Transcript Finish Crossing Over and Karyotype and

6. On your journal page ‘Crossing Over/ Genetic Variation’
Based on what is dominant and recessive below, write what
characteristics this person physically has based on their gene
pairs.
Here is my example:
Crossing Over
Based on the homologous chromosome pair, my
person has: dimples
curly hair
can curl tongue
straight thumbs
no cleft chin
During Meiosis
Prophase I
Homologous Chromosomes
break and exchange genes
(Crossing Over)
In my example I
exchanged
bands #2 and #6
7. Cut any two bands on both
chromosomes, exchange them,
and tape them up in the correct
order
This is crossing over and
happens to your paired
homologous chromosomes
before your sex cells are
made.
This ‘mixes it up’- causes
GENETIC VARIATION
So your chromosomes should
still have the same genes in
the same order 1-6, BUT have
a different mix of
characteristics than before.
During Anaphase II
chromosomes are parted
from each other and are
put in different sex cells.
When one of these sex
cells unites with another
then the new baby will
have a complete set of
homologous
chromosomes.
Pretend you and a classmate have
created siblings
(two children from the same parents)
8. Swap Mom chromosomes with a
chosen classmate.
10. Tape/glue the ‘offspring’ homologous
pair in your comp book under the
parent’s characteristics (one chromosome
came from you, one came from your classmate)
Answer the questions on the next slide
about crossing over and genetic variation.
Answer these questions in your comp. book:
1. How does Crossing Over create genetic variation?
2. List the offspring’s characteristics based on the same chart you used for
the parent.
3. Specifically how were the physical characteristics from the parent
different from the offspring?
4. Did the siblings that came from the same parents have different
characteristics from each other (check with the classmate you swapped
with)? If so, how were they different?
5. Why is Crossing over important in Meiosis?
-Dimples are dominant over no dimples
When finished with the
questions, tape the kid’s
chromosomes on this page.
You can also fold them.
-Curly hair is dominant over wavy hair
-Wavy hair is dominant over straight hair
- Tongue curling is dominant over no tongue curling
-Straight thumb is dominant to hitch-hikers thumb
-Cleft chin is dominant over no cleft chin
-Freckles are dominant to no freckles
How could a chart like this be
useful for scientists, doctors, or
the individual themself?
• A photo of homologous chromosome pairs from
largest to smallest is called a karyotype, and it
is valuable in identifying gender, unusual
chromosome shapes, or unusual amounts of
chromosomes.
Non-disjunction
• What does the word “Junction” mean?
Junction means ‘being joined’
• So, what would “Dis-junction” mean?
Dis-Junction means ‘becoming un-joined/
separating’
• So, define Non-disjunction.
Not separating
Non-disjunction
• 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 in Anaphase I
Down syndrome: Trisomy 21
• Down syndrome is a genetic disorder
caused by an extra chromosome 21
Down syndrome: Trisomy 21
• Extra chromosome on 21
• 1 in every 1100 live births
• Range from mild to severe
physical and mental disabilities
• The incidence of Down syndrome births is higher in
older mothers, especially those over 40.
Turners Syndrome
• Absence of one X
chromosome
• Occurs in 1 out of every
2,500 live female births.
• Physical characteristicsincluding being infertile
• No mental disability