Graded notes

Review Meiosis

2 mitosises, chromosomes replicated in interphase 1, homologous pairs, crossing over, 4 haploid daughter cells

Review Meiosis

Pair of homologous chromosomes vs. homologous chromosomes….s phase…..

Gregor Mendel: Austrian Monk who studied pea plants

Pea plants(1st Mendel did this: )

True-breeding: if self-pollinate, produce offspring identical to themselves

Cross pollinate: male sex cells in pollen from one plant fertilize egg cells of flower in another plant(Then he tested flowers together w/2 different characteristics; purple/white)

Traits: specific characteristics (seed color, height, texture)

Monohybrid Cross

Mono = one trait (flower color)

Hybrid = Offspring of two different breeding varieties

Mendel reasoned that F1 plants carried two factors for the flower color trait (Purple and White).

“Factors” called genes

Mendel’s crosses:

P: Parental generationF1: Offspring or 1st generationHybrids: Offspring of crosses between parents with different traits

Testing of other traits…one trait disappears in F1, Reappears in F2

Conclusions of Mendel’s crosses:

Genes: Chemical factors that determine traits passes on from one generation to another

Alleles: Different forms of genes for trait

Ex. Plant height has two forms produces tall plants & short ones

Alleles on Homologous chromosomes

Principle of Dominance: states that some alleles are dominant and other are recessive

Dominant: Trait will always show up; Shown with capital letters

Recessive: Trait does not show up; Shown with lower case letters

Homozygous: (TT) organism has 2 identical alleles for particular trait

Heterozygous: (Tt) organism has 2 different alleles for particular trait

Phenotype: physical characteristics you see (yellow, round)

Genotype: genetic makeup (Tt); what we write

What are alleles?

Since one allele is inherited from each parent,two letters are needed to represent the alleles of a gene

Different forms of gene

Where do alleles come from?

One from each parent

GENOTYPE?

Don’t Copy

-two letters that represent the alleles of a geneEX. RR, Rr, rr

Phenotype?

the outward appearance of an organism (what it looks like)

If a farmer has a red flower (RR) give genotype and phenotype

- the genotype is RR- the phenotype is red

Don’t copy

1. A brown dog (bb)

the genotype ________

the phenotype _______

 

2. A long haired cat (Hh)

the genotype _______

the phenotype _______

(Review)

Mendel learned that the alleles of each individual separate and end up in gametes because of

MEIOSIS!!MEIOSIS!!

Replication of chromosomes

Ex. A female pure brown dog (bb)

b b

bb

Dominant or Recessive?

PRACTICE on paper

A hybrid male yellow canary (Yy) 

Y y

Y y

Dominant?

A pure female white flower (rr)

r r

Practice!

r r

Dominant? Recessive?

If a male red flower (Rr) and a female pure white (rr) flower from above got their

gametes together (fertilization)

What kind of combinations could be formed?

X

Practice on own paper before showing next slide! Write out male=Rr, female=rr.

Which is dominant, recessive? What are we crossing? (Write Genotypes)

Male red flower (Rr) Female white flower (rr)

Rr

Sperm 1 Sperm 2

rr

Egg 1 Egg 2

Answers? Write out alleles for each gamete of cross.

R r r r

+

+

+

+

=

=

=

=

1 1

1 2

2 1

2 2

Genotype Phenotype

Show possible offspring of crossing different alleles.

R

r

r

R

r

r

r

r

A punnet square is a chart that helps us predict the probability that an offspring with a particular genotype and phenotype will be produced

Punnett Squares show the chances that one male’s

sperm & one female’s eggs can make certain offspring

Create a punnett square using male red (Rr) and female white (rr) flowers.

To Make a punnet square there are a few simple steps to follow:

 

1) Draw a box and divide it into four parts

2) Label the left hand side of the box with the genotype of male parent

(R=Red, r=White)

R

r

3) Label the top of the box with the genotype of the female parent

R

r

r r

4) In the middle boxes place 2 alleles. One letter comes from the left side and one from the top

R

r

r r

Rr

r r

Rr

r r

You have predicted what kind of

offspring these 2 parents could

have!!!

R= Red r= White

Red______% White______%

You now know the possible genotypes for the offspring of these two parents.

• The genotypes of the offspring are: 

R

r

r r

Rr Rr

r r r r

2: Rr, 2: rr Red=50% White=50%

2: Red, 2: White

•The phenotypes of the offspring are:

1. A cross between a female with straight hair (SS) and a male with curly hair (ss). Draw out punnett square:

 

genotypes_____________

phenotypes______________

Straight______% Curly_______%

2. A cross between a black dog (Bb) and a brown dog (bb). Draw out Punnett Square.

 

 genotypes_____________phenotypes_______________Black_______% Brown________%Ratio_____:______

3. A cross between a yellow corn (Yy) and another yellow corn (Yy) (y = white corn). Draw out Punnett Square.

    genotypes_________________phenotypes_________________Yellow corn_______% White corn________%Ratio_____:______