1. Standard Biology Chapter 26 Inheritance of Traits
Section 1 Genetics, How and Why

2. 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

3. 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

4. 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)

5. 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

6. Genes on Chromosomes
Genes are arranged on a chromosome like beads on a necklace
Chromosomes are paired, so genes are paired (except sex cells)

7. Passing Traits to Offspring
Female
egg
Traits are passes from parent to offspring in sex cells
Example: Ear Lobe Shape p. 548 A A AF F
Child will have free ear lobes F
Male
sperm
A= attached ear lobes
F= free ear lobes

8. 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)

9. Traits of Plants and Animals
Trait found in
Dominant Trait
Recessive Trait
Flies
Long wings
Short wings
Pea plants
Purple flowers
White flowers
Humans
Can roll tongue
Can’t roll tongue
Corn plants
Normal height
Dwarf
Dogs
Short hair
Long hair

10. 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

11. 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

12. Standard Biology Chapter 26 Inheritance of Traits
Section 2 Expected and Observed Results

13. 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

14. Punnett Square Example: Mother’s genes 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

15. Punnett Square Example when parents are heterozygous: Mother’s genes FFF Ff
Father’s genes ff f Ff

16. Directions for Punnett Square
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.

17. Expected Results Get from Punnett Square What you expect to happen
Probability
Expected Results

18. Observed Results The numbers you actually get
Expected Results
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
Observed results when you count the pods of this one cross:
71 yellow pods and 24 green pods

19. 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)

20. Mendel’s Work
Traits he studied:
Plant height
Pod color Pod shape
Seed color
Seed shape
Flower color
Flower position
Always found 3 dominate to 1 recessive when heterozygous parents were crossed