heredity the passing of traits from parent to offspring traits: physical characteristics of an...
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Heredity
• The passing of traits from parent to offspring
• Traits: physical characteristics of an organism
–Example: eye color, hair color, & height
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Genetics
• The study of how traits are passed from parent to offspring by looking at genes– Genes are small sections of DNA on a
chromosomes that has information about a trait
• Each chromosome has a gene for the same trait (eye color from mom & eye color from dad)– Traits are determined by alleles on the
chromosomes
• Each gene of a gene pair is called an allele– Inherited traits are determined by the alleles on
the chromosome
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Genes on a Chromosome
• Chromosomes are made up of many genes joined together like beads on a string.
• The chromosomes in a pair may have different alleles for some genes and the same allele for others.
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Types of Alleles
• Dominant Alleles describe a genetic factor that is always expressed. – It prevents a recessive trait from showing
up in offspring.– Represented by capital letters (B)
• Recessive Alleles describe a genetic factor that is not always expressed. – It only expresses itself when both of the
recessive traits are inherited – Represented by lowercase letters (b)
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Examining & Studying Traits
• Two ways scientist study traits– Phenotype: outside expression of a gene
• Blue Eyes– Genotype: the two alleles a person has
inherited that can only be seen on the DNA• BB, Bb, or bb
• Two categories of genotypes– Homozygous: inherited two identical alleles
• BB (pure dominant) or bb (pure recessive)– Heterozygous: inherited two different alleles
• Bb (hybrid)
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Punnett Squares• Shows all possible
combinations of alleles that children can inherit from parents
• Mom’s genotype for brown eyes (Bb)
• Dad’s genotype for brown eyes (Bb)
• Offspring’s Phenotype– 75% brown, 25% blue
• Offspring’s Genotype– 25% BB, 50% Bb, 25% bb
B b
B BB Bb
b Bb bb
MomMom
DDaadd
brownbrown
blueblue
brownbrown
brownbrown
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Punnett Square Practice
• What is the genotype and the phenotype for each parent?
• What are the possible genotypes and the phenotypes for the offspring?
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Selective Breeding
• Selective Breeding is an intentional mating of organisms to produce offspring with specific traits – Two types:
• Pure bred• Hybrid
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Selective Breeding: pure bred
• Pure breeding– Crossing two individuals that have identical
or similar sets of alleles.
• Example: breeding only fast horses, breeding only labs
– Con – decreases genetic variety therefore makes it harder to adapt, resist diseases, and higher chance of genetic disorders
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Selective Breeding: hybrid
• Hybridization– Crossing two genetically different individuals. The
Hybrid organism is bred to have the best traits from both parents.
• Example: Labradoodles, corn produces lots of kernels with one resistant to disease
– Con – doesn’t always turn out the planned way & is time consuming
• Can not easily predict whether the dominant or recessive trait will appear