Life Science Chapter 5 notes

Life Science – Chapter 5
Heredity
Section 1 – Mendel and His Peas
Gregor Mendel – Known as the father of genetics
In 1865 he published his results of genetics and pea plants
Found patterns – some parents would have a trait
The trait would not be in the next generation
Then it would show up again in the following generation
Why Mendel used pea plants
There are many different types of pea plants
They reproduce quickly
Self pollinating plants ( fig 3)
Seed shape – round, wrinkled
Plant height – tall, short
Flower color – purple, white
True breeding plants – always produce offspring with the same characteristics (seed shape, color etc.)
Mendel’s experiments
Crossed two pure parents with different traits
Round seeds to Wrinkled seeds
All offspring were round seeds
This showed that round was dominant and wrinkled recessive
Crossed two 2nd generation plants (all showed round seeds)
Their offspring had some wrinkled seeds
　
　
Mendel counted the seeds, flowers etc. of many crosses of plants and found the ratio’s of Dominant to Recessive ( page 110)
Punnett Squares
Used to estimate the possible alleles from two parents
Genes – the set of instructions found in DNA
Alleles – the genes that could appear
Round seed and wrinkled seed
Each organism has two alleles
One from its mother and one from its father
The "letters" in a Punnett square represent the Genotype – the genes they got from their parents
The way an offspring looks is its phenotype
Round seeds, purple flowers etc.
punnett square practice (click here)
Probability
The mathematical chance that an event will occur
½ x 100 = 50%
½ x ½ = ¼ = 25%
Section 2: Meiosis
Two kinds of reproduction
1. Asexual reproduction – one cell divides and makes two (mitosis) Only one parent involved
2. Sexual reproduction – two parent cells combine to make one offspring
The parent cells are called sex cells
Sex cells must have ½ the number of chromosomes as a regular cell or the offspring would have too many
Meiosis produces sex cells

Walter Sutton
Studied sperm cells in grasshoppers.
Compared them to eggs and realized that they both contained chromosomes
Realized that Genes must be located on chromosomes
This was a very important discovery in genetics
Mitosis – 6 steps
1. Copies of chromosomes are made
2. Chromosomes thicken and shorten
3. Chromosomes line up at the equator middle of the cell
4. Chromatids pull apart
5. New nuclear membranes form
6. Two identical cells are made.

Meiosis 8 steps
1.Chromosomes copy themselves
2.Homologous chromosomes line up (one from each parent
3.Chromosomes separate
4. Nuclear membrane forms
5. Each new cell now contains on chromosome pair
6. They line up at the equator
7. They separate to opposite sides of the cell
8. A new nuclear membrane forms, each new cell has ½ the number of chromosomes
　
Meiosis Animation (click here)
Meiosis and Mendel
Meiosis helps to explain why Mendel’s theories work
If the allele’s from each parent separate during meiosis then each new generation receives 1 allele from each parent.

Male or female
A female has 23 matched pairs of chromosomes
A male has 22 matched pairs of chromosomes and 1 unmatched pair
The father determines if the offspring will be boys or girls (page 119)
Girls XX chromosomes
Boys XY Chromosomes
Karoytyping
What Can Our Chromosomes Tell Us? (click here)