Genetics and Inheritance © by Dr H – W Winter Pukekohe High School NZ

Cells & their Nuclei All living things are made up by “cells”, the building blocks of tissue. Most cells have a “nucleus”, the place where the plans (or “blue-prints”) for making the cell (and the rest of the whole organism) are kept.

Chromosomes The plans for your body (these blue-prints) are called chromosomes. They are pairs of strands of thread-like, very long molecules made of a material called DNA. One of the strands in a pair came from the male, the other from the female sex cell, when the organism was conceived. A pair of chromosomes made from DNA

Magnifying Details chromosomes in the nucleus one gene a pair of chromosomes made from DNA cell nucleus chromosome inherited from mother chromosome inherited from father

Magnifying Details

Genes On the chromosomes are many tiny units called genes (many thousands). One gene is responsible for one genetic feature. (e.g. tongue rolling or left-handedness etc) Gene for left/right - handedness R r

Alleles, dominant & recessive If the genetic information from one parent says something different from the other parent, we have 2 different alleles. In our example mother’s allele says: “right handed” and father’s allele says “left-handed”. The “more influential one” of the 2 alleles will win and will be used; it is called the dominant allele; it is given a capital letter (R). The allele that loses the competition is called the recessive allele; it is given a lower case letter (r). In our example right-handedness is dominant over left-handedness, the child is right-handed (but is also a carrier of the allele for left-handedness). Gene for left/right - handedness R r

Fertilisation at Chromosomal Level A sperm contains 50% of the chromosomes (in blue) An egg contains the other 50% of the chromosomes (in red) Fertilisation: The sperm penetrates the egg and its chromosomes enter – male and female chromosomes pair up, the egg becomes a zygote

Mitosis Mitosis is the process of making identical copies of cells …. it is used to repair damaged tissue …. and when an organism grows identical copying

Meiosis Is a 2 stage cell division that makes 4 gametes with half the chromosomes from one normal cell. In this process the alleles from the 2 strands of chromosomes are mixed up to provide the basis for variation. 1 st division after the mother’s and father’s chromosomes were mixed up randomly 2 nd division producing sex cells that are only having half of the chromosomes

Discontinuous Variation (aka either/or variation or discrete variation) You either have it or you don’t. Examples: left-handedness, gender, tongue rolling, widow’s peak, curly hair etc. Usually expressed as a % value (e.g. 25% of the children of this family cannot roll their tongue). Usually dependent on one gene that has one dominant and one recessive allele.

Continuous Variation A wide range of values is possible Examples: height, shoe size, hair colour, hand span etc. A “bell-shaped” curve shows the distribution Number of Y 10 students Height of Y 10 students 1.60 m Average height

Georg Mendel Austrian monk born in 1822 in monastery known for research and teaching after his death (1884) acknowledgment of his discoveries in 1900

Experiments with Pea Plants - Seed coat colour (gray or white) - Seed shape (round or wrinkled) - Seed colour (yellow or green) - Pod colour (green or yellow) - Flower position (axial or terminal) - Pod shape (inflated or constricted) - Stem length (tall or dwarf)

Definitions you must know: Homozygous or “true breeding“ means that an organism (like a pea plant) has only one type of alleles in its genetic make-up eg: GG or gg Heterozygous is the opposite to homozygous, 2 different alleles are found in the gene eg: Gg or gG

Definitions you must know: Genotype describes the genetic make-up of an organism, the allele combinations eg: Gg or gg or GG, heterozygous or homozygous Phenotype describes the appearance of an organism, the looks or type (tongue roller, left-hander, green seed pod, white flower etc)

Punnet Squares are systematic diagrams to show the statistical probability of either/or variation in the offspring. makes gametes G G Parent 1 (genotype GG) makes gametes Parent 2 (genotype gg) gggg G G gggg gggg

The thing that puzzled Mendel

Cross-Pollination of Pure-breed Plants - cross-pollination between homozygous (true breeding) green and yellow pods - all F1 green F1 Generation Gg = heterozygous

F2 Generation - self-pollination of green F1 plants - ¾ in F2 green, ¼ yellow - 3 : 1 ratio in pod colour in F2 G = dominant = green g = recessive = yellow GG, gg = homozygous