1. Think. Pair. Share:
• Do humans have the greatest number of
chromosomes per cell because we are “the
most intelligent animals on Earth?”
– Why or why not? Write your ideas down in your
notebook
– Share with a partner
– Discuss as a class

2. Human Heredity
Chapter 8
Miss Pollack

3. Chromosome Numbers
• Each species has a set number of
chromosomes in each cell

4. Insects
Ant
# of
chromosomes:
2
Plant
Adder’s fern
# of
chromosomes:
1262
Mammals
Dog
# of
chromosomes:
78
Humans
Mr.
Manuppelli
# of
chromosomes:
46
Organisms & Their Chromosomes

5. Be aware that
• So no… we don’t have the greatest amount of
chromosomes and the number of chromosomes
does not relate to intelligence
• Some species of organisms have the same
number of chromosomes: (48)
– Potatoes
– Plums
– Orangutan
– Gorilla
• FOR THE MOST PART each species has a
different number

6. Humans & Chromosomes
• Total of 46 individual chromosomes
– kid gets an equal amount of chromosomes from
mom & dad
• 23 from mom’s egg = 1 set = haploid (1n)
• 23 from dad’s sperm = 1 set = haploid (1n)

7. Mom
23
Individual
chromosomes
Dad
23
Individual
chromosomes
Child
46
total
chromosomes
(2n = diploid)

8. • Chromosomes come in pairs (2)
• If we know we have 46 individual
chromosomes… how many pairs do we have?
– 46 ÷ 2 = 23 pairs
• Humans have 23 pairs of chromosomes
46
individual 23 pairs

9. What is a karyotype?

10. • Photograph shows the complete set of
chromosomes for an organism
• Photograph organizes chromosomes by pairs
– Pairs are matched together as homologous
chromosomes
– You can look at a karyotype and identify:
1. Species
2. Sex
Karyotype

11. 23

12. • Sex chromosomes
– Carries genetic information: male or female
• Autosomes
– Carries genetic information: what the species
will look like
– Information for everything else the cell requires
to live
2 Types of Chromosomes

13. • 2 chromosomes (1 pair) are called sex
chromosomes
– Always the last pair, #23, in the photograph
• They determine your sex
– Female
– Male
• If you are a female you get XX (large in size)
• If you are a male you get XY (X is large but Y is
only ½ the size)
Sex Chromosomes

14. the last pair
#23
23

15. • Other 44 chromosomes (22 pairs) are called
autosomes
– Perfectly matched up
– The first 22 pairs in the photograph
• They tell us what the species will look like, and all
other information required for the cell to live
• Get 1 copy from mom, 1 copy from dad to get a
pair
– 2 copies of each autosome are called homologous
chromosomes; same size, shape and genes
Autosomes

16. the first 22 pairs
# 1 -22

17. Human Karyotyping
• How do you write what you see in a
karyotype of a healthy, normal male
or female? “#, sex chromosomes”
Male = 46, XY
Female = 46, XX

18. • Chromosomes are in ordered pairs
numbered 1-23
– Pairs 1 through 22 are the autosomes
– The last pair, the 23rd pair, are the sex chromosomes
(XX or XY)
• Pairs are matched up as close as possible, based
on their “bands” or “stripes” which are genes
– These are the HOMOLOGOUS chromosomes
How to read a Karyotype

21. • Egg carry 23 chromosomes
– 1 is an X sex chromosome
• Sperm carry 23 chromosomes
– 50:50 chance that the sex chromosome is
X or Y
Who determines the sex of the child?
Sex Determination
Males, fathers

22. KARYOTYPE LAB
• Pass out the packets.
• Go over instructions together.
• PART C in class today
– Materials on front table

23. Homework
• Section 1 review:
– Questions 1-8
– Complete sentences for all except:
• 1 and 5