Reproduction and Heredity

Reproduction and Heredity

Chapters 8-9

Heredity

•  Heredity = biological inheritance

–  Or why we look like our parents!

•  Genetics is study of heredity

Sexual reproduction

•  Alternation between meiosis and fertilization

–  Meiosis is the process of nuclear division in which the chromosome number is halved

•  Usually 2n to n

–  Fertilization is the process where two haploid cells (gametes) fuse

Homologs

•  In each diploid cell, chromosomes have a partner or homologous chromosome or homolog

Chromosome structure

Meiosis

•  Through meiosis and cytokinesis, a single diploid cell becomes four haploid cells

–  Haploid cells can be gametes

•  Unite to form zygote then divides

–  Haploid cells can be meiospores

•  Divides without uniting with another cell

Meiosis

•  Meiosis produces genetic variability through genetic recombination

–  Crossing over, as well as possible haploid chromosome combinations

Meiosis vs. mitosis

•  Two nuclear divisions in meiosis, only one in mitosis

•  Four haploid cells result from meiosis, Two diploid cells result from mitosis

•  Nuclei produced by mitosis have identical gene combinations

Genetics

•  Alleles are alternate forms of the same gene

•  Alleles occupy the same locus (plural = loci) on homologous chromosomes

Mendel’s crosses

•  Complete dominant versus recessive alleles

Mendel’s two principles

•  Principle of segregation

–  Alleles (of one gene) separate during meiosis

•  Principle of independent assortment

–  Alleles separate independently of alleles of other genes

Linkage

•  Genes found in close proximity do not always segregate independently

•  Linkage maps are created

Mutations

•  Change in heredity state of an organism is a mutation

–  Point mutation

–  Deletion

–  Duplication

–  Transposons

Chromosomal mutations

•  Pieces of chromosomes

–  Inversion

•  Piece of chromosome inserted backwards

–  Translocation

•  Exchange of parts between two non-homologous chromsomes

•  Entire chromosomes

–  Aneuploidy is any number different from normal

–  Polyploidy is duplication of entire set of chromosomes

Allele interactions

•  Incomplete dominance can occur

•  Multiple alleles can occur

•  Epistasis can occur

•  Some traits are controlled by more than one gene – polygenic traits

•  Pleiotropy can occur

Genes in plastids

•  Plastids and mitochondria contain their own DNA

•  Cytoplasmic inheritance is usually determined by female parent, and is therefore known as maternal inheritance

•  Leaf mottling is a character controlled by maternal inheritance in chloroplasts

Role of the environment

•  Phenotype is a product of genes, environment and a gene by environmental interaction

Asexual reproduction

•  Also known as vegetative reproduction

•  Progeny are identical to parent, or are clones

Strawberry

Kalanchoë

Fern

Advantages of sexual reproduction

•  Produces genetic diversity, which allows the population to adapt through the process of evolution by natural selection

•  Requires a lot of energy (so it must be advantageous!)

•  Widely used

Chemistry of heredity

DNA

•  Double helix with sugar-phosphate backbone and nitrogenous base pairs

•  Strands are antiparallel and complementary

DNA Replication

•  Copying DNA

•  Catalyzed by DNA polymerase

RNA

•  Nucleotide sugar is ribose rather than deoxyribose

•  Thymine replaced by uracil

•  Single-stranded

Information transfer

Transcription

•  RNA polymerase is used in transcription

Genetic code is universal

RNA

•  mRNA is translated into protein

•  tRNA has two attachment sites, one for mRNA and one for amino acid

•  Translation occurs at ribosome

Polypeptide sorting

•  Polypeptide targeting assures that each peptide moves to the correct location within a cell

–  Cotranslational transport

•  Ribosomes on endoplasmic reticulum

–  Posttranslational transport

•  Free ribosomes

Gene regulation

•  Only certain genes are expressed

•  Totipotency – an entire plant can be regenerated from a differentiated cell

–  Points towards regulation of gene expression

•  Transcription factors directly or indirectly affect the initiation of transcription

Genome size varies

Repetitive sequences

•  Tandemly repeated DNA

–  Repeated DNA are arranged in tandem series

–  Simple-sequence repeated DNA (satellite DNA)

•  Interspersed repeated DNA units

–  Dispersed throughout the DNA

–  20-40% of most multicellular organisms is this type

Unique DNA

•  50-70% of genome is single-copy DNA

–  Protein-coding DNA

Introns and extrons

•  The protein coding sequences of DNA or structural genes are not continuous

•  Interrupted by noncoding introns

•  Exons are coding sequences

Next time….

•  Plant biotechnology and genomics