Download Chapter 6.1 Lecture

Section 6-1
“Chromosomes
& Meiosis”
6.1 Chromosomes and Meiosis
Biology Essential Question:
• At the end of this section you will need to be
able to answer this question …
• How does a gamete differ from a body
cell?
• Why does a gamete have only half the
number of chromosomes as a body
cell?
6.1 Chromosomes and Meiosis
KEY CONCEPT
You have body cells (somatic cells) and gametes.
• Cells in your body can be divided into two
types:
somatic cells and germ cells.
• Somatic cells (BODY CELLS) – make
up most of your tissues and organs.
(Not passed on to offspring)
• Examples: brain cells, kidney, eyeballs, skin
body cells
• Cells in your body can be divided into
two types: somatic cells and germ
cells.
• Germ cells- cells that make
up your reproductive organs
Gametes - sex cells
also called germ cells
– ova (eggs) in female and
spermatozoa (sperm
cells) in male. This DNA
is what is passed on to
your children (offspring)
sex
cells
(sperm)
sex
cells
(egg)
• Which of the cells below are somatic cells?
• Which would be gametes?
Rod
Cells
Hair
Cells
Sperm
Cells
Muscle
Cells
Egg
Cells
Nerve
Cells
Chromosome and Meiosis
Power Notes
List 3 facts about Somatic Cells
List 2 facts about Gametes
• Somatic Cells
Body cells
Make up tissues
and organs
Not passed on to
offspring
Gametes
Sex cells
Passed on to offspring
6.1 Chromosomes and Meiosis
• Chromosome - a grouping of
coiled strands of DNA, containing
many genes.
Chromosome number does not seem to be
related to the complexity of an organism
• Yeast: 32 chromosomes –
(16 pairs)
• Fruit flies: 8 chromosomes (4 pairs)
• Indian Fern: 1248- (624 pairs)
• Humans: 46 chromosomes –
(23 pairs)
6.1 Chromosomes and Meiosis
Your cells have autosomes and sex chromosomes
The human cell has 46
chromosomes, which are
in pairs. --23 pairs.
Chromosomes are large
DNA structures made up
of many genes. These 23
pairs encode you, 23 came
from your father and 23
from your mother, and
each gave you one of each
pair.
Each pair of chromosomes are
referred to as homologous pair.
Homologous chromosomes
are 2 chromosomes (pairs) one
from mother and one from father.
These chromosomes have copies of the
same genes (although the 2 copies may
differ – both may be the genes for eyes
but one form mother may be for
brown and the one for father blue)
The homologous pairs are numbered 1 -23
from largest to smallest. The first 1-22
make up the autosomes.
– Homologous
chromosomes
are pairs of
chromosomes have
genes for the same
traits
• The first 22 pairs of
chromosomes are
autosomes
• Autosomes contain
genes that are not
directly related to the
sex of the organism
Sex Chromosomes
(23rd pair in humans)
relate directly to the
development of sexual
characterisitics.
Humans have very
different sex
chromosomes
X and Y
Chromosomes that contain
genes not directly related to sex
of organisms
Homologous Chromosomes
pairs, one from each parent
Sex Chromosomes that contain
a gene that is directly related to
sex of organisms
Body cells are diploid; gametes are haploid.
• Sexual Reproduction = the fusion of two
gametes that result in an offspring that
are a genetic mixture of both parents.
• Fertilization: the actual fusion of an egg
and sperm.
When fertilization occurs, the nuclei of the egg and
sperm cell fuse to form one nucleus.
This nucleus needs the correct number of
chromosomes so the egg and sperm each must
contain half
– one chromosome form each homologous pair.
6.1 Chromosomes and Meiosis
Diploid - (2n) cells have two
copies of every chromosome
–Body cells are diploid
–Half the chromosomes come
from each parent
• Haploid (n) cells have one copy of
every chromosome
–Gametes (sex cells) are haploid
–Gametes have 22 autosomes and 1
sex chromosome
Fertilization: When the egg and sperm
cell unite
• 2 haploid cells unite to form a cell
(zygote) that once again has the
diploid number of chromosomes
• Chromosome number must be
maintained in animals
• Many plants have more than two copies
of each chromosome
• A zygote fertilized egg cell that
grows to be a human
• Mitosis makes more identical diploid
cells
• Meiosis makes haploid cells from diploid
cells and:
– occurs in sex cells
– produces gametes
6.1 Chromosomes and Meiosis
Has two copies of
each chromosome
– one from each
parent
Has 1 of each
chromosome
Body Cells
Result of
MEIOSIS
Result of mitosis
Gamete (sex cell)
6.1 Chromosomes and Meiosis
How are Mitosis and Meiosis similar?
• Mitosis and Meiosis are both
types of cell division
• They both involve the DNA
coiling up to make
chromosomes
• The nucleus divides in both
processes using many different
steps
Create identical
cells
Make diploid cells
Happens throughout
organisms life time
Creates genetically
unique cells
Haploid cells
Takes place at only
certain times in life
cycle
Sexual reproduction
• How are mitosis and meiosis
alike?
• Both involve division of the
nucleus followed by the
formation of new cells.
•
What word pairs in the accompanying
descriptions of mitosis and meiosis
point to the differences between the two
types of division?
Mitosis • identical / unique Meiosis
• diploid / haploid,
• asexual / sexual