Chapters 10 and 12

 1 st studies of heredity  genetics  Traits  characteristics that are inherited

 Contrasting traits were easily seen  Short generation time  Many offspring per generation  Sexes on 1 flower  control of pollination  Mathematical analysis of data

 Physical appearance  Expressed in words  tall, short

 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)

 Homozygous  2 identical alleles (TT, tt)  Heterozygous (hybrid)  2 different alleles (Tt)  Different genotypes can have the same phenotype  Tall  TT or Tt

A single trait

 Original parents  P generation  Offspring  F 1 generation  All F 1 were tall

 F 2  75% were tall, 25% short  3:1 ratio

 Each organism has 2 factors (alleles) that control each trait

 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

 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

 Height and seed color

 Genes for different traits are inherited independently of each other  Exception  genes on the same chromosome

 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

TY Ty tY ty TY TTYY TTYy TtYY TtYy Ty TTYy TTyy TtYy Ttyy tY TtYY TtYy ttYY ttYy ty TtYy Ttyy ttYy ttyy

Type of cell division in which daughter cells receive only half the # of chromosomes of the parent cell

 Chromosomes occur in pairs  1 allele is on each of the paired chromosomes

Diploid Cell with 2 of each kind of chromosome (2n) Body cells (somatic)

Monoploid Cell with 1 of each kind of chromosome (n) also called haploid Gametes  sperm and egg

 Each of a pair has genes for the same traits  They may carry different alleles

 Associated with sexual reproduction  2 parents  Allows offspring to have the same number of chromosomes as parents  No doubling of chromosome number

Meiosis I and II 2 separate divisions

 Replication of the chromosomes  Same as in mitosis

 Each pair of homologous chromosomes comes together to form a tetrad  This is known as synapsis

Crossing-over may occur at this point  Exchange of genetic material between nonsister chromatids  Results in genetic variation or mutation  Completely random and unpredictable

 Tetrads line up at cell equator  metaphase plate

 Homologous chromosomes separate and move to opposite poles  disjunction  Critical step  without disjunction, gametes would have abnormal numbers of chromosomes

 Cytokinesis forms 2 daughter cells  Each cell has only 1 chromosome from each homologous pair  Each chromosome is still doubled  another division is required

 Identical to mitosis

 Meiosis Overview Meiosis Overview

 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

 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

 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

 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

 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

Chapter 12

 Graphic representation of genetic inheritance  A chart showing familial relationships and patterns of trait inheritance

Sample pedigree chart Squares  male Circles  female Filled in  afflicted Blank  not afflicted Half filled in  carrier

2 copies of allele are needed (Most genetic disorders)

 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

 Buildup of lipids in brain cells (lethal)  Missing the gene coding for an enzyme  Amish and eastern European Jews

 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

 Abnormally shaped red blood cells  Mutation in hemoglobin gene  Most afflicted don’t survive childhood  Carriers are more resistant to malaria  Africans

 1 allele is needed  Tongue rolling  Hitchhiker’s thumb  Huntington’s chorea  Degeneration of brain cells  lethal  Onset of symptoms at years of age  50% chance of passing on the allele

 Dominant allele is only partially expressed when recessive allele is present  Genetic blending

 Both alleles are expressed equally  Cattle  red coat and white coat codominant  Hybrid  roan (mixture of red and white hairs)

 More than 2 possible alleles within a species  Human blood type  3 possible alleles

 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

 Controlled by genes on the X chromosome  Males are more likely to be afflicted  Females may be carriers  Color blindness  Hemophilia  Male pattern baldness *

 Trait controlled by 2 or more genes  Not expressed in 2 contrasting forms, but varies between the 2 extremes  Human height

 Genes located on the same chromosome  Inherited together

 External  temperature, light, nutrition, infectious agents  Internal  hormones, age, sex

 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

 Red-green color blindness  Most common  Hemophilia  Commonly missing clotting factor VIII

 Eye color, skin color, height  Almost all human traits

 Autosomes  Down syndrome  Sex chromosomes  Turner syndrome  XO  Klinefelter syndrome  XXY  OY  lethal

 Comparing specimen chromosomes to normal chromosomes

 Sample of free-floating fetal cells  Make a karyotype

 Compare your genes to known disease markers