Download Mendelian Genetics

Classes of chromosomes
22 pairs of autosomes
Common to both male and female
1 pair of sex
chromosomes
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How were these
brown eyes made?
Genetics
Why do we look the way we do?
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 Genes
 Sections of DNA

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that contains
instructions for
making proteins
Control the
TRAITS of the
individual
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?)
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eye color
(blue or
brown?)
Inheritance of genes
 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
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How does this work?
 Paired chromosomes have same kind of
genes

but may be different alleles
eye
color
(blue?)
hair
color
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eye
color
(brown?)
hair
color
Traits are inherited as separate units
 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
1 from Mom
homologous chromosomes
1 from Dad
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Will you have blue or brown eyes?
 Dominant traits (upper case)


Hides recessive alleles
Can be expressed if you inherited 1 dominant allele or
both dominant alleles
 Recessive alleles (lower case)


Hidden by dominant alleles
The recessive trait will only be expressed if you
inherited both recessive alleles
eye color
(B = Brown)
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eye color
(b = blue)
 brown is dominant over blue
 blue is recessive to brown
How do we say it?
2 of the same alleles
Homozygous
BB = brown eyes
bb = blues eyes
homozygous dominant
homozygous recessive
2 different alleles
Heterozygous
Bb = brown eyes
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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
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Biology
Making gametes
BB = brown eyes
bb = blues eyes
Bb = brown eyes
BB
bb
Remember, only one version for
each gene goes into each gamete
Bb
Remember meiosis!
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Punnett squares: A way to predict
possible offspring
Bb
x
possible male sperm
Bb
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Possible female eggs
X
B
b
BB
Bb
Bb
bb
B
b
Genetics of Sex
 In humans & other mammals, there are 2
sex chromosomes: X & Y

2 X chromosomes
 develop as a female: XX

an X & Y chromosome
 develop as a male: XY
X
Y
X
XX
XY
X
XX
XY
50% female : 50% male
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IN PEA PLANTS
Tall is dominant over
short
TALL = ____
SHORT = ____
LET’S MAKE A CROSS!
TALL
X
SHORT
What do you need to know before you begin?
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TALL parent
What are the parent
alleles?
TT

Genotype:____________

What gametes
can it make?
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SHORT parent
What are the parent
alleles?
tt

Genotype:____________

What gametes
can it make?
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_____%
of the
offspring
or
___/4
will be…
GENOTYPE
_____
PHENOTYPE
_______
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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
Regents
Biology
Co-dominance
 2 alleles affect the phenotype equally &
separately
not blended phenotype
 human ABO blood groups
 3 alleles

 IA, IB, i
 IA & IB alleles are co-dominant
 glycoprotein antigens on RBC
 IAIB = both antigens are produced
 i allele recessive to both
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Codominance
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Environmental effects
 Phenotype is controlled by
both
environment & genes
Human skin color is influenced
by both genetics &
environmental conditions
Coat color in arctic
fox influenced by
heat sensitive alleles
Color of Hydrangea flowers
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Biologyby soil pH
is
influenced