Heredity The passing on of characteristics from parents to offspring. What characteristics do you share with your parents?  Hair color  Eye color

Inheritance Terms  Genes – unit of information on your DNA passed down from parents to offspring Diploid cells (somatic cells) have one gene for a trait on each homologous chromosome. 2 total These different forms of a gene are called alleles.

GenotypesPhenotypes  The actual combination of alleles that an organism has  Always arranged in this order: 1. Homozygous dominant 2. Heterozygous 3. Homozygous recessive TT : Tt : tt  The physical expression of the genotype  What we look like  Always arranged in this order: 1. Homozygous dominant trait 2. Heterozygous trait (If there is one) 3. Homozygous recessive trait #Tall : # Short # Tall : # Medium : # Short

Punnet Squares and Ratios

Remember!  Your phenotypic ratio depends on the number of phenotype options  Not all crosses are complete!

Practice crosses  Flower  Red is dominant  White is recessive  Cross a homozygous dominant with a heterozygous  What is the genotypic and phenotypic ratios?  Seeds  Green is dominant  Yellow is recessive  Cross a homozygous recessive with a homozygous dominant  What is the genotypic and phenotypic ratios?

Who is Gregor Mendel and Why Did He Have a Funny Name?  Lived  He had a funny name because he was Austrian  He was a monk who liked to play in the garden.  He became a monk in order to get an education  He wanted to be a science teacher

Mendel: Not a Pea Brain  He was the first person to be able to predict how traits were transmitted through generations

Mendel looked at several characteristics of his pea plants

Mendel and Cross Pollination  Mendel used cross-pollination in order to study his plants Cross pollination – pollination in which pollen is transferred between flowers of two different plants Plants were bred for several generations that were true-breeding for specific traits (have the same versions of an allele) and called those the “P generation”.  Pure strain

Monohybrid Cross  The purple traits was dominate Covers up the other trait in a complete dominance cross  The white trait was recessive Only shows up physically when there are 2 recessive genes  First generation = F1 Hybrids – have non- identical alleles

How traits show up  P generation = tt * TT  First generation of offspring are called F1 Hybrids = Tt  Offspring of the F1 generation were called F2. TT – Tt - tt

Second Generation  F2  Three-fourths purple  One-fourth white  Where did the white come from?  A trait must have passed down from the parental generation.

Law of Dominance  Mendel concluded that inherited characteristics are controlled by factors that occur in pairs  He found that one factor in the pair masked the other. Dominant – the trait that could be observed  The trait that covers up the other trait in the F1 generation is dominant  Dominant traits are indicated by capital letters Recessive – the trait that was masked  The trait that disappeared is recessive  Recessive traits are indicated by lower case letters

Law of Segregation  Every individual has two alleles of each gene and when gametes (sex cells) are made, each gamete receives one of these alleles.

Law of Independent Assortment  Genes for individual characteristics are distributed to gametes independent of one another  The genes can not be on the same chromosome

Types of Crosses  Complete – Dominant and recessive alleles R = Red r = White  Incomplete – Intermediate, a blending of both traits RR = Red Rr = Pink rr = White  Codominance – Both traits show RR = Red Rr = Red and white stripes rr = White

Incomplete Dominance  Long water melon (LL) * Round watermelon (ll)  Do the cross  What is the genotypic ratio?  What is the phenotypic ratio? Remember – The phenotype in the case has 3 possibilities – homozygous dominant trait, heterozygous trait, and homozygous recessive trait.

Codominance Crosses  Horse with red coat (RR) * horse with white coat (rr)  Do the cross  What is the genotypic ratio?  What is the phenotypic ratio? Remember that both traits will show equally in a heterozygous individual You have 3 options for phenotype

Multiple alleles  Most genes only have 2 alleles, some have more than 2  Ex: blood types – A, B, O

Blood types A and B are codominant Type O is recessive to A and B

Human Blood Types and Genotypes Blood TypeGenotype AHomozygous AI A I A AHybrid AI A i BHomozygous BI B I B BHybrid BI B i ABABI A I B Oiiii

Punnet Square For Blood Types IAIA IBIB i i

Test Crosses An individual of unknown genotype X homozygous recessive individual  It is used to determine the genotype of the unknown individual ?? t t t t t t ?? t t t t? ? ? ? tt Tt tt Tt

Law of Independent Assortment  Genes from different traits are inherited independently of each other. If an organism has an allele for height  T = Tall  t = Short And color  Y = Yellow  y = Green Their genotype is TtYy They can pass on combinations of these alleles  TY  Ty  tY  Ty Some genes are linked and so will not independently assort

Dihybrid Cross  A cross involving two different traits instead of just one.  Shows the law of independent assortment  Genotype RrTt  Possible combinations of genes donated to a gamete RT Rt rT rt

RrTt * RRtt RT Rt rTrt Do the cross!

Environmental influence on Gene Expression  The ability for one single gene to affect an organism in several or many ways  Ex:

Polygenic inheritance When a characteristic, such as eye color, is controlled by two or more genes

Sex-Linked Genes  Sex linked Genes found on the X chromosome are “X- linked genes”. A sex-linked trait is a trait whose allele is located on the sex chromosome. Males have only 1 X chromosome. So, a male who carries a recessive allele on the x chromosome will exhibit the sex linked trait.  Ex. colorblindness

Sex Influenced Genes  A trait that is expressed differently in men than in women, even if the gene is on an autosome and both sexes have the same genotype Hormones dictate expression Ex. Male pattern baldness

Pedigree  A diagram that reveals inheritance patterns of genes  Geneticists use pedigrees to trace diseases or traits through families

Examples of some Genetic Diseases  Autosomal Dominant Huntington’s disease Caused by a single dominant allele Onset in 30’s and 40’s Causes loss of muscle control and severe mental illness. Results in death. Carrier genotype HH, Hh  Autosomal Recessive Cystic Fibrosis Tay-Sachs disease Phenylketonuria (PKU) Sickle cell anemia All are caused by inheriting two recessive alleles. Carrier genotype dd

Autosomal Recessive Diseases continued…  Phenylketonuria (PKU) Autosomal recessive Failure of the brain to develop in infancy and can cause death if untreated Defective form of an enzyme need to digest the amino acid phenylalanine  Cystic fibrosis Autosomal recessive Thick mucus clogs the lungs, liver and pancreas More common in white population  Sickle Cell Anemia Autosomal recessive Impaired blood circulation causes damage to organs Caused by a point mutation making the hemoglobin molecules abnormal Common in African Americans  Tay-Sachs disease Autosomal recessive Deterioration of the central nervous system in infancy; death occurs in early childhood. More common in Jews of European descent

Sex-linked diseases….  Hemophilia Recessive X-linked trait Defective form of blood- clotting factor causing failure of blood to clot  Muscular dystrophy Recessive X-linked trait Muscle fibers degenerate; shortened life expectancy  Colorblindness Recessive X-linked trait Inability to distinguish between certain colors 8% of males are colorblind

Hemophilia – Offspring of Queen Victoria