GENETICS

GENETICS TERMS Gene – section of chromosome that codes for a trait Gene – section of chromosome that codes for a trait –Remember it’s the sequence of DNA nucleotides! Trait - a characteristic that varies from one organism to the next Trait - a characteristic that varies from one organism to the next –Hair color, flower color, etc. Allele - a different form of a gene Allele - a different form of a gene –represented by letters

Different alleles: Dominant allele – always expressed when present Dominant allele – always expressed when present –UPPER CASE (Y for yellow peas) Recessive allele - expressed only when the dominant allele is not present Recessive allele - expressed only when the dominant allele is not present –lower case (y for green peas)

Allele

GENETICS TERMS Genotype - genetic makeup Genotype - genetic makeup –BB, Bb, bb Phenotype – physical characteristic Phenotype – physical characteristic –Green eyes –Brown hair

GENOTYPES Homozygous - two identical alleles in a gene pair (TT or tt) Homozygous - two identical alleles in a gene pair (TT or tt) Heterozygous - different alleles in a gene pair (Tt) Heterozygous - different alleles in a gene pair (Tt)

GENOTYPES (cont’d) Purebred or True Breeding - organism that receives the same alleles from both of its parents Purebred or True Breeding - organism that receives the same alleles from both of its parents –Gene pair ex: BB or bb

Hybrid - organism that received different alleles from each parent Hybrid - organism that received different alleles from each parent –Gene pairs ex: Bb Chiweenie Labradoodle

Fertilization – process of joining male and female gametes Fertilization – process of joining male and female gametes –Gametes are egg and sperm cells Expression – when genes are transcribed and translated into proteins Expression – when genes are transcribed and translated into proteins

REVIEW FROM YESTERDAY

Allele for Widow’s PeakAllele for Widow’s Peak is dominant is dominant A person with WW or Ww will have Widow’s PeakA person with WW or Ww will have Widow’s Peak Allele for Straight HairlineAllele for Straight Hairline is recessive is recessive A person with ww will have a Straight HairlineA person with ww will have a Straight Hairline

Genotype vs. Phenotype Genotype refers to the allelesGenotype refers to the alleles Phenotype refers to the appearancePhenotype refers to the appearance Example: Genotype - Phenotype WW - person has a widow’s peak Ww - person has a widow’s peak ww - person has a straight hair line

GREGOR MENDEL and GENETICS LAWS

GREGOR MENDEL ( ) “Father of Genetics” “Father of Genetics” Scientist and Monk Scientist and Monk Worked with pea plants to study how traits are passed from one generation to next Worked with pea plants to study how traits are passed from one generation to next

Why do you think scientists use rats, rabbits, insects, worms in laboratory experiments? Experiments such as -medicine -studying genes -genetic diseases

Blast from the past: What characteristics make a good experiment?

Pea plants were used because: Visible traits that contrast Visible traits that contrast –tall OR short; yellow OR green Produce large number of offspring Produce large number of offspring Crosses (matings) can be controlled b/c of flower structure Crosses (matings) can be controlled b/c of flower structure Scientist can isolate and control variables in laboratory Scientist can isolate and control variables in laboratory Repeatable experiment Repeatable experiment

Structure of Pea Flower Filament Male Parts of Flowers Anther Female Parts of Flowers Stigma Style Ovary EggPetals

GENERATIONS: A – purple flowers a – white flowers 1 st cross = Parental or P generation 1 st cross = Parental or P generation –Homozygous dominant and homozygous recessive – AA X aa 1 st generation created= F 1 generation 1 st generation created= F 1 generation –Heterozygous – 100% Aa AA aa AaAaAaAa Parental

2 nd generation created (F 1 x F 1 ) = F 2 2 nd generation created (F 1 x F 1 ) = F 2 –1:2:1 genotypic ratio – 1 AA : 2 Aa : 1 aa –3:1 phenotypic ratio – 3 purple : 1 white AaAa AaAa AAaa

MENDEL’S LAWS Law of Segregation - each gene pair separates during meiosis Law of Segregation - each gene pair separates during meiosis egg egg BB  B B **this states that sister chromatids must separate during Anaphase II**

MENDEL’S LAWS Law of Independent Assortment - gene pairs separate into gametes randomly and independently of each other Law of Independent Assortment - gene pairs separate into gametes randomly and independently of each other –Homologous chromosomes line up randomly and independently in Metaphase I EVERY POSSIBLE COMBINATION HAS TO BE CONSIDERED EVERY POSSIBLE COMBINATION HAS TO BE CONSIDERED **this explains how sister chromatids separate**

Independent Assortment when gametes are formed

MENDEL’S LAWS Law of Dominance – if the dominant allele is present in the gene pair, it is always expressed Law of Dominance – if the dominant allele is present in the gene pair, it is always expressed –In other words, if you inherit a dominant allele, you will always show the dominant phenotype

RANDOM FERTILIZATION How many combos of human zygotes can be formed? Remember – ovum + sperm = Zygote How many combos of human zygotes can be formed? Remember – ovum + sperm = Zygote –1 ovum = 8 million different chromosome combos –Fertilized by 1 sperm = 8 million different combos = 64 trillion different combos for one zygote –2 23 x 2 23 = over 70 trillion PLUS crossing over variations!

X inactivation

Used on pregnant women over 35 years of ageUsed on pregnant women over 35 years of age Performed during weeks of pregnancyPerformed during weeks of pregnancy A needle is inserted into the amniotic sacA needle is inserted into the amniotic sac Amniotic fluid with fetal cells is removedAmniotic fluid with fetal cells is removed A karyotype of the fetal chromosomes is preparedA karyotype of the fetal chromosomes is prepared Amniocentesis

Risk of Miscarriage Risk of Down Syndrome Risk of Having Child with Down Syndrome versus Risk of Miscarriage