1. Chapter 6
Heredity

3. Section 1: Mendel and His Peas
Humans share common characteristics
i.e. feet, eyes, hands, etc.
But what makes you different than your fellow classmates?
Heredity – the passing of traits from parents to offspring
How heredity works was the topic of Gregor Mendel’s experiments

4. Who Was Gregor Mendel Mendel was born in 1822 in Austria
He grew up on a farm and learned about cultivating flowers
After attending college, Mendel entered a monastery, where he worked in the garden
He used the monasteries plants (garden peas) to study how traits where passed on from parents to offspring

5. Unraveling the Mystery
Mendel’s choice of garden peas was a good one for several reasons
1) they grow quickly
2) they are self-pollinating
3) they come in many varieties
Self-pollinating plant – a plant that contains both male and female reproductive structures

7. Peas Be My Ponder
To keep things simple Mendel decided to study only one trait at a time
i.e. height or flower color
Pea plants have two forms for each characteristic
i.e. tall vs. short plants or purple vs. white flowers

9. True –Breeding Plants
Mendel was careful to use plants that were true-breeding
True-breeding plant – plants that self-pollinate and always produce off-spring that have the same trait as the parent plant
i.e. tall parent plant produces 100% tall offspring
Mendel decided to “cross” two plants with different forms of the same trait
i.e. tall plant and short plant
He used a method called “cross-pollination”

11. Mendel’s First Experiment
In his first experiment Mendel studied seven different characteristics (we will focus on one – flower color)
Mendel crossed a true-breeding purple flowered plant with a true breeding white flowered plant (parental generation)
The offspring are known as the first generation(f1)
All of the offspring had purple flowers!
Mendel got similar results from all his different crosses
What happened to the white flowers?
One trait always appeared in the f1 generation, while the other seemed to vanish
Dominant trait – the trait that appeared
Recessive trait – the trait that seemed to vanish

13. Mendel’s Second Experiment
Mendel allowed the f1 generation to self pollinate
Do you know what happened?
The recessive trait (white flower) showed up again
The results were 75% purple to 25% white
This is a 3:1 ratio

15. A Brilliant Idea
Mendel realized that his results could be explained only if each plant had two sets of instructions for each characteristic
Each parent could only donate one set of instructions to the offspring
Genes – the set of instructions
What do these instructions control?
Alleles – two genes that govern the same characteristic

16. The Proof Is in the Punnett Square
Punnett Square – a tool used to visualize all the possible combinations of alleles
Lets do some examples on the board
Genotype – The inherited combination of alleles
Phenotype – The organism’s outward appearance

17. What Are the Chances? It is important to understand that offspring
are equally likely to inherit either parents
allele
Even though there seems to be a 50/50
chance of inheriting either allele, it is more
similar to a coin toss and is completely random
Because of this the laws of probability must be
considered
Probability - is the mathematical chance
that an event will occur

18. Genotype Probability The same method is used to calculate the
probability that an offspring will inherit a
certain genotype
For example in Mendel’s 2nd experiment what is the probability that an offspring will inherit two lowercase p’s (pp) and be white?
(1/2 x 1/2 = 1/4 = 25%)

19. Chapter 6 Quiz 1 1)_________ is the passing of traits from
parents to offspring
2) _________ is a plant that contains both male and female reproductive structures
3) _________ the name Mendel gave to the trait that seemed to disappear in his 1st experiment
4) _________ are two forms of the same gene (one on moms chromosome and one on Dads)
5) __________ is a tool used to visualize all possible combinations of inherited genes
Bonus) __________ carry the genes that determine whether and organism is male or female

20. Section 2: Meiosis

21. Two Kinds of Reproduction
Asexual Reproduction – only one parent is needed
1) the internal structures are copied (mitosis)
2) the cell then divides producing two identical cells
Most single-celled organisms reproduce this way as well as most of the cells in your body
Sexual Reproduction – two parent cells join together to form a new individual
Sex cells – the parent cells (sperm/eggs)
contain half the normal amount of chromosomes
Homologous chromosomes – Identical chromosome pairs
i.e. Humans have 23 pairs of chromosomes (46 total), 23 from mom and 23 from dad
Why do sex cells have ½ the amount of chromosomes?

22. Meiosis to the Rescue
Walter Sutton discovered that genes are located on chromosomes
Sex cells are made during meiosis
Meiosis – produces new cells with ½ the usual number of chromosomes
During meiosis the cells are copied once, but go through two rounds of divisions producing sperm and eggs with ½ the normal amount of chromosomes

24. Male or Female
Sex chromosomes – Chromosomes that carry genes that determine whether an offspring will be male or female
In humans females have two X chromosomes, while males have one X and one Y

25. Chapter 6 Quiz 2
________ is the processes that produces
new cells with half the number of chromosomes
2.________ are pairs of chromosomes that
contain the similar genes for the same traits
3.________ is the phase of meiosis where
crossing over occurs
4.________ is the scientist who discovered that
genes where located on chromosomes
Bonus) ________ are flowers that always have
offspring identical to themselves