Regents Biology 2006-2007

Genetics

Why do we look the way we do?

Regents Biology

Inheritance of chromosomes Egg + sperm → zygote

egg

sperm

zygote

fertilizationmitosis &

development

meiosis

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?)

Regents Biology

Effect of genes Genes come in different versions

brown vs. blue eyes brown vs. blonde hair alleles

Regents Biology

Genes affect what you look like

XBBbb

Bb Bb Bb Bb

Where did the blue eyes go??

Regents Biology

Genes affect what you look like…

XBbbb

Bb Bb bb bb

Why did the blue eyes stay??

Regents Biology

Genes affect what you look like…

XBbBb

BB or Bb BB or Bb BB or Bb bb

Where did the blue eyes come from??

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

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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

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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

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Making gametes

BB = brown eyesbb = blues eyesBb = brown eyes

BB

bb

Bb

→ brown is dominant over blue

→ blue is recessive to brown

Remember meiosis!

B

B

b

b

B

b

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How do we say it?

BB = brown eyesbb = blues eyes

Bb = brown eyes

2 of the sameHomozygous

2 differentHeterozygous

BB

B

B

bb

b

b

Bb

B

b

homozygous dominanthomozygous recessive

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Punnett squaresBb x Bb

male / sperm

fem

ale

/ eg

gs

X

BB

Bb bb

BbB

b

B b

Regents Biology

Genetics vs. appearance

There can be a difference between how an organism looks & its geneticsappearance or trait = phenotype

brown eyes vs. blue eyesgenetic makeup = genotype

BB, Bb, bb

2 people can have the same appearance but have different genetics: BB vs Bb

Regents Biology

Genetics vs. appearance

eye color(brown)

eye color(brown)

eye color(blue)

eye color(brown)

vs.

BB

B

BBb

B

b

How were these brown eyes made?How were these brown eyes made?

Regents Biology 2005-2006

Woof! Woof!Any Questions?