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Chapters 10 and 12
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1 st studies of heredity genetics Traits characteristics that are inherited
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Contrasting traits were easily seen Short generation time Many offspring per generation Sexes on 1 flower control of pollination Mathematical analysis of data
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Physical appearance Expressed in words tall, short
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Genetic makeup Expressed in terms of alleles Allele form of a gene for a trait Dominant allele always expressed (T tall) Recessive allele if present, may not be expressed (t short)
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Homozygous 2 identical alleles (TT, tt) Heterozygous (hybrid) 2 different alleles (Tt) Different genotypes can have the same phenotype Tall TT or Tt
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A single trait
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Original parents P generation Offspring F 1 generation All F 1 were tall
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F 2 75% were tall, 25% short 3:1 ratio
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Each organism has 2 factors (alleles) that control each trait
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When an individual is hybrid for a pair of contrasting traits, only the dominant trait can be seen TT x tt Tt **recessive trait is masked** Crossing 2 hybrids always results in 3:1
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Pairs of alleles for a trait are separated during the formation of gametes and are recombined during fertilization Tt T (egg) + t (sperm) Tt (zygote) Explains appearance of recessive traits in subsequent generations
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Height and seed color
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Genes for different traits are inherited independently of each other Exception genes on the same chromosome
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Predict the ratio of all possible results for a certain genetic cross Not what will happen, but what could happen Exact ratios are not seen in nature due to chance
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TY Ty tY ty TY TTYY TTYy TtYY TtYy Ty TTYy TTyy TtYy Ttyy tY TtYY TtYy ttYY ttYy ty TtYy Ttyy ttYy ttyy
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Type of cell division in which daughter cells receive only half the # of chromosomes of the parent cell
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Chromosomes occur in pairs 1 allele is on each of the paired chromosomes
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Diploid Cell with 2 of each kind of chromosome (2n) Body cells (somatic)
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Monoploid Cell with 1 of each kind of chromosome (n) also called haploid Gametes sperm and egg
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Each of a pair has genes for the same traits They may carry different alleles
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Associated with sexual reproduction 2 parents Allows offspring to have the same number of chromosomes as parents No doubling of chromosome number
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Meiosis I and II 2 separate divisions
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Replication of the chromosomes Same as in mitosis
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Each pair of homologous chromosomes comes together to form a tetrad This is known as synapsis
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Crossing-over may occur at this point Exchange of genetic material between nonsister chromatids Results in genetic variation or mutation Completely random and unpredictable
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Tetrads line up at cell equator metaphase plate
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Homologous chromosomes separate and move to opposite poles disjunction Critical step without disjunction, gametes would have abnormal numbers of chromosomes
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Cytokinesis forms 2 daughter cells Each cell has only 1 chromosome from each homologous pair Each chromosome is still doubled another division is required
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Identical to mitosis
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Meiosis Overview Meiosis Overview
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Crossing-over results in genetic recombination gene shuffling Almost endless number of different possible chromosomes You are not the exact blend of your parents Explains Mendel’s results
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Failure of homologous chromosomes to separate Both chromosomes move to the same pole 1 cell has an extra chromosome 1 cell is missing a chromosome
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A gamete with and extra chromosome fuses with a normal gamete Zygote has 1 extra chromosome 47 instead of 46 in humans Trisomy 21 Down syndrome
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A gamete with a missing chromosome fuses with a normal gamete Zygote has 1 missing chromosome 45 instead of 46 in humans Lethal most of the time Turner syndrome XO
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Total lack of chromosomal separation Lethal in animals Frequent in plants Larger and healthier fruits and flowers Plant breeders induce polyploidy by using chemicals that cause nondisjunction
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Chapter 12
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Graphic representation of genetic inheritance A chart showing familial relationships and patterns of trait inheritance
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Sample pedigree chart Squares male Circles female Filled in afflicted Blank not afflicted Half filled in carrier
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2 copies of allele are needed (Most genetic disorders)
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Formation and accumulation of mucus in lungs and pancreas Due to a defective protein 1 in 25 white Americans carry the allele Resistance against tuberculosis
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Buildup of lipids in brain cells (lethal) Missing the gene coding for an enzyme Amish and eastern European Jews
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Accumulation of phenylalanine (amino acid) in brain cells Causes mental retardation Missing the enzyme needed to break down the amino acid Standard test for all newborn infants PKU mothers can damage unborn child
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Abnormally shaped red blood cells Mutation in hemoglobin gene Most afflicted don’t survive childhood Carriers are more resistant to malaria Africans
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1 allele is needed Tongue rolling Hitchhiker’s thumb Huntington’s chorea Degeneration of brain cells lethal Onset of symptoms at 30-50 years of age 50% chance of passing on the allele
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Dominant allele is only partially expressed when recessive allele is present Genetic blending
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Both alleles are expressed equally Cattle red coat and white coat codominant Hybrid roan (mixture of red and white hairs)
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More than 2 possible alleles within a species Human blood type 3 possible alleles
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Sex chromosomes only unmatched pair All other are autosomes 22 pairs Female XX Male XY It is the male that determines the sex of the offspring
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Controlled by genes on the X chromosome Males are more likely to be afflicted Females may be carriers Color blindness Hemophilia Male pattern baldness *
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Trait controlled by 2 or more genes Not expressed in 2 contrasting forms, but varies between the 2 extremes Human height
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Genes located on the same chromosome Inherited together
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External temperature, light, nutrition, infectious agents Internal hormones, age, sex
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3 possible alleles I A and I B are codominant i is recessive 6 possible genotypes I A I A or I A i type A I B I B or I B i type B I A I B type AB ii type O
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Red-green color blindness Most common Hemophilia Commonly missing clotting factor VIII
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Eye color, skin color, height Almost all human traits
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Autosomes Down syndrome Sex chromosomes Turner syndrome XO Klinefelter syndrome XXY OY lethal
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Comparing specimen chromosomes to normal chromosomes
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Sample of free-floating fetal cells Make a karyotype
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Compare your genes to known disease markers
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