Download genetics - Fall River Public Schools

GENETICS
The study of
Heredity
How traits are passed
from generation to
generation
‘Father’ of
genetics
Gregor Mendel
Law of
Segregation
Law of
Independent
Assortment
Tool used in
genetics
Punnett Square
Monohybrid
Cross
Focuses on
1 trait
http://www.youtube.com/watch?v=CBezq1fFUEA –crash course-heredity- 10:18
Dihybrid
Cross
Focuses on
2 traits
MENDELIAN GENETICS
•Genetics- study of heredity
http://player.discoveryeducation.com/index.cfm?g
uidAssetId=70359E7A-6264-4331-9290736B7DF57396&blnFromSearch=1&productcode=
US Mendel’s Genetic Theory – 2:19
•Heredity- how genes are passed on from 1 generation to the next
HISTORY: in the 1860’s
•Gregor Mendel is known as the ‘father of genetics’
•He studied heredity by using pea plants
-Q: Why did he study these plants?
-A: 3 reasons:
o1: they are easy to grow
o2: they grow quickly
o3: they reproduce in large quantities (have lots of offspring)
•He studied many different traits of the pea plant
-Q: What’s a trait?
-A: a characteristic
•Some of the traits that Mendel looked at were: plant height, flower color, seed color, seed
texture, pod color, pod texture…
http://www.youtube.com/watch?v=Mehz7tCxjSE&list=PLXvgPXXk9zE539QSFSIbBc
19e_2P-Ssqi – Mendel 3:07
MENDEL’S EXPERIMENTS:
STEP 1:
•He crossed (mated) 1 purple flower with 1 white flower
•These 2 plants are called pure-breeding plants because ALL of their offspring (children)
will be the same color as the parent
-For example:
oA pure-breeding PURPLE plant will ALWAYS have PURPLE offspring.
oA pure-breeding WHITE plant will ALWAYS have WHITE offspring.
•These 2 plants are called the Parental generation (P)
**You can think of it in terms of DOGS (pure-breeds are 100% one type of dog)**
His results of Step 1:
•When he mated a purebred purple with a purebred white, the result was:
oALL Purple flowers!!!!
•The offspring of the Parental generation are called the F1 generation
STEP 2:
•Once he had his F1 generation, he then mated 2 of these plants to get
NEW offspring- called the F2 generation.
•Q: What are the colors of the 2 plants in his F1 generation?
•A: both are Purple
His results of Step 2:
• 75% (3 out of 4) of the offspring were Purple
• 25% (1 out of 4) of the offspring were White
MENDEL’S CONCLUSIONS:
•Mendel said that every person has 2 alleles for every trait
•Allele- an alternative form of a trait
For example:
trait- HEIGHT
1 allele would be for TALL
1 allele would be for SHORT
Q: Why does each person only have 2 alleles for each trait?
A: 1 comes from mom the other comes from dad
•When mom makes her eggs and when dad makes his sperm the alleles randomly
separate so that it only gets 1 copy of the allele
-For example- Let’s say mom’s alleles for Freckles are Ff
•When she makes her eggs, these alleles will separate so that some eggs
get the F allele and some eggs get the f allele
F
f
F
F
f
F
f
f
•Mendel also said that if that person had the SAME allele then they are homozygous for that trait.
•If the 2 alleles were DIFFERENT, then they are heterozygous for that trait.
•A person’s genotype is their makeup of alleles (their ‘genes’)
Examples of GENOTYPES: Aa
BB
cc
Dd
EE
ff
Q1: Which genotype examples are heterozygous?
Q2: Which genotype examples are homozygous?
•A person’s phenotype is their physical appearance for that trait
Examples of PHENOTYPES: tall
hair texture
freckles
dimples
eye color
hair color
•If someone is HETEROZYGOUS for a trait then only dominant allele (capital letter) is expressed.
The recessive allele (lowercase letter) is NOT expressed.
•For example: trait- eye color
Alleles: B- brown eyes
or
b- blue eyes
GENOTYPE
PHENOTYPE
BB
Brown eyes
Bb
Brown eyes
bb
Blue eyes
MENDEL’S LAWS:
1st LAW- Law of Segregation- When a gamete (sex cell) is formed it will only receive 1
allele or the other.
Examples of this law:
- the gamete being made in the example below are egg cells!
Genotypes:
Aa
BB
Cc
dd
A
B
c
d
A
B
C
d
a
B
c
d
A
B
c
d
a
B
c
d
2nd LAW- Law of Independent Assortment-2 or more alleles will separate independently of one another (this just
means that the ‘capital’ letters don’t always stay together and the
‘lowercase’ letters don’t always stay together)
Examples of this law: - the gamete being made in the example below are egg cells!
Use the following 2 traits:
1. EYE COLOR (B or b)
2. HEIGHT (T or t)
Genotypes:
BbTt
BBTt
bbTT
BT
BT
bT
Bt
Bt
bT
bt
VOCABULARY REVIEW:
•ALLELE•HOMOZYGOUS•HETEROZYGOUS•RECESSIVE-
•DOMINANT•GENOTYPE•PHENOTYPE-
PUNNETT SQUARES
http://player.discoveryeducation.com/index.cfm?guidAssetId=7570E857-9BAE-4732-920FCF79EACA9201&blnFromSearch=1&productcode=US Mendel’s Rule of Heredity:
Punnett Square- 5:04
•Punnett square- used to visualize a cross between 2 organisms
EXAMPLE #1:
HOMOZYGOUS
X
HOMOZYGOUS
TRAIT: height
• H= tall
• h= short
Q: If both parents are homozygous, then
what are their genotypes?
Parent 1: HH or hh
Parent 2: HH or hh
Q1: What are the genotypes of the
offspring?
Q2: What are the phenotypes of the
offspring?
EXAMPLE #2:
HOMOZYGOUS
X
HETEROZYGOUS
TRAIT: height
• H= tall
• h= short
Q: What is the genotype of the homozygous
parent? HH or hh
Q: What is the genotype of the heterozygous
parent? Hh
Q1: What are the genotypes of the
offspring?
Q2: What are the phenotypes of the
offspring?
EXAMPLE #2:
HETEROZYGOUS
X
HETEROZYGOUS
TRAIT: height
• H= tall
• h= short
Q: If both parents are heterozygous, then
what are their genotypes?
Parent 1: Hh
Parent 2: Hh
Q1: What are the genotypes of the
offspring?
** All 3 examples are called
Monohybrid crosses
because they focus on only
1 trait**
Q2: What are the phenotypes of the
offspring?
DIHYBRID CROSSES- focuses on 2 traits
Example:
-trait 1- seed color
-trait 2- seed shape
Trait 1:
G- yellow seed
g- green seed
Trait 2:
R- round shape
r- wrinkled shape
Cross 2 plants that are both Heterozygous yellow and Heterozygous round
Plant 1 – Genotype: GgRr
Plant 2 - Genotype:
GgRr
Q: What are the
phenotypes of
the offspring?
Incomplete Dominance-
results in a ‘mixture’ between the 2 traits
Ex #1- Cross between a red snapdragon (flower) & a white snapdragon
RR = Red
rr = White
Rr= Pink
F1 generation results:
Q: What are the genotypes of the offspring?
Q: What are the phenotypes of the offspring?
Ex #2- Cross 2 snapdragons from the F1 generation
F2 generation results:
Q: What are the genotypes of the offspring?
Q: What are the phenotypes of the offspring?
Codominance-
2 genes in a heterozygous individual are BOTH fully expressed.
Ex) flower- petal color
RR = red
WW = white
RW = Red & White
Ex#1- Cross a red flower with a white flower:
F1 generation results:
Q: What are the genotypes of the offspring?
Q: What are the phenotypes of the offspring?
Ex #2- Cross 2 flowers from the F1 generation:
F2 generation results:
Q: What are the genotypes of the offspring?
Q: What are the phenotypes of the offspring?
Multiple Alleles -
traits controlled by 3 or more alleles
Ex) human blood- Alleles are: A, B, O
In the table below, fill in ALL the possible genotypes with their phenotypes:
GENOTYPE
PHENOTYPE
Q: Can a woman with AO blood and a man with BB blood have a baby with OO blood? Explain! Use
a punnett square to prove your answer!
Q: What are the genotypes of the babies?
Q: What are the phenotypes (blood-types) of the
babies?
Sex- linked Traits:
traits found on the sex chromosomes
•most are found on the X chromosome
(because it’s bigger than the Y chromosome)
•There is ‘missing’ DNA on the top portion of the Y chromosome
compared to the X chromosome
•X- linked genes are very common in males
-If MOM is a ‘carrier’ (which means that she DOESN’T have the ‘disorder’ but
CARRIES the gene for it!), then her son has a 50/50 chance of getting the disorder!
•Ex) Hemophilia – disorder where a person’s blood doesn’t clot properly
-Construct a punnett square of a mom that is a ‘carrier’ and a normal dad
Results of the punnett square:
• Color blindness is another example of a sex-linked trait
• Color blindness is mostly found in males
•Here are some tests for color blindness:
Pedigree-
family record that shows how a trait is
inherited over several generations.
Questions:
1.
How many generations are in the
pedigree?
2.
How many males are in the 2nd
generation?
3.
Do any of them have the trait?
4.
How many females are in the 2nd
generation?
5.
Do any of them have the trait?
6.
How many children does the 1st
generation have?
7.
How many girls? Boys?
8.
Are there any ‘carriers’ in the
pedigree? If so, who?
9.
Does anyone have the trait? If so,
who?
•Symbols in a pedigreeMale WITHOUT trait=
Male WITH trait =
Male ‘carrier’ =
Horizontal lines =
Female WITHOUT trait =
Female WITH trait =
Female ‘carrier’ =
Vertical lines =
10. How many males total are there in
the pedigree? Females?