B16.Inheritance

• Inheritance is the transmission of genetic information from generation to generation

1. Chromosomes and genes

• Chromosomes: a long thin thread

  • Found in the nucleus

  • made of one long molecule of DNA that contains genetic information in the form of genes

• Gene: part of the DNA for one kind of protein

• Alleles: different forms of a gene

  • 2 alleles of each gene exists

• Sex is determined by an entire chromosome pair

  • females: XX

  • males: XY

Chromosomes in haploid and diploid cells

• Haploid: a cell with a single set of chromosomes, eg. a gamete

• Diploid: 2 haploid cells that fused to have a complete set of chromosomes eg. a zygote

  • humans have 23 pairs of chromosomes

2. Cell division

-Mitosis:

• The division of the nucleus of the cell that produces genetically identical cells

• Used for: eg. hair

  • Asexual reproduction

  • Growth and repair of tissues

  • Produces new cells

• Chromosomes get replicated before mitosis occurs

• After seperation, the same number of chromosomes are present in each daughter cell

-Meiosis: eg. ovaries and testes

• type of nuclear division that makes cells that are genetically different

  • used to produce gametes

• one diploid cell produces haploid daughter cells

• Number of chromosomes is halved during meiosis

3. Monohybrid inheritance

• Phenotype: observable characteristics of an organism

• Genotype: the combination of alleles that control each characteristic

-Alleles:

• Can be dominant or recessive

+ Dominant: only needs to be inherited from one parent

+ Recessive: needs to be inherited from both parents

• Homozygous: 2 alleles of the same gene

+ Homozygous dominant: 2 copies of the dominant allele

+ Homozygous recessive: 2 copies of the recessive allele

• Heterozygous: 2 different alleles

• Pure breeding: identical homozygous parents produce offspring with exactly the same genotype and phenotype

• Not pure breeding: heterozygous individuals with different alleles produce offspring with a different genotype and phenotype than the parents.

4. Monohybrid inheritance

• The inheritance of characteristics controlled by a single gene

• Monohybrid cross: the genetic mix between two individuals which determines a characteristic controlled by a single one.

• Pedigree diagrams: usually used to trace the pattern of inheritance of a specific characteristic through a generations of a family.