Unit 3.1

Year 10

INHERITANCE

GREGOR MENDEL• Monk in a Austrian monastery

• Studied inheritance of characteristics from about 1856

• Studied the inherited characteristics in peas.

• His conclusions/results were largely ignored until the early 1900’s

GENETIC TERMS• Inheritance: the passing on of characteristics

from one generation to the next

• Chromosome: a threadlike structure found in cells consisting of a single DNA molecule and proteins. Each chromosome can be thought as a string of beads where every bead represents a gene.

GENETIC TERMS• Autosome: chromosomes that exist in pair in

diploid cells and are not sex chromosomes

• Sex chromosome: an X or Y chromosome which are different from the 22 autosomes

• Haploid cells: a cell possessing only one set of chromosomes (n), such as a egg or sperm.

• Diploid cell: a cell possessing two sets of chromosomes (2n).

GENETIC TERMS• Allele – There are usually two or more forms of

a gene. These forms are called alleles.

• A dominant gene will always control the appearance of the characteristic.

• A recessive gene will only appear when both recessive alleles in an organism are the same.

GENETIC TERMS• Codominance is when the phenotype is a

blending of the characteristics of the parent alleles (e.g. page 85 roan cattle)

• Genotype: the genetic makeup of an organism, used to describe the combination of alleles e.g. Bb

• Phenotype: the actual physical appearance on the characteristic in the organism

GENETIC TERMS• Homozygous indicates that the individual has

two copies of an allele e.g. YY or yy

• Heterozygous indicates that the individual has different copies of an allele e.g. Yy

MITOSIS• process by which cells divide and multiply.

• Mitosis is a process of cell division which results in the production of two daughter cells from a single parent cell. The daughter cells are identical to one another and to the original parent cell.

• In a typical animal cell, mitosis can be divided into four principals stages:

MITOSIS• Prophase: The chromatin, diffuse in interphase,

condenses into chromosomes. Each chromosome has duplicated and now consists of two sister chromatids. At the end of prophase, the nuclear envelope breaks down into vesicles.

MITOSIS• Metaphase: The chromosomes align at the

equatorial plate and are held in place by spindle fibres which attach to the centromere.

MITOSIS• Anaphase: The centromeres divide. Sister

chromatids separate and move toward the corresponding poles.

MITOSIS• Telophase: Daughter chromosomes arrive at the

poles and the spindle fibres disappear. The condensed chromosome's expand and the nuclear envelope reappears.

MITOSIS• Cytokinesis: The cytoplasm divides, the cell

membrane pinches inward ultimately producing two daughter cells .

MEIOSIS• process by which a single parent diploid

cell divides to produce four daughter haploid cells

DNA replication → cell division (meiosis I) → cell division (meiosis II)

MEIOSIS

MEIOSIS• Interphase: Before meiosis begins, genetic

material is duplicated.

MEIOSIS I • First division of meiosis

• Prophase 1: Duplicated chromosomes condense. Each chromosome consists of two, identical sister chromatids.

• Metaphase 1: Homologous chromosomes align at the equatorial plate.

MEIOSIS I [CONT]

• Anaphase 1: Homologous pairs separate with sister chromatids remaining together.

• Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair.

MEIOSIS II• Second division of meiosis: Gamete formation

• Prophase 2: DNA does not replicate.

• Metaphase 2: Chromosomes align at the equatorial plate.

MEIOSIS II [CONT]

• Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole.

• Telophase 2: Cell division is completed. Four haploid daughter cells are obtained.

MEIOSIS• One parent cell [diploid] produces four daughter

cells. Daughter cells [haploid] have half the number of chromosomes found in the original parent cell, are genetically different to each other.

• Meiosis differs from mitosis primarily because there are two cell divisions in meiosis, resulting in cells with a haploid number of chromosomes.

COM

PARI

SON

COPY AND COMPLETE THE FOLLOWING TABLEMitosis Meiosis

Site of process

Parent cells, haploid/diploidChromosomal replication

Line up in homologous pairsSpindle fibres and centriolesNumber of daughter cells

Daughter cells, haploid/diploid