Genetics Heredity  passing down of traits or characteristics from parents to offspring Genetics  study of heredity

Gregor Mendel ( ) Worked with Pea Plants. 2 major traits for each plant Plants were either tall (T) or short (t) Plants were either Purple (P) or white (p)

Mendel’s Experiment Male and Female sex organs in pea plants are on the same flower (stamen have pollen and stigma contains the egg) Pure Traits  Traits established through self-fertilization Stamen  Stigma  Stigma

Genetics Pure white individuals x pure purple individualsPure white individuals x pure purple individuals F1  All purple offspringF1  All purple offspring F1 x F1  3:1 ratio of purple to white pea plantsF1 x F1  3:1 ratio of purple to white pea plants Out of 1000 plants 750 were purple and 250 were whiteOut of 1000 plants 750 were purple and 250 were white Results of the Parental cross showed that one trait covered up the other traitResults of the Parental cross showed that one trait covered up the other trait X=

Genetics Vocabulary Dominant Trait  Trait that masks the recessive trait Recessive Trait  Trait that is being covered up In this cross PURPLE color was dominant

Mendel’s Hypothesis Gene  sequence of DNA on a chromosome Each pea plant trait is a combination of 2 genes, one from mom and one from dad Each alternative gene is called an allele Dominant Gene  shown by a capital letter (P) Recessive Gene  shown by a lower case letter (p) Pure Purple plants  PP Pure white plants  pp PP x pp  all Pp Pp x Pp  PP or Pp or pP or pp

Mendel’s Terms Homozygous  2 of the same allele (PP or pp) Heterozygous  2 different alleles (Pp) Punnett Square  Results of a cross can be predicted

Incomplete Dominance Some traits do not have dominant alleles Heterozygotes appear as a mix between 2 parents 1 trait = 3 phenotypes 4 O’clock Flowers Rr x Rr Ratio of Offspring 1 Red 2 Pink 1 white

Codominance Neither allele is dominant. Multiple alleles are expressed Presence of heterozygote means both alleles are expressed equally Blood type is an example

Sex Determination Thomas Morgan discovered that chromosomes differed in males and females Females- XX Males- XY Called Sex Chromosomes All other chromosomes are called autosomes

Sex-linked Inheritance Morgan crossed white-eyed male with red-eyed female F1Ratio: All Red Eyes F2 Ratio: 3:1 ratio, but never any white females Reasoned that there are genes on sex chromosomes Allele for eye color is on X chromosome No gene for eye color on Y chromosome Presence of homozygous recessive, or ONLY a recessive allele, yields recessive trait Morgan’s Crosses

Sex Influenced Traits (Not on test!) Sex-influenced traits are autosomal traits that are influenced by sex. If a male has one recessive allele, he will show that trait, but it will take two recessive for the female to show that same trait. One such gene is baldness. BB  normal male & female Bb  bald male; normal female bb  bald male; bald female

Dihybrid Crosses Dihybrid Cross: Cross: Cross of 2 individuals for 2 different traits Example: In Pea Plants Tall(T) is dominant to short Purple(P) is dominant to white Crossing homozygous tall, purple plant with a homozygous short, white plant TTPP x ttpp Crossing heterozygous tall, purple plant with a heterozygous tall, purple plant TtPp x TtPp

Genetic Diseases Autosomal dominant disease  Presence of dominant allele means that individual will have the disease Autosomal recessive disease  Disease only present when BOTH recessive alleles are present Sex-linked Dominant  Disease present when dominant allele is present on either sex chromosome Sex-linked Recessive  Disease present when recessive allele is present oneither sex chromosome Sex-linked Recessive  Disease present when recessive allele is present on either sex chromosome

Common Genetic Diseases Huntington’s Disease  Autosomal dominant ; Neuromuscular disease; degeneration of muscle tissue; onset in early 30’s. Folk Singer Woody Guthrie had the disease Cystic Fibrosis  Autosomal Recessive; Defective Protein is made that creates excess mucus; clogs lungs. Color Blindness  Sex-linked recessive Inablity to distinguish colors (8% of male population)

Some Genetics Diseases Hemophilia  Sex-linked recessive Inablity of blood to clot Nicholas, Czar of Russia (Mid 1800’s) child was hemophiliac Muscular Dystrophy  Sex-linked recessive Tay-Sach’s Disease  Autosomal Recessive Degeneration of Central Nervous System; infant mortality

Changes in Chromosome Number Nondisjunction – occurs when: In meiosis I, homologous pair both go into the same daughter cell or In meiosis II, the sister chromatids both go into the same gamete. The result: Trisomy (3 copies of a single chromosome) or Monosomy (1 copy of a single chromosome)

Nondisjunction in meiosis I

Changes in Chromosome Structure Mutation - a permanent genetic change. Chromosome mutation - a change in chromosome structure Radiation, organic chemicals, or even viruses may cause chromosomes to break, leading to mutations. Types of chromosomal mutations: inversion, translocation, deletion, and duplication.

Deletions Deletions occur when a single break causes a lost end piece, or two breaks result in a loss in the interior. An individual inherits a normal chromosome from one parent and a chromosome with a deletion from the other parent No longer has a pair of alleles for each trait A syndrome can result – type depends on chromosome(s) affected.

Williams Syndrome Chromosome 7 loses an end piece Children have a pixie look (turned-up noses, wide mouth, small chin, large ears) Poor academic skills, good verbal and musical abilities Skin ages prematurely from lack of the gene that controls the production of elastin (also affects cardiovascular health).

Duplication Duplication results in a chromosome segment being repeated in the same chromosome Produces extra alleles for a trait. Ex: An inverted duplication in chromosome 15 causes inv dup 15 syndrome Poor muscle tone, mental retardation, seizures, curved spine, and autistic characteristics

Duplication

Translocation Translocation is exchange of chromosomal segments between two, non-homologous chromosomes. Ex: Alagille syndrome results from a deletion of chromosome 20 or a translocation that disrupts an allele on chromosome 20. Distinctive face, abnormalities of eyes & internal organs, and severe itching.

Translocation

Inversion Inversion involves a segment of a chromosome being turned 180 degrees The reverse sequence of alleles can alter gene activity. Crossing-over between inverted and normal chromosomes can cause duplications and deletions in resulting chromosomes.

Inversion