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Biology AHSGE Standard VII- Applying Mendels Laws.

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Presentation on theme: "Biology AHSGE Standard VII- Applying Mendels Laws."— Presentation transcript:

1 Biology AHSGE Standard VII- Applying Mendels Laws

2 Heredity The passing of characters from parents to offspring Genetics- Branch of Biology dealing with heredity –Gregor Mendel- Austrian monk who developed rules of heredity Experimented with pea plants

3 Mendels Experiments Monohybrid cross- Cross of parents involving one pair of contrasting traits –True breeding- All offspring display one characteristic P generation- First two individuals crossed F1 generation (filial)- First offspring from P generation F2 generation- Second offspring resulting from F1 generation

4 Mendels Hypotheses 1.For each inherited trait, an individual has two copies of the gene- one from each parent. 2.There are alternative versions of genes- alleles 3.When two different alleles are present, the individual may completely express one, while the other allele has no observable affect Dominant- Expressed allele; only one copy needed for expression; capital letter Recessive- Allele not expressed when dominant allele is present; need both copies for expression; lowercase letter 4.When gametes are formed, each genes alleles separate independently, therefore gametes have one allele for each gene

5 Modern Terms Homozygous- Having two of the same alleles for a gene –Ex: AA, BB, aa or bb Heterozygous- Having two different alleles for a particular gene –Ex: Aa or Bb Genotype- The set of alleles for a characteristic or trait (the letters) Phenotype- The expressed trait or physical appearance of a genotype

6 Laws of Heredity The Law of Segregation- When gametes are formed, each genes alleles separate (segregate) independently, therefore gametes have one allele for each gene The Law of Independent Assortment- Alleles of different genes separate independently of one another during meiosis

7 Punnett Square Diagram that predicts the outcome of a genetic cross by considering all possible combinations of gametes in the cross Test cross- An individual whose phenotype is dominant, but whose genotype is not known, is crossed with a homozygous recessive individual Monohybrid cross- Cross of parents involving one pair of contrasting traits Dihybrid Cross- Cross of parents involving two pairs of contrasting traits

8 Monohybrid Cross Cross a heterozygous, brown-haired woman with a heterozygous, brown- haired man; Brown hair is dominant, while blonde is recessive

9 Probability The likelihood that a specific event will occur –Expressed as percentages or ratios Probability = number of one kind of possible outcome total number of all possible outcomes Genotypic ratio- Ratio of genotypes from a punnett square Phenotypic ratio- Ratio of phenotypes from a punnett square

10 Punnett Square and Probability - Probability of offspring with brown hair; blonde Genotypic RatioPhenotypic Ratio

11 Dihybrid Cross Cross two heterozygous pea plants for seed shape (R= round; r= wrinkled) and color (Y= yellow; y= green); RrYy 1 st - Complete a monohybrid cross of the two traits for each parent to determine possible gametes

12 Dihybrid Cross

13 Calculate the genotypic and phenotypic ratios for the previous cross Genotypic Ratio 1 RRYY: 3 RRYy: 2 RrYY: 3 RrYy: 1 RRyy: 2 Rryy: 1 rrYY: 2 rrYy: 1rryy Phenotypic Ratio 9 Round; yellow: 3 Round; green: 3 Wrinkled; yellow: 1 Wrinkled; green

14 Inheritance of Traits Pedigree- Family history that shows how a trait is inherited over several generations –Circles- female –Squares- male –Horizontal lines show mating –Vertical lines indicate offspring –Completely shaded are affected –Partial shading represents a carrier

15 Pedigree-Albinism

16 Albino

17 Sex-linked Genes Allele is found on the X or Y chromosome XX- female; XY- male Mostly carried on X and recessive –Males receiving this on the X would exhibit the condition due to having only one X (Ex: Hemophilia)

18 Genetic Disorder Dominant or Recessive SymptomDefectFrequency Sickle Cell Anemia Recessive Poor blood circulation Abnormal hemoglobin 1/500 (African american) Hyperchol- esterolemia Dominant Excessive cholesterol in blood; heart disease Abnormal cell surface receptor for cholesterol 1/500 Tay-Sachs Disease Recessive Deterioration of nervous system; death Defective form of brain enzyme 1/3,500 (Ashkenazi Jews) Cystic Fibrosis Recessive Mucus clogging or organs; do not survive to old age Defective chloride- ion transport protein 1/2,500 (Caucasians) Hemophilia A Sex-linked recessive Failure of blood to clot Defective form of blood-clotting factor 1/10,000 (males) Huntingtons Disease Dominant Gradual deterioration of brain tissue in middle age Inhibitor of brain cell metabolism 1/10,000

19 Downs Syndrome Chromosomal mutation resulting in mental retardation and physical abnormalities –1 in every 1,000 people born –Having an extra chromosome on the 21 st pair of human chromosomes –Trisomy-21 –Caused by nondisjunction of the 21 st pair during Anaphase I of meiosis

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