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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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slide2
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
Mendel
  • “father” of modern genetics = laid the groundwork
  • experimented with

garden peas

- looked for traits = specific characteristics

mendel cont
Mendel (cont)

- P1 generation = parental generation

- F1 generation = offspring of the parental generation

- F2 generation = offspring of the F1 generation

mendel cont1
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 cont2
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
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
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 cont1
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

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

basics of genetics cont2
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
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
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
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
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
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
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
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
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 testcross1
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 testcross2
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
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
Example 1:

Homozygous Dominant X

Homozygous Recessive

BBRR

bbrr

example 1 homozygous dominant x homozygous recessive
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
Example 2:

Heterozygous X

Heterozygous

BbRr

BbRr

example 2 heterozygous x heterozygous
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
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
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
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
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
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
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
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
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
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

slide39
25 min. Review:

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

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