Genetics SC Biology Standard B-4.6-4.9- The students will be able to predict inherited traits by using the principles of Mendelian Genetics, summarize the chromosome theory of inheritance and compare the consequences of mutations in body cells. The students will be able to exemplify ways that introduce new genetic characteristics into an organism.

Genetics Study of patterns of inheritance and variation Genes control each trait of a living thing by controlling the formation of an organism’s proteins All cells are diploid- 2 sets of chromosomes- except gametes. This means each cell contains two genes for each trait- one from mom and one from dad. The two genes may be the same form or they may be different. Different forms of a gene are called alleles The two alleles segregate during Meiosis II Genetics

Principle of Dominance: Principle of Dominance states that some alleles are dominant whereas others are recessive If a dominant allele is present, that trait will always show An organism with a recessive trait will only show if the dominant allele is not present Since organisms receive one gene for a chromosome pair from each parent, they can be heterozygous or homozygous. Principle of Dominance:

Continued: When an organism has 2 identical alleles for a particular trait- it is homozygous for that trait This can be two dominant alleles or two recessive alleles When an organism has two different alleles for a trait, it is heterozygous- one is dominant and one is recessive Genotype- genetic makeup of an organism- reveals the type of alleles an organism has inherited for a particular trait. Usually represented by a letter. Capital letter= dominant allele Lower case letter= recessive allele

More: Examples: Genotypes: TT= homozygous dominant Tt= heterozygous dominant tt= homozygous recessive Phenotype- physical characteristics- the way the traits are expressed TT=tall Tt= tall tt= short More:

Law of Segregation Explains how alleles are separated during Meiosis. Each gamete receives one of two alleles that the parent carries for each trait During fertilization (sperm + egg) each parent donates one copy of each gene to the offspring Law of Segregation

Principle of Independent Assortment States that the segregation of the alleles of one trait does not affect the segregation of the alleles of another trait. Genes on separate chromosomes separate independently during meiosis Holds true for ALL genes unless the genes are linked. If this is the case, the genes are too close on the same chromosome to segregate independently Principle of Independent Assortment

Principles of Mendelian genetics Used to predict inherited traits Punnett squares can be used to predict the probable genetic combinations in the offspring Monohybrid cross looks at one trait Punnett square represents the probable outcome and the ratio Dihybrid cross examines the inheritance of two different traits Principles of Mendelian genetics

Dihybrid crosses: studies inheritance of 2 different alleles. The alleles independently assort resulting in offspring possibilities. KNOW- 1-3, 1-4, 2-3, 2-4 This will help you know how to independently assort and get your possible gametes. Multiple alleles- blood types. 3 alleles exist for blood types- only 2 are inherited. Polygenic traits- traits controlled by 2 or more genes. often result in a variety of phenotypes. Example = skin color Continued:

Mendel’s Principles of Genetics includes segregation, independent assortment, and dominance, but couldn’t explain the more complex theories- polygenic traits, inheritance patterns and genetic variation Chromosome theory of Inheritance states that genes are located on chromosomes and that the behavior of chromosomes during Meiosis accounts for inheritance patterns. Mendel’s theories support this. More:

Gene linkage- simply means that genes that are located on the same chromosome will be inherited together. ( exception to Mendel’s independent assortment because linked genes do not segregate) Crossing over- process in which alleles in close proximity to each other on homologous chromosomes are exchanged= new combination of alleles Incomplete dominance- when one allele is not completely dominant over another. Phenotype is expressed as a blend. Codominance- when both alleles for a gene are expressed completely. Phenotype shows both alleles New since Mendel

Multiple alleles- can exist for a particular trait even though only 2 are inherited. Example- blood types A, B, O which result in 4 different blood types. Polygenic traits- traits that are controlled by 2 or more gene. Often shows great variety of phenotypes. Example- skin color Sex linked traits- genes that are carried on either the x or y chromosome. Mendel didn’t explain sex linked traits. Females = XX, Males= Xy Y chromosome carries very few genes X chromosome has many genes that affect many traits More New since Mendel:

If a gene is linked on the X chromosome- females will inherit the gene as they do all others (dom/rec) Male offspring will inherit the gene on their X chromosome but not on the Y. Since males have only one X, they express their allele whether it is dominant or recessive. There is no second allele to mask the effects of the other allele. Color blindness and Hemophilia are sex linked. In rare cases, the female can be affected Sex linked continued:

Is a chart to show inheritance pattern (trait, disease, disorder) within a family throughout multiple generations. Pedigree: