Meiosis and Mendel MEIOSIS I: Separates homologous chromosomes

Meiosis and Mendel

? Review Meiosis

? Rules of Inheritance

? Calculating offspring proportions in the F1 and F2

? Monohybrid and dihybrid crosses

? Probability rules (if time)

24 January 2022

MEIOSIS I: Separates homologous chromosomes

Prophase I

Metaphase I

Anaphase I

Telophase I and Cytokinesis

Crossing over

Sister chromatids Remain attached

Pair of homoogous chromosomes

Homologous chromosomes separate

Haploid cells

MEIOSIS II: Separates sister chromatids

Prophase II Metaphase II Anaphase II

Telophase II and Cytokinesis

Meiosis produces genetic variation through

Independent Assortment Crossing over

Sister chromatids Four haploid

separate

cells

Gregor Mendel

1

P Generation

Phenotype: Genotype:

Gametes:

Purple flowers White flowers

PP

pp

P

p

F1 Generation

Phenotype: Genotype: Gametes:

F2 Generation

Purple flowers Pp

1/2 P

1/2 p

Sperm

P

p

P

Eggs

PP

Pp

p

Pp

pp

3

1

Fig. 14-6

Purple

3

Purple

"Alleles" are different

versions of the same gene

Purple

Pp

1

White

Ratio 3:1

Genotype

PP (homozygous)

1

Pp (heterozygous)

2

Pp (heterozygous)

pp (homozygous)

1

Alleles are different forms of the same gene

Allele for purple flowers

C T A A A T C GG T G A T T T AG C C A

CTAAATCGGT

Locus for flowercolor gene

Pair of homologous

chromosomes

Enzyme

Enzyme that helps synthesize purple pigment

Allele for white flowers

A T AAAT CGGT T A T T T AGCCA

ATAAATCGGT

No enzyme produced

One allele results in

sufficient pigment.

Fig. 14-6

Phenotype

Purple

3

Purple

Purple

1

White

Ratio 3:1

Genotype

PP (homozygous)

1

Pp (heterozygous)

2

Pp (heterozygous)

pp

(homozygous)

1

2

Bb x Bb

1) Determine the genotypes of the parents

2) Write down the gametes each parent can produce

3) Combine all gametes to to make a table of offspring genotypes

4) Determine offspring phenotypes

The F2 black mice contain a mixture of genotypes-- how can you tell which are which?

Make a Test Cross to a homozygous recessive

What progeny would you

?

expect for each of these black mice if each were

mated to a brown mouse?

Independent Assortment

? Now consider pairs of characters.

? Mendel asserted that different traits assort independently when gametes are produced.

(Only true if traits are on different chromosomes or are far enough apart that crossing over occurs each generation.)

1. Write down the genotypes of the parents

2. Determine the possible GAMETES made by each parent

3. Combine gametes to make a table of offspring genotypes

4. Determine the offspring phenotypes

What will you see in the F1

offspring?

What will you see in the F2? (YyRr x YyRr)

1. Write down the genotypes of the parents

2. Determine the possible GAMETES made by each parent

3. Combine gametes to make a table of offspring genotypes

4. Determine the offspring phenotypes

Rules of probability

? And rule

? The probability of both of two independent events is the product of the probabilities

? Or rule:

? The probability of either of two independent and mutually exclusive events is the sum of the probabilities

3

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