Presentation on theme: "Introduction to Genetics and Heredity Hypotheses about genes In the 1800’s scientist argued between two hypothesis regarding genes and how they are passed."— Presentation transcript:
Hypotheses about genes In the 1800’s scientist argued between two hypothesis regarding genes and how they are passed on to offspring Blended hypothesis - states that the traits from two parents are mixed to become a third trait Particulate hypothesis – states that the traits from two parents are joined but remain discrete, and can be separated again to their original forms Which hypothesis seems more logical to you?
Remember from Meiosis All organisms pass on inherited information using haploid gametes. X XX X X Human zygotes have 23 pairs of chromosomes
Who was Gregor Mendel? -Austrian monk -Did work with pea plants -Know as the “Father of Genetics” Genetics – the scientific study of heredity
Mendel’s work He selectively bred pea plants Fertilization – when male and female reproductive cells join Male – pollen or sperm Female – eggs Gamete – the individual egg or sperm Seed – fertilized egg or new cell (zygote)
Selective breeding True-breeding – if they were allowed to self-breed they would have identical offspring Self-breeding – Sperm and egg from the same flower fertilize Selective breeding Cross-pollination oMendel took pollen from one plant and fertilized eggs from other plants
Genes and Dominance Traits – a specific characteristic (ex. Brown hair) Seed color Plant height Parental generation (P) – Original pair of plants Filial generation (F 1 ) – offspring, progeny Hybrids – offspring of crosses between parents with different traits
Remember from Meiosis Genes – chemical factors that determine traits (Hair color) Alleles – different forms of traits (Brown hair, blue eyes) (like T or t for tallness in pea plants).
What Mendel found….. Dominant Trait – the observed trait that masks another trait (written as an upper case letter). Recessive Trait – trait that can be masked by a dominant trait (written as a lower case letter). Tall is dominant to short in pea plants, so the gene for tallness is represented by an upper case “T” and shortness is represented by a lower-case “t”.
Mendel's observations from these experiments can be summarized in two principles: The principle of segregation A parent passes on at random only one allele for each trait to each offspring The two alleles for each trait separate during meiosis. The principle of independent assortment A random distribution of alleles occurs during gamete formation. Genes on separate chromosomes sort independently during meiosis.
Diploid – A cell with two of each kind of chromosome (1 from each parent) We say the cell is a diploid cell or 2n ( This supports Mendel’s conclusion that organisms have two factors – alleles – for each trait) Haploid – A cell with one of each kind of chromosome (gametes) We say the cell is a haploid or n (This supports Mendel’s conclusion that parents give one allele for each trait to their offspring)
Phenotype & Genotype Phenotype The way an organism looks and behaves Ex. Tall, yellow, blond, blue eyes Genotype The gene combination an organism contains Ex. TT or Tt for tall Homozygous – two alleles are the same, TT Heterozygous – two alleles are different, Tt