3. Chromosome: a long chain of genes
Genes and Chromosomes
Write these down p. 74
Chromosomes are found in the nucleus of a cell.
Chromosome: a long chain of genes

4. Chromosomes – Genes - DNA

5. Chapter 3 Section 1
What is Heredity?

6. Austrian monk born in 1822
Son of a farmer
Ordained as a priest
Lived in a monastery where over many years, he performed hundreds of experiments on pea plants relating to heredity
Known as the FATHER OF GENETICS

7. Heredity p. 74
Passing of physical characteristics from parent to offspring
Mendel’s study of pea plants would forever change biology

8. A trait is a gene
Each person gets two genes (one from their mother and one from their father)
An allele is a different forms of a gene

10. Two alleles must be present in order for a trait to show up in the offspring. One comes from mom and the other from dad
When fertilization occurs, the new offspring will have 2 alleles for every trait.

11. Mendel’s Experiments p. 75
Genetics: The scientific study of heredity
Mendel wondered why different pea plants had different characteristics: some tall, some short, some with green seeds, some with yellow seeds…

12. FERTILIZATION: when egg and sperm join together
MENDEL’S EXPERIMENTS
Mendel “crossed” pea plants with different traits and recorded results
“Crossed” means he took pollen from one plant and put it on another plant to fertilize it
FERTILIZATION: when egg and sperm join together

13. Birds and the Bees in flowering plants
Flowers have both male and female reproductive structures.
The female part of the flower: pistil
produces egg cells.
The male part of the flower: stamen
produces sperm cells (found in pollen)
p. 75

14. The birds and the bees of plants…
When pollen lands on the pistil of a flower, sperm travels down to the egg cell, and the result is fertilization
Fertilization produces a tiny embryo, which is enclosed inside a seed

15. Pea plants are usually self pollinating
Since the reproductive structures are inside the flower, the sperm of the flower will usually fertilize the egg of the same flower.
Resulting embryos will have the same characteristics as their parents
Even though sexual reproduction has occurred – there is only 1 parent – 2 sex cells though…

16. MENDEL’S EXPERIMENTS Crossing Pea Plants
Mendel devised a way to cross-pollinate pea plants.

17. Mendel started with PUREBRED ORGANISMS
PUREBRED: The offspring of many generations that have the same form of a trait
Example: Purebred tall pea plants always come from tall parent plants.

18. Before we move on, you must be familiar with the following terms:
P generation: Parent generation
F1 generation: First generation of offspring
F2 generation: second generation of offspring
Hybrids: offspring of parents with different traits

22. F1 Offspring p. 76 – no need to write this, just info for you…
The offspring from the parent cross
Filial comes from filia and filius – the Latin words for “daughter” and “son”

23. F1 Offspring
The offspring from the parent cross – (1st generation offspring)
purebred tall plants crossed with purebred short plants all F1 offspring were tall

24. F2 Offspring
The offspring from the F1 generation (2nd generation offspring)
Hybrid tall plants from the first generation allowed to self pollinate – the result was a mix of tall and short plants. ¾ were tall and ¼ were short.

25. So….what’s going on???
Evidently the F1 “tall” offspring must have been carrying the short trait, but it had been hidden.
The short trait had been passed down to the offspring and it reappeared in the F2 generation.

26. Experiments with other traits
Mendel studied other traits such as seed shape and color, pea pod shape and color.
In all of Mendel’s crosses, he found that only one form of the trait appeared in the F1 generation. However in the F2 generation, the “lost” form of the trait always reappeared in about ¼ of the plants.
Example…P generation (tall x short)
F1 generation = all tall
F2 generation = ¾ tall, ¼ short

27. Results of a Cross – figure 2 pg. 76

28. Results of a Cross – figure 2 pg. 76

29. Stop Here for Today

30. Genes and Alleles Gene A factors that controls a trait
A segment of DNA
Do you know this Gene???

31. ALLELES Different forms of a gene Genes and Alleles
EXAMPLE: The gene that controls stem height in peas has one allele for tall stems and one for short stems.

32. ALLELES ARE INHERITED
Each pea plant inherits two alleles from its parents – one allele from MOM (the egg) and the other from DAD (the sperm)
Our little sweet pea!!

33. ALLELES ARE INHERITED
An organism’s traits are controlled by the alleles it inherits from its parents. Some alleles are dominant, while other alleles are recessive
A dominant allele can cover up or mask a recessive allele

34. Dominant vs. Recessive Alleles
Dominant alleles: allele that is exhibited when the allele is present in the DNA
Indicated by a capital letter Ex: T
Recessive Alleles: allele that is exhibited only when the dominant allele isn’t present in the DNA
(this trait will be hidden if the dominant allele is present)
Indicated by a lower case letter. Ex: t

35. Some Human Traits controlled by a single gene w/ 2 alleles…just for fun

36. Having a Widow’s peak is dominant over not having one – this doesn’t mean it’s more common – just that if the allele is in your DNA…the trait is expressed.

37. Having a Free earlobes is dominant over attached earlobes
Having a Free earlobes is dominant over attached earlobes. For a child to have free earlobes – one of their parents had to have them as well.

38. Having a straight thumb is dominant over having a hitchhiker’s thumb – this doesn’t mean it’s more common – just that if the allele is in your DNA…the trait is expressed.

39. Having Syndactyly in the hands is dominant too
Having Syndactyly in the hands is dominant too. Again, this doesn’t mean it’s more common – just that if the allele is in your DNA…the trait is expressed. (happens in about 1/10,000 births)

40. Alleles in Mendel’s Crosses
Hybrid: An organism with two different alleles for a trait
(1 dominant and 1 recessive)
The F1 plants were all hybrids - one tall allele and one short allele
The dominant allele masked the recessive allele, so all the plants were tall in the F1

41. Dominant and Recessive Alleles
Figure 4
Fill in the missing allele symbols and descriptions.
Use the word bank to complete the statements. (Terms will be used more than once).
Draw the two possible ways the F2 offspring could look. T t
Tall
dominant t
recessive
Hybrid
dominant
dominant
recessive
recessive

42. Apply it! P. 79
WW and ww
About ¾ will have long wings and ¼ will have short wings
All will have long wings; Ww

43. Significance of Mendel’s Contribution
Mendel’s discovery of genes and alleles eventually changed scientists’ minds about heredity
Before Mendel, most people thought traits were just a blend of the parent’s characteristics.
Mendel showed that offspring traits are determined by the individual, separate alleles inherited from each parent.

44. Significance of Mendel’s Contribution
Known as the Father of Genetics