Genetics

Genetics Genetics: the study of patterns of inheritance and variations in organisms. Genes control each trait by controlling the formation of an organism’s proteins.

Diploid Cells In all diploid cells there are 2 sets of chromosomes Therefore, each cell contains two genes for each trait The two genes can be alike or different for a trait. For example, a gene for plant height might occur in a tall form and a short form. The different forms of a gene are called alleles.

Law (Principle) of Segregation Alleles are separated during meiosis Each gamete only receives 1 of the 2 alleles 50:50 chance of which one it gets Ex: 50% chance of getting tall allele 50% chance of getting short allele

Law (Principle) of Dominance Some alleles are dominant whereas others are recessive. Dominant is always expressed (seen) Even if there is only one dominant allele Written as a capital letter Recessive will only show if there is not a dominant allele present Need 2 recessive alleles to show the recessive trait Written as a lower case letter

Genotype Genotype: genetic makeup of an organism Homozygous = same alleles = TT, tt They are either both dominant or both recessive Heterozygous = different alleles = Tt Shows dominant trait

Examples: TT represents a ____________ genotype.

Phenotype Phenotype: physical characteristics of an organism TT or Tt – shows dominant characteristic tt – shows recessive characteristic Ex: If T is tall then: TT = Tt = tt =

Dominant phenotypes It is not possible to determine the genotype of an organism with a dominant phenotype by looking at it.

Phenotype vs. genotype 2 organisms can have the same phenotype but have different genotypes PP homozygous dominant purple Pp heterozygous purple

Punnett Squares Used to predict the inherited traits of offspring based on the parents A monohybrid cross examines the inheritance of one trait. The parents are the P generation; the resulting offspring possibilities are the F1 generation.

T t TT Tt tt

Punnett squares Pp x Pp PP P p Pp P p Pp PP Pp pp Pp pp 25% 75% 50% genotype % phenotype PP 25% 75% P p male / sperm Pp 50% P p female / eggs Pp PP Pp pp 25% 25% Pp pp 1:2:1 3:1

Incomplete Incomplete dominance is a condition in which one allele is not completely dominant over another the phenotype shown is somewhere between the two extremes usually in plants

Co-dominance Co-dominance occurs when both alleles for a gene are expressed completely the phenotype shown has evidence of both alleles usually in animals

A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together). What percentage of kittens would have tan fur if a tabby cat is crossed with a black cat?

Multiple Alleles Multiple allele traits have two or more variations of the same gene only two are inherited blood types is an example Three alleles are A, B, and o Four blood types Type A—AA or Ao Type B—BB or Bo Type AB—AB Type O—oo

If a man has type O blood and his wife has type AB, what are the possible genotypes and phenotypes for their offspring? If a man is type A and his wife is type B, can they have a baby with type O blood? Explain your answer using a Punnett square.

Sex-Linked Traits Sex-linked traits: are the result of genes that are carried on either the X or the Y chromosome. Male: XY Can give offspring X or Y, determines sex of offspring Female: XX Can only give an X to offspring

autosomal chromosomes Sex chromosomes autosomal chromosomes sex chromosomes

X chromosome more than 60 diseases traced to genes on X chromosome

Y chromosome Less than 30 genes on Y chromosome SRY

Sex-linked traits Hh x HH XHXh XHY XHXh XH Xh XH Y XHXH XHXH XHY XHY sex-linked recessive XHXh XHY Hh x HH XHXh XH Xh XH Y male / sperm XHXH XHXH XHY XHY XH Xh female / eggs XHY Y XH XHXh XHXh XhY XhY

Sex-linked traits Males only have one X Females have 2 X’s If X has recessive trait, it will be seen Females have 2 X’s Need both to have recessive trait to be shown Traits on X: Color blindness Hemophilia

Polygenic Traits Polygenic traits are traits that are controlled by two or more genes these traits often show a great variety of phenotypes examples in human’s include eye color hair color skin tone predisposition to height

Pedigrees a chart constructed to show an inheritance of a trait within a family through multiple generations through the use of a pedigree the genotype and phenotype of the family members and the genetic characteristics of the trait can be tracked

Pedigree Symbols marriage line female male offspring lines normal has trait

Pedigree Example 1 Autosomal Recessive

Pedigree Example 2 Autosomal Dominant

Pedigree Example 3 Sex-linked Recessive

Chromosomal Theory of Inheritance genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns

Law of Independent Assortment each pair of alleles segregates into gametes independently 4 classes of gametes are produced in equal amounts YR, Yr, yR, yr only true for genes on separate chromosomes YyRr Yr Yr yR yR YR YR yr yr

Gene Linkage genes that are located on the same chromosome will be inherited together these genes travel together during gamete formation

Crossing Over process in which alleles in close proximity to each other on homologous chromosomes are exchanged this results in new combinations of alleles. When chromosomes pair up during meiosis I, sometimes sections of the two chromosomes become crossed. The two crossed sections break off and usually reattach. When the genes are rearranged, new combinations of alleles are formed

Mutations any change in the nucleotide sequence of DNA can result from a malfunction during the process of meiosis or from exposure to a physical or a chemical agent, a mutagen two general categories substitution insertion or deletion most mutations are automatically repaired by the organism’s enzymes and therefore have no effect if not repaired mutations can causes changes in the amino acids in proteins

Figure 10.22a

Figure 10.22b

If the mutant cell is a body cell (somatic cell), the daughter cells will be affected by the altered DNA can contribute to the aging process or the development of many types of cancer the mutation will not be passed to the offspring

If the mutant cell is a gamete (sex cell), the altered DNA will be passed on to the offspring Gamete cell mutations can result in genetic disorders If the mutation affects a single gene, it is known as a gene mutation. Examples: sickle-cell disease, Tay-Sachs disease, Huntington’s disease, cystic fibrosis, or albinism

If the mutation affects a group of genes or an entire chromosome, it is know as a chromosomal mutation Nondisjunction occurs when chromosomes do not separate during anaphase of meiosis

Sex chromosome examples: Klinefelter’s syndrome (male) and Turner’s syndrome (female) Autosomal chromosome examples: Down syndrome

in some cases mutations are useful to organisms in different or changing environments these mutations result in phenotypes that are favored by natural selection and increase in a population

Biotechnology biotechnology is the use of genetic and cellular processes to do work to improve life

Genetic Engineering the process of replacing specific genes in an organism in order to ensure that the organism expresses a desired trait usually by taking specific genes from one organism and placing them into another organism usually the receiving organism is a bacterium

scientists need to know exactly where particular genes for particular traits is on specific chromosomes A gene map shows the relative location of each known gene on a chromosome.

Human Genome Project Genome refers to all the genetic material in an organism the Human Genome Project mapped the DNA sequence of human genes

Cloning an identical copy of a gene or an entire organism is produced can result in an organism with genetic disorders or health problems

Gene Therapy inserting a normal gene into an absent or abnormal gene once inserted the normal gene begins to produce the correct protein or enzyme, eliminating the cause of the disorder

Stem Cells undifferentiated cells that have the potential to become specialized in structure or function primarily found in embryos they are also found in adult body therapy using stem cells can replace tissue that is deficient due to disease or damage

Selective Breeding method of artificially selecting and breeding only organisms with a desired trait to produce the next generation almost all domesticated animals and most crop plants are the result of selective breeding

hybridization another form of selective breeding is the choosing and breeding organisms that show strong expression for two different traits in order to produce offspring that express both traits