Genetics unit punnett squares
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Genetics Unit: Punnett Squares. Genetics = the field of biology devoted to understanding how characteristics are transmitted from parents to offspring Heredity = the transmission of characteristics from parents to offspring. Mendel. “father” of modern genetics = laid the groundwork

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Genetics Unit: Punnett Squares

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Genetics Unit: Punnett Squares


Genetics = the field of biology devoted to understanding how characteristics are transmitted from parents to offspring

Heredity = the transmission of characteristics from parents to offspring


Mendel

  • “father” of modern genetics = laid the groundwork

  • experimented with

    garden peas

    - looked for traits = specific characteristics


Mendel (cont)

- P1 generation = parental generation

- F1 generation = offspring of the parental generation

- F2 generation = offspring of the F1 generation


Mendel (cont)

Mendel’s 1st Law = Law of Segregation

  • Organisms inherit two copies of each gene, one from each parent

    2) Organisms donate one copy of each gene in their gametes.


Mendel (cont)

Mendel’s 2nd Law = Law of Independent Assortment

1) The presence of one trait does not affect the appearance of another trait


Basics of Genetics

- Gene = a segment of DNA on a chromosome that controls a specific trait

- because chromosomes come in pairs, genes come in pairs


Basics of Genetics (cont)

- Allele = each of several forms of a gene

- aka: letters

- each allele has a specific location on a chromosome (= locus)

- capital letters = dominant alleles - lowercase letters = recessive alleles


Basics of Genetics (cont)

- homozygous = both alleles are alike

  • homozygous dominant = both capital letters = BB

    - homozygous recessive = both lowercase letters = bb

    heterozygous = alleles are different = Bb


Polydactyly

Polydactyly is the condition of having more than the typical number of fingers or toes. The allele for polydactyly is dominant.


Basics of Genetics (cont)

- Genotype = genetic makeup of an organism

- consists of alleles (letters)

- Phenotype = the appearance of an organism as a result of its genotype

- aka: what does it look like

- human phenotype can be altered by behavior

BB

Green Eyes


Monohybrid Crosses

= a cross between individuals that involves one pair of traits

- Example: Black hair (B) in guinea pigs is dominant to brown hair (b)


Example 1:Homozygous Dominant X Homozygous Dominant

B

B

Genotypic Ratio

Phenotypic Ratio

4 BB :

0 Bb :

0 bb

BB

B

BB

BB

BB

B

4 Black :

0 Brown


Example 2:Homozygous Recessive X Homozygous Recessive

b

b

Genotypic Ratio

Phenotypic Ratio

0 BB :

0 Bb :

4 bb

bb

b

bb

bb

bb

b

0 Black :

4 Brown


Example 3:Homozygous Dominant X Heterozygous

B

B

Genotypic Ratio

Phenotypic Ratio

2 BB :

2 Bb :

0 bb

BB

B

BB

Bb

Bb

b

4 Black :

0 Brown


Example 4:Homozygous Recessive X Heterozygous

b

b

Genotypic Ratio

Phenotypic Ratio

0 BB :

2 Bb :

2 bb

Bb

B

Bb

bb

bb

b

2 Black :

2 Brown


Example 5:Heterozygous X Heterozygous

B

b

Genotypic Ratio

Phenotypic Ratio

1 BB :

2 Bb :

1 bb

BB

B

Bb

Bb

bb

b

3 Black :

1 Brown


Testcross

= an individual of unknown genotype is crossed with a homozygous recessive individual

- can be used to determine the genotype of any phenotype that is dominant


Example 6: Testcross

b

b

Genotypic Ratio

Phenotypic Ratio

0 BB :

2 Bb :

2 bb

Bb

B

Bb

bb

bb

b

2 Black :

2 Brown


Example 6: Testcross

b

b

Genotypic Ratio

Phenotypic Ratio

0 BB :

4 Bb :

0 bb

Bb

B

Bb

Bb

Bb

B

4 Black :

0 Brown


Example 6: Testcross

b

b

Genotypic Ratio

Phenotypic Ratio

0 BB :

0 Bb :

4 bb

b

bb

bb

bb

bb

b

0 Black :

4 Brown


Dihybrid Cross

= a cross between individuals that involves two pairs of traits

- Example: Black hair (B) in guinea pigs is dominant to brown hair (b) and rough coat (R) is dominant to smooth coat (r)


Example 1:

Homozygous Dominant X

Homozygous Recessive

BBRR

bbrr


Example 1: Homozygous Dominant X Homozygous Recessive

BR

BR

BR

BR

BbRr

BbRr

BbRr

BbRr

br

br

BbRr

BbRr

BbRr

BbRr

br

BbRr

BbRr

BbRr

BbRr

BbRr

BbRr

BbRr

BbRr

br


Example 2:

Heterozygous X

Heterozygous

BbRr

BbRr


Example 2: Heterozygous X Heterozygous

BR

Br

bR

br

BBRR

BBRr

BbRR

BbRr

BR

Br

BBRr

BBrr

BbRr

Bbrr

bR

BbRR

BbRr

bbRR

bbRr

Bbrr

bbRr

bbrr

BbRr

br


Incomplete Dominance

= the F1 Generation will have a phenotype in between that of the parents

- Example: Red flowers (R) and White flowers (r) can make Pink flowers (Rr)


Example 7: Incomplete Dominance Pink Flower X Pink Flower

R

Genotypic Ratio

Phenotypic Ratio

r

1 RR :

2 Rr :

1 rr

RR

R

Rr

Rr

rr

1 Red:

2 Pink :

1 White

r


Example 7: Incomplete Dominance Pink Flower X Red Flower

R

r

Genotypic Ratio

Phenotypic Ratio

2 RR :

2 Rr :

0 rr

RR

R

Rr

RR

Rr

R

2 Red:

2 Pink :

0 White


Example 7: Incomplete Dominance White Flower X Red Flower

Genotypic Ratio

Phenotypic Ratio

r

r

0 RR :

4 Rr :

0 rr

Rr

R

Rr

Rr

Rr

R

0 Red:

4 Pink :

0 White


Example 7: Incomplete Dominance Pink Flower X White Flower

R

r

Genotypic Ratio

Phenotypic Ratio

0 RR :

2 Rr :

2 rr

Rr

r

rr

Rr

rr

0 Red:

2 Pink :

2 White

r


Codominance

= when both alleles for a gene are expressed in a heterozygous offspring

- Example: Red coat color (R) in horses is codominant with white coat color (R’) to make a horse with a mix of red and white coat color (RR’)


Example 8: Codominance Red Coat X White Coat

R

R

Genotypic Ratio

Phenotypic Ratio

0 RR :

0 R'R' :

4 RR'

RR'

RR'

R'

RR'

RR'

R'

0 Red Coat :

0 White Coat :

4 Red/White Coat


Example 8: Codominance Red/White Coat X White Coat

R

R'

Genotypic Ratio

Phenotypic Ratio

0 RR :

2 R'R' :

2 RR'

RR'

R'R'

R'

RR'

R'R'

R'

0 Red Coat :

2 White Coat :

2 Red/White Coat


Example 8: Codominance Red/White Coat X Red Coat

R

R'

Genotypic Ratio

Phenotypic Ratio

2 RR :

0 R'R' :

2 RR'

RR

RR'

R

RR

RR'

R

2 Red Coat :

0 White Coat :

2 Red/White Coat


25 min. Review:

https://www.khanacademy.org/science/biology/heredity-and-genetics/v/punnett-square-fun


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