Download Chapter 4 – Patterns of Heredity

Chapter 4 – Patterns of Heredity
4.1 Living things inherit traits in patterns.
Inherited Traits – traits you get from one or more parents.
Acquired Traits – a trait that is developed during your life.
Sexual Reproduction – A cell containing genetic information from
the mother and a cell containing genetic information from the
father combine into a completely new cell, which becomes the
offspring.
Genes and Chromosomes
Gene- Unit of heredity that occupies a specific location on a
chromosome and codes for a particular product.
Heredity – passing of genes from parents to offspring.
 In most eukaryotes, cells contain pairs of chromosomes,
with one chromosome of each pair coming from each of the
two parents.
 Homologs – the chromosomes in a pair. The chromosomes
have the same size and shape, and carry genetic information
for particular traits.
 On each homolog are sites where specific genes are located.
 The genes may not always be identical.
Alleles – The variations of the same gene.
Chromosomes
- Each organism has a specific number.
- Humans have 23 pairs of chromosomes (total of 46).
- Chromosomes are referred to by their pair number.
- In humans the 23rd pair of chromosomes determines the
sex.
- 2 X chromosomes = a female
- 1 Y and 1 X = a male
Gregor Mendal (pg 104-105)
 Monk who examined traits in pea plants; 3 conlcusions:
 Concluded that some traits skipped a generation but came
back in the next
 Each trait must have two factors: one from each parent.
 Some traits can be masked; only shown when both factors
are for the trait.
Phenotype vs. Genotype
Phenotype – describes the actual characteristics that can be
observed.
Ex. Height, eye color, size of your feet, etc.
Genotype – the name for genes that an organism has.
Dominant and Recessive Alleles
Dominant Alleles – one that is expressed in the phenotype even if
only one copy is present in the genotype.
Recessive Alleles – one that is expressed in the phenotype only
when two copies of it are present on the homologs.
* If one chromosome in the pair contains a dominant allele and
the other contains a recessive allele, the dominant allele will be
expressed in your phenotype.
4.2 Patterns of heredity can be predicted.
Punnett Squares
- Illustrate how parents’ alleles might combine for offspring traits.
B
b
BB
Bb
bB
bb
- ¼ 2 dominant alleles
- 2/4 or ½ 1 dominant + 1 recessive
- ¼ 2 recessive alleles
Ratios and Percentages
Ratio – Shows a relationship between two quantities (4:4 or 4/4)
Probability – chance that a specific outcome will happen
Percentage – ratio that compares a number to 100.
4/4 x 100 = 100%
¼ x 100 = .25 x 100 = 25%
4.3 Meiosis is a special form of cell division.
 Most human cells (body cells) contain 46 chromosomes – the
full number of chromosomes that is normal for a human
being.
 Any cell that contains the full number of chromosomes (two
sets) for a species is a 2n cell, also called a diploid cell.
Gametes – cells that contain half the usual number of
chromosomes – one chromosome from each pair.
- Gametes are 1n cells, also called haploid cells.
- Gametes are found in the reproductive organs of
plants and animals. (Egg-female, sperm-male)
- Human gametes contain 23 unpaired chromosomes
Fertilization – the process that takes place when a sperm and
an egg combine to form one new cell. (pg. 118)
Meiosis- Special kind of cell division that produces haploid (1n)
cells.
- A cell goes through 2 cell divisions Meiosis I and Meiosis
II.
**- Meiosis takes place only in the reproductive tissues of
an organism.
- One cell in an organism’s reproductive system divides twice
to produce four 1n cells or gametes
Meiosis I diagram on page 121
 Prophase I
- The duplicated chromosomes pair up with their
partners.
- There are 2 sets of each of the chromosomes pairs
in the parent cell. (twice as many)
- The chromatids are attached together.
- There are pairs of doubled homologs.
 Metaphase I
- The chromosomes pairs line up in the middle of the
cell.
 Anaphase I
- The two copies of one homolog are pulled apart from
the two copies of the other homolog.
*Most significant step*
 Telophase I and Cytokinesis
- A new cell membrane forms at the center of the cell,
dividing the parent cell into 2 daughter cells.
Meiosis II
 Prophase II
- In each daughter cell, there are two copies of each
of n chromosomes.
- The copies are attached together.
 Metaphase II
- Each duplicated chromosome lines up separately
along each cell’s center.
 Anaphase II
- The two attached copies of each chromosome
separate and
are pulled to opposite poles in each other.
 Telophase II and Cytokinesis
- A new cell membrane forms in the center of each ell,
as each
cell divides into two 1n daughter cells, producing
a total of four 1n cells.
Mitosis vs. Meiosis
 Only cells that are to become gametes go through
meiosis.
 A cell that divides by meiosis goes through two cell
divisions, but the chromosomes are not copied before the
second division.
 In mitosis, the chromosomes are always copied before
division.
 Daughter cells produced by meiosis, which are haploid
(1n), contain only half of the genetic material of the
parent cell (one homolog from a chromosome pair).
 Daughter cells produced by mitosis, which are diploid
(2n), contain exactly the same genetic material as the
parent (pairs of chromosomes).