Unit 7 Section 1

Evidence 1: Why do you think siblings don’t look exactly the same if all of

their DNA comes from the same mother and father?

Evidence 2: What do you think the chances are that there is someone in

the world exactly like you?

As you recall, our DNA is the genetic material in organisms. DNA codes

for proteins and contains the information that determines when proteins

are made. DNA is packed with these proteins inside of chromosomes and

are found in the nucleus of the cell.

We have 46 chromosomes in our body or 23 pairs of chromosomes.

One pair or set of 23 chromosomes comes from each parent (one

set from mom and one set from dad)

Each pair is said to be homologous or having the same structure

Evidence 3: What percentage of your genetic material is from your mother, and what percentage is from your father?

Evidence 4: What might happen if humans had more or fewer chromosomes?

A karyotype is the number and appearance of chromosomes in the nucleus of a eukaryotic cell. The karyotype of an organism is usually displayed in photomicrographs wherein chromosomes are arranged in homologous pairs, and in descending order of size and relative position of the centromere.

Karyotypes describe the chromosome count of an organism and what these chromosomes look like under a light microscope. Attention is paid to their length, the position of the centromeres, banding pattern, any

differences between the sex chromosomes, and any other physical characteristics.

Normal Karyotype

Karyotype of Down Syndrome

Evidence 5: Do the chromosomes in Figure 2 on page 305 belong to a

female of a male? Explain how you know.

Your body is made up of two types of chromosomes

1. Autosomes

a. Made up of pairs 1-22

b. These are homologous chromosomes

i. These homologous chrosomes come from the mother and

the father. (1 from each)

2. Sex chromosome

a. Made up from pair 23

b. These determine if you are male (XY) or female (XX)

c. The X chromosome is bigger and can only be given by the

mother since that is all that she has to give. Contains other

genes that are unrelated to sexual characteristics.

d. The Y chromosome is smaller and only contains genes for male

sex traits.

e. Gametes are sex cells (sperm and egg cells)

Evidence 6: What is the difference between the genetic material on two

sister chromatids and the genetic material on homologous

chromosomes?

Your body is made up of many types of specialized cells, but all of them

can be divided into two major categories

1. Somatic cells AKA body cells

a. These make up most of your body tissues and organs

2. Gametes AKA sex cells

a. These are cells that make up the reproductive organs

b. In females – called ova or eggs

c. In male – called spermatozoa or sperm

d. DNA is found in our sex cells and can be passed down to our

children.

Gene

a segment of DNA (on a specific site on a chromosome) that is

responsible for the physical and inheritable characteristics or

phenotype of an organism.

A gene is formerly called a factor

Genome is all of an organism’s genetic material

Allele is any of the alternative forms of a gene that may occur at a specific location.

Cells have 2 alleles for each gene

1 on each homologous chromosome

1 given from each parent

There are 2 types of alleles

1. Homozygous a. Alleles are identical to each other

i. Both for purple flowers or both or white flowers 2. Heterozygous

a. Alleles are different from each other i. Ex one for purple flowers and one for white flowers

Sexual reproduction vs fertilization

Sexual reproduction involves the fusion of two gametes that results

in offspring that are a genetic mixture of both parents.

Fertilization is the actual fusion of an egg and a sperm

Diploid cells have 2 copies of each chromosome, one from the mother

and one from the father

Di means double

Represented in charts as a 2n

Autosomal cells are diploids

Haploid cells have only one copy of each chromosome

Hap means half

Represented in charts as an n

Sex cells are haploids

Polyploids are cells with many copies of each chromosome

Can be commonly found in plants and some animals such as

goldfish, salmon and salamanders.

These organisms will usually have even chromosome sets such

as 54, 72 or 90.

Evidence 7: What is an example of body cell in your body?

Evidence 8: How does the genetic material in gametes compare to that in

body cells?

Evidence 9:Why do gametes have half a set of DNA? What would happen

if they had a full set of DNA? Explain your answer.

Meiosis is a form of nuclear division that divides a diploid cell into haploid

cells.

Has to occur to produce gametes

This process is also called reduction division because it reduces

the number of chromosomes by half.

Gamatogenesis

Production of gametes

Spermatogenesis is the production of the sperm cell in males

Oogenesis is the production of the egg cell in females

Evidence 10: Make a venn diagram to compare and contrast egg

production and sperm production.

There are two cell divisions that occur.

Mitosis is a process of cell division that results in two genetically identical daughter cells developing from a single parent cell.

Meiosis is the division of a germ cell involving two fissions of the nucleus and giving rise to four gametes, or sex cells, each possessing half the number of chromosomes of the original cell.

Mitosis is used by single-celled organisms to reproduce; it is also used for the organic growth of tissues, fibers, and membranes.

Meiosis is found in sexual reproduction of organisms. The male and female sex cells (i.e., egg and sperm) are the end result of meiosis; they combine to create new, genetically different offspring.

Mitosis has one division and meiosis has two divisions. You still have to remember PMAT, but now you do it twice. You also need to remember that four cells are created where there was originally one. That's four (4) cells with half of the amount of DNA needed by a cell. When a cell goes through meiosis, it's not concerned about creating another working cell. Meiosis happens when it's time to reproduce an organism. The steps of meiosis are very simple. When you break it down its just two PMAT's in a row. Scientists say Meiosis I and Meiosis II, but it's just two PMATs. The interphase that happens between the two processes is very short and the DNA is not duplicated.

Step One aka PMAT 1

MEIOSIS I:

This is basically like the PMAT of a regular mitosis.

Prophase I the duplicated DNA condenses into compact structures, the nuclear envelope surrounding the DNA begins to break down.

Metaphase I the chromosomes align in the center of the cell, centrioles move to the polar ends of the cell and project thin spindle fibers to connect to the center (centromeres) of each chromosome.

Anaphase I the centrioles will begin to pull each chromosome into two halves called sister chromatids.

Telophase I the nuclear membrane forms around the chromatids and they are completely located at opposite ends of the cell. Usually after Telophase the cell will also divide its cytoplasm and pinch off into two separate but identical daughter cells.

Step Two aka PMAT 2

MEIOSIS II:

In Prophase II the DNA that remains in the cell begins to

condense and form short chromosomes.

In Metaphase II all of the chromosomes line up along the center

of the cell and the centrioles are in position for the duplication.

Anaphase II shows the chromosomes split and move to

opposite sides of the cell. Each one splits into two pieces. They

don't divide up the DNA between the new cells; they split the

DNA that exists. Each daughter cell will get one-half of the DNA

needed to make a functioning cell.

Telophase II shows the DNA completely pulled to the sides and

the cell membrane begins to pinch.

When it's all over, you are left with four haploid cells that are

called gametes.

Mitosis

Produces genetically identical cells

Results in diploid cells

Takes place throughout an organisms lifetime

Involved in asexual reproduction

Chromosomes are divided here

1 cell division

Meiosis

Produces genetically unique cells

Results in haploid cells

Takes place only at certain times in an organisms life cycle

Involved in sexual reproduction

Sister chromatids are divided here

2 cell divisions

Evidence 11: Make a table to compare mitosis and meiosis in terms of the

number and type of cells produced, the genetic material in the cells, and

the roll of each process in the body. Does meiosis or mitosis occur more

frequently in your body? Explain you answer.

Genetic variation refers to differences in the genetic material of

individuals in a population.

Meiosis and sexual reproduction increase genetic diversity, or genetic

variation, within a population.

Independent assortment refers to the assortment of chromosomes being

a matter of chance. One homologous pair arrangement does not depend

on another pair.

Crossing over is an exchange of genes or chromosomes.

o The genes are mixed up, not resulting in a perfect duplicate like

mitosis.

o The cell divides, leaving two new cells with a pair of chromosomes

each.

o This allows for increased genetic diversity

o Occurs in Prophase 1 of meiosis 1

o Very important because it allows genetic combinations to be

practically unlimited

Meiosis is an important process that allows for the rapid generation of

new genetic combinations

3 mechanisms make key contributions to the genetic variations

1. Independent assortment

2. Crossing over

3. Random fertilization

Importance of genetic variations

o Speeds up the process of evolution by genetic recombination’s

o Combining genes from two organisms resulting in a third not identical to either parent