1. Regents Biology 2006-2007
Genetics
Why do we look the way we do?

2. Regents Biology
Inheritance of chromosomes
 Egg + sperm → zygote
egg
sperm
zygote
fertilization
mitosis &
development
meiosis

3. Regents Biology
Inheritance of genes
 On the chromosomes passed from
Mom & Dad to offspring are genes
 may be same information
 may be different information
eye color
(blue or
brown?)
eye color
(blue or
brown?)

4. Regents Biology
Effect of genes
 Genes come in different versions
 brown vs. blue eyes
 brown vs. blonde hair
 alleles

5. Regents Biology
Genes affect what you look like
X
BBbb
Bb Bb Bb Bb
Where did the blue eyes go??

6. Regents Biology
Genes affect what you look like…
X
Bbbb
Bb Bb bb bb
Why did the blue eyes stay??

7. Regents Biology
Genes affect what you look like…
X
BbBb
BB or Bb BB or Bb BB or Bb bb
Where did the blue eyes come from??

8. Regents Biology
What did we show here?
 Genes come in “versions”
 brown vs. blue eye color
 alleles
 Alleles are inherited separately from
each parent
 brown & blue eye colors are separate &
do not blend
 either have brown or blue eyes, not a blend
 Some alleles mask others
 brown eye color masked blue

9. Regents Biology
How does this work?
eye color
(brown?)
hair
color
hair
color
eye color
(blue?)
 Paired chromosomes have same kind of
genes
 but may be different alleles

10. Regents Biology
Traits are inherited as separate units
1 from Mom
1 from Dad
 For each trait, an organism inherits
2 copies of a gene, 1 from each parent
 a diploid organism inherits
1 set of chromosomes from each parent
 diploid = 2 sets of chromosomes
homologous chromosomes

11. Regents Biology
Making gametes
BB = brown eyes
bb = blues eyes
Bb = brown eyes
BB
bb
Bb
→ brown is dominant over blue
→ blue is recessive to brown
Remember meiosis!
B
B
b
b
B
b

12. Regents Biology
How do we say it?
BB = brown eyes
bb = blues eyes
Bb = brown eyes
2 of the same
Homozygous
2 different
Heterozygous
BB
B
B
bb
b
b
Bb
B
b
homozygous dominant
homozygous recessive

13. Regents Biology
Punnett squares
Bb x Bb
male / sperm
female/eggs
X
BB
Bb bb
Bb
B
b
B b

14. Regents Biology
Genetics vs. appearance
 There can be a difference between
how an organism looks & its
genetics
 appearance or trait = phenotype
 brown eyes vs. blue eyes
 genetic makeup = genotype
 BB, Bb, bb
2 people can have the same appearance but
have different genetics: BB vs Bb

15. Regents Biology
Genetics vs. appearance
eye color
(brown)
eye color
(brown)
eye color
(blue)
eye color
(brown)
vs.
BB
B
B
Bb
B
b
How were these
brown eyes made?
How were these
brown eyes made?

16. Regents Biology 2005-2006
Woof! Woof!
Any Questions?