Fundamentals of Genetics

Patterns of Inheritance The History of Genetics The History of Genetics Genetics – scientific study of heredity Genetics – scientific study of heredity Trait – characteristic that can be passed from parents to offspring Trait – characteristic that can be passed from parents to offspring

Father of Genetics Gregor Mendel (born 1822) Gregor Mendel (born 1822) Austrian Monk Austrian Monk Studied 7 different pea plant traits that are true-breeding Studied 7 different pea plant traits that are true-breeding Produce offspring identical to themselves Produce offspring identical to themselves

Mendel’s 1 st Conclusion Biological inheritance is passed from one generation to the next- Genes Biological inheritance is passed from one generation to the next- Genes Alleles- different forms of a gene Alleles- different forms of a gene

Parental Cross Cross-pollinated flowers with opposite traits (tall, short) Cross-pollinated flowers with opposite traits (tall, short) P generation P generation Plants from the first cross were all tall- hybrids. Plants from the first cross were all tall- hybrids. F 1 generation F 1 generation

F 1 Cross Allowed plants from P cross to self- fertilize Allowed plants from P cross to self- fertilize The recessive trait had reappeared!! The recessive trait had reappeared!! About 25% of the offspring (F 2 generation) were short. About 25% of the offspring (F 2 generation) were short.

Mendel’s 2 nd Conclusion Principle of Dominance Principle of Dominance Some alleles are dominant Some alleles are dominant Capital Letter -R,D Capital Letter -R,D This trait will be always be seen This trait will be always be seen Some alleles are recessive Some alleles are recessive Lower case Letter –r,d Lower case Letter –r,d This trait will only be seen when a dominant allele is NOT present This trait will only be seen when a dominant allele is NOT present

Mendel’s 3 rd Conclusion Principle of Segregation Principle of Segregation Alleles separate from each other during formation of sex cells, or gametes. Alleles separate from each other during formation of sex cells, or gametes.

Purebred – organism receives the same genetic traits form both of its parents Purebred – organism receives the same genetic traits form both of its parents Homozygous – AA or aa Homozygous – AA or aa Hybrid – organism receives different forms of a genetic trait Hybrid – organism receives different forms of a genetic trait Heterozygous - Aa Heterozygous - Aa

Important Terms Genes – sections of a chromosome that code for a trait Genes – sections of a chromosome that code for a trait Allele – distinct form of a gene Allele – distinct form of a gene Dominant Allele – expressed when two different alleles are present; represented with capital letter Dominant Allele – expressed when two different alleles are present; represented with capital letter Recessive Allele – form of gene that is not expressed when paired with a dominant allele; represented with lower case letter Recessive Allele – form of gene that is not expressed when paired with a dominant allele; represented with lower case letter

Genes Represent Traits Genotype – genes that make up an organism Genotype – genes that make up an organism Includes both genes in a homologous pair Includes both genes in a homologous pair Phenotype – outward expression of the trait Phenotype – outward expression of the trait Homozygous – two alleles are identical (AA or aa) Homozygous – two alleles are identical (AA or aa) Heterozygous – two alleles are different (Aa) Heterozygous – two alleles are different (Aa) Also known as a hybrid organism Also known as a hybrid organism

Genetics and Prediction

Predictions for One Trait Probability – predict likelihood of an event or outcome Probability – predict likelihood of an event or outcome Punnett square – grid for organizing genetic information Punnett square – grid for organizing genetic information Can be used to make predictions about a cross between two organsims Can be used to make predictions about a cross between two organsims Monohybrid Cross – cross between two parents and one trait Monohybrid Cross – cross between two parents and one trait

Monohybrid Cross

Predictions for Two Traits Dihybrid Cross – cross between two parents and two traits Dihybrid Cross – cross between two parents and two traits Use a 4 x 4 Punnett square Use a 4 x 4 Punnett square Sixteen possible outcomes Sixteen possible outcomes

Incomplete Dominance Heterozygous offspring show a phenotype that is in-between the phenotypes of the two homozygous parents Heterozygous offspring show a phenotype that is in-between the phenotypes of the two homozygous parents Blending of traits Blending of traits Color in snapdragons; Color in snapdragons; instead of white or red, instead of white or red, color is pink color is pink

Codominance Both alleles are expressed Both alleles are expressed Example: Blood type Example: Blood type I A, I B, i(O), or I A I B blood type I A, I B, i(O), or I A I B blood type Both A and B are dominant so they are both expressed in the I A I B blood type Both A and B are dominant so they are both expressed in the I A I B blood type

Polygenic Trait Trait controlled by more than one gene Trait controlled by more than one gene Example: eye color Example: eye color

Pleiotropy Single gene affects more than one trait Single gene affects more than one trait Example: sickle cell anemia Example: sickle cell anemia Effects include blood cell shape, anemia, weakness, brain damage, spleen damage, and heart damage Effects include blood cell shape, anemia, weakness, brain damage, spleen damage, and heart damage

Environmental Effects Phenotype is a combination of genetic and environmental influences Phenotype is a combination of genetic and environmental influences Example: Himalayan rabbit – fur color depends on body temperature Example: Himalayan rabbit – fur color depends on body temperature

Human Genetics

Difficulties in Studying Human Heredity Controlled experiments are not possible Controlled experiments are not possible Small numbers of offspring per generation Small numbers of offspring per generation Long periods between generations Long periods between generations

Sex Determination Autosomes – body chromosomes – first 22 pair Autosomes – body chromosomes – first 22 pair Same in both male and female Same in both male and female Sex Chromosomes – 1 pair, last pair Sex Chromosomes – 1 pair, last pair XX – Female XX – Female XY - Male XY - Male

XX = 50% XY = 50% You always have a 50% chance of having a girl and a 50% chance of having a boy!

Sex Linked Traits Traits controlled by recessive genes located on sex chromosomes (normally associated with the X chromosome) Traits controlled by recessive genes located on sex chromosomes (normally associated with the X chromosome) Hemophilia – blood clotting enzyme Hemophilia – blood clotting enzyme is absent Queen Victoria’s family affected Queen Victoria’s family affected

Sex Linked Traits Red – Green Colorblindness – individuals cannot distinguish between these two colors Red – Green Colorblindness – individuals cannot distinguish between these two colors

Sex Linked Traits Duchene Muscular Dystrophy – wasting away of skeletal muscle Duchene Muscular Dystrophy – wasting away of skeletal muscle

Females X R X R = normal X R X r = carrier X r X r = disease Males X R Y = normal X r Y = disease

Sex – Limited Traits Controlled by genes located in the autosomes Controlled by genes located in the autosomes Only expressed in the presence of sex hormone Only expressed in the presence of sex hormone Only expressed in one gender Only expressed in one gender First seen at puberty (hormones produced in large enough quantities First seen at puberty (hormones produced in large enough quantities

Sex – Limited Traits Examples: Examples: Male bird’s colorful plumage Male bird’s colorful plumage Beard growth in males Beard growth in males Milk production in females Milk production in females

Sex Influenced Traits Traits that are caused by a gene whose expression differs in males and females Traits that are caused by a gene whose expression differs in males and females Also located on autosomes Also located on autosomes Expressed in the presence of male or female hormones Expressed in the presence of male or female hormones Example: male pattern baldness Example: male pattern baldness BB = normal BB = normal Bb = males bald, females normal Bb = males bald, females normal bb = males and females bald bb = males and females bald

Hereditary Disorders Techniques for detecting genetic disorders Techniques for detecting genetic disorders Amniocentesis – technique used that removes and studies amniotic fluid Amniocentesis – technique used that removes and studies amniotic fluid during pregnancy; identifies only identifies only chromosomal disorders

Hereditary Disorders Karyotyping – an enlarged photo of the chromosome pairs (map) to identify any abnormalities in the chromosomes Karyotyping – an enlarged photo of the chromosome pairs (map) to identify any abnormalities in the chromosomes

Chromosomal Disorders Chromosomes fail to separate during meiosis Chromosomes fail to separate during meiosis Nondisjuction-abnormal numbers of chromosomes enter gametes Nondisjuction-abnormal numbers of chromosomes enter gametes

Pedigree Charts Chart which shows how a trait and the genes that control it are inherited within a family Chart which shows how a trait and the genes that control it are inherited within a family Identifies the presence or absence of particular trait in members of each generation Identifies the presence or absence of particular trait in members of each generation

Pedigree Charts Males = Males = Females = Females = Generations = Roman Numerals Generations = Roman Numerals Individuals = Numbered sequentially Individuals = Numbered sequentially Trait Expressed = Filled in Trait Expressed = Filled in Non Carriers = Empty Non Carriers = Empty Carrier (not ill) = Half filled Carrier (not ill) = Half filled Individual who carries a recessive allele that is not expressed Individual who carries a recessive allele that is not expressed