I told you before that we categorize human cells in two categories: body cells and sex cells, what...
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Transcript of I told you before that we categorize human cells in two categories: body cells and sex cells, what...
I told you before that we categorize human cells in two categories: body cells and sex cells, what do
you THINK makes them so different?
HOW MANY CHROMOSOMES ARE FOUND IN EACH HUMAN BODY CELL?
• In the body cells of animals and most plants, chromosomes occur in pairs.
• In each pair, one you inherited from your mom, the other from your dad.
Diploid Cells
From Mom
From Dad
• The two chromosomes of a pair are called homologous chromosomes.
• Each pair of homologous chromosomes has genes for the same traits.
Homologous Chromosomes
• A cell with two of each kind of chromosome is called a diploid cell.
• All of your body cells are diploid.
Diploid Cells
• Body cells (diploid) are different from sex cells.
• Each person can only pass on ONE of their homologous chromosomes to their young.
HUMANS = 46 CHROMOSOMES
IN THEIR BODY CELLS
Each parent passes 23 to their young, so that when the sperm and egg combine- it
will equal 46 Chromosomes.
• So, sex cells CANNOT be diploid.
•A cell containing only one of each kind of chromosome is called a haploid cell.
Haploid Cells
Chromosome Numbers of Common Organisms
Organism Body Cell
Fruit fly 8
Garden pea 14
Corn 20
Tomato 24
Leopard Frog 26 13
Apple 34
Human 46
Chimpanzee 48
Dog 78
Adder’s tongue fern 1260
Sex Cell
4
7
10
12
17
23
24
39
630
Diploid and Haploid Cells
In Humans, how many chromosomes would each of these cells have…..
CHEEK CELL
46
SPERM CELL
23
EGG CELL
23
NERVE CELL
46
Since they have different amounts of chromosomes, the way they are made differ.
● Body cells are made by the division process MITOSIS.
● Sex cells are made by the division process MEIOSIS.
Before a cell can divide by either method, it must first prepare for cell division.
The cell cycle (or entire life cycle of the cell) consists of:
INTERPHASE: The longest/busiest stage in a cell’s life
1. Chromosomes (DNA) replicates
2. Cell grows bigger
CELL DIVISION: Mitosis or Meiosis
CYTOKINESIS: When the cytoplasm divides and the cell completely separates.
Mitosis: cell division that makes BODY CELLS.
It starts with a DIPLOID cell 46
Chromosomes Replicate
92
4646
It ends with TWO IDENTICAL DIPLOID cells
MeiosisMeiosis I I
MeiosisMeiosisIIII
The kind of cell division that produces sex cells (haploid) containing half the number of chromosomes as a body cell, is called meiosis.
Meiosis: cell division that makes SEX CELLS.
It starts with a DIPLOID cell 46
Chromosomes Replicate
92
46 46
23 23 23 23
It ends with FOUR HAPLOID cells (not identical)
Crossing-Over Crossing-Over
In Meiosis:
Before the sex cells are created, Homologous chromosomes actually break and exchange traits- in a process known as crossing over.
FROM MOM
FROM DAD
This chromosome inherited by mom could code for straight hair, brown hair, and green eyes…
This chromosome
inherited by dad could code for
curly hair, black hair, and brown eyes…
After crossing-over
Now one chromosome passed on to offspring could have traits from
both homologous… curly hair, brown hair, and
green eyes…
Crossing-OverCrossing-Over
Crossing over can occur at any location on a chromosome, and it can occur at several locations at the same time.
This causes the traits found in each gamete varied. This is why siblings of the same parents can look so different from
each other.
• These haploid cells are called sex cells— gametes.
• Male gametes are called sperm.
• Female gametes are called eggs.
Meiosis
• When a sperm fertilizes an egg, the resulting zygote once again has the diploid number of chromosomes.
Meiosis
• This chart of chromosome pairs is called a karyotype, and it is valuable in identifying unusual chromosome
numbers in cells.
• The failure of homologous chromosomes to separate properly during meiosis is called nondisjunction.
•This would occur when homologous chromosomes are suppose to separate from each other.
Nondisjunction
• Down syndrome is the only autosomal trisomy in which affected individuals
survive to adulthood.
Down syndrome: Trisomy 21
Down syndrome: Trisomy 21
• The incidence of Down syndrome births is higher in older mothers, especially those over 40.
• Extra chromosome on 21
• 1 in every 1100 live births
• Range from mild to severe physical and mental disabilities
A cell with two of each kind of chromosome is __________.
Question 1
D. polyploid
C. biploid
B. haploid
A. diploid
The answer is A. The two chromosomes of each pair in a diploid cell are called homologous chromosomes. Each has genes for the same traits.
Homologous Chromosome 4
a A
Terminal Axial
InflatedD
Constrictedd
Tall
T
Short
t
Why do organisms need meiosis for
reproduction?
Question 2Meiosis
Meiosis
Sperm Cell
Egg Cell
Haploid gametes
(n=23)
Fertilization
Diploid zygote
(2n=46)
Mitosis and Development
Multicellular
diploid adults
(2n=46)
Meiosis is cell division that produces haploid gametes. If meiosis did not occur, each generation would have twice as many chromosomes as the preceding generation.
Meiosis
Meiosis
Sperm Cell
Egg Cell
Haploid gametes
(n=23)
Fertilization
Diploid zygote
(2n=46)
Mitosis and Development
Multicellular
diploid adults
(2n=46)
Trisomy usually results from _______.(TX Obj 2; 6C)
Question 2
D. twenty-two pairs of chromosomes
C. nondisjunction
B. incomplete dominance
A. polygenic inheritance
The answer is C.