in pairs• Both chromosomes in a pair have the same
genes• Allele- different forms of a gene• An organism has 2 alleles for each trait, one from
each parent
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Dominant and Recessive Alleles
• Dominant allele- one whose trait always shows up in the organism
• Recessive allele- hidden, covered up trait in an organism
• Two dominant alleles express the dominant trait• Two recessive alleles express the recessive trait• One dominant and one recessive trait expresses
a dominant trait
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Review• What is a gene?
• Why are offspring that result from asexual reproduction so much like their parents, while the offspring of sexually reproducing organisms are not exactly like their parents?
• What is the difference between a dominant and recessive allele? Give an example.
• What kind of alleles must an organism inherit in order for a recessive trait to show up?
• Baby Amanda Ortiz inherited one allele for attached earlobes and one for free earlobes. Predict the shape of her earlobes.