Mendel and punnett squares
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Transcript of Mendel and punnett squares
• What is the difference between acquired and inherited traits?
• Austrian monk considered the “Father of Genetics”
• Did his experiments in 1866• He did plant experiments
using the garden pea plant• He discovered the pattern in
which organisms inherit traits
• Mendel chose to use the garden pea in his experiments for several reasons.
1. Availability
2. Easy to manipulate for breeding
3. Distinct traits
Mendel chose his subject carefully
What traits did Mendel study?
•Two different forms of the same gene =
•The factors that carry all traits =
• When he wanted to breed, or cross, one plant with another, Mendel opened the petals of a flower and removed the male organs.
Remove male parts
Mendel chose his subject carefully
• He then dusted the female organ with pollen from the plant he wished to cross it with.
Female part
Transfer pollen
Pollen grains
Maleparts
Cross-pollination
Mendel chose his subject carefully
PP pp
Pp Pp Pp PpHybrids
Purebred = Homozygous
Hybrid = Heterozygous
Pp Pp
PP Pp Pp pp
• Mendel called the observed trait dominant (represented by a CAPITAL letter) and the trait that disappeared recessive (represented by a lowercase letter).
The rule of dominance
P = purple, p = white
• Principle of Dominance: when there is a dominant allele and a recessive allele inherited together for a particular gene, the dominant allele will be expressed.
Mendel’s 1st Law of Inheritance
• Dominant
•Round
• Recessive
•wrinkled
• Express the dominant allele for
Round
• PHENOTYPE – physical characteristics that you SEE
• Ex. Round, wrinkled, green, yellow, purple flower, white flower
♦GENOTYPE – genetic
makeup represented
by letters
♦Ex. RR, rr, Rr, Yy,
PP, Ppyy
•Paternal •Maternal
wrinkledROUND
Pea Shape
You inherit two alleles for each gene (trait).
1 from MOM! 1 from DAD!
• The law of segregation states that every individual has two alleles of each gene and when gametes are produced, each gamete receives one of these alleles.
The law of segregation
• During fertilization, these gametes randomly pair to produce four combinations of alleles.
RR rr
Rr Rr Rr Rr
Mendel’s 3Mendel’s 3rdrd Law of Inheritance Law of Inheritance Principle of Independent Assortment: the
alleles for different genes usually separate and inherited independently of one another. So, in
dihybrid crosses you will see more combinations of the two genes.
•BBbbTTtt
•diploid (2n)
•sperm
•haploid (n)
•meiosis II
•BBTT
•BBtt
•bbTT
•bbtt
The first generationDihybrid Cross round yellow x wrinkled green
Round yellow Wrinkled green
All round yellow
Round yellow Round green Wrinkled yellow Wrinkled green9 3 3 1
P1
F1
F2
Reginald Punnett
1.(1875-1967)
2.In 1902, created the
Punnett Square - a chart
which helped to determine
the probable results of a
genetic cross
•http://vector.cshl.org/dnaftb/concept_5/con5bio.html
Punnett Square
3.each parent can only contribute one allele per
gene4.these genes are found on the chromosomes carried
in the sex cells.5.offspring will inherit 2 alleles to express that
gene
•Male gametes
•Female gametes
Punnett SquaresPunnett Squares
•Steps to Solve Punnett SquaresSteps to Solve Punnett Squares
•Step 1Step 1: Assign letters for alleles.
•Step 2Step 2: Write down the cross you will make.
What are the genotypes of the parents?
•Step 3Step 3: Set up and solve the Punnett square.
How many squares will you need?
•Step 4Step 4: Answer questions, find ratios,
percentages or proportions.
MONOHYBRID CROSSESMONOHYBRID CROSSES - 1 trait crossed
Monohybrid CrossesMonohybrid Crosses
•CrossCross
•Bb x BbBb x Bb
•B •b•female gametes
•B
•b
•male gametes
•BB
•Bb
•Bb
•bb •Phenotypes
•%
•75% Brown eyed, 25% Blue eyed
•Ratio
•3 Brown eyed: 1 Blue eyed
•Genotypes
•%
•25% BB, 50% Bb, 25% bb
•Ratios
•1BB:2Bb:1bb
•STEP
•STEP
•STEP
•STEP
BB = brown eyes Bb = brown eyes bb = blue eyes
Cross two Alaskan huskies that are heterozygous for
brown eyes (Bb).
Your Turn
YY x Yy (Y-yellow, y-green)
Steps to Solve DIHYBRID Punnett Square word problem.
DIHYBRID CROSSES – 2 traits crossed
1. Assign letters to the different alleles for the trait.
2. Write the cross that you will be making.
3. Use the FOIL method to determine the combination of
alleles for each gamete.
4. Set up the Punnett Square by separating your female and
male gametes. Solve.
5. Answer the question and circle or square off the answer.
DIHYBRID CROSS•Problem: In pea plants round seeds are dominant to wrinkled
seeds and green pods are dominant to yellow. If 2 plants that
were heterozygous for both traits were crossed, what would be
the phenotypic and genotypic ratios?
•Cross: RrGg X RrGg
Gene Trait AppearanceR Roundr WrinkledG Greeng Yellow
•STEP
•STEP
DIHYBRID CROSSES
•
•Cross: RrGg X RrGg
•EXTRA STEP - Finding the possible gametes
•(R r) (Gg)•F.O.I.L
First
Outer
Inner
Last
•STEP
•
•PRACTICE F.O.I.L.
•Finding the possible gametes
•(r r) (Y y)
•F.O.I.L
First
Outer
Inner
Last•Try These:
TtBB
DDee
ffPp
•Phenotypic ratioPhenotypic ratio: 9 round, green: 3 round, yellow: 3 wrinkled, green: 1 wrinkled, yellow
(9:3:3:1)
• •RG •Rg •rG •rg
•RRGg •RrGG •RrGg
•RRGg •RRgg •RrGg •Rrgg
•RrGG •RrGg •rrGG •rrGg
•RG
•Rg
•rG
•rg •RrGg •Rrgg •rrGg •rrgg
•STEP
•STEP
•RRGG
•Genotypic ratioGenotypic ratio: 1 RRGG: 2 RRGg: 2 RrGG: 4 RrGg: 1 RRgg: 2 Rrgg: 2 rrGg: 1 rrGG: 1
rrgg
PROBLEM: A pea plant that is heterozygous for round and yellow is crossed with one that is wrinkled and
green. What are the genotypic and phenotypic ratios for this cross?
R = round
r = wrinkledY = yellowy = green
Cross: RrYy X rryy
•Gametes: RrYy rryy
RY ry
Ry ry
rY ry
ry ry
• •RY •Ry •rY •ry
•ry •RrYy •Rryy •rrYy •rryy
•Genotypic ratioGenotypic ratio - 1RrYy : 1 Rryy: 1 rrYy: 1 rryy (1:1:1:1)
•Phenotypic ratioPhenotypic ratio - 1 round, yellow: 1 round, green: 1 wrinkled,
yellow: 1 wrinkled, green (1:1:1:1)
Practice Problems1. TTyy x TtYY (T = tall, t = short, Y = yellow, y =
green)2. In llamas, floppy ears (F) are dominant to pointy
ears (f). Also, bowlegs are recessive (l). A bowlegged llama heterozygous for floppy ears is crossed with a llama that is heterzygous for both traits. Show the genotypes of these two parents.
3. In starfish, pink body color (P) is dominant to orange (p), and thick eyebrows (T) are dominant over thin (t). Patrick, who is heterozygous for body color but purebred for thick eyebrows, has met Patti, who is recessive for both traits. Is it possible for the new couple to have an offsprings that resembles their mother?
Punnett Square
Click image to view movie.