Cheatsheet: Heredity | AP Biology - Grade 9 PDF Download

 Page 1


UNIT V: HEREDITY 
A. Mendelian Genetics 
? Genetics=study of heredity 
? Explains how certain characteristics are passed from parents to children 
? Heredity=transmission of traits from one generation to the next 
? Variation is demonstrated by the differences in appearance that offspring show from parents and 
siblings 
? Physical traits are not inherited; genes are inherited 
? Gregor Mendel=”father of genetics” 
? Traits 
? Expressed characteristics 
¦ character=feature(ex. Eye color); trait =specific version of that feature (ex. blue 
eyes) 
? Influenced by one or more genes 
¦ Gene=chunk of DNA that codes for a particular “recipe” 
? DNA is passed from generation to generation, and genes/traits go along with it 
? Chromosome contains many genes, each controlling the inheritance of a particular trait 
? Locus=position of a gene on a chromosome 
? Children do not inherit physical traits; they inherit genes, which influence physical traits 
¦ Genes passed along by gametes (sperm/egg) 
? clone=group of genetically identical individuals from same parent 
?  common in asexual reproduction 
? Sexual reproduction creates genetic diversity 
? Diploid organisms typically have 2 copies of a gene, one on each homologous chromosome 
? Copies of chromosome may be different from each other, containing different alleles 
? Homozygous=organism has 2 identical alleles for a given trait 
? heterozygous=organisms has 2 different alleles for a given trait 
? Phenotype=physical appearance 
? Genotype=genetic makeup 
? Dominant vs. recessive allele 
? Dominant allele is determined by which allele is the phenotype of a heterozygous 
organism 
? Dominant allele showed by capital letter; recessive allele showed by lowercase of same 
letter 
 
NAME GENOTYPE PHENOTYPE 
Homozygous dominant TT Tall 
Homozygous recessive tt Short 
Heterozygous Tt Tall 
? Crosses 
 
Page 2


UNIT V: HEREDITY 
A. Mendelian Genetics 
? Genetics=study of heredity 
? Explains how certain characteristics are passed from parents to children 
? Heredity=transmission of traits from one generation to the next 
? Variation is demonstrated by the differences in appearance that offspring show from parents and 
siblings 
? Physical traits are not inherited; genes are inherited 
? Gregor Mendel=”father of genetics” 
? Traits 
? Expressed characteristics 
¦ character=feature(ex. Eye color); trait =specific version of that feature (ex. blue 
eyes) 
? Influenced by one or more genes 
¦ Gene=chunk of DNA that codes for a particular “recipe” 
? DNA is passed from generation to generation, and genes/traits go along with it 
? Chromosome contains many genes, each controlling the inheritance of a particular trait 
? Locus=position of a gene on a chromosome 
? Children do not inherit physical traits; they inherit genes, which influence physical traits 
¦ Genes passed along by gametes (sperm/egg) 
? clone=group of genetically identical individuals from same parent 
?  common in asexual reproduction 
? Sexual reproduction creates genetic diversity 
? Diploid organisms typically have 2 copies of a gene, one on each homologous chromosome 
? Copies of chromosome may be different from each other, containing different alleles 
? Homozygous=organism has 2 identical alleles for a given trait 
? heterozygous=organisms has 2 different alleles for a given trait 
? Phenotype=physical appearance 
? Genotype=genetic makeup 
? Dominant vs. recessive allele 
? Dominant allele is determined by which allele is the phenotype of a heterozygous 
organism 
? Dominant allele showed by capital letter; recessive allele showed by lowercase of same 
letter 
 
NAME GENOTYPE PHENOTYPE 
Homozygous dominant TT Tall 
Homozygous recessive tt Short 
Heterozygous Tt Tall 
? Crosses 
 
? 1st generation in an experiment is always called the parent/P1 generation 
? Offspring of P1 are called the filial/F1 generation  
? Offspring of F1 are called F2 generation, etc. 
? true-breeder=genetically pure; consistently produces same traits 
? Law of Dominance 
? One dominant trait masks the effect of the other trait 
? Law of Segregation 
? Monohybrid Cross 
¦ 2 heterozygous individuals are crossed 
¦ Ratios for cross of two heterozygotes 
? Phenotype ratio= 3 dom.:1 rec. 
? Genotype ratio= 1 homo dom: 2 het: 1 homo rec 
? Gametes only get one of the 2 copies of a gene 
? Law of Independent Assortment 
? Each allele of the two traits will get segregated into two gametes independently and 
randomly along Metaphase plate of meiosis I 
? Each pair of chromosomes sorts maternal/paternal homologues independently of the other 
pairs 
? For humans, (n=23), there are more than 8 million (2
23 
possible combinations of 
chromosomes, not including crossing over, mutations, etc.  
? Dihybrid cross 
¦ 2 heterozygotes for two genes are crossed 
¦ 9:3:3:1 ratio 
¦ Easier to use probability rather than a punnett square 
? Random Fertilization also creates genetic variability 
? Any sperm can fuse with any ovum 
? 70 trillion diploid combinations 
? Rules of Probability 
? Probability of 2 independent traits occurring together= probability of trait A*probability 
of trait B 
? Test Cross 
? How to tell if an organism displaying dominant phenotype is homo-dom or het: USE 
TESTCROSS 
? Breed mystery organism with a homo-rec 
¦ If all offspring display dom phenotype, the organism is homo-dom 
¦ If any offspring display rec phenotype, the  organism is het 
? Linked Genes: group of genes on same chromosome tend to stay together/inherited together 
? Cannot segregate independently since they are on the same chromosome, violating the 
law of independent assortment 
? Can only be separated by crossing-over 
? recombinant=offspring formed from recombination events 
¦ Percentage of recombination=  
S(?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? )
?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? 
Page 3


UNIT V: HEREDITY 
A. Mendelian Genetics 
? Genetics=study of heredity 
? Explains how certain characteristics are passed from parents to children 
? Heredity=transmission of traits from one generation to the next 
? Variation is demonstrated by the differences in appearance that offspring show from parents and 
siblings 
? Physical traits are not inherited; genes are inherited 
? Gregor Mendel=”father of genetics” 
? Traits 
? Expressed characteristics 
¦ character=feature(ex. Eye color); trait =specific version of that feature (ex. blue 
eyes) 
? Influenced by one or more genes 
¦ Gene=chunk of DNA that codes for a particular “recipe” 
? DNA is passed from generation to generation, and genes/traits go along with it 
? Chromosome contains many genes, each controlling the inheritance of a particular trait 
? Locus=position of a gene on a chromosome 
? Children do not inherit physical traits; they inherit genes, which influence physical traits 
¦ Genes passed along by gametes (sperm/egg) 
? clone=group of genetically identical individuals from same parent 
?  common in asexual reproduction 
? Sexual reproduction creates genetic diversity 
? Diploid organisms typically have 2 copies of a gene, one on each homologous chromosome 
? Copies of chromosome may be different from each other, containing different alleles 
? Homozygous=organism has 2 identical alleles for a given trait 
? heterozygous=organisms has 2 different alleles for a given trait 
? Phenotype=physical appearance 
? Genotype=genetic makeup 
? Dominant vs. recessive allele 
? Dominant allele is determined by which allele is the phenotype of a heterozygous 
organism 
? Dominant allele showed by capital letter; recessive allele showed by lowercase of same 
letter 
 
NAME GENOTYPE PHENOTYPE 
Homozygous dominant TT Tall 
Homozygous recessive tt Short 
Heterozygous Tt Tall 
? Crosses 
 
? 1st generation in an experiment is always called the parent/P1 generation 
? Offspring of P1 are called the filial/F1 generation  
? Offspring of F1 are called F2 generation, etc. 
? true-breeder=genetically pure; consistently produces same traits 
? Law of Dominance 
? One dominant trait masks the effect of the other trait 
? Law of Segregation 
? Monohybrid Cross 
¦ 2 heterozygous individuals are crossed 
¦ Ratios for cross of two heterozygotes 
? Phenotype ratio= 3 dom.:1 rec. 
? Genotype ratio= 1 homo dom: 2 het: 1 homo rec 
? Gametes only get one of the 2 copies of a gene 
? Law of Independent Assortment 
? Each allele of the two traits will get segregated into two gametes independently and 
randomly along Metaphase plate of meiosis I 
? Each pair of chromosomes sorts maternal/paternal homologues independently of the other 
pairs 
? For humans, (n=23), there are more than 8 million (2
23 
possible combinations of 
chromosomes, not including crossing over, mutations, etc.  
? Dihybrid cross 
¦ 2 heterozygotes for two genes are crossed 
¦ 9:3:3:1 ratio 
¦ Easier to use probability rather than a punnett square 
? Random Fertilization also creates genetic variability 
? Any sperm can fuse with any ovum 
? 70 trillion diploid combinations 
? Rules of Probability 
? Probability of 2 independent traits occurring together= probability of trait A*probability 
of trait B 
? Test Cross 
? How to tell if an organism displaying dominant phenotype is homo-dom or het: USE 
TESTCROSS 
? Breed mystery organism with a homo-rec 
¦ If all offspring display dom phenotype, the organism is homo-dom 
¦ If any offspring display rec phenotype, the  organism is het 
? Linked Genes: group of genes on same chromosome tend to stay together/inherited together 
? Cannot segregate independently since they are on the same chromosome, violating the 
law of independent assortment 
? Can only be separated by crossing-over 
? recombinant=offspring formed from recombination events 
¦ Percentage of recombination=  
S(?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? )
?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? 
? Can be used as a measure of how far apart genes are/order 
? Distance on a chromosome is measured in map units aka centimorgans 
on a linkage map 
? One map unit=1% recombination frequency 
? Farther apart 2 linked alleles are on a chromosome the more often the 
chromosome will cross over between them 
? Genes on different chromosomes have 50% recombination frequency 
? Karyotype: ordered display of the pairs of chromosomes in a cell 
? 2 chromosomes in a pair=homologous chromosomes 
? PEdigrees: show family history of allele(S) 
? Describes interrelationships of parents and children across generations 
? Inheritance patterns of particular traits can be traced back and described using pedigrees 
? Alterations of Chromosome Number/Structure 
? Nondisjunction 
¦ Pairs of homologous chromosomes don’t separate properly during meiosis 
¦ One gamete receives 2 of the same type of chromosome (trisome) while the other 
receives none (monosome) 
¦ Results in Aneuploidy 
? Deletion 
¦ Removes a chromosomal segment 
¦ CDE ?CE 
? Duplication 
¦ Repeats a segment 
¦ CDE ?CDCDE 
? Inversion 
¦ Reverses orientation of segment within a chromosome 
¦ CDE ?EDC 
? Translocation 
¦ Moves a segment from one chromosome to another 
? Genome imprinting 
? Phenotype depends on which parent passed along alleles for trait 
? Involves silencing of certain genes that are “stamped” with an imprint during gamete 
production 
? Extranuclear genes are inherited maternally because the zygote’s cytoplasm comes from 
the egg 
B. Sex-Linked Traits 
? autosomes=non sex chromosomes 
? Sex chromosomes determines sex of individual 
? female=XX 
? male=XY 
? Some traits carried on sex chromosomes 
? Ex. color blindness/hemophilia 
? Most only found on X-chromosome (“X-linked traits”) 
 
Page 4


UNIT V: HEREDITY 
A. Mendelian Genetics 
? Genetics=study of heredity 
? Explains how certain characteristics are passed from parents to children 
? Heredity=transmission of traits from one generation to the next 
? Variation is demonstrated by the differences in appearance that offspring show from parents and 
siblings 
? Physical traits are not inherited; genes are inherited 
? Gregor Mendel=”father of genetics” 
? Traits 
? Expressed characteristics 
¦ character=feature(ex. Eye color); trait =specific version of that feature (ex. blue 
eyes) 
? Influenced by one or more genes 
¦ Gene=chunk of DNA that codes for a particular “recipe” 
? DNA is passed from generation to generation, and genes/traits go along with it 
? Chromosome contains many genes, each controlling the inheritance of a particular trait 
? Locus=position of a gene on a chromosome 
? Children do not inherit physical traits; they inherit genes, which influence physical traits 
¦ Genes passed along by gametes (sperm/egg) 
? clone=group of genetically identical individuals from same parent 
?  common in asexual reproduction 
? Sexual reproduction creates genetic diversity 
? Diploid organisms typically have 2 copies of a gene, one on each homologous chromosome 
? Copies of chromosome may be different from each other, containing different alleles 
? Homozygous=organism has 2 identical alleles for a given trait 
? heterozygous=organisms has 2 different alleles for a given trait 
? Phenotype=physical appearance 
? Genotype=genetic makeup 
? Dominant vs. recessive allele 
? Dominant allele is determined by which allele is the phenotype of a heterozygous 
organism 
? Dominant allele showed by capital letter; recessive allele showed by lowercase of same 
letter 
 
NAME GENOTYPE PHENOTYPE 
Homozygous dominant TT Tall 
Homozygous recessive tt Short 
Heterozygous Tt Tall 
? Crosses 
 
? 1st generation in an experiment is always called the parent/P1 generation 
? Offspring of P1 are called the filial/F1 generation  
? Offspring of F1 are called F2 generation, etc. 
? true-breeder=genetically pure; consistently produces same traits 
? Law of Dominance 
? One dominant trait masks the effect of the other trait 
? Law of Segregation 
? Monohybrid Cross 
¦ 2 heterozygous individuals are crossed 
¦ Ratios for cross of two heterozygotes 
? Phenotype ratio= 3 dom.:1 rec. 
? Genotype ratio= 1 homo dom: 2 het: 1 homo rec 
? Gametes only get one of the 2 copies of a gene 
? Law of Independent Assortment 
? Each allele of the two traits will get segregated into two gametes independently and 
randomly along Metaphase plate of meiosis I 
? Each pair of chromosomes sorts maternal/paternal homologues independently of the other 
pairs 
? For humans, (n=23), there are more than 8 million (2
23 
possible combinations of 
chromosomes, not including crossing over, mutations, etc.  
? Dihybrid cross 
¦ 2 heterozygotes for two genes are crossed 
¦ 9:3:3:1 ratio 
¦ Easier to use probability rather than a punnett square 
? Random Fertilization also creates genetic variability 
? Any sperm can fuse with any ovum 
? 70 trillion diploid combinations 
? Rules of Probability 
? Probability of 2 independent traits occurring together= probability of trait A*probability 
of trait B 
? Test Cross 
? How to tell if an organism displaying dominant phenotype is homo-dom or het: USE 
TESTCROSS 
? Breed mystery organism with a homo-rec 
¦ If all offspring display dom phenotype, the organism is homo-dom 
¦ If any offspring display rec phenotype, the  organism is het 
? Linked Genes: group of genes on same chromosome tend to stay together/inherited together 
? Cannot segregate independently since they are on the same chromosome, violating the 
law of independent assortment 
? Can only be separated by crossing-over 
? recombinant=offspring formed from recombination events 
¦ Percentage of recombination=  
S(?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? )
?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? 
? Can be used as a measure of how far apart genes are/order 
? Distance on a chromosome is measured in map units aka centimorgans 
on a linkage map 
? One map unit=1% recombination frequency 
? Farther apart 2 linked alleles are on a chromosome the more often the 
chromosome will cross over between them 
? Genes on different chromosomes have 50% recombination frequency 
? Karyotype: ordered display of the pairs of chromosomes in a cell 
? 2 chromosomes in a pair=homologous chromosomes 
? PEdigrees: show family history of allele(S) 
? Describes interrelationships of parents and children across generations 
? Inheritance patterns of particular traits can be traced back and described using pedigrees 
? Alterations of Chromosome Number/Structure 
? Nondisjunction 
¦ Pairs of homologous chromosomes don’t separate properly during meiosis 
¦ One gamete receives 2 of the same type of chromosome (trisome) while the other 
receives none (monosome) 
¦ Results in Aneuploidy 
? Deletion 
¦ Removes a chromosomal segment 
¦ CDE ?CE 
? Duplication 
¦ Repeats a segment 
¦ CDE ?CDCDE 
? Inversion 
¦ Reverses orientation of segment within a chromosome 
¦ CDE ?EDC 
? Translocation 
¦ Moves a segment from one chromosome to another 
? Genome imprinting 
? Phenotype depends on which parent passed along alleles for trait 
? Involves silencing of certain genes that are “stamped” with an imprint during gamete 
production 
? Extranuclear genes are inherited maternally because the zygote’s cytoplasm comes from 
the egg 
B. Sex-Linked Traits 
? autosomes=non sex chromosomes 
? Sex chromosomes determines sex of individual 
? female=XX 
? male=XY 
? Some traits carried on sex chromosomes 
? Ex. color blindness/hemophilia 
? Most only found on X-chromosome (“X-linked traits”) 
 
? Since males have one X and one Y chromosome, he’ll express the trait even if it is recessive since 
there is no second allele that would cover it up 
? Female will only express sex-linked trait if trait is dominant or individual is homo rec 
? carrier=female that carries trait but does not exhibit it 
? Barr Bodies 
? X chromosome that is condensed and visible 
? Females only have one X chromosome activated; other X deactivated during embryonic 
development 
¦ Deactivated chromosome chosen randomly by each cell 
? Incomplete dominance 
? Aka blending inheritance 
? Traits blend 
? Alleles equally expressed 
? Ex. red white=pink offspring 
? Non dominant trait 
? Codominance 
? Equal expression of multiple alleles 
? 2 alleles affect phenotype differently 
¦ Ex. blood type options: I
A
, I
B
, i 
? Polygenic inheritance 
? Trait results from the interaction of many genes 
? Non-nuclear inheritance 
? Affected by genetic material in mitochondria 
? Mitochondria always provided by egg during sexual reproduction  
? Most genes have pleiotropy (have multiple phenotypic effects) 
? Responsible for the multiple symptoms of hereditary diseases 
? Epistasis: a gene at one locus alters the phenotypic expression of a gene at another locus 
? Norm of Reaction: phenotypic range of a genotype influenced by environmental factors 
? Multifactorial characters