Ap Bio Ch. 14 And 15

Front 1

• Gene idea

Back 1

parents pass on discrete heritable genes to offspring

Front 2

• True breeding

Back 2

homozygous→ when the parent self fertilizes and gives rise to offspring that are exactly alike

• Mendel only used true breeding plants

Front 3

• Hybridization

Back 3

• Hybridization→ crossing of two true breeding varieties

Front 4

• P generation

Back 4

• P generation→ parental generation

Front 5

• F1 generation

Back 5

• F1 generation→ offspring of parental generation

Front 6

• F2 generation

Back 6

• F2 generation→ offspring of F1 generation

Front 7

• Mendel’s model

Back 7

• Mendel identified the concept of dominant and recessive traits
o Explains why traits can disappear in one generation and reappear in the next generation


Mendel's model

o Alternative versions of genes account for variations in inherited characters
• Ex: flower color in pea plants exists in two versions→ one version for purple and one version for white

o For each character an organism inherits two alleles, one from each parent

o If the two alleles at a locus differ, then the dominant allele determines the organism’s appearance and the recessive allele has no noticeable effect

• Law of segregation→ the two alleles for a heritable character separate during gamete formation and end up in different gametes

Front 8

• Homozygous

Back 8

→ having a pair of identical alleles for a gene
o True breeding

Front 9

• Heterozygous

Back 9

having two different alleles for a gene
o not true breeding

Front 10

• Phenotype

Back 10

• Phenotype→ an organism’s traits

Front 11

• Genotype

Back 11

• Genotype→ an organism’s genetic makeup

Front 12

• Testcross

Back 12

• Testcross→ the breeding of a recessive homozygote with an organism of dominant phenotype but unknown genotype will determine the genotype of the organism with the dominant phenotype

Front 13

• Monohybrids

Back 13

• Monohybrids→ being heterozygous for one character

Front 14

• Monohybrid cross

Back 14

• Monohybrid cross→ cross between two monohybrids

Front 15

• Dihybrid

Back 15

• Dihybrid→ being heterozygous for two characters

Front 16

• Law of independent assortment

Back 16

• Law of independent assortment-→ each pair of alleles segregates independently of other pairs of alleles during gamete formation
o If you have RrWw the R’s will separate independently of the W’s (and vis versa)

Front 17

• Spectrum of dominance

Back 17

• Spectrum of dominance→ alleles can show different degrees of dominance and recessiveness in relation to each other
o Complete dominance
o Incomplete dominance
o Codominance

Front 18

• Complete dominance

Back 18

• Complete dominance→ when one allele is completely dominant over the other→ extreme end of the spectrum of dominance

Front 19

• Codominance

Back 19

• Codominance→ when the two alleles both affect the phenotype in separate distinguishable ways (ex: roan colored cattle) → neither allele is dominant→ the other extreme end of the spectrum of dominance

Front 20

• Incomplete dominance

Back 20

• Incomplete dominance→ when both alleles blend together so the offspring doesn’t look like the parent (ex: pink flowers RW)→ middle of the spectrum of dominance

Front 21

Relation between dominance and phenotype

Back 21

• Dominant alleles and recessive alleles are both expressed- it’s just that the dominant trait dominates the recessive trait and masks the recessive trait’s effect

• Dominant alleles are dominant b/c their phenotype is dominant to the recessive phenotype

• In diseases that occur b/c of a double recessive, it’s only a disease b/c the combined effects of both recessive traits are harmful, compared to the effects of just one recessive trait which isn’t harmful

Front 22

• Pleiotropy

Back 22

• Pleiotropy-→ when a gene has multiple phenotypic effects

Front 23

• Epistasis

Back 23

• Epistasis→ when a gene at one locus alters the phenotypic expression of a gene at a second locus

o When genes influence each other

o Ex: Mice have genes that code for color, but another gene codes for whether or not the mice will have pigmentation in their fur

• If a mouse is Aa bb and bb means it doesn’t have pigmentation that means the mouse is albino, even though it has genes that code for black coloring

• The pigmentation gene influences the color gene

Front 24

o Quantitative characters

Back 24

o Quantitative characters→ characteristics that vary along a continuum (example: height, skin color, etc. ) there are tons of possible phenotypes

Front 25

o Polygenic inheritance

Back 25

o Polygenic inheritance→ when two or more genes affect a single phenotypic character

Front 26

o Pleiotropy

Back 26

o Pleiotropy→ when a single gene affects several phenotypic characters

Front 27

• Norm of reaction

Back 27

• Norm of reaction→ a genotype is associated with a range of phenotypic possibilities due to environmental influences

Front 28

• Multifactorial

Back 28

• Multifactorial→ many factors, both genetic and environmental, influence phenotype

Front 29

Mendel has two laws

Back 29

• Mendel has two laws→ law of segregation, law of independent assortment

Front 30

• Pedigree

Back 30

• Pedigree→ chart depicting relationships between parents and children across generations
• Pedigrees predict the future

Front 31

• Carriers

Back 31

• Carriers-→ heterozygotes- b/c they can transmit their recessive allele to future generations


• Most genetic disorders are caused by recessive alleles

• Heterozygotes are normal in phenotype because the normal allele produces enough normal protein to overpower the abnormal allele- the recessive abnormal allele is still expressed


• Heterozygous people for sickle cell have normal and abnormal blood cells- they’re codominant

Front 32

Mating of close relatives

Back 32

• If two people are close relatives, the probability of them passing on recessive traits to their offspring increases greatly b/c they share similar ancestors
• Consanguineous matings (matings between close relatives)
• People with recent common ancestors are more likely to carry the same recessive alleles in comparison to unrelated people

Front 33

Dominantly inherited disorders

Back 33

• Dominantly inherited disorders are unlikely to be lethal- if they were lethal the person would die before they can pass their gene to their offspring

o If they are lethal- the person usually doesn’t experience symptoms until he/she is older

• Recessively inherited disorders are more likely to be lethal b/c they can be passed through generations through heterozygous healthy people


the minority of genetic diseases are dominant

Front 34

Multifactorial Disorders

Back 34

• Most diseases have a multifactorial basis→ influenced by genes and significant environmental influence
• Lifestyle can influence your risk for disease

Front 35

• Chromosome theory of inheritance

Back 35

o Genes have specific loci on chromosomes and it is the chromosomes that undergo segregation and independent assortment

• Behavior of homologous chromosomes during meiosis accounts for the segregation of the alleles at each gene locus to different gametes

• Behavior of chromosomes during meiosis and random fertilization accounts for the diversity in phenotype

• Specific genes belong on specific chromosomes

Front 36

• Thomas Hunt Morgan

Back 36

provided the first solid evidence associating a specific gene with a specific chromosome

• Morgan studied abnormal white eyed fruit flies in comparison to normal red eyed fruit flies

• Found that the wild type allele (red eyes) is dominant

• Found that the white eyed trait only appeared in males

• Realized that the gene that coded for eye color was located exclusively on the X chromosome

• Provided evidence for the chromosome theory of inheritance → a specific gene is carried on a specific chromosome

Front 37

• Wild type→

Back 37

• Wild type→ normal phenotype for a character- the phenotype most common in natural populations

Front 38

• Linked genes

Back 38

• Linked genes→ genes located on the same chromosome that tend to be inherited together

• Morgan realized that the genes for body color and wing size in fruit flies are usually inherited together in specific combinations b/c the genes are located on the same chromosome

• But linked genes are not always inherited together b/c of genetic recombination

Front 39

• Genetic recombination

Back 39

• Genetic recombination→ the production of offspring with combinations of traits differing from those found in either parent

Front 40

• Parental types

Back 40

• Parental types→ offspring that inherit a phenotype that matches one of the parental phenotypes

Front 41

• Recombinant types/Recombinants

Back 41

• Recombinant types/Recombinants→ offspring that inherit combinations of genes that are different from the parents

o For example a yellow round pea crosses with a green wrinkled pea and produces a yellow wrinkled pea→ the yellow wrinkled pea doesn’t look like the parent

o Frequency of recombination→ ex: if 50% of offspring are recombinants, there’s a 50% frequency of recombination

• The physical basis for recombination between unlinked genes is the random orientation of homologous chromosomes at metaphase I of meiosis and crossing over

Front 42

• Crossing over

Back 42

mixes genes up so that not all offspring will look like the parent

o Breaks the physical connection between genes on the same chromosome

o Accounts for recombination of linked genes

o Occurs during Prophase 1 of Meiosis

o One maternal and one paternal chromatid break at corresponding parts and rejoin with each other to form two completely new chromosomes

o Recombination frequency is related to the distance between linked genes

Front 43

• Genetic map

Back 43

• Genetic map→ ordered list of the genetic loci along a particular chromosome

Front 44

Sturtevant

Back 44

• Sturtevant developed a method for constructing a genetic map
• Sturtevant hypothesized that recombination frequencies depend on the distance between genes on a chromosome

• Predicted that genes that are far apart are more likely to cross over and have a higher recombination frequency
o The greater the distance between two genes the more points there are between them where crossing over can occur

Front 45

• Linkage map

Back 45

• Linkage map→ genetic map based on recombination frequencies

• But the frequency of crossing over is not actually uniform over the length of a chromosome as Sturtevant assumed – so map units do not correspond with physical distances

Front 46

Map unit

Back 46

• Morgan developed the concept of a Map unit→ 1 map unit= 1% recombination frequency


• But the frequency of crossing over is not actually uniform over the length of a chromosome as Sturtevant assumed – so map units do not correspond with physical distances

Front 47

• Cytogenetic maps

Back 47

• Cytogenetic maps→ locate genes with respect to chromosomal features like stained bands that can be seen with a microscope

Front 48

• SRY gene

Back 48

• SRY gene→ required for the development of testes
o In the absence of SRY the gonads develop into ovaries

Front 49

• Sex linked genes

Back 49

• Sex linked genes→ genes located on sex chromosomes
o Most sex linked genes are on the X chromosome
• More males have sex linked diseases than females b/c males only need one recessive allele to express the disease while females need two recessive alleles

Front 50

X inactivation in Female Mammals

Back 50

• Even though females have two X chromosomes, one of them becomes inactivated during embryonic formation
o This way, females and males are affected by the X chromosome in the same way b/c both females and males have only one active X chromosome

Front 51

• Barr Body

Back 51

• Barr Body→ the inactive X chromosome in female cells condenses into a Barr Body
o Lies along the inside of the nuclear envelope
o Most of the genes of the X chromosome that forms the Barr body are not expressed

Front 52

• Mary Lyon

Back 52

• Mary Lyon→ demonstrated that selection of which X chromosome will form the Barr body occurs randomly and independently in each embryonic cell present at the time of X inactivation

o So females have two kinds of cells- ones with an active maternal X chromosome and ones with an active paternal X chromosome

o After an X chromosome is inactivated in a particular cell, all mitotic descendants of that cell have the same inactive X

o So if a female is heterozygous for a sex linked trait, half of her cells will express the disease
• Ex: multicolored cats

Front 53

• Nondisjunction

Back 53

• Nondisjunction→ when homologues do not move apart properly during meiosis I or when sister chromatids do not move apart properly during meiosis II
o One gamete receives two of the same type of chromosome and the other gamete receives no copy of the chromosome

Front 54

• Aneuploidy

Back 54

• Aneuploidy→ when an offspring has an abnormal number of a particular chromosome

Front 55

• Trisomic

Back 55

• Trisomic→ when an offspring has three copies of the same chromosome

Front 56

• Monosomic

Back 56

• Monosomic→ when an offspring is missing a chromosome

Front 57

• Polyploidy

Back 57

• Polyploidy→ having more than two complete chromosome sets

o Polyploidy is common in plants
o Polyploidy does not occur as often in animals- but more likely in fish and amphibians

• Polyploids are more normal looking than aneuploids- one extra or missing chromosome disrupts genetic balance more than does an entire set of chromosomes

Front 58

o Triploidy

Back 58

o Triploidy→ 3n- 3 chromosome sets
• Forms when an abnormal diploid egg produced by nondisjunction unites with a normal sperm

Front 59

o Tetraploidy

Back 59

o Tetraploidy→ 4n- 4 chromosome sets
• Forms when a zygote fails to divide after replicating its chromosomes

Front 60

Alternations of Chromosome Structure

Back 60

• Mistakes can happen during crossing over

Deletion

Duplication

Inversion

Translocation

Front 61

• Deletion

Back 61

• Deletion→ when a chromosomal fragment lacking a centromere is lost
o So the affected chromosome is missing genes
o Deletions delete segments

Front 62

• Duplication

Back 62

• Duplication→ when a deleted fragment attaches as an extra segment to a sister chromatid
o The affected sister chromatid has double the amount of those genes
o Duplications repeat segments

Front 63

• Inversion

Back 63

• Inversion→ when a chromosomal fragment reattaches to the original chromosome but in the reverse orientation
o Inversions reverse segments

Front 64

• Translocation

Back 64

• Translocation→ when a chromosomal fragment joins a nonhomologous chromosome
o A Translocation moves a segment from one chromosome to another

Front 65

• Trisomic

Back 65

• Trisomic→ when an offspring has three copies of the same chromosome

Front 66

• Monosomic

Back 66

• Monosomic→ when an offspring is missing a chromosome

Front 67

• Polyploidy

Back 67

• Polyploidy→ having more than two complete chromosome sets

o Polyploidy is common in plants
o Polyploidy does not occur as often in animals- but more likely in fish and amphibians

• Polyploids are more normal looking than aneuploids- one extra or missing chromosome disrupts genetic balance more than does an entire set of chromosomes

Front 68

o Triploidy

Back 68

o Triploidy→ 3n- 3 chromosome sets
• Forms when an abnormal diploid egg produced by nondisjunction unites with a normal sperm

Front 69

o Tetraploidy

Back 69

o Tetraploidy→ 4n- 4 chromosome sets
• Forms when a zygote fails to divide after replicating its chromosomes

Front 70

Alternations of Chromosome Structure

Back 70

• Mistakes can happen during crossing over

Deletion

Duplication

Inversion

Translocation

Front 71

• Deletion

Back 71

• Deletion→ when a chromosomal fragment lacking a centromere is lost
o So the affected chromosome is missing genes
o Deletions delete segments

Front 72

• Duplication

Back 72

• Duplication→ when a deleted fragment attaches as an extra segment to a sister chromatid
o The affected sister chromatid has double the amount of those genes
o Duplications repeat segments

Front 73

• Inversion

Back 73

• Inversion→ when a chromosomal fragment reattaches to the original chromosome but in the reverse orientation
o Inversions reverse segments

Front 74

• Translocation

Back 74

• Translocation→ when a chromosomal fragment joins a nonhomologous chromosome
o A Translocation moves a segment from one chromosome to another

Front 75

• Nonreciprocal cross over

Back 75

• Nonreciprocal cross over→ when non sister chromatids break and rejoin at incorrect places so one chromosome gives up more genes than it receives
o the result is one chromosome has a deletion and the other has a duplication

Front 76

• Down syndrome

Back 76

• Down syndrome→ an aneuploidy condition
o Down syndrome people have three copies of chromosome 21
o People have 47 chromosomes
o Older women are more likely to have a child with down syndrome
o Down syndrome is not genetic- you can’t give down syndrome to your child- it’s caused by a mistake that happens during meiosis
o Happens b/c of nondisjunction during meiosis I

Front 77

o Klinefelter syndrome

Back 77

• Men have XXY
• The extra X is inactivated, but the man is still abnormal

Front 78

o Turner’s syndrome

Back 78

• Females have only one X
• They are phenotypically female but they’re sterile
• They are otherwise normal

Front 79

• Cri du chat

Back 79

o Results from a deletion in chromosome 5
o Mental retardation, small head size, unusual facial features, cry that sounds like a cat

Front 80

• CML- Chronic myelogenous leukemia

Back 80

o Results from a translocation between a large portion of chromosome 22 and a small portion of chromosome 9
o Results in a shortened chromosome 22 called the Philadelphia chromosome

Front 81

• Genomic imprinting

Back 81

• Some traits depend on which parent passed along the alleles for those traits

• Genomic imprinting→ when phenotype varies depending on whether an allele is inherited from the male or female parent

• Most imprinted genes are autosome genes

• Occurs during the formation of gametes and results in the silencing of one allele of certain genes

• These genes are imprinted differently in sperm and ova- so a zygote expresses only one allele of an imprinted gene- either the maternal allele or the paternal allele

• Imprinted genes are always imprinted in the same way

o So a gene imprinted for maternal allele expression will always be imprinted for maternal allele expression, generation after generation

• Ex: Only the paternal allele for insulin like growth factor 2 is expressed

Front 82

• Extranuclear genes

Back 82

• Some genes are located on organelles
• Extranuclear genes→ genes located on organelles
• Mitochondria and chloroplasts have genes
o They reproduce on their own and transmit genes to daughter organelles
o Organelles do not display Mendelian inheritance b/c organelle genes are not distributed to offspring like chromosomes are

Front 83

• Karl Correns→

Back 83

• Karl Correns→ provided the idea that not all genes were in chromosomes

Front 84

chi squared equation

Back 84

(Observed-expected)^2/expected

Then you take that value and figure out what the P value is using a P value chart

P<0.05 means the data is influenced by an outside force

Front 85

how to find distance between genes (map units)

Back 85

1 map unit = 1% rate of recombination

Number of recombinants/total number of offspring= percentage of recombinants

percentage of recombinants=rate of recombination=distance between genes

Front 86

what are the two exceptions to Mendelian laws

Back 86

Genetic imprinting and extra nuclear genes

Front 87

extra nuclear genes tend to be maternally inherited or paternally inherited?

Back 87

maternally inherited b/c the egg has the most organelles in it

eggs have more organelles than sperm