1. Genetics of Organisms Chapter 7

2. Remember… Genes are parts of DNA In human beings, genes come in pairs.
Chromosomes make copies of themselves, thus giving the genes that lie among them the ability to be passes on through generations.
Genes that control a specific trait are found at the same location on a matching pair of chromosomes. (one from the egg, one from the sperm)

3. Genetics: the study of the inheritance (passing from parents to offspring) of traits.
In the 1800’s, a Roman Catholic Monk- Gregor Mendel made significant discoveries in regards to genetics.

4. Mendel experimented with pea plants to discover how organisms passed along traits.
He studied seven different types of physical traits in pea plants, and kept careful records of his findings.

5. Mendel’s Experiments
Mendel began his experiments with purebred pea plants.
Purebred: traits have remained the same for many years.
He mated two purebred pea plants that manifested a different trait to see what would happen.
Tall purebred (T)
Short purebred (t)

6. Mendel’s Experiments
When he mated a tall purebred with a short purebred, the offspring were not purebred because their ancestors were not alike.
Hybrid offspring: dissimilar parent genes
7A-3 Picture

7. Mendel’s Experiments
So what were these hybrid offspring (F1), Tall or short?
Tall… Why?
First generation offspring: F1
Second generation offspring: F2

8. Mendel’s Experiments
He then mated two hybrid offspring (F1)to create a second offspring generation (F2)
These were about ¾ tall, and ¼ short.
Why?

10. Explanation for what he discovered.
Mendel wrote a set of theories to explain his discoveries.
The trait he was studying (lets say height of the plant) was controlled by factors.
Factors are today know as genes, but then the term had not been coined.
For each trait in the offspring, one factor was supplied by each parent.

11. Each offspring, thus, had two factors for each trait
Each offspring, thus, had two factors for each trait. If these two factors were the same, the plant was purebred for that trait. If they were different, the plant was hybrid.

12. Each factor in one of two things
While looking at a specific trait, when both factors were dominant, the offspring showed the dominant trait.
Each factor in one of two things
Dominant: tends to appear in all generations. Only requires one gene to appear
Recessive: tends to remain hidden in certain generations. Covered by the dominant gene
Requires two genes to show.
Dominant has more influence on a trait then recessive.

13. If both factors were dominant, the plant showed the dominant trait.
If both factors were recessive, the plant showed the recessive trait.
If one factor was dominant and one was recessive, the plant showed the dominant trait.
The recessive trait is “hidden” or masked by the dominant trait.

14. Phenotype: physical characteristics.
Trait that appears in an organism.
Physical, behavioral, physiological
Genotype: the genetic make up.
Determines the organism’s Phenotype.
Combination of genes received.
Two organisms can have the same Phenotype, but different genotypes. TT Tt
Three Possible genotypes for pea plant height
TT – Tt – tt (two of those are going to appear tall)

15. The genetic principles Mendel discovered with pea plants apply to humans as well as plants and animals.
Many human traits are very hard to predict because of the complexity, but others are rather simple.
Dimples, rolling tongue, curly hair, long eyelashes, etc…

16. For example, if you have dimples, you express the dominant trait for that gene. Those who lack express the recessive trait.
A person with dimples either has two dominant genes (purebred for dimples), or one dominant, one recessive (hybrid for dimples).
Recessive genes only express themselves when dominant is not present, so if you do not have dimples, you are purebred for recessive.

17. Genes, Chromosomes, and Heredity
Chapter 7b

18. Chromosomes Chromosome number varies depending on the organism
Humans have 46
A housefly has 12
A tomato has 24
Within each cell the number of chromosomes is usually the same.

19. Chromosomes Remember… Chromosomes come in pairs.
Each member of a pair of chromosomes have the same type of genes.
One chromosome contains the gene for dimples, its partner will have a gene for dimples, though maybe not the same code.

20. Chromosomes…
When a sperm and egg unite, the zygote formed has 46 chromosomes (23 pairs), and has one gene from each parent.

21. Punnett Squares
Punnett squares are used to visualize the way Mendel’s theories worked.
Symbols represent genes
He started with purebred tall ,and purebred short.
These organisms form gametes (egg and sperm), and each gamete will only have one gene from the pair.

22. Punnett Squares
Punnett squares show the possible genotypes for an offspring.
Coin flipping- not an exact science, but a PROBABILITY.
Same with genetics. Shows probability.
The number of boxes in a Punnett square only shows the genetic possibilities, not the number of offspring.

23. Variations in Mendel’s Theories
All inherited traits are not as easy as simple dominant/recessive genes, there are many variations.
One type of variation is called Incomplete Dominance.
Two traits combine or blend together to produce a different trait.
Red snapdragon flowers

24. Another Variation
Codominance – dominant and recessive traits both expressed.
For example, shorthorn cattle have red and white hair which are both purebred traits. The hybrid offspring have both red and white hair in their coats.
Black and white chickens can mate and produce blue hybrid chickens which have one black gene and one white.

25. A third variation
Multiple gene inheritance- More than two genes are responsible for producing a single trait.
Why are there so many different colors of hair?

26. Sex chromosomes
The 23rd chromosome in a human determines the sex of the organism.
Only chromosome that appears different in males and females.
Female has two X chromosomes.
Male has one X and one Y chromosome.

27. When women produce an egg, each egg always gets an X chromosome.
The male produces sperm, and normally half the sperm gets and X and the other a Y chromosome.
Who determines the child’s sex?
Karyotype

28. Male or Female?

29. Sex- Linked Traits
Some inherited traits have genes located on the sex chromosome.
Sex linked trait- inherited trait that has a gene on the X chromosome but no corresponding gene on the Y chromosome.
When this happens, the unpaired gene on the male’s X chromosome will automatically express themselves.
Females, however, have a corresponding gene on the X chromosome, so if one X chromosome has a recessive gene and the other dominant, the dominant will express itself.

30. Sex- linked Traits Colorblindness – sex linked trait.
Notice example from book
Carrier – people who have a gene for a trait but do not express that trait themselves.

31. Inherited Disorders
Abnormal traits that are passed on through genes are called inherited disorders.
Why does God allow a person to be born with an inherited disorder? Is it a mistake?