Transcript Mendelian Genetics - Mrs. Cindy Williams Biology website

Review…
1. My somatic cells have ____ (#) chromosomes
2. My sperm/egg (pick one) cells have ____
chromosomes
3. Each sex cell is genetically unique because:
4. I have ____ sets of chromosomes in all of my body
cells, which means they are haploid/diploid (pick one).
5. I got these chromosomes from:
• 3210.4.4 Determine the probability of a
particular trait in an offspring based on the
genotype of the parents and the particular
mode of inheritance.
Heredity
Important things Mendel learned 11-1
– SEGREGATION - genes occur in pairs (one
from each homologous chromosome), which
separate during meiosis to form gametes with
1 copy of each gene
– INDEPENDENT ASSORTMENT – the 23
chromosomes you inherit from each parent are
randomly selected [For instance: 10 of them
might be from your grandpa and 13 from
grandma]
– DOMINANCE - some genes can block others
from being seen
Alleles
Dominant vs. Recessive
+
=
+
=
+
=
Ex: Tall is dominant to short
• Genotype
TT
Phenotype
_________
Tt
_________
tt
_________
Xh Y
dd
tt
Ee
CC
bb
Mm
Genotype
Receding Hair Line
Dimples
Short
Detached earlobe
Curly Hair
Blonde hair
Melanin Produced
Phenotype
Heterozygous
•
•
•
•
•
•
Tt
Bb
Gg
Nn
Aa
Dd
Homozygous
•
•
•
•
•
•
TT
bb
gg
NN
aa
dd
Hybrid
•
•
•
•
•
•
Tt
Bb
Gg
Nn
Aa
Dd
Purebred/ True breeding
•
•
•
•
•
•
TT
bb
gg
NN
aa
dd
Examples
TT
_________
Tt
_________
tt
_________
• https://docs.google.com/present/view?id=d
fh23k67_2272cxrkhdgf
…So what can we do with all this
vocab???
• Is there an easier way to understand
this??
• 11-2. p. 268
Reginald Punnett sure thinks so!
A Punnett Square is a device used
to predict the results of a cross.
T
T
EGGS
(from
who?)
x
t
t
Sperm
(from
who?)
We are going to figure out the
offspring if we were to cross a
true Tall Pea Plant with a true
short pea plant!
TTx tt
TTx tt
t
t
Sperm
(from
who?)
T
TT
EGGS
(from
who?)
You just did exactly what Mendel
DID!! How Many…
T
t
T
Genotype
TT=
Tt=
tt=
Ratio=
t
Phenotype
Tall=
Short=
Ratio=
Your Turn!
• Show a Punnett Square and Analysis of
two tall heterozygous plants being crossed
• Remember
– (show the egg & sperm)
– Fill in the punnett square
– ANALYZE
A Heterozygous Cross
How Many…
Genotype
TT=
Tt=
tt=
Ratio=
Phenotype
Tall=
Short=
Ratio=
Punnett Square
• Black fur is dominant to white fur in
rabbits. If a heterozygous black rabbit
mates with a white rabbit, what is the
chance they will have a white bunny?
Punnett Square Practice
• The color red in roses is dominant to
yellow. If a homozygous red rose is
crossed with a heterozygous red rose,
what is the chance a yellow rose will be
produced.
Big Punnett Squares Example
•If having brown eyes
(B) is dominant to blue
eyes (b), then what is
the phenotypic ratio
of the offspring when
crossing a
heterozygous brown
eye father with a blue
eyed mother?
• If two plants were crossed and they had 52
offspring that were white and 58 that were
red, what is the ratio of red to white
• Perform a Punnett Square between a man
and woman to determine the chances of
having a baby girl
Genetics Joke
What do you get if you cross a bridge with a
bicycle?
To the other side!
Dihybrid Cross 11-3, p. 270
 The simultaneous inheritance of two traits in
the same plant is a dihybrid cross (16
squares).
Your numbers should always add up to 16!
Dihybrid Cross
• The ear of corn represents two genes—
Purple kernels (P), which is dominant to
yellow (p) and smooth (S) kernels which
is dominant to shrunken (s).
• What will you get if you cross two
heterozygous parents? PpSs x PpSs
What is the
phenotypic
ratio? 9:3:3:1
9 Purple, Smooth
(P_S_)
3 Purple, shrunken
(P_ss)
3 Yellow, smooth
(ppS_)
1 yellow, shrunken
(ppss)
Dihybrid Cross
PpSs x PpSs
PS
Ps
pS
ps
PS PPSS PPSs PpSS PpSs
Ps
PPSs PPss
pS
PpSS PpSs ppSS ppSs
ps
PpSs Ppss
PpSs Ppss
ppSs ppss
Gene Linkage and Polyploidy
Gene Linkage
Some genes are usually inherited
together=linkage (especially if they are close
together on the chromosome).
Each chromosome is a group of linked genes.
Fruit Flies
• Mendel’s principles were tested
to see if they applied to more
than plants.
Why Fruit Flies?
– Reproduce quickly (about 2 weeks)
– Reproduce in large quantity
– Have only 8 chromosomes
– Small
– Cheap and easy to keep
– Genes on the same chromosome are not
always linked.
– Crossing-over sometimes separates
linked genes to form new allele
combinations.
– This allows for greater genetic diversity.
Genetic Recombination
 The combining of genes produced by
crossing over and independent assortment.
 Use the formula 2n, where n is the number of
chromosome pairs to calculate. Ex.-pea
plants 27 =128.
 After fertilization in humans 223 x 223 =more
than 70 trillion.
 Polyploidy is the occurrence of one or more
extra sets of all chromosomes in a plant.
It occurs in oats
(6n),
sugar cane (8n)
and wheat (6n).
 A triploid organism, for
instance, would be
designated 3n,
which means that
it has three complete sets of chromosomes.
How did Mendel miss gene
linkage?
• 6 of the 7 genes were on different
chromosomes.
• 2 genes on the same chromosome
were very far apart, so they assorted
independently.
• His principles apply to plants, animals
and humans.
• So, Mendel was very lucky!