1. Principles of Genetics - the Study of Heredity -
Betsy Sanford
7th Life Science
Lost Mountain Middle School

2. trait – are hereditary (passed from parent to offspring through DNA)
DNA – the chemical code for building proteins
proteins – create cell structure and function
chromosomes – threadlike strands of DNA
genes – sections of chromosomes that code for specific proteins
humans – about 20-25,000 genes on 46 chromosomes

3. DNA Diagrams

4. DNA Diagrams

5. DNA Diagrams

7. Human Chromosomes
23 pair = 46 total
the last pair determines gender

8. Gregor Mendel: The Father of Genetics
born 1822 in Austria
college & monastery; worked in gardens
wondered why similar plants had different characteristics
decided to study pea plants because they grow fast, are self-pollinating, and come in many varieties
did not know about DNA; made his theories based on the results of his experiments.
in eight years ( ), he grew over 30,000 pea plants

9. Gregor Mendel: The Father of Genetics

11. cross-pollination - occurs when pollen from one plant pollinates the egg of another plant

12. true-breeding – when a plant self-pollinates and always shows the same trait as the parent
Mendel crossed true-breeding plants

14. Alleles the different forms of a gene flower color = purple or white
purple flower color
stronger, dominant
represented with a capital letter
white flower color
recessive, weaker
represented with a lower case letter

15. Mendel’s Pea Plants

16. Reginald Punnett English zoologist and geneticist
created a table that predicts number and variety of genetic possibilities in offspring
the Punnett square is still used today in genetic counseling

17. Punnett Square
the letters on the inside of the square show the possible offspring

20. Genes you get genes from each parent
each pair of genes is represented by a two letter combination
the letter combination shows the possible alleles (forms) of the genes
two capitals, PP
two lower case pp
or one capital and one lowercase Pp
always write the capital letter first

21. Genotype the exact genetic make up of the gene (the exact 2 alleles)
represented by the letter combinations
PP, Pp, pp

22. Phenotype the results of the genotype what the letters show
what you can see of the trait
PP = purple flower color
Pp = purple flower color
pp = white flower color

23. Homozygous the alleles of a gene are exactly the same
PP = homozygous dominant
pp = homozygous recessive
also called purebred

24. Heterozygous the alleles of the gene are different
Pp = heterozygous dominant
also called hybrid

25. Human Chromosomes
23 pair = 46 total
the last pair determines gender

26. Sex Determination
23rd pair of chromosomes causes an organism to be either male or female
two X chromosomes = female
An X and a Y chromosome = male
women always pass their offspring an X
men pass their offspring either an X or a Y
therefore, the father determines the sex of the offspring
even though these are whole chromosomes (long strands of DNA, thousands of genes), a Punnett square can be used to show these results

27. 23rd Pair of Chromosomes

28. Sex-linked Gene any gene found on the 23rd pair of chromosomes
X chromosome is dominant over Y chromosome
any disease or disorder carried on the X will appear in males
to appear in females, both X’s would have to have the disease or disorder
example = females who can see color can pass color-blindness to their sons.

29. Color-blindness is a Sex-linked Gene

30. Incomplete Dominance
neither allele is strong enough to overcome the other
the alleles look blended

31. Co-Dominance both alleles are strong enough to show up on their own
both alleles are seen in the offspring

32. Multiple Alleles more than two different forms of a gene
example = blood type
A = dominant
B = dominant
O = recessive
6 possible genotypes (letter combinations)
4 phenotypes (results)

33. Multiple Alleles

34. Polygenic Inheritance
one trait produced from many genes
several sections of DNA cause the result of a single trait
examples = shades of eye color, shades of hair color, fingerprints

35. Polygenic Inheritance