Transcript Ch 26 Inheritance of Traits
Standard Biology Chapter 26 Inheritance of Traits
Section 1 Genetics, How and Why 1
Genetics
Genetics: the study of how traits are passed from parent to offspring
– Mystery for a long
time
– Now know traits
are passed in sex cells
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Chromosomes
Nucleus found in center of cell which directs the cell’s activities Chromosomes are found in nucleus Chromosomes are thickened and easy to see Remember, chromosomes are duplicated before cell reproduction
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Chromosomes
Two kinds of cells Body cells chromosomes in pairs ( diploid) Sex cells- single chromosomes (so ½ the number of chromosomes as body cells) (haploid)
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Genes on Chromosomes
Gene
– Small section of
chromosome that determines a specific trait; examples
Eye color Wing shape Chemical process
– Humans have about
23,000 genes
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Genes on Chromosomes
Genes are arranged on a chromosome like beads on a necklace Chromosomes are paired, so genes are paired (except sex cells)
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Passing Traits to Offspring
Traits are passes from parent to offspring in sex cells Example: Ear Lobe Shape p. 548 Female egg A F F A AF Male sperm Child will have free ear lobes A= attached ear lobes F= free ear lobes
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Dominant and Recessive Genes
One trait dominates another like free dominates attached Free=dominate and Attached=recessive Mother is pure attached (AA) or homozygous recessive (homo means same) Father is pure dominate (FF) or homozygous dominate Child is one Free and one Attached (FA) or heterozygous (hetero means different)
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Traits of Plants and Animals
Trait found in Dominant Trait
Flies Long wings Pea plants Purple flowers Humans Corn plants Dogs Normal height Short hair
Recessive Trait
Short wings White flowers Can roll tongue Can’t roll tongue Dwarf Long hair 9
When Both Parents are Heterozygous
If mother is heterozygous (FA), she can make F eggs and A eggs
If father is Heterozygous (FA), he can make F sperm and A sperm
How many combinations of traits in children as possible? Table 26-2 p. 551
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When Both Parents are Heterozygous
Mother’s eggs: F and A Father’s sperm: F and A Child: FF, FA, AF or AA So four combinations of genes possible (although FA and AF are the same) Child will have free ear lobes if FF, FA or AF Child will have attached ear lobes if AA
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Standard Biology Chapter 26 Inheritance of Traits
Section 2 Expected and Observed Results 12
Punnett Square
Easy way to look at combinations of traits is with a Punnett Square
– Letters used represent
genes
– Capital letters dominant – Lower case letters
recessive
– Trait’s letter based on
dominant
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Punnett Square
Mother’s genes Example:
Free ear lobes dominant F Attached ear lobes recessive f Homozygous recessive mother ff Homozygous dominant father FF F F f Ff Ff Ff f Ff Father’s genes
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Punnett Square
Mother’s genes Example when parents are heterozygous: F f F FF Ff Father’s genes f Ff ff
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Directions for Punnett Square 1.
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3.
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Draw a Punnett Square (4 boxes). Each box shows possible combination of genes in offspring.
Decide what genes will be in the sex cells of each parent.
Write mother’s genes on top; write father’s genes on side.
Copy the letters that appear at the top of the square into the boxes below each letter.
Copy the letters that appear at the side into the boxes next to each letter.
Look at the 4 small boxes in the Punnett Square, these are possible combinations in the offspring.
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Expected Results
Get from Punnett Square What you expect to happen Probability Expected Results
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Observed Results
Expected Results Observed results when you count the pods of this one cross: 71 yellow pods and 24 green pods
The numbers you actually get They don’t match up exactly with what you expect The greater the number of offspring, the closer you should get to the expected results.
Table 26-3 p. 557
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Mendel’s Work
Gregor Mendel
– Father of Genetics – 1865 Austrian
monk/teacher in Czech
– Grew garden peas,
came up with ideas about how traits are inherited
– Counted 1000’s of traits
in pea plants and conducted scientific investigations (applied math to science)
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Mendel’s Work
– Traits he studied:
Plant height Pod color Pod shape
Seed color Seed shape
Flower color
Flower position Always found recessive when heterozygous parents were crossed 3 dominate to 1
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