1. Mitosis & Meiosis
What’s the difference?

2. Write down these terms:
Mitosis
Meiosis
Diploid
Haploid
Sex chromosomes in a Male?
Sex chromosomes in a Female?
Number of chromosomes in a person?
Karyotype
Allele
Genotype
Phenotype
Dominant
Recessive
Homozygous
Heterozygous
Pedigree

3. Mitosis
Mitosis is the process where one cell divides into 2 identical cells
This is how we go from 1 cell (the fertilized egg) to millions of cells!
It is also HOW we grow & repair our bodies.
What has to happen BEFORE mitosis can occur?

4. Answer: The DNA has to
replicate ( be copied!)
All 46 chromosomes (yes, MOST human cells have 46 chromosomes) have to be copied so both DAUGHTER cells get the same 46 chromosomes that were in the parent cell.

5. Parent cell
Chromosomes are copied and double in number (sister chromatids are attached at by the centromere
Chromosomes now split
2 daughter cells identical to original

6. What is a Chromosome? The structure that the DNA forms in our cells
The DNA is associated with proteins that compact it so it fits and is organized inside the nucleus!

7. Animation of mitosis:

8. So, we’ve got 46 chromosomes.
How many different PAIRS of chromosomes do we have?
Are ALL the pairs the same?
23 pairs of chromosomes
Yes & No- 2 copies of chrom 1, copies chrom 2……, except for the sex chromosomes (X & Y) in MEN ( XY) & Women (XX)

9. What are diploid and haploid for us?
CHROMOSOME NUMBER
Number of chromosomes in body cells of a species is diploid = 2n (n is the number of different chromosomes; 2n = 2 copies of each different chromosome)
The number of chromosomes in egg and sperm cells (gametes) is haploid which is “n”, or 1 copy of each different chromosome
What are diploid and haploid for us?

10. Answer:
Diploid= 46chromosomes =2 copies of 23 different chromosomes ( XX or XY)
Haploid = 1 copy of 23 different chromosomes ( X or Y)

11. Where does each chromosome of the pair come from. (Ex
Where does each chromosome of the pair come from? (Ex. You’ve got 2 copies of chr 1- where did each copy come from?)
One chromosome comes from MOM, and one chromosome comes from Dad
So, who determines the sex of the baby????
DAD- He is the ONLY parent that can contribute the Y chromosome that makes the fetus male.

12. How do the gametes (sex cells) end up with only 23 chromosomes
How do the gametes (sex cells) end up with only 23 chromosomes? THINK MEIOSIS!!
WHY do they need to be haploid (only 1 copy of each chromosome or 23 total chromosomes)?

13. IT’S ALL ABOUT SEXUAL REPRODUCTION…
MEIOSIS
IT’S ALL ABOUT SEXUAL REPRODUCTION…

14. MEIOSIS
A type of cell division where the number of chromosomes is reduced by half
ONLY occurs in gonads (ovaries or testes) during formation of gametes (egg or sperm)
Human body cells have 46 chromosomes; human sperm and egg cells each have 23 chromosomes

15. Gametes are haploid for SEXUAL REPRODUCTION!
When egg and sperm combine during fertilization, each brings half the total number of chromosomes for that species
Half + half = whole
In humans, 23 chromosomes (from Dad) + 23 chromosomes (from Mom) = 46 chromosomes (child) !!!

16. FERTILIZATION egg + sperm = zygote 23 + 23 = 46 n n 2n
Haploid haploid = diploid

17. Summary of Meiosis
Type of cell division used to form the gametes (egg & sperm) where chromosome number is reduced to haploid (n).
It involves 2 rounds of cell division, NOT 1 like in mitosis.
Results in 4 HAPLOID daughter cells!

18. Animation of Meiosis

19. MORE ABOUT CHROMOSOMES
In humans, there are 22 different “regular” chromosomes (numbered 1 to 22 by size & shape) and 2 different sex chromosomes
The sex chromosomes are X and Y
Which sex chromosomes are in a girl? XX
Which are in a boy? XY

20. Karyotype A photograph of all of an organisms chromosomes.
Scientists freeze cells at the metaphase of mitosis. At this stage, chromosomes are easy to isolate and stain.

21. Why perform a karyotype?
Verify chromosome number (some genetic diseases are caused by MORE copies of a chrom.)
Confirm chromosome shape, structure and size.

22. Down’s Syndrome Karyotype (Trisomy 21)

23. ALL HUMANS HAVE THE SAME GENES ON THE SAME CHROMOSOMES!
If mom’s chromosome #1 carries the genes for eye color, hair color, and height, then dad’s chromosome #1 also carries the genes for eye color, hair color, and height
Each chromosome of the pair contains an ALLELE (or copy) of every gene.

24. Different versions of the same Gene are known as Alleles!!)
CHROMOSOME PAIR #1
BLUE EYES
BROWN HAIR
TALL
BLUE EYES
BLOND HAIR
SHORT
= A GENE (allele) ON A CHROMOSOME

25. What is Phenotype? What is Genotype? Outward expression of an allele
(how it looks- PHYSICAL)
Ex.: Blue or Brown eyes, Tall or short, Artistic, Athletic
What is Genotype?
Genetic makeup (the GENES) of an organism
Ex. Ff, FF, ff

26. DOMINANCE
Some genes are “stronger” than others; they are called dominant
The weaker gene is recessive
EXAMPLES:
BROWN EYES ARE DOMINANT OVER BLUE EYES- A person may have BOTH genes, but we ONLY see the Brown eyes
Tall is dominant over short

27. In many cases, one gene is NOT stronger than the other.
This is called Incomplete
Dominance
This can cause a MIXED phenotype-
For Ex.: Incomplete dominance of the gene for red and white flower color will result in PINK flowers.

28. Combinations of alleles
FF and ff are Homozygous for the genes and traits
FF= homozygous dominant; phenotype is DOMINANT trait
ff = homozygous recessive; phenotype is RECESSIVE trait

29. Combinations of alleles
Ff is Heterozygous for the genes (genotype).
If F is dominant, a person who is Ff will look the SAME as someone who is FF (different genotype, same phenotype!)

30. How do we PREDICT which traits an offspring will inherit?
A Punnett square!!!
Put MOM’s 2 genes (alleles) on the top; Dad’s 2 genes (alleles) on the side
Match up the possibilities in every square.
For 1 trait, there are 4 possible offspring!

31. Example: F= dominant= fuzzy seed & f= recessive= smooth seed
What are the genotype and phenotype for homozygous dominant?
What are the genotype and phenotype for homozygous recessive?

32. What are the genotype and phenotype for heterozygous?
Cross Ff x Ff (Punnett Square)- what are the POSSIBLE genotypes and phenotypes of offspring?

33. Answers: Homozygous dominant= FF= fuzzy
Homozygous recessive= ff= smooth
HETEROZYGOUS= Ff= fuzzy

34. Our genes determine a LOT of who we are (but NOT everything)
Have you ever noticed that certain traits run in families? Like musical ability, athletic, mechanical ability, more intellectual, etc.
Our genes determine a LOT of who we are (but NOT everything)
What we are good at- sports, music, schoolwork
Our height, eye color, hair color
personality traits

35. Do Chromosomes ever change?
YES! Changes can occur in the chromosome (a BIG change- deletion, repeat, extra copy) or in the sequence of the DNA (LITTLE change- switch the nucleotide base (letter); delete 1 or more bases; insert extra 1 or more bases).
Both these types of changes are called MUTATIONS.

36. What MAY happen when there is a mutation in the DNA or chromosome?
The offspring may develop a GENETIC DISEASE.
How is a GENETIC DISEASE (like cystic fibrosis) different from an INFECTIOUS DISEASE (strep throat)?