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31

Dihybrid Cross

F1 Generation

F1 Generation self crossed

TtPp x TtPp

4 phenotypes

9:3:3:1

(sorts as it would in monohybrid:

3:1 ratio favor dominant)

32

Non-Mendelian Inheritance

Complications with Mendelian

Genotype doesn't translate into phenotype 100% 

not 100% of recessive phenotype have 100% recessive genotype

33

Incomplete Dominance

(complications with mendelian genetics)

phenotype of heterozygote is intermediate of phenotypes of homozygotes 

34

incomplete dominance 

example:

snapdragon flowers

P: RR x rr 

(red x white)

F1 genotypic ratio: 100% Rr

F1 phenotypic ratio: Rr = pink

F1: Rr x Rr

(pink x pink)

F2 genotypic ratio: 1 RR: 2 Rr: 1 rr

F2 phenotypic ratio: 1 red: 2 pink: 1 white

35

Codominance

(non-mendelian inheritance)

multiple alleles exist for given gene

more than one is dominant

each dominant allele fully dominant when combined with recessive

two dominant alleles:

phenotype is result of expression by both dominant alleles simultaneously

36

Codominance 

example:

ABO blood groups

Blood type determined by three alleles:

IA, IB, i

only 2/3 allele present in individuals

all alleles present in human population

IA, IB - dominant

i - recessive

IAIA or IAi - blood type A

IBIB or IBi - blood type B

ii - blood type O

IAIB - blood type AB

 

37

Sex Determination

(Mendelian genetics)

for every mating event, 50% chance boy, 50% girl

38

autosomes

non sex chromosomes

22/23 chromosome pairs

39

sex chromosomes

1/23 pairs

determine sex of organism

females - XX

males XY

40

gender determination

females produce only X chromosome

male determine gender of zygote - produce X or Y

41

sex linked chromosomes

genes located on X or Y chromosomes 

42

most sex linked chromosomes carried on the ___ chromosome

X chromosome

43

Sex Linkage

(Mendelian Genetics) 

recessive genes carried on X chromosome will produce recessive phenotype in males

(only one X)

no dominant allele present to mask

recessive phenotype much more common in males

44

examples of sex linked recessives

hemophilia

color-blindness

45

sex-linkage inheritance

affected males pass on trait to all daughters (X), no sons (Y)

can be passed from father to grandson via carrier daughter

 

46

Drosophila melanogaster

helped provide explanations for mendelian genetic patterns

advantages for genetic research

47

Advantages of Drosophila melanogaster for genetic research

(5)

  • reproduce often (short life cycle)
  • reproduce large numbers
  • large chromosomes
  • few chromosomes (4 pairs; 2n=8
  • frequent mutations

48

analyses of D. melanogaster led to discoveries

(2)

pattners of embryological dev.

how genes expressed in early dev affect adult organism

49

Environmental Factors

(Mendelian Genetics)

interaction between environment and genotype produces phenotype

50

Enviornmental factors in genetics and Drosophila

with given set of wings:

crooked wings at low T

straight wings at high T

51

environmental factors in mendelian genetics in Himalayan hare

same color genes

white on warmer parts of body

black on colder parts of body

(if naturally warm parts cooled with ice, hair will grow black)

52

Genetic Problems

chromosome number and structure maybe altered by abnornal cell division

  • during meiosis
  • by mutagenic agents

53

Nondisjunction 

(genetic problems)

failure of homologous chromosomes to sep. properly during

meiosis I 

failure of sister chromatids to separate properly during

meiosis II

54

result of nondisjunction

(genetic problems)

3 copies of a chromosome - trisomy 

(somatic cells - 2N + 1)

1 copy of chromosome - monosomy

(somatic cells - 2N - 1)

55

most monosomies and trisomies result in

spontaneous abortion of embryo early in term

56

nondisjunction may also occur in sex chromosomes, resulting in

extra or missing copies of X and/or Y

57

Chromosomal Breakage

(genetic problems)

occur spontaneously

or induced by environmental factors 

58

environmental factors causing chromosomal breakage

X-rays, mutagenic agents

59

deficiency

(chromosomal breakage - genetic problems)

chromosome that loses fragment

60

Mutations

definition

(genetic problems)

changes in genetic information of a cell

coded in DNA